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Source file src/net/http/transport.go

Documentation: net/http

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // HTTP client implementation. See RFC 7230 through 7235.
     6  //
     7  // This is the low-level Transport implementation of RoundTripper.
     8  // The high-level interface is in client.go.
     9  
    10  package http
    11  
    12  import (
    13  	"bufio"
    14  	"compress/gzip"
    15  	"container/list"
    16  	"context"
    17  	"crypto/tls"
    18  	"errors"
    19  	"fmt"
    20  	"io"
    21  	"log"
    22  	"net"
    23  	"net/http/httptrace"
    24  	"net/textproto"
    25  	"net/url"
    26  	"os"
    27  	"reflect"
    28  	"strings"
    29  	"sync"
    30  	"sync/atomic"
    31  	"time"
    32  
    33  	"golang.org/x/net/http/httpguts"
    34  	"golang.org/x/net/http/httpproxy"
    35  )
    36  
    37  // DefaultTransport is the default implementation of Transport and is
    38  // used by DefaultClient. It establishes network connections as needed
    39  // and caches them for reuse by subsequent calls. It uses HTTP proxies
    40  // as directed by the $HTTP_PROXY and $NO_PROXY (or $http_proxy and
    41  // $no_proxy) environment variables.
    42  var DefaultTransport RoundTripper = &Transport{
    43  	Proxy: ProxyFromEnvironment,
    44  	DialContext: (&net.Dialer{
    45  		Timeout:   30 * time.Second,
    46  		KeepAlive: 30 * time.Second,
    47  	}).DialContext,
    48  	ForceAttemptHTTP2:     true,
    49  	MaxIdleConns:          100,
    50  	IdleConnTimeout:       90 * time.Second,
    51  	TLSHandshakeTimeout:   10 * time.Second,
    52  	ExpectContinueTimeout: 1 * time.Second,
    53  }
    54  
    55  // DefaultMaxIdleConnsPerHost is the default value of Transport's
    56  // MaxIdleConnsPerHost.
    57  const DefaultMaxIdleConnsPerHost = 2
    58  
    59  // Transport is an implementation of RoundTripper that supports HTTP,
    60  // HTTPS, and HTTP proxies (for either HTTP or HTTPS with CONNECT).
    61  //
    62  // By default, Transport caches connections for future re-use.
    63  // This may leave many open connections when accessing many hosts.
    64  // This behavior can be managed using Transport's CloseIdleConnections method
    65  // and the MaxIdleConnsPerHost and DisableKeepAlives fields.
    66  //
    67  // Transports should be reused instead of created as needed.
    68  // Transports are safe for concurrent use by multiple goroutines.
    69  //
    70  // A Transport is a low-level primitive for making HTTP and HTTPS requests.
    71  // For high-level functionality, such as cookies and redirects, see Client.
    72  //
    73  // Transport uses HTTP/1.1 for HTTP URLs and either HTTP/1.1 or HTTP/2
    74  // for HTTPS URLs, depending on whether the server supports HTTP/2,
    75  // and how the Transport is configured. The DefaultTransport supports HTTP/2.
    76  // To explicitly enable HTTP/2 on a transport, use golang.org/x/net/http2
    77  // and call ConfigureTransport. See the package docs for more about HTTP/2.
    78  //
    79  // Responses with status codes in the 1xx range are either handled
    80  // automatically (100 expect-continue) or ignored. The one
    81  // exception is HTTP status code 101 (Switching Protocols), which is
    82  // considered a terminal status and returned by RoundTrip. To see the
    83  // ignored 1xx responses, use the httptrace trace package's
    84  // ClientTrace.Got1xxResponse.
    85  //
    86  // Transport only retries a request upon encountering a network error
    87  // if the request is idempotent and either has no body or has its
    88  // Request.GetBody defined. HTTP requests are considered idempotent if
    89  // they have HTTP methods GET, HEAD, OPTIONS, or TRACE; or if their
    90  // Header map contains an "Idempotency-Key" or "X-Idempotency-Key"
    91  // entry. If the idempotency key value is a zero-length slice, the
    92  // request is treated as idempotent but the header is not sent on the
    93  // wire.
    94  type Transport struct {
    95  	idleMu       sync.Mutex
    96  	closeIdle    bool                                // user has requested to close all idle conns
    97  	idleConn     map[connectMethodKey][]*persistConn // most recently used at end
    98  	idleConnWait map[connectMethodKey]wantConnQueue  // waiting getConns
    99  	idleLRU      connLRU
   100  
   101  	reqMu       sync.Mutex
   102  	reqCanceler map[cancelKey]func(error)
   103  
   104  	altMu    sync.Mutex   // guards changing altProto only
   105  	altProto atomic.Value // of nil or map[string]RoundTripper, key is URI scheme
   106  
   107  	connsPerHostMu   sync.Mutex
   108  	connsPerHost     map[connectMethodKey]int
   109  	connsPerHostWait map[connectMethodKey]wantConnQueue // waiting getConns
   110  
   111  	// Proxy specifies a function to return a proxy for a given
   112  	// Request. If the function returns a non-nil error, the
   113  	// request is aborted with the provided error.
   114  	//
   115  	// The proxy type is determined by the URL scheme. "http",
   116  	// "https", and "socks5" are supported. If the scheme is empty,
   117  	// "http" is assumed.
   118  	//
   119  	// If Proxy is nil or returns a nil *URL, no proxy is used.
   120  	Proxy func(*Request) (*url.URL, error)
   121  
   122  	// DialContext specifies the dial function for creating unencrypted TCP connections.
   123  	// If DialContext is nil (and the deprecated Dial below is also nil),
   124  	// then the transport dials using package net.
   125  	//
   126  	// DialContext runs concurrently with calls to RoundTrip.
   127  	// A RoundTrip call that initiates a dial may end up using
   128  	// a connection dialed previously when the earlier connection
   129  	// becomes idle before the later DialContext completes.
   130  	DialContext func(ctx context.Context, network, addr string) (net.Conn, error)
   131  
   132  	// Dial specifies the dial function for creating unencrypted TCP connections.
   133  	//
   134  	// Dial runs concurrently with calls to RoundTrip.
   135  	// A RoundTrip call that initiates a dial may end up using
   136  	// a connection dialed previously when the earlier connection
   137  	// becomes idle before the later Dial completes.
   138  	//
   139  	// Deprecated: Use DialContext instead, which allows the transport
   140  	// to cancel dials as soon as they are no longer needed.
   141  	// If both are set, DialContext takes priority.
   142  	Dial func(network, addr string) (net.Conn, error)
   143  
   144  	// DialTLSContext specifies an optional dial function for creating
   145  	// TLS connections for non-proxied HTTPS requests.
   146  	//
   147  	// If DialTLSContext is nil (and the deprecated DialTLS below is also nil),
   148  	// DialContext and TLSClientConfig are used.
   149  	//
   150  	// If DialTLSContext is set, the Dial and DialContext hooks are not used for HTTPS
   151  	// requests and the TLSClientConfig and TLSHandshakeTimeout
   152  	// are ignored. The returned net.Conn is assumed to already be
   153  	// past the TLS handshake.
   154  	DialTLSContext func(ctx context.Context, network, addr string) (net.Conn, error)
   155  
   156  	// DialTLS specifies an optional dial function for creating
   157  	// TLS connections for non-proxied HTTPS requests.
   158  	//
   159  	// Deprecated: Use DialTLSContext instead, which allows the transport
   160  	// to cancel dials as soon as they are no longer needed.
   161  	// If both are set, DialTLSContext takes priority.
   162  	DialTLS func(network, addr string) (net.Conn, error)
   163  
   164  	// TLSClientConfig specifies the TLS configuration to use with
   165  	// tls.Client.
   166  	// If nil, the default configuration is used.
   167  	// If non-nil, HTTP/2 support may not be enabled by default.
   168  	TLSClientConfig *tls.Config
   169  
   170  	// TLSHandshakeTimeout specifies the maximum amount of time waiting to
   171  	// wait for a TLS handshake. Zero means no timeout.
   172  	TLSHandshakeTimeout time.Duration
   173  
   174  	// DisableKeepAlives, if true, disables HTTP keep-alives and
   175  	// will only use the connection to the server for a single
   176  	// HTTP request.
   177  	//
   178  	// This is unrelated to the similarly named TCP keep-alives.
   179  	DisableKeepAlives bool
   180  
   181  	// DisableCompression, if true, prevents the Transport from
   182  	// requesting compression with an "Accept-Encoding: gzip"
   183  	// request header when the Request contains no existing
   184  	// Accept-Encoding value. If the Transport requests gzip on
   185  	// its own and gets a gzipped response, it's transparently
   186  	// decoded in the Response.Body. However, if the user
   187  	// explicitly requested gzip it is not automatically
   188  	// uncompressed.
   189  	DisableCompression bool
   190  
   191  	// MaxIdleConns controls the maximum number of idle (keep-alive)
   192  	// connections across all hosts. Zero means no limit.
   193  	MaxIdleConns int
   194  
   195  	// MaxIdleConnsPerHost, if non-zero, controls the maximum idle
   196  	// (keep-alive) connections to keep per-host. If zero,
   197  	// DefaultMaxIdleConnsPerHost is used.
   198  	MaxIdleConnsPerHost int
   199  
   200  	// MaxConnsPerHost optionally limits the total number of
   201  	// connections per host, including connections in the dialing,
   202  	// active, and idle states. On limit violation, dials will block.
   203  	//
   204  	// Zero means no limit.
   205  	MaxConnsPerHost int
   206  
   207  	// IdleConnTimeout is the maximum amount of time an idle
   208  	// (keep-alive) connection will remain idle before closing
   209  	// itself.
   210  	// Zero means no limit.
   211  	IdleConnTimeout time.Duration
   212  
   213  	// ResponseHeaderTimeout, if non-zero, specifies the amount of
   214  	// time to wait for a server's response headers after fully
   215  	// writing the request (including its body, if any). This
   216  	// time does not include the time to read the response body.
   217  	ResponseHeaderTimeout time.Duration
   218  
   219  	// ExpectContinueTimeout, if non-zero, specifies the amount of
   220  	// time to wait for a server's first response headers after fully
   221  	// writing the request headers if the request has an
   222  	// "Expect: 100-continue" header. Zero means no timeout and
   223  	// causes the body to be sent immediately, without
   224  	// waiting for the server to approve.
   225  	// This time does not include the time to send the request header.
   226  	ExpectContinueTimeout time.Duration
   227  
   228  	// TLSNextProto specifies how the Transport switches to an
   229  	// alternate protocol (such as HTTP/2) after a TLS ALPN
   230  	// protocol negotiation. If Transport dials an TLS connection
   231  	// with a non-empty protocol name and TLSNextProto contains a
   232  	// map entry for that key (such as "h2"), then the func is
   233  	// called with the request's authority (such as "example.com"
   234  	// or "example.com:1234") and the TLS connection. The function
   235  	// must return a RoundTripper that then handles the request.
   236  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
   237  	// automatically.
   238  	TLSNextProto map[string]func(authority string, c *tls.Conn) RoundTripper
   239  
   240  	// ProxyConnectHeader optionally specifies headers to send to
   241  	// proxies during CONNECT requests.
   242  	// To set the header dynamically, see GetProxyConnectHeader.
   243  	ProxyConnectHeader Header
   244  
   245  	// GetProxyConnectHeader optionally specifies a func to return
   246  	// headers to send to proxyURL during a CONNECT request to the
   247  	// ip:port target.
   248  	// If it returns an error, the Transport's RoundTrip fails with
   249  	// that error. It can return (nil, nil) to not add headers.
   250  	// If GetProxyConnectHeader is non-nil, ProxyConnectHeader is
   251  	// ignored.
   252  	GetProxyConnectHeader func(ctx context.Context, proxyURL *url.URL, target string) (Header, error)
   253  
   254  	// MaxResponseHeaderBytes specifies a limit on how many
   255  	// response bytes are allowed in the server's response
   256  	// header.
   257  	//
   258  	// Zero means to use a default limit.
   259  	MaxResponseHeaderBytes int64
   260  
   261  	// WriteBufferSize specifies the size of the write buffer used
   262  	// when writing to the transport.
   263  	// If zero, a default (currently 4KB) is used.
   264  	WriteBufferSize int
   265  
   266  	// ReadBufferSize specifies the size of the read buffer used
   267  	// when reading from the transport.
   268  	// If zero, a default (currently 4KB) is used.
   269  	ReadBufferSize int
   270  
   271  	// nextProtoOnce guards initialization of TLSNextProto and
   272  	// h2transport (via onceSetNextProtoDefaults)
   273  	nextProtoOnce      sync.Once
   274  	h2transport        h2Transport // non-nil if http2 wired up
   275  	tlsNextProtoWasNil bool        // whether TLSNextProto was nil when the Once fired
   276  
   277  	// ForceAttemptHTTP2 controls whether HTTP/2 is enabled when a non-zero
   278  	// Dial, DialTLS, or DialContext func or TLSClientConfig is provided.
   279  	// By default, use of any those fields conservatively disables HTTP/2.
   280  	// To use a custom dialer or TLS config and still attempt HTTP/2
   281  	// upgrades, set this to true.
   282  	ForceAttemptHTTP2 bool
   283  }
   284  
   285  // A cancelKey is the key of the reqCanceler map.
   286  // We wrap the *Request in this type since we want to use the original request,
   287  // not any transient one created by roundTrip.
   288  type cancelKey struct {
   289  	req *Request
   290  }
   291  
   292  func (t *Transport) writeBufferSize() int {
   293  	if t.WriteBufferSize > 0 {
   294  		return t.WriteBufferSize
   295  	}
   296  	return 4 << 10
   297  }
   298  
   299  func (t *Transport) readBufferSize() int {
   300  	if t.ReadBufferSize > 0 {
   301  		return t.ReadBufferSize
   302  	}
   303  	return 4 << 10
   304  }
   305  
   306  // Clone returns a deep copy of t's exported fields.
   307  func (t *Transport) Clone() *Transport {
   308  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   309  	t2 := &Transport{
   310  		Proxy:                  t.Proxy,
   311  		DialContext:            t.DialContext,
   312  		Dial:                   t.Dial,
   313  		DialTLS:                t.DialTLS,
   314  		DialTLSContext:         t.DialTLSContext,
   315  		TLSHandshakeTimeout:    t.TLSHandshakeTimeout,
   316  		DisableKeepAlives:      t.DisableKeepAlives,
   317  		DisableCompression:     t.DisableCompression,
   318  		MaxIdleConns:           t.MaxIdleConns,
   319  		MaxIdleConnsPerHost:    t.MaxIdleConnsPerHost,
   320  		MaxConnsPerHost:        t.MaxConnsPerHost,
   321  		IdleConnTimeout:        t.IdleConnTimeout,
   322  		ResponseHeaderTimeout:  t.ResponseHeaderTimeout,
   323  		ExpectContinueTimeout:  t.ExpectContinueTimeout,
   324  		ProxyConnectHeader:     t.ProxyConnectHeader.Clone(),
   325  		GetProxyConnectHeader:  t.GetProxyConnectHeader,
   326  		MaxResponseHeaderBytes: t.MaxResponseHeaderBytes,
   327  		ForceAttemptHTTP2:      t.ForceAttemptHTTP2,
   328  		WriteBufferSize:        t.WriteBufferSize,
   329  		ReadBufferSize:         t.ReadBufferSize,
   330  	}
   331  	if t.TLSClientConfig != nil {
   332  		t2.TLSClientConfig = t.TLSClientConfig.Clone()
   333  	}
   334  	if !t.tlsNextProtoWasNil {
   335  		npm := map[string]func(authority string, c *tls.Conn) RoundTripper{}
   336  		for k, v := range t.TLSNextProto {
   337  			npm[k] = v
   338  		}
   339  		t2.TLSNextProto = npm
   340  	}
   341  	return t2
   342  }
   343  
   344  // h2Transport is the interface we expect to be able to call from
   345  // net/http against an *http2.Transport that's either bundled into
   346  // h2_bundle.go or supplied by the user via x/net/http2.
   347  //
   348  // We name it with the "h2" prefix to stay out of the "http2" prefix
   349  // namespace used by x/tools/cmd/bundle for h2_bundle.go.
   350  type h2Transport interface {
   351  	CloseIdleConnections()
   352  }
   353  
   354  func (t *Transport) hasCustomTLSDialer() bool {
   355  	return t.DialTLS != nil || t.DialTLSContext != nil
   356  }
   357  
   358  // onceSetNextProtoDefaults initializes TLSNextProto.
   359  // It must be called via t.nextProtoOnce.Do.
   360  func (t *Transport) onceSetNextProtoDefaults() {
   361  	t.tlsNextProtoWasNil = (t.TLSNextProto == nil)
   362  	if strings.Contains(os.Getenv("GODEBUG"), "http2client=0") {
   363  		return
   364  	}
   365  
   366  	// If they've already configured http2 with
   367  	// golang.org/x/net/http2 instead of the bundled copy, try to
   368  	// get at its http2.Transport value (via the "https"
   369  	// altproto map) so we can call CloseIdleConnections on it if
   370  	// requested. (Issue 22891)
   371  	altProto, _ := t.altProto.Load().(map[string]RoundTripper)
   372  	if rv := reflect.ValueOf(altProto["https"]); rv.IsValid() && rv.Type().Kind() == reflect.Struct && rv.Type().NumField() == 1 {
   373  		if v := rv.Field(0); v.CanInterface() {
   374  			if h2i, ok := v.Interface().(h2Transport); ok {
   375  				t.h2transport = h2i
   376  				return
   377  			}
   378  		}
   379  	}
   380  
   381  	if t.TLSNextProto != nil {
   382  		// This is the documented way to disable http2 on a
   383  		// Transport.
   384  		return
   385  	}
   386  	if !t.ForceAttemptHTTP2 && (t.TLSClientConfig != nil || t.Dial != nil || t.DialContext != nil || t.hasCustomTLSDialer()) {
   387  		// Be conservative and don't automatically enable
   388  		// http2 if they've specified a custom TLS config or
   389  		// custom dialers. Let them opt-in themselves via
   390  		// http2.ConfigureTransport so we don't surprise them
   391  		// by modifying their tls.Config. Issue 14275.
   392  		// However, if ForceAttemptHTTP2 is true, it overrides the above checks.
   393  		return
   394  	}
   395  	if omitBundledHTTP2 {
   396  		return
   397  	}
   398  	t2, err := http2configureTransports(t)
   399  	if err != nil {
   400  		log.Printf("Error enabling Transport HTTP/2 support: %v", err)
   401  		return
   402  	}
   403  	t.h2transport = t2
   404  
   405  	// Auto-configure the http2.Transport's MaxHeaderListSize from
   406  	// the http.Transport's MaxResponseHeaderBytes. They don't
   407  	// exactly mean the same thing, but they're close.
   408  	//
   409  	// TODO: also add this to x/net/http2.Configure Transport, behind
   410  	// a +build go1.7 build tag:
   411  	if limit1 := t.MaxResponseHeaderBytes; limit1 != 0 && t2.MaxHeaderListSize == 0 {
   412  		const h2max = 1<<32 - 1
   413  		if limit1 >= h2max {
   414  			t2.MaxHeaderListSize = h2max
   415  		} else {
   416  			t2.MaxHeaderListSize = uint32(limit1)
   417  		}
   418  	}
   419  }
   420  
   421  // ProxyFromEnvironment returns the URL of the proxy to use for a
   422  // given request, as indicated by the environment variables
   423  // HTTP_PROXY, HTTPS_PROXY and NO_PROXY (or the lowercase versions
   424  // thereof). HTTPS_PROXY takes precedence over HTTP_PROXY for https
   425  // requests.
   426  //
   427  // The environment values may be either a complete URL or a
   428  // "host[:port]", in which case the "http" scheme is assumed.
   429  // An error is returned if the value is a different form.
   430  //
   431  // A nil URL and nil error are returned if no proxy is defined in the
   432  // environment, or a proxy should not be used for the given request,
   433  // as defined by NO_PROXY.
   434  //
   435  // As a special case, if req.URL.Host is "localhost" (with or without
   436  // a port number), then a nil URL and nil error will be returned.
   437  func ProxyFromEnvironment(req *Request) (*url.URL, error) {
   438  	return envProxyFunc()(req.URL)
   439  }
   440  
   441  // ProxyURL returns a proxy function (for use in a Transport)
   442  // that always returns the same URL.
   443  func ProxyURL(fixedURL *url.URL) func(*Request) (*url.URL, error) {
   444  	return func(*Request) (*url.URL, error) {
   445  		return fixedURL, nil
   446  	}
   447  }
   448  
   449  // transportRequest is a wrapper around a *Request that adds
   450  // optional extra headers to write and stores any error to return
   451  // from roundTrip.
   452  type transportRequest struct {
   453  	*Request                         // original request, not to be mutated
   454  	extra     Header                 // extra headers to write, or nil
   455  	trace     *httptrace.ClientTrace // optional
   456  	cancelKey cancelKey
   457  
   458  	mu  sync.Mutex // guards err
   459  	err error      // first setError value for mapRoundTripError to consider
   460  }
   461  
   462  func (tr *transportRequest) extraHeaders() Header {
   463  	if tr.extra == nil {
   464  		tr.extra = make(Header)
   465  	}
   466  	return tr.extra
   467  }
   468  
   469  func (tr *transportRequest) setError(err error) {
   470  	tr.mu.Lock()
   471  	if tr.err == nil {
   472  		tr.err = err
   473  	}
   474  	tr.mu.Unlock()
   475  }
   476  
   477  // useRegisteredProtocol reports whether an alternate protocol (as registered
   478  // with Transport.RegisterProtocol) should be respected for this request.
   479  func (t *Transport) useRegisteredProtocol(req *Request) bool {
   480  	if req.URL.Scheme == "https" && req.requiresHTTP1() {
   481  		// If this request requires HTTP/1, don't use the
   482  		// "https" alternate protocol, which is used by the
   483  		// HTTP/2 code to take over requests if there's an
   484  		// existing cached HTTP/2 connection.
   485  		return false
   486  	}
   487  	return true
   488  }
   489  
   490  // alternateRoundTripper returns the alternate RoundTripper to use
   491  // for this request if the Request's URL scheme requires one,
   492  // or nil for the normal case of using the Transport.
   493  func (t *Transport) alternateRoundTripper(req *Request) RoundTripper {
   494  	if !t.useRegisteredProtocol(req) {
   495  		return nil
   496  	}
   497  	altProto, _ := t.altProto.Load().(map[string]RoundTripper)
   498  	return altProto[req.URL.Scheme]
   499  }
   500  
   501  // roundTrip implements a RoundTripper over HTTP.
   502  func (t *Transport) roundTrip(req *Request) (*Response, error) {
   503  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   504  	ctx := req.Context()
   505  	trace := httptrace.ContextClientTrace(ctx)
   506  
   507  	if req.URL == nil {
   508  		req.closeBody()
   509  		return nil, errors.New("http: nil Request.URL")
   510  	}
   511  	if req.Header == nil {
   512  		req.closeBody()
   513  		return nil, errors.New("http: nil Request.Header")
   514  	}
   515  	scheme := req.URL.Scheme
   516  	isHTTP := scheme == "http" || scheme == "https"
   517  	if isHTTP {
   518  		for k, vv := range req.Header {
   519  			if !httpguts.ValidHeaderFieldName(k) {
   520  				req.closeBody()
   521  				return nil, fmt.Errorf("net/http: invalid header field name %q", k)
   522  			}
   523  			for _, v := range vv {
   524  				if !httpguts.ValidHeaderFieldValue(v) {
   525  					req.closeBody()
   526  					return nil, fmt.Errorf("net/http: invalid header field value %q for key %v", v, k)
   527  				}
   528  			}
   529  		}
   530  	}
   531  
   532  	origReq := req
   533  	cancelKey := cancelKey{origReq}
   534  	req = setupRewindBody(req)
   535  
   536  	if altRT := t.alternateRoundTripper(req); altRT != nil {
   537  		if resp, err := altRT.RoundTrip(req); err != ErrSkipAltProtocol {
   538  			return resp, err
   539  		}
   540  		var err error
   541  		req, err = rewindBody(req)
   542  		if err != nil {
   543  			return nil, err
   544  		}
   545  	}
   546  	if !isHTTP {
   547  		req.closeBody()
   548  		return nil, badStringError("unsupported protocol scheme", scheme)
   549  	}
   550  	if req.Method != "" && !validMethod(req.Method) {
   551  		req.closeBody()
   552  		return nil, fmt.Errorf("net/http: invalid method %q", req.Method)
   553  	}
   554  	if req.URL.Host == "" {
   555  		req.closeBody()
   556  		return nil, errors.New("http: no Host in request URL")
   557  	}
   558  
   559  	for {
   560  		select {
   561  		case <-ctx.Done():
   562  			req.closeBody()
   563  			return nil, ctx.Err()
   564  		default:
   565  		}
   566  
   567  		// treq gets modified by roundTrip, so we need to recreate for each retry.
   568  		treq := &transportRequest{Request: req, trace: trace, cancelKey: cancelKey}
   569  		cm, err := t.connectMethodForRequest(treq)
   570  		if err != nil {
   571  			req.closeBody()
   572  			return nil, err
   573  		}
   574  
   575  		// Get the cached or newly-created connection to either the
   576  		// host (for http or https), the http proxy, or the http proxy
   577  		// pre-CONNECTed to https server. In any case, we'll be ready
   578  		// to send it requests.
   579  		pconn, err := t.getConn(treq, cm)
   580  		if err != nil {
   581  			t.setReqCanceler(cancelKey, nil)
   582  			req.closeBody()
   583  			return nil, err
   584  		}
   585  
   586  		var resp *Response
   587  		if pconn.alt != nil {
   588  			// HTTP/2 path.
   589  			t.setReqCanceler(cancelKey, nil) // not cancelable with CancelRequest
   590  			resp, err = pconn.alt.RoundTrip(req)
   591  		} else {
   592  			resp, err = pconn.roundTrip(treq)
   593  		}
   594  		if err == nil {
   595  			resp.Request = origReq
   596  			return resp, nil
   597  		}
   598  
   599  		// Failed. Clean up and determine whether to retry.
   600  		if http2isNoCachedConnError(err) {
   601  			if t.removeIdleConn(pconn) {
   602  				t.decConnsPerHost(pconn.cacheKey)
   603  			}
   604  		} else if !pconn.shouldRetryRequest(req, err) {
   605  			// Issue 16465: return underlying net.Conn.Read error from peek,
   606  			// as we've historically done.
   607  			if e, ok := err.(transportReadFromServerError); ok {
   608  				err = e.err
   609  			}
   610  			return nil, err
   611  		}
   612  		testHookRoundTripRetried()
   613  
   614  		// Rewind the body if we're able to.
   615  		req, err = rewindBody(req)
   616  		if err != nil {
   617  			return nil, err
   618  		}
   619  	}
   620  }
   621  
   622  var errCannotRewind = errors.New("net/http: cannot rewind body after connection loss")
   623  
   624  type readTrackingBody struct {
   625  	io.ReadCloser
   626  	didRead  bool
   627  	didClose bool
   628  }
   629  
   630  func (r *readTrackingBody) Read(data []byte) (int, error) {
   631  	r.didRead = true
   632  	return r.ReadCloser.Read(data)
   633  }
   634  
   635  func (r *readTrackingBody) Close() error {
   636  	r.didClose = true
   637  	return r.ReadCloser.Close()
   638  }
   639  
   640  // setupRewindBody returns a new request with a custom body wrapper
   641  // that can report whether the body needs rewinding.
   642  // This lets rewindBody avoid an error result when the request
   643  // does not have GetBody but the body hasn't been read at all yet.
   644  func setupRewindBody(req *Request) *Request {
   645  	if req.Body == nil || req.Body == NoBody {
   646  		return req
   647  	}
   648  	newReq := *req
   649  	newReq.Body = &readTrackingBody{ReadCloser: req.Body}
   650  	return &newReq
   651  }
   652  
   653  // rewindBody returns a new request with the body rewound.
   654  // It returns req unmodified if the body does not need rewinding.
   655  // rewindBody takes care of closing req.Body when appropriate
   656  // (in all cases except when rewindBody returns req unmodified).
   657  func rewindBody(req *Request) (rewound *Request, err error) {
   658  	if req.Body == nil || req.Body == NoBody || (!req.Body.(*readTrackingBody).didRead && !req.Body.(*readTrackingBody).didClose) {
   659  		return req, nil // nothing to rewind
   660  	}
   661  	if !req.Body.(*readTrackingBody).didClose {
   662  		req.closeBody()
   663  	}
   664  	if req.GetBody == nil {
   665  		return nil, errCannotRewind
   666  	}
   667  	body, err := req.GetBody()
   668  	if err != nil {
   669  		return nil, err
   670  	}
   671  	newReq := *req
   672  	newReq.Body = &readTrackingBody{ReadCloser: body}
   673  	return &newReq, nil
   674  }
   675  
   676  // shouldRetryRequest reports whether we should retry sending a failed
   677  // HTTP request on a new connection. The non-nil input error is the
   678  // error from roundTrip.
   679  func (pc *persistConn) shouldRetryRequest(req *Request, err error) bool {
   680  	if http2isNoCachedConnError(err) {
   681  		// Issue 16582: if the user started a bunch of
   682  		// requests at once, they can all pick the same conn
   683  		// and violate the server's max concurrent streams.
   684  		// Instead, match the HTTP/1 behavior for now and dial
   685  		// again to get a new TCP connection, rather than failing
   686  		// this request.
   687  		return true
   688  	}
   689  	if err == errMissingHost {
   690  		// User error.
   691  		return false
   692  	}
   693  	if !pc.isReused() {
   694  		// This was a fresh connection. There's no reason the server
   695  		// should've hung up on us.
   696  		//
   697  		// Also, if we retried now, we could loop forever
   698  		// creating new connections and retrying if the server
   699  		// is just hanging up on us because it doesn't like
   700  		// our request (as opposed to sending an error).
   701  		return false
   702  	}
   703  	if _, ok := err.(nothingWrittenError); ok {
   704  		// We never wrote anything, so it's safe to retry, if there's no body or we
   705  		// can "rewind" the body with GetBody.
   706  		return req.outgoingLength() == 0 || req.GetBody != nil
   707  	}
   708  	if !req.isReplayable() {
   709  		// Don't retry non-idempotent requests.
   710  		return false
   711  	}
   712  	if _, ok := err.(transportReadFromServerError); ok {
   713  		// We got some non-EOF net.Conn.Read failure reading
   714  		// the 1st response byte from the server.
   715  		return true
   716  	}
   717  	if err == errServerClosedIdle {
   718  		// The server replied with io.EOF while we were trying to
   719  		// read the response. Probably an unfortunately keep-alive
   720  		// timeout, just as the client was writing a request.
   721  		return true
   722  	}
   723  	return false // conservatively
   724  }
   725  
   726  // ErrSkipAltProtocol is a sentinel error value defined by Transport.RegisterProtocol.
   727  var ErrSkipAltProtocol = errors.New("net/http: skip alternate protocol")
   728  
   729  // RegisterProtocol registers a new protocol with scheme.
   730  // The Transport will pass requests using the given scheme to rt.
   731  // It is rt's responsibility to simulate HTTP request semantics.
   732  //
   733  // RegisterProtocol can be used by other packages to provide
   734  // implementations of protocol schemes like "ftp" or "file".
   735  //
   736  // If rt.RoundTrip returns ErrSkipAltProtocol, the Transport will
   737  // handle the RoundTrip itself for that one request, as if the
   738  // protocol were not registered.
   739  func (t *Transport) RegisterProtocol(scheme string, rt RoundTripper) {
   740  	t.altMu.Lock()
   741  	defer t.altMu.Unlock()
   742  	oldMap, _ := t.altProto.Load().(map[string]RoundTripper)
   743  	if _, exists := oldMap[scheme]; exists {
   744  		panic("protocol " + scheme + " already registered")
   745  	}
   746  	newMap := make(map[string]RoundTripper)
   747  	for k, v := range oldMap {
   748  		newMap[k] = v
   749  	}
   750  	newMap[scheme] = rt
   751  	t.altProto.Store(newMap)
   752  }
   753  
   754  // CloseIdleConnections closes any connections which were previously
   755  // connected from previous requests but are now sitting idle in
   756  // a "keep-alive" state. It does not interrupt any connections currently
   757  // in use.
   758  func (t *Transport) CloseIdleConnections() {
   759  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   760  	t.idleMu.Lock()
   761  	m := t.idleConn
   762  	t.idleConn = nil
   763  	t.closeIdle = true // close newly idle connections
   764  	t.idleLRU = connLRU{}
   765  	t.idleMu.Unlock()
   766  	for _, conns := range m {
   767  		for _, pconn := range conns {
   768  			pconn.close(errCloseIdleConns)
   769  		}
   770  	}
   771  	if t2 := t.h2transport; t2 != nil {
   772  		t2.CloseIdleConnections()
   773  	}
   774  }
   775  
   776  // CancelRequest cancels an in-flight request by closing its connection.
   777  // CancelRequest should only be called after RoundTrip has returned.
   778  //
   779  // Deprecated: Use Request.WithContext to create a request with a
   780  // cancelable context instead. CancelRequest cannot cancel HTTP/2
   781  // requests.
   782  func (t *Transport) CancelRequest(req *Request) {
   783  	t.cancelRequest(cancelKey{req}, errRequestCanceled)
   784  }
   785  
   786  // Cancel an in-flight request, recording the error value.
   787  // Returns whether the request was canceled.
   788  func (t *Transport) cancelRequest(key cancelKey, err error) bool {
   789  	t.reqMu.Lock()
   790  	cancel := t.reqCanceler[key]
   791  	delete(t.reqCanceler, key)
   792  	t.reqMu.Unlock()
   793  	if cancel != nil {
   794  		cancel(err)
   795  	}
   796  
   797  	return cancel != nil
   798  }
   799  
   800  //
   801  // Private implementation past this point.
   802  //
   803  
   804  var (
   805  	// proxyConfigOnce guards proxyConfig
   806  	envProxyOnce      sync.Once
   807  	envProxyFuncValue func(*url.URL) (*url.URL, error)
   808  )
   809  
   810  // defaultProxyConfig returns a ProxyConfig value looked up
   811  // from the environment. This mitigates expensive lookups
   812  // on some platforms (e.g. Windows).
   813  func envProxyFunc() func(*url.URL) (*url.URL, error) {
   814  	envProxyOnce.Do(func() {
   815  		envProxyFuncValue = httpproxy.FromEnvironment().ProxyFunc()
   816  	})
   817  	return envProxyFuncValue
   818  }
   819  
   820  // resetProxyConfig is used by tests.
   821  func resetProxyConfig() {
   822  	envProxyOnce = sync.Once{}
   823  	envProxyFuncValue = nil
   824  }
   825  
   826  func (t *Transport) connectMethodForRequest(treq *transportRequest) (cm connectMethod, err error) {
   827  	cm.targetScheme = treq.URL.Scheme
   828  	cm.targetAddr = canonicalAddr(treq.URL)
   829  	if t.Proxy != nil {
   830  		cm.proxyURL, err = t.Proxy(treq.Request)
   831  	}
   832  	cm.onlyH1 = treq.requiresHTTP1()
   833  	return cm, err
   834  }
   835  
   836  // proxyAuth returns the Proxy-Authorization header to set
   837  // on requests, if applicable.
   838  func (cm *connectMethod) proxyAuth() string {
   839  	if cm.proxyURL == nil {
   840  		return ""
   841  	}
   842  	if u := cm.proxyURL.User; u != nil {
   843  		username := u.Username()
   844  		password, _ := u.Password()
   845  		return "Basic " + basicAuth(username, password)
   846  	}
   847  	return ""
   848  }
   849  
   850  // error values for debugging and testing, not seen by users.
   851  var (
   852  	errKeepAlivesDisabled = errors.New("http: putIdleConn: keep alives disabled")
   853  	errConnBroken         = errors.New("http: putIdleConn: connection is in bad state")
   854  	errCloseIdle          = errors.New("http: putIdleConn: CloseIdleConnections was called")
   855  	errTooManyIdle        = errors.New("http: putIdleConn: too many idle connections")
   856  	errTooManyIdleHost    = errors.New("http: putIdleConn: too many idle connections for host")
   857  	errCloseIdleConns     = errors.New("http: CloseIdleConnections called")
   858  	errReadLoopExiting    = errors.New("http: persistConn.readLoop exiting")
   859  	errIdleConnTimeout    = errors.New("http: idle connection timeout")
   860  
   861  	// errServerClosedIdle is not seen by users for idempotent requests, but may be
   862  	// seen by a user if the server shuts down an idle connection and sends its FIN
   863  	// in flight with already-written POST body bytes from the client.
   864  	// See https://github.com/golang/go/issues/19943#issuecomment-355607646
   865  	errServerClosedIdle = errors.New("http: server closed idle connection")
   866  )
   867  
   868  // transportReadFromServerError is used by Transport.readLoop when the
   869  // 1 byte peek read fails and we're actually anticipating a response.
   870  // Usually this is just due to the inherent keep-alive shut down race,
   871  // where the server closed the connection at the same time the client
   872  // wrote. The underlying err field is usually io.EOF or some
   873  // ECONNRESET sort of thing which varies by platform. But it might be
   874  // the user's custom net.Conn.Read error too, so we carry it along for
   875  // them to return from Transport.RoundTrip.
   876  type transportReadFromServerError struct {
   877  	err error
   878  }
   879  
   880  func (e transportReadFromServerError) Unwrap() error { return e.err }
   881  
   882  func (e transportReadFromServerError) Error() string {
   883  	return fmt.Sprintf("net/http: Transport failed to read from server: %v", e.err)
   884  }
   885  
   886  func (t *Transport) putOrCloseIdleConn(pconn *persistConn) {
   887  	if err := t.tryPutIdleConn(pconn); err != nil {
   888  		pconn.close(err)
   889  	}
   890  }
   891  
   892  func (t *Transport) maxIdleConnsPerHost() int {
   893  	if v := t.MaxIdleConnsPerHost; v != 0 {
   894  		return v
   895  	}
   896  	return DefaultMaxIdleConnsPerHost
   897  }
   898  
   899  // tryPutIdleConn adds pconn to the list of idle persistent connections awaiting
   900  // a new request.
   901  // If pconn is no longer needed or not in a good state, tryPutIdleConn returns
   902  // an error explaining why it wasn't registered.
   903  // tryPutIdleConn does not close pconn. Use putOrCloseIdleConn instead for that.
   904  func (t *Transport) tryPutIdleConn(pconn *persistConn) error {
   905  	if t.DisableKeepAlives || t.MaxIdleConnsPerHost < 0 {
   906  		return errKeepAlivesDisabled
   907  	}
   908  	if pconn.isBroken() {
   909  		return errConnBroken
   910  	}
   911  	pconn.markReused()
   912  
   913  	t.idleMu.Lock()
   914  	defer t.idleMu.Unlock()
   915  
   916  	// HTTP/2 (pconn.alt != nil) connections do not come out of the idle list,
   917  	// because multiple goroutines can use them simultaneously.
   918  	// If this is an HTTP/2 connection being “returned,” we're done.
   919  	if pconn.alt != nil && t.idleLRU.m[pconn] != nil {
   920  		return nil
   921  	}
   922  
   923  	// Deliver pconn to goroutine waiting for idle connection, if any.
   924  	// (They may be actively dialing, but this conn is ready first.
   925  	// Chrome calls this socket late binding.
   926  	// See https://www.chromium.org/developers/design-documents/network-stack#TOC-Connection-Management.)
   927  	key := pconn.cacheKey
   928  	if q, ok := t.idleConnWait[key]; ok {
   929  		done := false
   930  		if pconn.alt == nil {
   931  			// HTTP/1.
   932  			// Loop over the waiting list until we find a w that isn't done already, and hand it pconn.
   933  			for q.len() > 0 {
   934  				w := q.popFront()
   935  				if w.tryDeliver(pconn, nil) {
   936  					done = true
   937  					break
   938  				}
   939  			}
   940  		} else {
   941  			// HTTP/2.
   942  			// Can hand the same pconn to everyone in the waiting list,
   943  			// and we still won't be done: we want to put it in the idle
   944  			// list unconditionally, for any future clients too.
   945  			for q.len() > 0 {
   946  				w := q.popFront()
   947  				w.tryDeliver(pconn, nil)
   948  			}
   949  		}
   950  		if q.len() == 0 {
   951  			delete(t.idleConnWait, key)
   952  		} else {
   953  			t.idleConnWait[key] = q
   954  		}
   955  		if done {
   956  			return nil
   957  		}
   958  	}
   959  
   960  	if t.closeIdle {
   961  		return errCloseIdle
   962  	}
   963  	if t.idleConn == nil {
   964  		t.idleConn = make(map[connectMethodKey][]*persistConn)
   965  	}
   966  	idles := t.idleConn[key]
   967  	if len(idles) >= t.maxIdleConnsPerHost() {
   968  		return errTooManyIdleHost
   969  	}
   970  	for _, exist := range idles {
   971  		if exist == pconn {
   972  			log.Fatalf("dup idle pconn %p in freelist", pconn)
   973  		}
   974  	}
   975  	t.idleConn[key] = append(idles, pconn)
   976  	t.idleLRU.add(pconn)
   977  	if t.MaxIdleConns != 0 && t.idleLRU.len() > t.MaxIdleConns {
   978  		oldest := t.idleLRU.removeOldest()
   979  		oldest.close(errTooManyIdle)
   980  		t.removeIdleConnLocked(oldest)
   981  	}
   982  
   983  	// Set idle timer, but only for HTTP/1 (pconn.alt == nil).
   984  	// The HTTP/2 implementation manages the idle timer itself
   985  	// (see idleConnTimeout in h2_bundle.go).
   986  	if t.IdleConnTimeout > 0 && pconn.alt == nil {
   987  		if pconn.idleTimer != nil {
   988  			pconn.idleTimer.Reset(t.IdleConnTimeout)
   989  		} else {
   990  			pconn.idleTimer = time.AfterFunc(t.IdleConnTimeout, pconn.closeConnIfStillIdle)
   991  		}
   992  	}
   993  	pconn.idleAt = time.Now()
   994  	return nil
   995  }
   996  
   997  // queueForIdleConn queues w to receive the next idle connection for w.cm.
   998  // As an optimization hint to the caller, queueForIdleConn reports whether
   999  // it successfully delivered an already-idle connection.
  1000  func (t *Transport) queueForIdleConn(w *wantConn) (delivered bool) {
  1001  	if t.DisableKeepAlives {
  1002  		return false
  1003  	}
  1004  
  1005  	t.idleMu.Lock()
  1006  	defer t.idleMu.Unlock()
  1007  
  1008  	// Stop closing connections that become idle - we might want one.
  1009  	// (That is, undo the effect of t.CloseIdleConnections.)
  1010  	t.closeIdle = false
  1011  
  1012  	if w == nil {
  1013  		// Happens in test hook.
  1014  		return false
  1015  	}
  1016  
  1017  	// If IdleConnTimeout is set, calculate the oldest
  1018  	// persistConn.idleAt time we're willing to use a cached idle
  1019  	// conn.
  1020  	var oldTime time.Time
  1021  	if t.IdleConnTimeout > 0 {
  1022  		oldTime = time.Now().Add(-t.IdleConnTimeout)
  1023  	}
  1024  
  1025  	// Look for most recently-used idle connection.
  1026  	if list, ok := t.idleConn[w.key]; ok {
  1027  		stop := false
  1028  		delivered := false
  1029  		for len(list) > 0 && !stop {
  1030  			pconn := list[len(list)-1]
  1031  
  1032  			// See whether this connection has been idle too long, considering
  1033  			// only the wall time (the Round(0)), in case this is a laptop or VM
  1034  			// coming out of suspend with previously cached idle connections.
  1035  			tooOld := !oldTime.IsZero() && pconn.idleAt.Round(0).Before(oldTime)
  1036  			if tooOld {
  1037  				// Async cleanup. Launch in its own goroutine (as if a
  1038  				// time.AfterFunc called it); it acquires idleMu, which we're
  1039  				// holding, and does a synchronous net.Conn.Close.
  1040  				go pconn.closeConnIfStillIdle()
  1041  			}
  1042  			if pconn.isBroken() || tooOld {
  1043  				// If either persistConn.readLoop has marked the connection
  1044  				// broken, but Transport.removeIdleConn has not yet removed it
  1045  				// from the idle list, or if this persistConn is too old (it was
  1046  				// idle too long), then ignore it and look for another. In both
  1047  				// cases it's already in the process of being closed.
  1048  				list = list[:len(list)-1]
  1049  				continue
  1050  			}
  1051  			delivered = w.tryDeliver(pconn, nil)
  1052  			if delivered {
  1053  				if pconn.alt != nil {
  1054  					// HTTP/2: multiple clients can share pconn.
  1055  					// Leave it in the list.
  1056  				} else {
  1057  					// HTTP/1: only one client can use pconn.
  1058  					// Remove it from the list.
  1059  					t.idleLRU.remove(pconn)
  1060  					list = list[:len(list)-1]
  1061  				}
  1062  			}
  1063  			stop = true
  1064  		}
  1065  		if len(list) > 0 {
  1066  			t.idleConn[w.key] = list
  1067  		} else {
  1068  			delete(t.idleConn, w.key)
  1069  		}
  1070  		if stop {
  1071  			return delivered
  1072  		}
  1073  	}
  1074  
  1075  	// Register to receive next connection that becomes idle.
  1076  	if t.idleConnWait == nil {
  1077  		t.idleConnWait = make(map[connectMethodKey]wantConnQueue)
  1078  	}
  1079  	q := t.idleConnWait[w.key]
  1080  	q.cleanFront()
  1081  	q.pushBack(w)
  1082  	t.idleConnWait[w.key] = q
  1083  	return false
  1084  }
  1085  
  1086  // removeIdleConn marks pconn as dead.
  1087  func (t *Transport) removeIdleConn(pconn *persistConn) bool {
  1088  	t.idleMu.Lock()
  1089  	defer t.idleMu.Unlock()
  1090  	return t.removeIdleConnLocked(pconn)
  1091  }
  1092  
  1093  // t.idleMu must be held.
  1094  func (t *Transport) removeIdleConnLocked(pconn *persistConn) bool {
  1095  	if pconn.idleTimer != nil {
  1096  		pconn.idleTimer.Stop()
  1097  	}
  1098  	t.idleLRU.remove(pconn)
  1099  	key := pconn.cacheKey
  1100  	pconns := t.idleConn[key]
  1101  	var removed bool
  1102  	switch len(pconns) {
  1103  	case 0:
  1104  		// Nothing
  1105  	case 1:
  1106  		if pconns[0] == pconn {
  1107  			delete(t.idleConn, key)
  1108  			removed = true
  1109  		}
  1110  	default:
  1111  		for i, v := range pconns {
  1112  			if v != pconn {
  1113  				continue
  1114  			}
  1115  			// Slide down, keeping most recently-used
  1116  			// conns at the end.
  1117  			copy(pconns[i:], pconns[i+1:])
  1118  			t.idleConn[key] = pconns[:len(pconns)-1]
  1119  			removed = true
  1120  			break
  1121  		}
  1122  	}
  1123  	return removed
  1124  }
  1125  
  1126  func (t *Transport) setReqCanceler(key cancelKey, fn func(error)) {
  1127  	t.reqMu.Lock()
  1128  	defer t.reqMu.Unlock()
  1129  	if t.reqCanceler == nil {
  1130  		t.reqCanceler = make(map[cancelKey]func(error))
  1131  	}
  1132  	if fn != nil {
  1133  		t.reqCanceler[key] = fn
  1134  	} else {
  1135  		delete(t.reqCanceler, key)
  1136  	}
  1137  }
  1138  
  1139  // replaceReqCanceler replaces an existing cancel function. If there is no cancel function
  1140  // for the request, we don't set the function and return false.
  1141  // Since CancelRequest will clear the canceler, we can use the return value to detect if
  1142  // the request was canceled since the last setReqCancel call.
  1143  func (t *Transport) replaceReqCanceler(key cancelKey, fn func(error)) bool {
  1144  	t.reqMu.Lock()
  1145  	defer t.reqMu.Unlock()
  1146  	_, ok := t.reqCanceler[key]
  1147  	if !ok {
  1148  		return false
  1149  	}
  1150  	if fn != nil {
  1151  		t.reqCanceler[key] = fn
  1152  	} else {
  1153  		delete(t.reqCanceler, key)
  1154  	}
  1155  	return true
  1156  }
  1157  
  1158  var zeroDialer net.Dialer
  1159  
  1160  func (t *Transport) dial(ctx context.Context, network, addr string) (net.Conn, error) {
  1161  	if t.DialContext != nil {
  1162  		return t.DialContext(ctx, network, addr)
  1163  	}
  1164  	if t.Dial != nil {
  1165  		c, err := t.Dial(network, addr)
  1166  		if c == nil && err == nil {
  1167  			err = errors.New("net/http: Transport.Dial hook returned (nil, nil)")
  1168  		}
  1169  		return c, err
  1170  	}
  1171  	return zeroDialer.DialContext(ctx, network, addr)
  1172  }
  1173  
  1174  // A wantConn records state about a wanted connection
  1175  // (that is, an active call to getConn).
  1176  // The conn may be gotten by dialing or by finding an idle connection,
  1177  // or a cancellation may make the conn no longer wanted.
  1178  // These three options are racing against each other and use
  1179  // wantConn to coordinate and agree about the winning outcome.
  1180  type wantConn struct {
  1181  	cm    connectMethod
  1182  	key   connectMethodKey // cm.key()
  1183  	ctx   context.Context  // context for dial
  1184  	ready chan struct{}    // closed when pc, err pair is delivered
  1185  
  1186  	// hooks for testing to know when dials are done
  1187  	// beforeDial is called in the getConn goroutine when the dial is queued.
  1188  	// afterDial is called when the dial is completed or cancelled.
  1189  	beforeDial func()
  1190  	afterDial  func()
  1191  
  1192  	mu  sync.Mutex // protects pc, err, close(ready)
  1193  	pc  *persistConn
  1194  	err error
  1195  }
  1196  
  1197  // waiting reports whether w is still waiting for an answer (connection or error).
  1198  func (w *wantConn) waiting() bool {
  1199  	select {
  1200  	case <-w.ready:
  1201  		return false
  1202  	default:
  1203  		return true
  1204  	}
  1205  }
  1206  
  1207  // tryDeliver attempts to deliver pc, err to w and reports whether it succeeded.
  1208  func (w *wantConn) tryDeliver(pc *persistConn, err error) bool {
  1209  	w.mu.Lock()
  1210  	defer w.mu.Unlock()
  1211  
  1212  	if w.pc != nil || w.err != nil {
  1213  		return false
  1214  	}
  1215  
  1216  	w.pc = pc
  1217  	w.err = err
  1218  	if w.pc == nil && w.err == nil {
  1219  		panic("net/http: internal error: misuse of tryDeliver")
  1220  	}
  1221  	close(w.ready)
  1222  	return true
  1223  }
  1224  
  1225  // cancel marks w as no longer wanting a result (for example, due to cancellation).
  1226  // If a connection has been delivered already, cancel returns it with t.putOrCloseIdleConn.
  1227  func (w *wantConn) cancel(t *Transport, err error) {
  1228  	w.mu.Lock()
  1229  	if w.pc == nil && w.err == nil {
  1230  		close(w.ready) // catch misbehavior in future delivery
  1231  	}
  1232  	pc := w.pc
  1233  	w.pc = nil
  1234  	w.err = err
  1235  	w.mu.Unlock()
  1236  
  1237  	if pc != nil {
  1238  		t.putOrCloseIdleConn(pc)
  1239  	}
  1240  }
  1241  
  1242  // A wantConnQueue is a queue of wantConns.
  1243  type wantConnQueue struct {
  1244  	// This is a queue, not a deque.
  1245  	// It is split into two stages - head[headPos:] and tail.
  1246  	// popFront is trivial (headPos++) on the first stage, and
  1247  	// pushBack is trivial (append) on the second stage.
  1248  	// If the first stage is empty, popFront can swap the
  1249  	// first and second stages to remedy the situation.
  1250  	//
  1251  	// This two-stage split is analogous to the use of two lists
  1252  	// in Okasaki's purely functional queue but without the
  1253  	// overhead of reversing the list when swapping stages.
  1254  	head    []*wantConn
  1255  	headPos int
  1256  	tail    []*wantConn
  1257  }
  1258  
  1259  // len returns the number of items in the queue.
  1260  func (q *wantConnQueue) len() int {
  1261  	return len(q.head) - q.headPos + len(q.tail)
  1262  }
  1263  
  1264  // pushBack adds w to the back of the queue.
  1265  func (q *wantConnQueue) pushBack(w *wantConn) {
  1266  	q.tail = append(q.tail, w)
  1267  }
  1268  
  1269  // popFront removes and returns the wantConn at the front of the queue.
  1270  func (q *wantConnQueue) popFront() *wantConn {
  1271  	if q.headPos >= len(q.head) {
  1272  		if len(q.tail) == 0 {
  1273  			return nil
  1274  		}
  1275  		// Pick up tail as new head, clear tail.
  1276  		q.head, q.headPos, q.tail = q.tail, 0, q.head[:0]
  1277  	}
  1278  	w := q.head[q.headPos]
  1279  	q.head[q.headPos] = nil
  1280  	q.headPos++
  1281  	return w
  1282  }
  1283  
  1284  // peekFront returns the wantConn at the front of the queue without removing it.
  1285  func (q *wantConnQueue) peekFront() *wantConn {
  1286  	if q.headPos < len(q.head) {
  1287  		return q.head[q.headPos]
  1288  	}
  1289  	if len(q.tail) > 0 {
  1290  		return q.tail[0]
  1291  	}
  1292  	return nil
  1293  }
  1294  
  1295  // cleanFront pops any wantConns that are no longer waiting from the head of the
  1296  // queue, reporting whether any were popped.
  1297  func (q *wantConnQueue) cleanFront() (cleaned bool) {
  1298  	for {
  1299  		w := q.peekFront()
  1300  		if w == nil || w.waiting() {
  1301  			return cleaned
  1302  		}
  1303  		q.popFront()
  1304  		cleaned = true
  1305  	}
  1306  }
  1307  
  1308  func (t *Transport) customDialTLS(ctx context.Context, network, addr string) (conn net.Conn, err error) {
  1309  	if t.DialTLSContext != nil {
  1310  		conn, err = t.DialTLSContext(ctx, network, addr)
  1311  	} else {
  1312  		conn, err = t.DialTLS(network, addr)
  1313  	}
  1314  	if conn == nil && err == nil {
  1315  		err = errors.New("net/http: Transport.DialTLS or DialTLSContext returned (nil, nil)")
  1316  	}
  1317  	return
  1318  }
  1319  
  1320  // getConn dials and creates a new persistConn to the target as
  1321  // specified in the connectMethod. This includes doing a proxy CONNECT
  1322  // and/or setting up TLS.  If this doesn't return an error, the persistConn
  1323  // is ready to write requests to.
  1324  func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (pc *persistConn, err error) {
  1325  	req := treq.Request
  1326  	trace := treq.trace
  1327  	ctx := req.Context()
  1328  	if trace != nil && trace.GetConn != nil {
  1329  		trace.GetConn(cm.addr())
  1330  	}
  1331  
  1332  	w := &wantConn{
  1333  		cm:         cm,
  1334  		key:        cm.key(),
  1335  		ctx:        ctx,
  1336  		ready:      make(chan struct{}, 1),
  1337  		beforeDial: testHookPrePendingDial,
  1338  		afterDial:  testHookPostPendingDial,
  1339  	}
  1340  	defer func() {
  1341  		if err != nil {
  1342  			w.cancel(t, err)
  1343  		}
  1344  	}()
  1345  
  1346  	// Queue for idle connection.
  1347  	if delivered := t.queueForIdleConn(w); delivered {
  1348  		pc := w.pc
  1349  		// Trace only for HTTP/1.
  1350  		// HTTP/2 calls trace.GotConn itself.
  1351  		if pc.alt == nil && trace != nil && trace.GotConn != nil {
  1352  			trace.GotConn(pc.gotIdleConnTrace(pc.idleAt))
  1353  		}
  1354  		// set request canceler to some non-nil function so we
  1355  		// can detect whether it was cleared between now and when
  1356  		// we enter roundTrip
  1357  		t.setReqCanceler(treq.cancelKey, func(error) {})
  1358  		return pc, nil
  1359  	}
  1360  
  1361  	cancelc := make(chan error, 1)
  1362  	t.setReqCanceler(treq.cancelKey, func(err error) { cancelc <- err })
  1363  
  1364  	// Queue for permission to dial.
  1365  	t.queueForDial(w)
  1366  
  1367  	// Wait for completion or cancellation.
  1368  	select {
  1369  	case <-w.ready:
  1370  		// Trace success but only for HTTP/1.
  1371  		// HTTP/2 calls trace.GotConn itself.
  1372  		if w.pc != nil && w.pc.alt == nil && trace != nil && trace.GotConn != nil {
  1373  			trace.GotConn(httptrace.GotConnInfo{Conn: w.pc.conn, Reused: w.pc.isReused()})
  1374  		}
  1375  		if w.err != nil {
  1376  			// If the request has been cancelled, that's probably
  1377  			// what caused w.err; if so, prefer to return the
  1378  			// cancellation error (see golang.org/issue/16049).
  1379  			select {
  1380  			case <-req.Cancel:
  1381  				return nil, errRequestCanceledConn
  1382  			case <-req.Context().Done():
  1383  				return nil, req.Context().Err()
  1384  			case err := <-cancelc:
  1385  				if err == errRequestCanceled {
  1386  					err = errRequestCanceledConn
  1387  				}
  1388  				return nil, err
  1389  			default:
  1390  				// return below
  1391  			}
  1392  		}
  1393  		return w.pc, w.err
  1394  	case <-req.Cancel:
  1395  		return nil, errRequestCanceledConn
  1396  	case <-req.Context().Done():
  1397  		return nil, req.Context().Err()
  1398  	case err := <-cancelc:
  1399  		if err == errRequestCanceled {
  1400  			err = errRequestCanceledConn
  1401  		}
  1402  		return nil, err
  1403  	}
  1404  }
  1405  
  1406  // queueForDial queues w to wait for permission to begin dialing.
  1407  // Once w receives permission to dial, it will do so in a separate goroutine.
  1408  func (t *Transport) queueForDial(w *wantConn) {
  1409  	w.beforeDial()
  1410  	if t.MaxConnsPerHost <= 0 {
  1411  		go t.dialConnFor(w)
  1412  		return
  1413  	}
  1414  
  1415  	t.connsPerHostMu.Lock()
  1416  	defer t.connsPerHostMu.Unlock()
  1417  
  1418  	if n := t.connsPerHost[w.key]; n < t.MaxConnsPerHost {
  1419  		if t.connsPerHost == nil {
  1420  			t.connsPerHost = make(map[connectMethodKey]int)
  1421  		}
  1422  		t.connsPerHost[w.key] = n + 1
  1423  		go t.dialConnFor(w)
  1424  		return
  1425  	}
  1426  
  1427  	if t.connsPerHostWait == nil {
  1428  		t.connsPerHostWait = make(map[connectMethodKey]wantConnQueue)
  1429  	}
  1430  	q := t.connsPerHostWait[w.key]
  1431  	q.cleanFront()
  1432  	q.pushBack(w)
  1433  	t.connsPerHostWait[w.key] = q
  1434  }
  1435  
  1436  // dialConnFor dials on behalf of w and delivers the result to w.
  1437  // dialConnFor has received permission to dial w.cm and is counted in t.connCount[w.cm.key()].
  1438  // If the dial is cancelled or unsuccessful, dialConnFor decrements t.connCount[w.cm.key()].
  1439  func (t *Transport) dialConnFor(w *wantConn) {
  1440  	defer w.afterDial()
  1441  
  1442  	pc, err := t.dialConn(w.ctx, w.cm)
  1443  	delivered := w.tryDeliver(pc, err)
  1444  	if err == nil && (!delivered || pc.alt != nil) {
  1445  		// pconn was not passed to w,
  1446  		// or it is HTTP/2 and can be shared.
  1447  		// Add to the idle connection pool.
  1448  		t.putOrCloseIdleConn(pc)
  1449  	}
  1450  	if err != nil {
  1451  		t.decConnsPerHost(w.key)
  1452  	}
  1453  }
  1454  
  1455  // decConnsPerHost decrements the per-host connection count for key,
  1456  // which may in turn give a different waiting goroutine permission to dial.
  1457  func (t *Transport) decConnsPerHost(key connectMethodKey) {
  1458  	if t.MaxConnsPerHost <= 0 {
  1459  		return
  1460  	}
  1461  
  1462  	t.connsPerHostMu.Lock()
  1463  	defer t.connsPerHostMu.Unlock()
  1464  	n := t.connsPerHost[key]
  1465  	if n == 0 {
  1466  		// Shouldn't happen, but if it does, the counting is buggy and could
  1467  		// easily lead to a silent deadlock, so report the problem loudly.
  1468  		panic("net/http: internal error: connCount underflow")
  1469  	}
  1470  
  1471  	// Can we hand this count to a goroutine still waiting to dial?
  1472  	// (Some goroutines on the wait list may have timed out or
  1473  	// gotten a connection another way. If they're all gone,
  1474  	// we don't want to kick off any spurious dial operations.)
  1475  	if q := t.connsPerHostWait[key]; q.len() > 0 {
  1476  		done := false
  1477  		for q.len() > 0 {
  1478  			w := q.popFront()
  1479  			if w.waiting() {
  1480  				go t.dialConnFor(w)
  1481  				done = true
  1482  				break
  1483  			}
  1484  		}
  1485  		if q.len() == 0 {
  1486  			delete(t.connsPerHostWait, key)
  1487  		} else {
  1488  			// q is a value (like a slice), so we have to store
  1489  			// the updated q back into the map.
  1490  			t.connsPerHostWait[key] = q
  1491  		}
  1492  		if done {
  1493  			return
  1494  		}
  1495  	}
  1496  
  1497  	// Otherwise, decrement the recorded count.
  1498  	if n--; n == 0 {
  1499  		delete(t.connsPerHost, key)
  1500  	} else {
  1501  		t.connsPerHost[key] = n
  1502  	}
  1503  }
  1504  
  1505  // Add TLS to a persistent connection, i.e. negotiate a TLS session. If pconn is already a TLS
  1506  // tunnel, this function establishes a nested TLS session inside the encrypted channel.
  1507  // The remote endpoint's name may be overridden by TLSClientConfig.ServerName.
  1508  func (pconn *persistConn) addTLS(name string, trace *httptrace.ClientTrace) error {
  1509  	// Initiate TLS and check remote host name against certificate.
  1510  	cfg := cloneTLSConfig(pconn.t.TLSClientConfig)
  1511  	if cfg.ServerName == "" {
  1512  		cfg.ServerName = name
  1513  	}
  1514  	if pconn.cacheKey.onlyH1 {
  1515  		cfg.NextProtos = nil
  1516  	}
  1517  	plainConn := pconn.conn
  1518  	tlsConn := tls.Client(plainConn, cfg)
  1519  	errc := make(chan error, 2)
  1520  	var timer *time.Timer // for canceling TLS handshake
  1521  	if d := pconn.t.TLSHandshakeTimeout; d != 0 {
  1522  		timer = time.AfterFunc(d, func() {
  1523  			errc <- tlsHandshakeTimeoutError{}
  1524  		})
  1525  	}
  1526  	go func() {
  1527  		if trace != nil && trace.TLSHandshakeStart != nil {
  1528  			trace.TLSHandshakeStart()
  1529  		}
  1530  		err := tlsConn.Handshake()
  1531  		if timer != nil {
  1532  			timer.Stop()
  1533  		}
  1534  		errc <- err
  1535  	}()
  1536  	if err := <-errc; err != nil {
  1537  		plainConn.Close()
  1538  		if trace != nil && trace.TLSHandshakeDone != nil {
  1539  			trace.TLSHandshakeDone(tls.ConnectionState{}, err)
  1540  		}
  1541  		return err
  1542  	}
  1543  	cs := tlsConn.ConnectionState()
  1544  	if trace != nil && trace.TLSHandshakeDone != nil {
  1545  		trace.TLSHandshakeDone(cs, nil)
  1546  	}
  1547  	pconn.tlsState = &cs
  1548  	pconn.conn = tlsConn
  1549  	return nil
  1550  }
  1551  
  1552  type erringRoundTripper interface {
  1553  	RoundTripErr() error
  1554  }
  1555  
  1556  func (t *Transport) dialConn(ctx context.Context, cm connectMethod) (pconn *persistConn, err error) {
  1557  	pconn = &persistConn{
  1558  		t:             t,
  1559  		cacheKey:      cm.key(),
  1560  		reqch:         make(chan requestAndChan, 1),
  1561  		writech:       make(chan writeRequest, 1),
  1562  		closech:       make(chan struct{}),
  1563  		writeErrCh:    make(chan error, 1),
  1564  		writeLoopDone: make(chan struct{}),
  1565  	}
  1566  	trace := httptrace.ContextClientTrace(ctx)
  1567  	wrapErr := func(err error) error {
  1568  		if cm.proxyURL != nil {
  1569  			// Return a typed error, per Issue 16997
  1570  			return &net.OpError{Op: "proxyconnect", Net: "tcp", Err: err}
  1571  		}
  1572  		return err
  1573  	}
  1574  	if cm.scheme() == "https" && t.hasCustomTLSDialer() {
  1575  		var err error
  1576  		pconn.conn, err = t.customDialTLS(ctx, "tcp", cm.addr())
  1577  		if err != nil {
  1578  			return nil, wrapErr(err)
  1579  		}
  1580  		if tc, ok := pconn.conn.(*tls.Conn); ok {
  1581  			// Handshake here, in case DialTLS didn't. TLSNextProto below
  1582  			// depends on it for knowing the connection state.
  1583  			if trace != nil && trace.TLSHandshakeStart != nil {
  1584  				trace.TLSHandshakeStart()
  1585  			}
  1586  			if err := tc.Handshake(); err != nil {
  1587  				go pconn.conn.Close()
  1588  				if trace != nil && trace.TLSHandshakeDone != nil {
  1589  					trace.TLSHandshakeDone(tls.ConnectionState{}, err)
  1590  				}
  1591  				return nil, err
  1592  			}
  1593  			cs := tc.ConnectionState()
  1594  			if trace != nil && trace.TLSHandshakeDone != nil {
  1595  				trace.TLSHandshakeDone(cs, nil)
  1596  			}
  1597  			pconn.tlsState = &cs
  1598  		}
  1599  	} else {
  1600  		conn, err := t.dial(ctx, "tcp", cm.addr())
  1601  		if err != nil {
  1602  			return nil, wrapErr(err)
  1603  		}
  1604  		pconn.conn = conn
  1605  		if cm.scheme() == "https" {
  1606  			var firstTLSHost string
  1607  			if firstTLSHost, _, err = net.SplitHostPort(cm.addr()); err != nil {
  1608  				return nil, wrapErr(err)
  1609  			}
  1610  			if err = pconn.addTLS(firstTLSHost, trace); err != nil {
  1611  				return nil, wrapErr(err)
  1612  			}
  1613  		}
  1614  	}
  1615  
  1616  	// Proxy setup.
  1617  	switch {
  1618  	case cm.proxyURL == nil:
  1619  		// Do nothing. Not using a proxy.
  1620  	case cm.proxyURL.Scheme == "socks5":
  1621  		conn := pconn.conn
  1622  		d := socksNewDialer("tcp", conn.RemoteAddr().String())
  1623  		if u := cm.proxyURL.User; u != nil {
  1624  			auth := &socksUsernamePassword{
  1625  				Username: u.Username(),
  1626  			}
  1627  			auth.Password, _ = u.Password()
  1628  			d.AuthMethods = []socksAuthMethod{
  1629  				socksAuthMethodNotRequired,
  1630  				socksAuthMethodUsernamePassword,
  1631  			}
  1632  			d.Authenticate = auth.Authenticate
  1633  		}
  1634  		if _, err := d.DialWithConn(ctx, conn, "tcp", cm.targetAddr); err != nil {
  1635  			conn.Close()
  1636  			return nil, err
  1637  		}
  1638  	case cm.targetScheme == "http":
  1639  		pconn.isProxy = true
  1640  		if pa := cm.proxyAuth(); pa != "" {
  1641  			pconn.mutateHeaderFunc = func(h Header) {
  1642  				h.Set("Proxy-Authorization", pa)
  1643  			}
  1644  		}
  1645  	case cm.targetScheme == "https":
  1646  		conn := pconn.conn
  1647  		var hdr Header
  1648  		if t.GetProxyConnectHeader != nil {
  1649  			var err error
  1650  			hdr, err = t.GetProxyConnectHeader(ctx, cm.proxyURL, cm.targetAddr)
  1651  			if err != nil {
  1652  				conn.Close()
  1653  				return nil, err
  1654  			}
  1655  		} else {
  1656  			hdr = t.ProxyConnectHeader
  1657  		}
  1658  		if hdr == nil {
  1659  			hdr = make(Header)
  1660  		}
  1661  		if pa := cm.proxyAuth(); pa != "" {
  1662  			hdr = hdr.Clone()
  1663  			hdr.Set("Proxy-Authorization", pa)
  1664  		}
  1665  		connectReq := &Request{
  1666  			Method: "CONNECT",
  1667  			URL:    &url.URL{Opaque: cm.targetAddr},
  1668  			Host:   cm.targetAddr,
  1669  			Header: hdr,
  1670  		}
  1671  
  1672  		// If there's no done channel (no deadline or cancellation
  1673  		// from the caller possible), at least set some (long)
  1674  		// timeout here. This will make sure we don't block forever
  1675  		// and leak a goroutine if the connection stops replying
  1676  		// after the TCP connect.
  1677  		connectCtx := ctx
  1678  		if ctx.Done() == nil {
  1679  			newCtx, cancel := context.WithTimeout(ctx, 1*time.Minute)
  1680  			defer cancel()
  1681  			connectCtx = newCtx
  1682  		}
  1683  
  1684  		didReadResponse := make(chan struct{}) // closed after CONNECT write+read is done or fails
  1685  		var (
  1686  			resp *Response
  1687  			err  error // write or read error
  1688  		)
  1689  		// Write the CONNECT request & read the response.
  1690  		go func() {
  1691  			defer close(didReadResponse)
  1692  			err = connectReq.Write(conn)
  1693  			if err != nil {
  1694  				return
  1695  			}
  1696  			// Okay to use and discard buffered reader here, because
  1697  			// TLS server will not speak until spoken to.
  1698  			br := bufio.NewReader(conn)
  1699  			resp, err = ReadResponse(br, connectReq)
  1700  		}()
  1701  		select {
  1702  		case <-connectCtx.Done():
  1703  			conn.Close()
  1704  			<-didReadResponse
  1705  			return nil, connectCtx.Err()
  1706  		case <-didReadResponse:
  1707  			// resp or err now set
  1708  		}
  1709  		if err != nil {
  1710  			conn.Close()
  1711  			return nil, err
  1712  		}
  1713  		if resp.StatusCode != 200 {
  1714  			f := strings.SplitN(resp.Status, " ", 2)
  1715  			conn.Close()
  1716  			if len(f) < 2 {
  1717  				return nil, errors.New("unknown status code")
  1718  			}
  1719  			return nil, errors.New(f[1])
  1720  		}
  1721  	}
  1722  
  1723  	if cm.proxyURL != nil && cm.targetScheme == "https" {
  1724  		if err := pconn.addTLS(cm.tlsHost(), trace); err != nil {
  1725  			return nil, err
  1726  		}
  1727  	}
  1728  
  1729  	if s := pconn.tlsState; s != nil && s.NegotiatedProtocolIsMutual && s.NegotiatedProtocol != "" {
  1730  		if next, ok := t.TLSNextProto[s.NegotiatedProtocol]; ok {
  1731  			alt := next(cm.targetAddr, pconn.conn.(*tls.Conn))
  1732  			if e, ok := alt.(erringRoundTripper); ok {
  1733  				// pconn.conn was closed by next (http2configureTransports.upgradeFn).
  1734  				return nil, e.RoundTripErr()
  1735  			}
  1736  			return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: alt}, nil
  1737  		}
  1738  	}
  1739  
  1740  	pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())
  1741  	pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())
  1742  
  1743  	go pconn.readLoop()
  1744  	go pconn.writeLoop()
  1745  	return pconn, nil
  1746  }
  1747  
  1748  // persistConnWriter is the io.Writer written to by pc.bw.
  1749  // It accumulates the number of bytes written to the underlying conn,
  1750  // so the retry logic can determine whether any bytes made it across
  1751  // the wire.
  1752  // This is exactly 1 pointer field wide so it can go into an interface
  1753  // without allocation.
  1754  type persistConnWriter struct {
  1755  	pc *persistConn
  1756  }
  1757  
  1758  func (w persistConnWriter) Write(p []byte) (n int, err error) {
  1759  	n, err = w.pc.conn.Write(p)
  1760  	w.pc.nwrite += int64(n)
  1761  	return
  1762  }
  1763  
  1764  // ReadFrom exposes persistConnWriter's underlying Conn to io.Copy and if
  1765  // the Conn implements io.ReaderFrom, it can take advantage of optimizations
  1766  // such as sendfile.
  1767  func (w persistConnWriter) ReadFrom(r io.Reader) (n int64, err error) {
  1768  	n, err = io.Copy(w.pc.conn, r)
  1769  	w.pc.nwrite += n
  1770  	return
  1771  }
  1772  
  1773  var _ io.ReaderFrom = (*persistConnWriter)(nil)
  1774  
  1775  // connectMethod is the map key (in its String form) for keeping persistent
  1776  // TCP connections alive for subsequent HTTP requests.
  1777  //
  1778  // A connect method may be of the following types:
  1779  //
  1780  //	connectMethod.key().String()      Description
  1781  //	------------------------------    -------------------------
  1782  //	|http|foo.com                     http directly to server, no proxy
  1783  //	|https|foo.com                    https directly to server, no proxy
  1784  //	|https,h1|foo.com                 https directly to server w/o HTTP/2, no proxy
  1785  //	http://proxy.com|https|foo.com    http to proxy, then CONNECT to foo.com
  1786  //	http://proxy.com|http             http to proxy, http to anywhere after that
  1787  //	socks5://proxy.com|http|foo.com   socks5 to proxy, then http to foo.com
  1788  //	socks5://proxy.com|https|foo.com  socks5 to proxy, then https to foo.com
  1789  //	https://proxy.com|https|foo.com   https to proxy, then CONNECT to foo.com
  1790  //	https://proxy.com|http            https to proxy, http to anywhere after that
  1791  //
  1792  type connectMethod struct {
  1793  	_            incomparable
  1794  	proxyURL     *url.URL // nil for no proxy, else full proxy URL
  1795  	targetScheme string   // "http" or "https"
  1796  	// If proxyURL specifies an http or https proxy, and targetScheme is http (not https),
  1797  	// then targetAddr is not included in the connect method key, because the socket can
  1798  	// be reused for different targetAddr values.
  1799  	targetAddr string
  1800  	onlyH1     bool // whether to disable HTTP/2 and force HTTP/1
  1801  }
  1802  
  1803  func (cm *connectMethod) key() connectMethodKey {
  1804  	proxyStr := ""
  1805  	targetAddr := cm.targetAddr
  1806  	if cm.proxyURL != nil {
  1807  		proxyStr = cm.proxyURL.String()
  1808  		if (cm.proxyURL.Scheme == "http" || cm.proxyURL.Scheme == "https") && cm.targetScheme == "http" {
  1809  			targetAddr = ""
  1810  		}
  1811  	}
  1812  	return connectMethodKey{
  1813  		proxy:  proxyStr,
  1814  		scheme: cm.targetScheme,
  1815  		addr:   targetAddr,
  1816  		onlyH1: cm.onlyH1,
  1817  	}
  1818  }
  1819  
  1820  // scheme returns the first hop scheme: http, https, or socks5
  1821  func (cm *connectMethod) scheme() string {
  1822  	if cm.proxyURL != nil {
  1823  		return cm.proxyURL.Scheme
  1824  	}
  1825  	return cm.targetScheme
  1826  }
  1827  
  1828  // addr returns the first hop "host:port" to which we need to TCP connect.
  1829  func (cm *connectMethod) addr() string {
  1830  	if cm.proxyURL != nil {
  1831  		return canonicalAddr(cm.proxyURL)
  1832  	}
  1833  	return cm.targetAddr
  1834  }
  1835  
  1836  // tlsHost returns the host name to match against the peer's
  1837  // TLS certificate.
  1838  func (cm *connectMethod) tlsHost() string {
  1839  	h := cm.targetAddr
  1840  	if hasPort(h) {
  1841  		h = h[:strings.LastIndex(h, ":")]
  1842  	}
  1843  	return h
  1844  }
  1845  
  1846  // connectMethodKey is the map key version of connectMethod, with a
  1847  // stringified proxy URL (or the empty string) instead of a pointer to
  1848  // a URL.
  1849  type connectMethodKey struct {
  1850  	proxy, scheme, addr string
  1851  	onlyH1              bool
  1852  }
  1853  
  1854  func (k connectMethodKey) String() string {
  1855  	// Only used by tests.
  1856  	var h1 string
  1857  	if k.onlyH1 {
  1858  		h1 = ",h1"
  1859  	}
  1860  	return fmt.Sprintf("%s|%s%s|%s", k.proxy, k.scheme, h1, k.addr)
  1861  }
  1862  
  1863  // persistConn wraps a connection, usually a persistent one
  1864  // (but may be used for non-keep-alive requests as well)
  1865  type persistConn struct {
  1866  	// alt optionally specifies the TLS NextProto RoundTripper.
  1867  	// This is used for HTTP/2 today and future protocols later.
  1868  	// If it's non-nil, the rest of the fields are unused.
  1869  	alt RoundTripper
  1870  
  1871  	t         *Transport
  1872  	cacheKey  connectMethodKey
  1873  	conn      net.Conn
  1874  	tlsState  *tls.ConnectionState
  1875  	br        *bufio.Reader       // from conn
  1876  	bw        *bufio.Writer       // to conn
  1877  	nwrite    int64               // bytes written
  1878  	reqch     chan requestAndChan // written by roundTrip; read by readLoop
  1879  	writech   chan writeRequest   // written by roundTrip; read by writeLoop
  1880  	closech   chan struct{}       // closed when conn closed
  1881  	isProxy   bool
  1882  	sawEOF    bool  // whether we've seen EOF from conn; owned by readLoop
  1883  	readLimit int64 // bytes allowed to be read; owned by readLoop
  1884  	// writeErrCh passes the request write error (usually nil)
  1885  	// from the writeLoop goroutine to the readLoop which passes
  1886  	// it off to the res.Body reader, which then uses it to decide
  1887  	// whether or not a connection can be reused. Issue 7569.
  1888  	writeErrCh chan error
  1889  
  1890  	writeLoopDone chan struct{} // closed when write loop ends
  1891  
  1892  	// Both guarded by Transport.idleMu:
  1893  	idleAt    time.Time   // time it last become idle
  1894  	idleTimer *time.Timer // holding an AfterFunc to close it
  1895  
  1896  	mu                   sync.Mutex // guards following fields
  1897  	numExpectedResponses int
  1898  	closed               error // set non-nil when conn is closed, before closech is closed
  1899  	canceledErr          error // set non-nil if conn is canceled
  1900  	broken               bool  // an error has happened on this connection; marked broken so it's not reused.
  1901  	reused               bool  // whether conn has had successful request/response and is being reused.
  1902  	// mutateHeaderFunc is an optional func to modify extra
  1903  	// headers on each outbound request before it's written. (the
  1904  	// original Request given to RoundTrip is not modified)
  1905  	mutateHeaderFunc func(Header)
  1906  }
  1907  
  1908  func (pc *persistConn) maxHeaderResponseSize() int64 {
  1909  	if v := pc.t.MaxResponseHeaderBytes; v != 0 {
  1910  		return v
  1911  	}
  1912  	return 10 << 20 // conservative default; same as http2
  1913  }
  1914  
  1915  func (pc *persistConn) Read(p []byte) (n int, err error) {
  1916  	if pc.readLimit <= 0 {
  1917  		return 0, fmt.Errorf("read limit of %d bytes exhausted", pc.maxHeaderResponseSize())
  1918  	}
  1919  	if int64(len(p)) > pc.readLimit {
  1920  		p = p[:pc.readLimit]
  1921  	}
  1922  	n, err = pc.conn.Read(p)
  1923  	if err == io.EOF {
  1924  		pc.sawEOF = true
  1925  	}
  1926  	pc.readLimit -= int64(n)
  1927  	return
  1928  }
  1929  
  1930  // isBroken reports whether this connection is in a known broken state.
  1931  func (pc *persistConn) isBroken() bool {
  1932  	pc.mu.Lock()
  1933  	b := pc.closed != nil
  1934  	pc.mu.Unlock()
  1935  	return b
  1936  }
  1937  
  1938  // canceled returns non-nil if the connection was closed due to
  1939  // CancelRequest or due to context cancellation.
  1940  func (pc *persistConn) canceled() error {
  1941  	pc.mu.Lock()
  1942  	defer pc.mu.Unlock()
  1943  	return pc.canceledErr
  1944  }
  1945  
  1946  // isReused reports whether this connection has been used before.
  1947  func (pc *persistConn) isReused() bool {
  1948  	pc.mu.Lock()
  1949  	r := pc.reused
  1950  	pc.mu.Unlock()
  1951  	return r
  1952  }
  1953  
  1954  func (pc *persistConn) gotIdleConnTrace(idleAt time.Time) (t httptrace.GotConnInfo) {
  1955  	pc.mu.Lock()
  1956  	defer pc.mu.Unlock()
  1957  	t.Reused = pc.reused
  1958  	t.Conn = pc.conn
  1959  	t.WasIdle = true
  1960  	if !idleAt.IsZero() {
  1961  		t.IdleTime = time.Since(idleAt)
  1962  	}
  1963  	return
  1964  }
  1965  
  1966  func (pc *persistConn) cancelRequest(err error) {
  1967  	pc.mu.Lock()
  1968  	defer pc.mu.Unlock()
  1969  	pc.canceledErr = err
  1970  	pc.closeLocked(errRequestCanceled)
  1971  }
  1972  
  1973  // closeConnIfStillIdle closes the connection if it's still sitting idle.
  1974  // This is what's called by the persistConn's idleTimer, and is run in its
  1975  // own goroutine.
  1976  func (pc *persistConn) closeConnIfStillIdle() {
  1977  	t := pc.t
  1978  	t.idleMu.Lock()
  1979  	defer t.idleMu.Unlock()
  1980  	if _, ok := t.idleLRU.m[pc]; !ok {
  1981  		// Not idle.
  1982  		return
  1983  	}
  1984  	t.removeIdleConnLocked(pc)
  1985  	pc.close(errIdleConnTimeout)
  1986  }
  1987  
  1988  // mapRoundTripError returns the appropriate error value for
  1989  // persistConn.roundTrip.
  1990  //
  1991  // The provided err is the first error that (*persistConn).roundTrip
  1992  // happened to receive from its select statement.
  1993  //
  1994  // The startBytesWritten value should be the value of pc.nwrite before the roundTrip
  1995  // started writing the request.
  1996  func (pc *persistConn) mapRoundTripError(req *transportRequest, startBytesWritten int64, err error) error {
  1997  	if err == nil {
  1998  		return nil
  1999  	}
  2000  
  2001  	// Wait for the writeLoop goroutine to terminate to avoid data
  2002  	// races on callers who mutate the request on failure.
  2003  	//
  2004  	// When resc in pc.roundTrip and hence rc.ch receives a responseAndError
  2005  	// with a non-nil error it implies that the persistConn is either closed
  2006  	// or closing. Waiting on pc.writeLoopDone is hence safe as all callers
  2007  	// close closech which in turn ensures writeLoop returns.
  2008  	<-pc.writeLoopDone
  2009  
  2010  	// If the request was canceled, that's better than network
  2011  	// failures that were likely the result of tearing down the
  2012  	// connection.
  2013  	if cerr := pc.canceled(); cerr != nil {
  2014  		return cerr
  2015  	}
  2016  
  2017  	// See if an error was set explicitly.
  2018  	req.mu.Lock()
  2019  	reqErr := req.err
  2020  	req.mu.Unlock()
  2021  	if reqErr != nil {
  2022  		return reqErr
  2023  	}
  2024  
  2025  	if err == errServerClosedIdle {
  2026  		// Don't decorate
  2027  		return err
  2028  	}
  2029  
  2030  	if _, ok := err.(transportReadFromServerError); ok {
  2031  		// Don't decorate
  2032  		return err
  2033  	}
  2034  	if pc.isBroken() {
  2035  		if pc.nwrite == startBytesWritten {
  2036  			return nothingWrittenError{err}
  2037  		}
  2038  		return fmt.Errorf("net/http: HTTP/1.x transport connection broken: %v", err)
  2039  	}
  2040  	return err
  2041  }
  2042  
  2043  // errCallerOwnsConn is an internal sentinel error used when we hand
  2044  // off a writable response.Body to the caller. We use this to prevent
  2045  // closing a net.Conn that is now owned by the caller.
  2046  var errCallerOwnsConn = errors.New("read loop ending; caller owns writable underlying conn")
  2047  
  2048  func (pc *persistConn) readLoop() {
  2049  	closeErr := errReadLoopExiting // default value, if not changed below
  2050  	defer func() {
  2051  		pc.close(closeErr)
  2052  		pc.t.removeIdleConn(pc)
  2053  	}()
  2054  
  2055  	tryPutIdleConn := func(trace *httptrace.ClientTrace) bool {
  2056  		if err := pc.t.tryPutIdleConn(pc); err != nil {
  2057  			closeErr = err
  2058  			if trace != nil && trace.PutIdleConn != nil && err != errKeepAlivesDisabled {
  2059  				trace.PutIdleConn(err)
  2060  			}
  2061  			return false
  2062  		}
  2063  		if trace != nil && trace.PutIdleConn != nil {
  2064  			trace.PutIdleConn(nil)
  2065  		}
  2066  		return true
  2067  	}
  2068  
  2069  	// eofc is used to block caller goroutines reading from Response.Body
  2070  	// at EOF until this goroutines has (potentially) added the connection
  2071  	// back to the idle pool.
  2072  	eofc := make(chan struct{})
  2073  	defer close(eofc) // unblock reader on errors
  2074  
  2075  	// Read this once, before loop starts. (to avoid races in tests)
  2076  	testHookMu.Lock()
  2077  	testHookReadLoopBeforeNextRead := testHookReadLoopBeforeNextRead
  2078  	testHookMu.Unlock()
  2079  
  2080  	alive := true
  2081  	for alive {
  2082  		pc.readLimit = pc.maxHeaderResponseSize()
  2083  		_, err := pc.br.Peek(1)
  2084  
  2085  		pc.mu.Lock()
  2086  		if pc.numExpectedResponses == 0 {
  2087  			pc.readLoopPeekFailLocked(err)
  2088  			pc.mu.Unlock()
  2089  			return
  2090  		}
  2091  		pc.mu.Unlock()
  2092  
  2093  		rc := <-pc.reqch
  2094  		trace := httptrace.ContextClientTrace(rc.req.Context())
  2095  
  2096  		var resp *Response
  2097  		if err == nil {
  2098  			resp, err = pc.readResponse(rc, trace)
  2099  		} else {
  2100  			err = transportReadFromServerError{err}
  2101  			closeErr = err
  2102  		}
  2103  
  2104  		if err != nil {
  2105  			if pc.readLimit <= 0 {
  2106  				err = fmt.Errorf("net/http: server response headers exceeded %d bytes; aborted", pc.maxHeaderResponseSize())
  2107  			}
  2108  
  2109  			select {
  2110  			case rc.ch <- responseAndError{err: err}:
  2111  			case <-rc.callerGone:
  2112  				return
  2113  			}
  2114  			return
  2115  		}
  2116  		pc.readLimit = maxInt64 // effectively no limit for response bodies
  2117  
  2118  		pc.mu.Lock()
  2119  		pc.numExpectedResponses--
  2120  		pc.mu.Unlock()
  2121  
  2122  		bodyWritable := resp.bodyIsWritable()
  2123  		hasBody := rc.req.Method != "HEAD" && resp.ContentLength != 0
  2124  
  2125  		if resp.Close || rc.req.Close || resp.StatusCode <= 199 || bodyWritable {
  2126  			// Don't do keep-alive on error if either party requested a close
  2127  			// or we get an unexpected informational (1xx) response.
  2128  			// StatusCode 100 is already handled above.
  2129  			alive = false
  2130  		}
  2131  
  2132  		if !hasBody || bodyWritable {
  2133  			replaced := pc.t.replaceReqCanceler(rc.cancelKey, nil)
  2134  
  2135  			// Put the idle conn back into the pool before we send the response
  2136  			// so if they process it quickly and make another request, they'll
  2137  			// get this same conn. But we use the unbuffered channel 'rc'
  2138  			// to guarantee that persistConn.roundTrip got out of its select
  2139  			// potentially waiting for this persistConn to close.
  2140  			alive = alive &&
  2141  				!pc.sawEOF &&
  2142  				pc.wroteRequest() &&
  2143  				replaced && tryPutIdleConn(trace)
  2144  
  2145  			if bodyWritable {
  2146  				closeErr = errCallerOwnsConn
  2147  			}
  2148  
  2149  			select {
  2150  			case rc.ch <- responseAndError{res: resp}:
  2151  			case <-rc.callerGone:
  2152  				return
  2153  			}
  2154  
  2155  			// Now that they've read from the unbuffered channel, they're safely
  2156  			// out of the select that also waits on this goroutine to die, so
  2157  			// we're allowed to exit now if needed (if alive is false)
  2158  			testHookReadLoopBeforeNextRead()
  2159  			continue
  2160  		}
  2161  
  2162  		waitForBodyRead := make(chan bool, 2)
  2163  		body := &bodyEOFSignal{
  2164  			body: resp.Body,
  2165  			earlyCloseFn: func() error {
  2166  				waitForBodyRead <- false
  2167  				<-eofc // will be closed by deferred call at the end of the function
  2168  				return nil
  2169  
  2170  			},
  2171  			fn: func(err error) error {
  2172  				isEOF := err == io.EOF
  2173  				waitForBodyRead <- isEOF
  2174  				if isEOF {
  2175  					<-eofc // see comment above eofc declaration
  2176  				} else if err != nil {
  2177  					if cerr := pc.canceled(); cerr != nil {
  2178  						return cerr
  2179  					}
  2180  				}
  2181  				return err
  2182  			},
  2183  		}
  2184  
  2185  		resp.Body = body
  2186  		if rc.addedGzip && strings.EqualFold(resp.Header.Get("Content-Encoding"), "gzip") {
  2187  			resp.Body = &gzipReader{body: body}
  2188  			resp.Header.Del("Content-Encoding")
  2189  			resp.Header.Del("Content-Length")
  2190  			resp.ContentLength = -1
  2191  			resp.Uncompressed = true
  2192  		}
  2193  
  2194  		select {
  2195  		case rc.ch <- responseAndError{res: resp}:
  2196  		case <-rc.callerGone:
  2197  			return
  2198  		}
  2199  
  2200  		// Before looping back to the top of this function and peeking on
  2201  		// the bufio.Reader, wait for the caller goroutine to finish
  2202  		// reading the response body. (or for cancellation or death)
  2203  		select {
  2204  		case bodyEOF := <-waitForBodyRead:
  2205  			replaced := pc.t.replaceReqCanceler(rc.cancelKey, nil) // before pc might return to idle pool
  2206  			alive = alive &&
  2207  				bodyEOF &&
  2208  				!pc.sawEOF &&
  2209  				pc.wroteRequest() &&
  2210  				replaced && tryPutIdleConn(trace)
  2211  			if bodyEOF {
  2212  				eofc <- struct{}{}
  2213  			}
  2214  		case <-rc.req.Cancel:
  2215  			alive = false
  2216  			pc.t.CancelRequest(rc.req)
  2217  		case <-rc.req.Context().Done():
  2218  			alive = false
  2219  			pc.t.cancelRequest(rc.cancelKey, rc.req.Context().Err())
  2220  		case <-pc.closech:
  2221  			alive = false
  2222  		}
  2223  
  2224  		testHookReadLoopBeforeNextRead()
  2225  	}
  2226  }
  2227  
  2228  func (pc *persistConn) readLoopPeekFailLocked(peekErr error) {
  2229  	if pc.closed != nil {
  2230  		return
  2231  	}
  2232  	if n := pc.br.Buffered(); n > 0 {
  2233  		buf, _ := pc.br.Peek(n)
  2234  		if is408Message(buf) {
  2235  			pc.closeLocked(errServerClosedIdle)
  2236  			return
  2237  		} else {
  2238  			log.Printf("Unsolicited response received on idle HTTP channel starting with %q; err=%v", buf, peekErr)
  2239  		}
  2240  	}
  2241  	if peekErr == io.EOF {
  2242  		// common case.
  2243  		pc.closeLocked(errServerClosedIdle)
  2244  	} else {
  2245  		pc.closeLocked(fmt.Errorf("readLoopPeekFailLocked: %v", peekErr))
  2246  	}
  2247  }
  2248  
  2249  // is408Message reports whether buf has the prefix of an
  2250  // HTTP 408 Request Timeout response.
  2251  // See golang.org/issue/32310.
  2252  func is408Message(buf []byte) bool {
  2253  	if len(buf) < len("HTTP/1.x 408") {
  2254  		return false
  2255  	}
  2256  	if string(buf[:7]) != "HTTP/1." {
  2257  		return false
  2258  	}
  2259  	return string(buf[8:12]) == " 408"
  2260  }
  2261  
  2262  // readResponse reads an HTTP response (or two, in the case of "Expect:
  2263  // 100-continue") from the server. It returns the final non-100 one.
  2264  // trace is optional.
  2265  func (pc *persistConn) readResponse(rc requestAndChan, trace *httptrace.ClientTrace) (resp *Response, err error) {
  2266  	if trace != nil && trace.GotFirstResponseByte != nil {
  2267  		if peek, err := pc.br.Peek(1); err == nil && len(peek) == 1 {
  2268  			trace.GotFirstResponseByte()
  2269  		}
  2270  	}
  2271  	num1xx := 0               // number of informational 1xx headers received
  2272  	const max1xxResponses = 5 // arbitrary bound on number of informational responses
  2273  
  2274  	continueCh := rc.continueCh
  2275  	for {
  2276  		resp, err = ReadResponse(pc.br, rc.req)
  2277  		if err != nil {
  2278  			return
  2279  		}
  2280  		resCode := resp.StatusCode
  2281  		if continueCh != nil {
  2282  			if resCode == 100 {
  2283  				if trace != nil && trace.Got100Continue != nil {
  2284  					trace.Got100Continue()
  2285  				}
  2286  				continueCh <- struct{}{}
  2287  				continueCh = nil
  2288  			} else if resCode >= 200 {
  2289  				close(continueCh)
  2290  				continueCh = nil
  2291  			}
  2292  		}
  2293  		is1xx := 100 <= resCode && resCode <= 199
  2294  		// treat 101 as a terminal status, see issue 26161
  2295  		is1xxNonTerminal := is1xx && resCode != StatusSwitchingProtocols
  2296  		if is1xxNonTerminal {
  2297  			num1xx++
  2298  			if num1xx > max1xxResponses {
  2299  				return nil, errors.New("net/http: too many 1xx informational responses")
  2300  			}
  2301  			pc.readLimit = pc.maxHeaderResponseSize() // reset the limit
  2302  			if trace != nil && trace.Got1xxResponse != nil {
  2303  				if err := trace.Got1xxResponse(resCode, textproto.MIMEHeader(resp.Header)); err != nil {
  2304  					return nil, err
  2305  				}
  2306  			}
  2307  			continue
  2308  		}
  2309  		break
  2310  	}
  2311  	if resp.isProtocolSwitch() {
  2312  		resp.Body = newReadWriteCloserBody(pc.br, pc.conn)
  2313  	}
  2314  
  2315  	resp.TLS = pc.tlsState
  2316  	return
  2317  }
  2318  
  2319  // waitForContinue returns the function to block until
  2320  // any response, timeout or connection close. After any of them,
  2321  // the function returns a bool which indicates if the body should be sent.
  2322  func (pc *persistConn) waitForContinue(continueCh <-chan struct{}) func() bool {
  2323  	if continueCh == nil {
  2324  		return nil
  2325  	}
  2326  	return func() bool {
  2327  		timer := time.NewTimer(pc.t.ExpectContinueTimeout)
  2328  		defer timer.Stop()
  2329  
  2330  		select {
  2331  		case _, ok := <-continueCh:
  2332  			return ok
  2333  		case <-timer.C:
  2334  			return true
  2335  		case <-pc.closech:
  2336  			return false
  2337  		}
  2338  	}
  2339  }
  2340  
  2341  func newReadWriteCloserBody(br *bufio.Reader, rwc io.ReadWriteCloser) io.ReadWriteCloser {
  2342  	body := &readWriteCloserBody{ReadWriteCloser: rwc}
  2343  	if br.Buffered() != 0 {
  2344  		body.br = br
  2345  	}
  2346  	return body
  2347  }
  2348  
  2349  // readWriteCloserBody is the Response.Body type used when we want to
  2350  // give users write access to the Body through the underlying
  2351  // connection (TCP, unless using custom dialers). This is then
  2352  // the concrete type for a Response.Body on the 101 Switching
  2353  // Protocols response, as used by WebSockets, h2c, etc.
  2354  type readWriteCloserBody struct {
  2355  	_  incomparable
  2356  	br *bufio.Reader // used until empty
  2357  	io.ReadWriteCloser
  2358  }
  2359  
  2360  func (b *readWriteCloserBody) Read(p []byte) (n int, err error) {
  2361  	if b.br != nil {
  2362  		if n := b.br.Buffered(); len(p) > n {
  2363  			p = p[:n]
  2364  		}
  2365  		n, err = b.br.Read(p)
  2366  		if b.br.Buffered() == 0 {
  2367  			b.br = nil
  2368  		}
  2369  		return n, err
  2370  	}
  2371  	return b.ReadWriteCloser.Read(p)
  2372  }
  2373  
  2374  // nothingWrittenError wraps a write errors which ended up writing zero bytes.
  2375  type nothingWrittenError struct {
  2376  	error
  2377  }
  2378  
  2379  func (pc *persistConn) writeLoop() {
  2380  	defer close(pc.writeLoopDone)
  2381  	for {
  2382  		select {
  2383  		case wr := <-pc.writech:
  2384  			startBytesWritten := pc.nwrite
  2385  			err := wr.req.Request.write(pc.bw, pc.isProxy, wr.req.extra, pc.waitForContinue(wr.continueCh))
  2386  			if bre, ok := err.(requestBodyReadError); ok {
  2387  				err = bre.error
  2388  				// Errors reading from the user's
  2389  				// Request.Body are high priority.
  2390  				// Set it here before sending on the
  2391  				// channels below or calling
  2392  				// pc.close() which tears down
  2393  				// connections and causes other
  2394  				// errors.
  2395  				wr.req.setError(err)
  2396  			}
  2397  			if err == nil {
  2398  				err = pc.bw.Flush()
  2399  			}
  2400  			if err != nil {
  2401  				if pc.nwrite == startBytesWritten {
  2402  					err = nothingWrittenError{err}
  2403  				}
  2404  			}
  2405  			pc.writeErrCh <- err // to the body reader, which might recycle us
  2406  			wr.ch <- err         // to the roundTrip function
  2407  			if err != nil {
  2408  				pc.close(err)
  2409  				return
  2410  			}
  2411  		case <-pc.closech:
  2412  			return
  2413  		}
  2414  	}
  2415  }
  2416  
  2417  // maxWriteWaitBeforeConnReuse is how long the a Transport RoundTrip
  2418  // will wait to see the Request's Body.Write result after getting a
  2419  // response from the server. See comments in (*persistConn).wroteRequest.
  2420  const maxWriteWaitBeforeConnReuse = 50 * time.Millisecond
  2421  
  2422  // wroteRequest is a check before recycling a connection that the previous write
  2423  // (from writeLoop above) happened and was successful.
  2424  func (pc *persistConn) wroteRequest() bool {
  2425  	select {
  2426  	case err := <-pc.writeErrCh:
  2427  		// Common case: the write happened well before the response, so
  2428  		// avoid creating a timer.
  2429  		return err == nil
  2430  	default:
  2431  		// Rare case: the request was written in writeLoop above but
  2432  		// before it could send to pc.writeErrCh, the reader read it
  2433  		// all, processed it, and called us here. In this case, give the
  2434  		// write goroutine a bit of time to finish its send.
  2435  		//
  2436  		// Less rare case: We also get here in the legitimate case of
  2437  		// Issue 7569, where the writer is still writing (or stalled),
  2438  		// but the server has already replied. In this case, we don't
  2439  		// want to wait too long, and we want to return false so this
  2440  		// connection isn't re-used.
  2441  		t := time.NewTimer(maxWriteWaitBeforeConnReuse)
  2442  		defer t.Stop()
  2443  		select {
  2444  		case err := <-pc.writeErrCh:
  2445  			return err == nil
  2446  		case <-t.C:
  2447  			return false
  2448  		}
  2449  	}
  2450  }
  2451  
  2452  // responseAndError is how the goroutine reading from an HTTP/1 server
  2453  // communicates with the goroutine doing the RoundTrip.
  2454  type responseAndError struct {
  2455  	_   incomparable
  2456  	res *Response // else use this response (see res method)
  2457  	err error
  2458  }
  2459  
  2460  type requestAndChan struct {
  2461  	_         incomparable
  2462  	req       *Request
  2463  	cancelKey cancelKey
  2464  	ch        chan responseAndError // unbuffered; always send in select on callerGone
  2465  
  2466  	// whether the Transport (as opposed to the user client code)
  2467  	// added the Accept-Encoding gzip header. If the Transport
  2468  	// set it, only then do we transparently decode the gzip.
  2469  	addedGzip bool
  2470  
  2471  	// Optional blocking chan for Expect: 100-continue (for send).
  2472  	// If the request has an "Expect: 100-continue" header and
  2473  	// the server responds 100 Continue, readLoop send a value
  2474  	// to writeLoop via this chan.
  2475  	continueCh chan<- struct{}
  2476  
  2477  	callerGone <-chan struct{} // closed when roundTrip caller has returned
  2478  }
  2479  
  2480  // A writeRequest is sent by the readLoop's goroutine to the
  2481  // writeLoop's goroutine to write a request while the read loop
  2482  // concurrently waits on both the write response and the server's
  2483  // reply.
  2484  type writeRequest struct {
  2485  	req *transportRequest
  2486  	ch  chan<- error
  2487  
  2488  	// Optional blocking chan for Expect: 100-continue (for receive).
  2489  	// If not nil, writeLoop blocks sending request body until
  2490  	// it receives from this chan.
  2491  	continueCh <-chan struct{}
  2492  }
  2493  
  2494  type httpError struct {
  2495  	err     string
  2496  	timeout bool
  2497  }
  2498  
  2499  func (e *httpError) Error() string   { return e.err }
  2500  func (e *httpError) Timeout() bool   { return e.timeout }
  2501  func (e *httpError) Temporary() bool { return true }
  2502  
  2503  var errTimeout error = &httpError{err: "net/http: timeout awaiting response headers", timeout: true}
  2504  
  2505  // errRequestCanceled is set to be identical to the one from h2 to facilitate
  2506  // testing.
  2507  var errRequestCanceled = http2errRequestCanceled
  2508  var errRequestCanceledConn = errors.New("net/http: request canceled while waiting for connection") // TODO: unify?
  2509  
  2510  func nop() {}
  2511  
  2512  // testHooks. Always non-nil.
  2513  var (
  2514  	testHookEnterRoundTrip   = nop
  2515  	testHookWaitResLoop      = nop
  2516  	testHookRoundTripRetried = nop
  2517  	testHookPrePendingDial   = nop
  2518  	testHookPostPendingDial  = nop
  2519  
  2520  	testHookMu                     sync.Locker = fakeLocker{} // guards following
  2521  	testHookReadLoopBeforeNextRead             = nop
  2522  )
  2523  
  2524  func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
  2525  	testHookEnterRoundTrip()
  2526  	if !pc.t.replaceReqCanceler(req.cancelKey, pc.cancelRequest) {
  2527  		pc.t.putOrCloseIdleConn(pc)
  2528  		return nil, errRequestCanceled
  2529  	}
  2530  	pc.mu.Lock()
  2531  	pc.numExpectedResponses++
  2532  	headerFn := pc.mutateHeaderFunc
  2533  	pc.mu.Unlock()
  2534  
  2535  	if headerFn != nil {
  2536  		headerFn(req.extraHeaders())
  2537  	}
  2538  
  2539  	// Ask for a compressed version if the caller didn't set their
  2540  	// own value for Accept-Encoding. We only attempt to
  2541  	// uncompress the gzip stream if we were the layer that
  2542  	// requested it.
  2543  	requestedGzip := false
  2544  	if !pc.t.DisableCompression &&
  2545  		req.Header.Get("Accept-Encoding") == "" &&
  2546  		req.Header.Get("Range") == "" &&
  2547  		req.Method != "HEAD" {
  2548  		// Request gzip only, not deflate. Deflate is ambiguous and
  2549  		// not as universally supported anyway.
  2550  		// See: https://zlib.net/zlib_faq.html#faq39
  2551  		//
  2552  		// Note that we don't request this for HEAD requests,
  2553  		// due to a bug in nginx:
  2554  		//   https://trac.nginx.org/nginx/ticket/358
  2555  		//   https://golang.org/issue/5522
  2556  		//
  2557  		// We don't request gzip if the request is for a range, since
  2558  		// auto-decoding a portion of a gzipped document will just fail
  2559  		// anyway. See https://golang.org/issue/8923
  2560  		requestedGzip = true
  2561  		req.extraHeaders().Set("Accept-Encoding", "gzip")
  2562  	}
  2563  
  2564  	var continueCh chan struct{}
  2565  	if req.ProtoAtLeast(1, 1) && req.Body != nil && req.expectsContinue() {
  2566  		continueCh = make(chan struct{}, 1)
  2567  	}
  2568  
  2569  	if pc.t.DisableKeepAlives &&
  2570  		!req.wantsClose() &&
  2571  		!isProtocolSwitchHeader(req.Header) {
  2572  		req.extraHeaders().Set("Connection", "close")
  2573  	}
  2574  
  2575  	gone := make(chan struct{})
  2576  	defer close(gone)
  2577  
  2578  	defer func() {
  2579  		if err != nil {
  2580  			pc.t.setReqCanceler(req.cancelKey, nil)
  2581  		}
  2582  	}()
  2583  
  2584  	const debugRoundTrip = false
  2585  
  2586  	// Write the request concurrently with waiting for a response,
  2587  	// in case the server decides to reply before reading our full
  2588  	// request body.
  2589  	startBytesWritten := pc.nwrite
  2590  	writeErrCh := make(chan error, 1)
  2591  	pc.writech <- writeRequest{req, writeErrCh, continueCh}
  2592  
  2593  	resc := make(chan responseAndError)
  2594  	pc.reqch <- requestAndChan{
  2595  		req:        req.Request,
  2596  		cancelKey:  req.cancelKey,
  2597  		ch:         resc,
  2598  		addedGzip:  requestedGzip,
  2599  		continueCh: continueCh,
  2600  		callerGone: gone,
  2601  	}
  2602  
  2603  	var respHeaderTimer <-chan time.Time
  2604  	cancelChan := req.Request.Cancel
  2605  	ctxDoneChan := req.Context().Done()
  2606  	pcClosed := pc.closech
  2607  	canceled := false
  2608  	for {
  2609  		testHookWaitResLoop()
  2610  		select {
  2611  		case err := <-writeErrCh:
  2612  			if debugRoundTrip {
  2613  				req.logf("writeErrCh resv: %T/%#v", err, err)
  2614  			}
  2615  			if err != nil {
  2616  				pc.close(fmt.Errorf("write error: %v", err))
  2617  				return nil, pc.mapRoundTripError(req, startBytesWritten, err)
  2618  			}
  2619  			if d := pc.t.ResponseHeaderTimeout; d > 0 {
  2620  				if debugRoundTrip {
  2621  					req.logf("starting timer for %v", d)
  2622  				}
  2623  				timer := time.NewTimer(d)
  2624  				defer timer.Stop() // prevent leaks
  2625  				respHeaderTimer = timer.C
  2626  			}
  2627  		case <-pcClosed:
  2628  			pcClosed = nil
  2629  			if canceled || pc.t.replaceReqCanceler(req.cancelKey, nil) {
  2630  				if debugRoundTrip {
  2631  					req.logf("closech recv: %T %#v", pc.closed, pc.closed)
  2632  				}
  2633  				return nil, pc.mapRoundTripError(req, startBytesWritten, pc.closed)
  2634  			}
  2635  		case <-respHeaderTimer:
  2636  			if debugRoundTrip {
  2637  				req.logf("timeout waiting for response headers.")
  2638  			}
  2639  			pc.close(errTimeout)
  2640  			return nil, errTimeout
  2641  		case re := <-resc:
  2642  			if (re.res == nil) == (re.err == nil) {
  2643  				panic(fmt.Sprintf("internal error: exactly one of res or err should be set; nil=%v", re.res == nil))
  2644  			}
  2645  			if debugRoundTrip {
  2646  				req.logf("resc recv: %p, %T/%#v", re.res, re.err, re.err)
  2647  			}
  2648  			if re.err != nil {
  2649  				return nil, pc.mapRoundTripError(req, startBytesWritten, re.err)
  2650  			}
  2651  			return re.res, nil
  2652  		case <-cancelChan:
  2653  			canceled = pc.t.cancelRequest(req.cancelKey, errRequestCanceled)
  2654  			cancelChan = nil
  2655  		case <-ctxDoneChan:
  2656  			canceled = pc.t.cancelRequest(req.cancelKey, req.Context().Err())
  2657  			cancelChan = nil
  2658  			ctxDoneChan = nil
  2659  		}
  2660  	}
  2661  }
  2662  
  2663  // tLogKey is a context WithValue key for test debugging contexts containing
  2664  // a t.Logf func. See export_test.go's Request.WithT method.
  2665  type tLogKey struct{}
  2666  
  2667  func (tr *transportRequest) logf(format string, args ...interface{}) {
  2668  	if logf, ok := tr.Request.Context().Value(tLogKey{}).(func(string, ...interface{})); ok {
  2669  		logf(time.Now().Format(time.RFC3339Nano)+": "+format, args...)
  2670  	}
  2671  }
  2672  
  2673  // markReused marks this connection as having been successfully used for a
  2674  // request and response.
  2675  func (pc *persistConn) markReused() {
  2676  	pc.mu.Lock()
  2677  	pc.reused = true
  2678  	pc.mu.Unlock()
  2679  }
  2680  
  2681  // close closes the underlying TCP connection and closes
  2682  // the pc.closech channel.
  2683  //
  2684  // The provided err is only for testing and debugging; in normal
  2685  // circumstances it should never be seen by users.
  2686  func (pc *persistConn) close(err error) {
  2687  	pc.mu.Lock()
  2688  	defer pc.mu.Unlock()
  2689  	pc.closeLocked(err)
  2690  }
  2691  
  2692  func (pc *persistConn) closeLocked(err error) {
  2693  	if err == nil {
  2694  		panic("nil error")
  2695  	}
  2696  	pc.broken = true
  2697  	if pc.closed == nil {
  2698  		pc.closed = err
  2699  		pc.t.decConnsPerHost(pc.cacheKey)
  2700  		// Close HTTP/1 (pc.alt == nil) connection.
  2701  		// HTTP/2 closes its connection itself.
  2702  		if pc.alt == nil {
  2703  			if err != errCallerOwnsConn {
  2704  				pc.conn.Close()
  2705  			}
  2706  			close(pc.closech)
  2707  		}
  2708  	}
  2709  	pc.mutateHeaderFunc = nil
  2710  }
  2711  
  2712  var portMap = map[string]string{
  2713  	"http":   "80",
  2714  	"https":  "443",
  2715  	"socks5": "1080",
  2716  }
  2717  
  2718  // canonicalAddr returns url.Host but always with a ":port" suffix
  2719  func canonicalAddr(url *url.URL) string {
  2720  	addr := url.Hostname()
  2721  	if v, err := idnaASCII(addr); err == nil {
  2722  		addr = v
  2723  	}
  2724  	port := url.Port()
  2725  	if port == "" {
  2726  		port = portMap[url.Scheme]
  2727  	}
  2728  	return net.JoinHostPort(addr, port)
  2729  }
  2730  
  2731  // bodyEOFSignal is used by the HTTP/1 transport when reading response
  2732  // bodies to make sure we see the end of a response body before
  2733  // proceeding and reading on the connection again.
  2734  //
  2735  // It wraps a ReadCloser but runs fn (if non-nil) at most
  2736  // once, right before its final (error-producing) Read or Close call
  2737  // returns. fn should return the new error to return from Read or Close.
  2738  //
  2739  // If earlyCloseFn is non-nil and Close is called before io.EOF is
  2740  // seen, earlyCloseFn is called instead of fn, and its return value is
  2741  // the return value from Close.
  2742  type bodyEOFSignal struct {
  2743  	body         io.ReadCloser
  2744  	mu           sync.Mutex        // guards following 4 fields
  2745  	closed       bool              // whether Close has been called
  2746  	rerr         error             // sticky Read error
  2747  	fn           func(error) error // err will be nil on Read io.EOF
  2748  	earlyCloseFn func() error      // optional alt Close func used if io.EOF not seen
  2749  }
  2750  
  2751  var errReadOnClosedResBody = errors.New("http: read on closed response body")
  2752  
  2753  func (es *bodyEOFSignal) Read(p []byte) (n int, err error) {
  2754  	es.mu.Lock()
  2755  	closed, rerr := es.closed, es.rerr
  2756  	es.mu.Unlock()
  2757  	if closed {
  2758  		return 0, errReadOnClosedResBody
  2759  	}
  2760  	if rerr != nil {
  2761  		return 0, rerr
  2762  	}
  2763  
  2764  	n, err = es.body.Read(p)
  2765  	if err != nil {
  2766  		es.mu.Lock()
  2767  		defer es.mu.Unlock()
  2768  		if es.rerr == nil {
  2769  			es.rerr = err
  2770  		}
  2771  		err = es.condfn(err)
  2772  	}
  2773  	return
  2774  }
  2775  
  2776  func (es *bodyEOFSignal) Close() error {
  2777  	es.mu.Lock()
  2778  	defer es.mu.Unlock()
  2779  	if es.closed {
  2780  		return nil
  2781  	}
  2782  	es.closed = true
  2783  	if es.earlyCloseFn != nil && es.rerr != io.EOF {
  2784  		return es.earlyCloseFn()
  2785  	}
  2786  	err := es.body.Close()
  2787  	return es.condfn(err)
  2788  }
  2789  
  2790  // caller must hold es.mu.
  2791  func (es *bodyEOFSignal) condfn(err error) error {
  2792  	if es.fn == nil {
  2793  		return err
  2794  	}
  2795  	err = es.fn(err)
  2796  	es.fn = nil
  2797  	return err
  2798  }
  2799  
  2800  // gzipReader wraps a response body so it can lazily
  2801  // call gzip.NewReader on the first call to Read
  2802  type gzipReader struct {
  2803  	_    incomparable
  2804  	body *bodyEOFSignal // underlying HTTP/1 response body framing
  2805  	zr   *gzip.Reader   // lazily-initialized gzip reader
  2806  	zerr error          // any error from gzip.NewReader; sticky
  2807  }
  2808  
  2809  func (gz *gzipReader) Read(p []byte) (n int, err error) {
  2810  	if gz.zr == nil {
  2811  		if gz.zerr == nil {
  2812  			gz.zr, gz.zerr = gzip.NewReader(gz.body)
  2813  		}
  2814  		if gz.zerr != nil {
  2815  			return 0, gz.zerr
  2816  		}
  2817  	}
  2818  
  2819  	gz.body.mu.Lock()
  2820  	if gz.body.closed {
  2821  		err = errReadOnClosedResBody
  2822  	}
  2823  	gz.body.mu.Unlock()
  2824  
  2825  	if err != nil {
  2826  		return 0, err
  2827  	}
  2828  	return gz.zr.Read(p)
  2829  }
  2830  
  2831  func (gz *gzipReader) Close() error {
  2832  	return gz.body.Close()
  2833  }
  2834  
  2835  type tlsHandshakeTimeoutError struct{}
  2836  
  2837  func (tlsHandshakeTimeoutError) Timeout() bool   { return true }
  2838  func (tlsHandshakeTimeoutError) Temporary() bool { return true }
  2839  func (tlsHandshakeTimeoutError) Error() string   { return "net/http: TLS handshake timeout" }
  2840  
  2841  // fakeLocker is a sync.Locker which does nothing. It's used to guard
  2842  // test-only fields when not under test, to avoid runtime atomic
  2843  // overhead.
  2844  type fakeLocker struct{}
  2845  
  2846  func (fakeLocker) Lock()   {}
  2847  func (fakeLocker) Unlock() {}
  2848  
  2849  // cloneTLSConfig returns a shallow clone of cfg, or a new zero tls.Config if
  2850  // cfg is nil. This is safe to call even if cfg is in active use by a TLS
  2851  // client or server.
  2852  func cloneTLSConfig(cfg *tls.Config) *tls.Config {
  2853  	if cfg == nil {
  2854  		return &tls.Config{}
  2855  	}
  2856  	return cfg.Clone()
  2857  }
  2858  
  2859  type connLRU struct {
  2860  	ll *list.List // list.Element.Value type is of *persistConn
  2861  	m  map[*persistConn]*list.Element
  2862  }
  2863  
  2864  // add adds pc to the head of the linked list.
  2865  func (cl *connLRU) add(pc *persistConn) {
  2866  	if cl.ll == nil {
  2867  		cl.ll = list.New()
  2868  		cl.m = make(map[*persistConn]*list.Element)
  2869  	}
  2870  	ele := cl.ll.PushFront(pc)
  2871  	if _, ok := cl.m[pc]; ok {
  2872  		panic("persistConn was already in LRU")
  2873  	}
  2874  	cl.m[pc] = ele
  2875  }
  2876  
  2877  func (cl *connLRU) removeOldest() *persistConn {
  2878  	ele := cl.ll.Back()
  2879  	pc := ele.Value.(*persistConn)
  2880  	cl.ll.Remove(ele)
  2881  	delete(cl.m, pc)
  2882  	return pc
  2883  }
  2884  
  2885  // remove removes pc from cl.
  2886  func (cl *connLRU) remove(pc *persistConn) {
  2887  	if ele, ok := cl.m[pc]; ok {
  2888  		cl.ll.Remove(ele)
  2889  		delete(cl.m, pc)
  2890  	}
  2891  }
  2892  
  2893  // len returns the number of items in the cache.
  2894  func (cl *connLRU) len() int {
  2895  	return len(cl.m)
  2896  }
  2897  

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