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Source file src/net/http/client.go

Documentation: net/http

     1  // Copyright 2009 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. See RFC 2616.
     6  //
     7  // This is the high-level Client interface.
     8  // The low-level implementation is in transport.go.
     9  
    10  package http
    11  
    12  import (
    13  	"crypto/tls"
    14  	"encoding/base64"
    15  	"errors"
    16  	"fmt"
    17  	"io"
    18  	"io/ioutil"
    19  	"log"
    20  	"net/url"
    21  	"sort"
    22  	"strings"
    23  	"sync"
    24  	"time"
    25  )
    26  
    27  // A Client is an HTTP client. Its zero value (DefaultClient) is a
    28  // usable client that uses DefaultTransport.
    29  //
    30  // The Client's Transport typically has internal state (cached TCP
    31  // connections), so Clients should be reused instead of created as
    32  // needed. Clients are safe for concurrent use by multiple goroutines.
    33  //
    34  // A Client is higher-level than a RoundTripper (such as Transport)
    35  // and additionally handles HTTP details such as cookies and
    36  // redirects.
    37  //
    38  // When following redirects, the Client will forward all headers set on the
    39  // initial Request except:
    40  //
    41  // • when forwarding sensitive headers like "Authorization",
    42  // "WWW-Authenticate", and "Cookie" to untrusted targets.
    43  // These headers will be ignored when following a redirect to a domain
    44  // that is not a subdomain match or exact match of the initial domain.
    45  // For example, a redirect from "foo.com" to either "foo.com" or "sub.foo.com"
    46  // will forward the sensitive headers, but a redirect to "bar.com" will not.
    47  //
    48  // • when forwarding the "Cookie" header with a non-nil cookie Jar.
    49  // Since each redirect may mutate the state of the cookie jar,
    50  // a redirect may possibly alter a cookie set in the initial request.
    51  // When forwarding the "Cookie" header, any mutated cookies will be omitted,
    52  // with the expectation that the Jar will insert those mutated cookies
    53  // with the updated values (assuming the origin matches).
    54  // If Jar is nil, the initial cookies are forwarded without change.
    55  //
    56  type Client struct {
    57  	// Transport specifies the mechanism by which individual
    58  	// HTTP requests are made.
    59  	// If nil, DefaultTransport is used.
    60  	Transport RoundTripper
    61  
    62  	// CheckRedirect specifies the policy for handling redirects.
    63  	// If CheckRedirect is not nil, the client calls it before
    64  	// following an HTTP redirect. The arguments req and via are
    65  	// the upcoming request and the requests made already, oldest
    66  	// first. If CheckRedirect returns an error, the Client's Get
    67  	// method returns both the previous Response (with its Body
    68  	// closed) and CheckRedirect's error (wrapped in a url.Error)
    69  	// instead of issuing the Request req.
    70  	// As a special case, if CheckRedirect returns ErrUseLastResponse,
    71  	// then the most recent response is returned with its body
    72  	// unclosed, along with a nil error.
    73  	//
    74  	// If CheckRedirect is nil, the Client uses its default policy,
    75  	// which is to stop after 10 consecutive requests.
    76  	CheckRedirect func(req *Request, via []*Request) error
    77  
    78  	// Jar specifies the cookie jar.
    79  	//
    80  	// The Jar is used to insert relevant cookies into every
    81  	// outbound Request and is updated with the cookie values
    82  	// of every inbound Response. The Jar is consulted for every
    83  	// redirect that the Client follows.
    84  	//
    85  	// If Jar is nil, cookies are only sent if they are explicitly
    86  	// set on the Request.
    87  	Jar CookieJar
    88  
    89  	// Timeout specifies a time limit for requests made by this
    90  	// Client. The timeout includes connection time, any
    91  	// redirects, and reading the response body. The timer remains
    92  	// running after Get, Head, Post, or Do return and will
    93  	// interrupt reading of the Response.Body.
    94  	//
    95  	// A Timeout of zero means no timeout.
    96  	//
    97  	// The Client cancels requests to the underlying Transport
    98  	// using the Request.Cancel mechanism. Requests passed
    99  	// to Client.Do may still set Request.Cancel; both will
   100  	// cancel the request.
   101  	//
   102  	// For compatibility, the Client will also use the deprecated
   103  	// CancelRequest method on Transport if found. New
   104  	// RoundTripper implementations should use Request.Cancel
   105  	// instead of implementing CancelRequest.
   106  	Timeout time.Duration
   107  }
   108  
   109  // DefaultClient is the default Client and is used by Get, Head, and Post.
   110  var DefaultClient = &Client{}
   111  
   112  // RoundTripper is an interface representing the ability to execute a
   113  // single HTTP transaction, obtaining the Response for a given Request.
   114  //
   115  // A RoundTripper must be safe for concurrent use by multiple
   116  // goroutines.
   117  type RoundTripper interface {
   118  	// RoundTrip executes a single HTTP transaction, returning
   119  	// a Response for the provided Request.
   120  	//
   121  	// RoundTrip should not attempt to interpret the response. In
   122  	// particular, RoundTrip must return err == nil if it obtained
   123  	// a response, regardless of the response's HTTP status code.
   124  	// A non-nil err should be reserved for failure to obtain a
   125  	// response. Similarly, RoundTrip should not attempt to
   126  	// handle higher-level protocol details such as redirects,
   127  	// authentication, or cookies.
   128  	//
   129  	// RoundTrip should not modify the request, except for
   130  	// consuming and closing the Request's Body. RoundTrip may
   131  	// read fields of the request in a separate goroutine. Callers
   132  	// should not mutate the request until the Response's Body has
   133  	// been closed.
   134  	//
   135  	// RoundTrip must always close the body, including on errors,
   136  	// but depending on the implementation may do so in a separate
   137  	// goroutine even after RoundTrip returns. This means that
   138  	// callers wanting to reuse the body for subsequent requests
   139  	// must arrange to wait for the Close call before doing so.
   140  	//
   141  	// The Request's URL and Header fields must be initialized.
   142  	RoundTrip(*Request) (*Response, error)
   143  }
   144  
   145  // refererForURL returns a referer without any authentication info or
   146  // an empty string if lastReq scheme is https and newReq scheme is http.
   147  func refererForURL(lastReq, newReq *url.URL) string {
   148  	// https://tools.ietf.org/html/rfc7231#section-5.5.2
   149  	//   "Clients SHOULD NOT include a Referer header field in a
   150  	//    (non-secure) HTTP request if the referring page was
   151  	//    transferred with a secure protocol."
   152  	if lastReq.Scheme == "https" && newReq.Scheme == "http" {
   153  		return ""
   154  	}
   155  	referer := lastReq.String()
   156  	if lastReq.User != nil {
   157  		// This is not very efficient, but is the best we can
   158  		// do without:
   159  		// - introducing a new method on URL
   160  		// - creating a race condition
   161  		// - copying the URL struct manually, which would cause
   162  		//   maintenance problems down the line
   163  		auth := lastReq.User.String() + "@"
   164  		referer = strings.Replace(referer, auth, "", 1)
   165  	}
   166  	return referer
   167  }
   168  
   169  // didTimeout is non-nil only if err != nil.
   170  func (c *Client) send(req *Request, deadline time.Time) (resp *Response, didTimeout func() bool, err error) {
   171  	if c.Jar != nil {
   172  		for _, cookie := range c.Jar.Cookies(req.URL) {
   173  			req.AddCookie(cookie)
   174  		}
   175  	}
   176  	resp, didTimeout, err = send(req, c.transport(), deadline)
   177  	if err != nil {
   178  		return nil, didTimeout, err
   179  	}
   180  	if c.Jar != nil {
   181  		if rc := resp.Cookies(); len(rc) > 0 {
   182  			c.Jar.SetCookies(req.URL, rc)
   183  		}
   184  	}
   185  	return resp, nil, nil
   186  }
   187  
   188  func (c *Client) deadline() time.Time {
   189  	if c.Timeout > 0 {
   190  		return time.Now().Add(c.Timeout)
   191  	}
   192  	return time.Time{}
   193  }
   194  
   195  func (c *Client) transport() RoundTripper {
   196  	if c.Transport != nil {
   197  		return c.Transport
   198  	}
   199  	return DefaultTransport
   200  }
   201  
   202  // send issues an HTTP request.
   203  // Caller should close resp.Body when done reading from it.
   204  func send(ireq *Request, rt RoundTripper, deadline time.Time) (resp *Response, didTimeout func() bool, err error) {
   205  	req := ireq // req is either the original request, or a modified fork
   206  
   207  	if rt == nil {
   208  		req.closeBody()
   209  		return nil, alwaysFalse, errors.New("http: no Client.Transport or DefaultTransport")
   210  	}
   211  
   212  	if req.URL == nil {
   213  		req.closeBody()
   214  		return nil, alwaysFalse, errors.New("http: nil Request.URL")
   215  	}
   216  
   217  	if req.RequestURI != "" {
   218  		req.closeBody()
   219  		return nil, alwaysFalse, errors.New("http: Request.RequestURI can't be set in client requests.")
   220  	}
   221  
   222  	// forkReq forks req into a shallow clone of ireq the first
   223  	// time it's called.
   224  	forkReq := func() {
   225  		if ireq == req {
   226  			req = new(Request)
   227  			*req = *ireq // shallow clone
   228  		}
   229  	}
   230  
   231  	// Most the callers of send (Get, Post, et al) don't need
   232  	// Headers, leaving it uninitialized. We guarantee to the
   233  	// Transport that this has been initialized, though.
   234  	if req.Header == nil {
   235  		forkReq()
   236  		req.Header = make(Header)
   237  	}
   238  
   239  	if u := req.URL.User; u != nil && req.Header.Get("Authorization") == "" {
   240  		username := u.Username()
   241  		password, _ := u.Password()
   242  		forkReq()
   243  		req.Header = cloneHeader(ireq.Header)
   244  		req.Header.Set("Authorization", "Basic "+basicAuth(username, password))
   245  	}
   246  
   247  	if !deadline.IsZero() {
   248  		forkReq()
   249  	}
   250  	stopTimer, didTimeout := setRequestCancel(req, rt, deadline)
   251  
   252  	resp, err = rt.RoundTrip(req)
   253  	if err != nil {
   254  		stopTimer()
   255  		if resp != nil {
   256  			log.Printf("RoundTripper returned a response & error; ignoring response")
   257  		}
   258  		if tlsErr, ok := err.(tls.RecordHeaderError); ok {
   259  			// If we get a bad TLS record header, check to see if the
   260  			// response looks like HTTP and give a more helpful error.
   261  			// See golang.org/issue/11111.
   262  			if string(tlsErr.RecordHeader[:]) == "HTTP/" {
   263  				err = errors.New("http: server gave HTTP response to HTTPS client")
   264  			}
   265  		}
   266  		return nil, didTimeout, err
   267  	}
   268  	if !deadline.IsZero() {
   269  		resp.Body = &cancelTimerBody{
   270  			stop:          stopTimer,
   271  			rc:            resp.Body,
   272  			reqDidTimeout: didTimeout,
   273  		}
   274  	}
   275  	return resp, nil, nil
   276  }
   277  
   278  // setRequestCancel sets the Cancel field of req, if deadline is
   279  // non-zero. The RoundTripper's type is used to determine whether the legacy
   280  // CancelRequest behavior should be used.
   281  //
   282  // As background, there are three ways to cancel a request:
   283  // First was Transport.CancelRequest. (deprecated)
   284  // Second was Request.Cancel (this mechanism).
   285  // Third was Request.Context.
   286  func setRequestCancel(req *Request, rt RoundTripper, deadline time.Time) (stopTimer func(), didTimeout func() bool) {
   287  	if deadline.IsZero() {
   288  		return nop, alwaysFalse
   289  	}
   290  
   291  	initialReqCancel := req.Cancel // the user's original Request.Cancel, if any
   292  
   293  	cancel := make(chan struct{})
   294  	req.Cancel = cancel
   295  
   296  	doCancel := func() {
   297  		// The newer way (the second way in the func comment):
   298  		close(cancel)
   299  
   300  		// The legacy compatibility way, used only
   301  		// for RoundTripper implementations written
   302  		// before Go 1.5 or Go 1.6.
   303  		type canceler interface {
   304  			CancelRequest(*Request)
   305  		}
   306  		switch v := rt.(type) {
   307  		case *Transport, *http2Transport:
   308  			// Do nothing. The net/http package's transports
   309  			// support the new Request.Cancel channel
   310  		case canceler:
   311  			v.CancelRequest(req)
   312  		}
   313  	}
   314  
   315  	stopTimerCh := make(chan struct{})
   316  	var once sync.Once
   317  	stopTimer = func() { once.Do(func() { close(stopTimerCh) }) }
   318  
   319  	timer := time.NewTimer(time.Until(deadline))
   320  	var timedOut atomicBool
   321  
   322  	go func() {
   323  		select {
   324  		case <-initialReqCancel:
   325  			doCancel()
   326  			timer.Stop()
   327  		case <-timer.C:
   328  			timedOut.setTrue()
   329  			doCancel()
   330  		case <-stopTimerCh:
   331  			timer.Stop()
   332  		}
   333  	}()
   334  
   335  	return stopTimer, timedOut.isSet
   336  }
   337  
   338  // See 2 (end of page 4) http://www.ietf.org/rfc/rfc2617.txt
   339  // "To receive authorization, the client sends the userid and password,
   340  // separated by a single colon (":") character, within a base64
   341  // encoded string in the credentials."
   342  // It is not meant to be urlencoded.
   343  func basicAuth(username, password string) string {
   344  	auth := username + ":" + password
   345  	return base64.StdEncoding.EncodeToString([]byte(auth))
   346  }
   347  
   348  // Get issues a GET to the specified URL. If the response is one of
   349  // the following redirect codes, Get follows the redirect, up to a
   350  // maximum of 10 redirects:
   351  //
   352  //    301 (Moved Permanently)
   353  //    302 (Found)
   354  //    303 (See Other)
   355  //    307 (Temporary Redirect)
   356  //    308 (Permanent Redirect)
   357  //
   358  // An error is returned if there were too many redirects or if there
   359  // was an HTTP protocol error. A non-2xx response doesn't cause an
   360  // error.
   361  //
   362  // When err is nil, resp always contains a non-nil resp.Body.
   363  // Caller should close resp.Body when done reading from it.
   364  //
   365  // Get is a wrapper around DefaultClient.Get.
   366  //
   367  // To make a request with custom headers, use NewRequest and
   368  // DefaultClient.Do.
   369  func Get(url string) (resp *Response, err error) {
   370  	return DefaultClient.Get(url)
   371  }
   372  
   373  // Get issues a GET to the specified URL. If the response is one of the
   374  // following redirect codes, Get follows the redirect after calling the
   375  // Client's CheckRedirect function:
   376  //
   377  //    301 (Moved Permanently)
   378  //    302 (Found)
   379  //    303 (See Other)
   380  //    307 (Temporary Redirect)
   381  //    308 (Permanent Redirect)
   382  //
   383  // An error is returned if the Client's CheckRedirect function fails
   384  // or if there was an HTTP protocol error. A non-2xx response doesn't
   385  // cause an error.
   386  //
   387  // When err is nil, resp always contains a non-nil resp.Body.
   388  // Caller should close resp.Body when done reading from it.
   389  //
   390  // To make a request with custom headers, use NewRequest and Client.Do.
   391  func (c *Client) Get(url string) (resp *Response, err error) {
   392  	req, err := NewRequest("GET", url, nil)
   393  	if err != nil {
   394  		return nil, err
   395  	}
   396  	return c.Do(req)
   397  }
   398  
   399  func alwaysFalse() bool { return false }
   400  
   401  // ErrUseLastResponse can be returned by Client.CheckRedirect hooks to
   402  // control how redirects are processed. If returned, the next request
   403  // is not sent and the most recent response is returned with its body
   404  // unclosed.
   405  var ErrUseLastResponse = errors.New("net/http: use last response")
   406  
   407  // checkRedirect calls either the user's configured CheckRedirect
   408  // function, or the default.
   409  func (c *Client) checkRedirect(req *Request, via []*Request) error {
   410  	fn := c.CheckRedirect
   411  	if fn == nil {
   412  		fn = defaultCheckRedirect
   413  	}
   414  	return fn(req, via)
   415  }
   416  
   417  // redirectBehavior describes what should happen when the
   418  // client encounters a 3xx status code from the server
   419  func redirectBehavior(reqMethod string, resp *Response, ireq *Request) (redirectMethod string, shouldRedirect, includeBody bool) {
   420  	switch resp.StatusCode {
   421  	case 301, 302, 303:
   422  		redirectMethod = reqMethod
   423  		shouldRedirect = true
   424  		includeBody = false
   425  
   426  		// RFC 2616 allowed automatic redirection only with GET and
   427  		// HEAD requests. RFC 7231 lifts this restriction, but we still
   428  		// restrict other methods to GET to maintain compatibility.
   429  		// See Issue 18570.
   430  		if reqMethod != "GET" && reqMethod != "HEAD" {
   431  			redirectMethod = "GET"
   432  		}
   433  	case 307, 308:
   434  		redirectMethod = reqMethod
   435  		shouldRedirect = true
   436  		includeBody = true
   437  
   438  		// Treat 307 and 308 specially, since they're new in
   439  		// Go 1.8, and they also require re-sending the request body.
   440  		if resp.Header.Get("Location") == "" {
   441  			// 308s have been observed in the wild being served
   442  			// without Location headers. Since Go 1.7 and earlier
   443  			// didn't follow these codes, just stop here instead
   444  			// of returning an error.
   445  			// See Issue 17773.
   446  			shouldRedirect = false
   447  			break
   448  		}
   449  		if ireq.GetBody == nil && ireq.outgoingLength() != 0 {
   450  			// We had a request body, and 307/308 require
   451  			// re-sending it, but GetBody is not defined. So just
   452  			// return this response to the user instead of an
   453  			// error, like we did in Go 1.7 and earlier.
   454  			shouldRedirect = false
   455  		}
   456  	}
   457  	return redirectMethod, shouldRedirect, includeBody
   458  }
   459  
   460  // Do sends an HTTP request and returns an HTTP response, following
   461  // policy (such as redirects, cookies, auth) as configured on the
   462  // client.
   463  //
   464  // An error is returned if caused by client policy (such as
   465  // CheckRedirect), or failure to speak HTTP (such as a network
   466  // connectivity problem). A non-2xx status code doesn't cause an
   467  // error.
   468  //
   469  // If the returned error is nil, the Response will contain a non-nil
   470  // Body which the user is expected to close. If the Body is not
   471  // closed, the Client's underlying RoundTripper (typically Transport)
   472  // may not be able to re-use a persistent TCP connection to the server
   473  // for a subsequent "keep-alive" request.
   474  //
   475  // The request Body, if non-nil, will be closed by the underlying
   476  // Transport, even on errors.
   477  //
   478  // On error, any Response can be ignored. A non-nil Response with a
   479  // non-nil error only occurs when CheckRedirect fails, and even then
   480  // the returned Response.Body is already closed.
   481  //
   482  // Generally Get, Post, or PostForm will be used instead of Do.
   483  //
   484  // If the server replies with a redirect, the Client first uses the
   485  // CheckRedirect function to determine whether the redirect should be
   486  // followed. If permitted, a 301, 302, or 303 redirect causes
   487  // subsequent requests to use HTTP method GET
   488  // (or HEAD if the original request was HEAD), with no body.
   489  // A 307 or 308 redirect preserves the original HTTP method and body,
   490  // provided that the Request.GetBody function is defined.
   491  // The NewRequest function automatically sets GetBody for common
   492  // standard library body types.
   493  func (c *Client) Do(req *Request) (*Response, error) {
   494  	if req.URL == nil {
   495  		req.closeBody()
   496  		return nil, errors.New("http: nil Request.URL")
   497  	}
   498  
   499  	var (
   500  		deadline      = c.deadline()
   501  		reqs          []*Request
   502  		resp          *Response
   503  		copyHeaders   = c.makeHeadersCopier(req)
   504  		reqBodyClosed = false // have we closed the current req.Body?
   505  
   506  		// Redirect behavior:
   507  		redirectMethod string
   508  		includeBody    bool
   509  	)
   510  	uerr := func(err error) error {
   511  		// the body may have been closed already by c.send()
   512  		if !reqBodyClosed {
   513  			req.closeBody()
   514  		}
   515  		method := valueOrDefault(reqs[0].Method, "GET")
   516  		var urlStr string
   517  		if resp != nil && resp.Request != nil {
   518  			urlStr = resp.Request.URL.String()
   519  		} else {
   520  			urlStr = req.URL.String()
   521  		}
   522  		return &url.Error{
   523  			Op:  method[:1] + strings.ToLower(method[1:]),
   524  			URL: urlStr,
   525  			Err: err,
   526  		}
   527  	}
   528  	for {
   529  		// For all but the first request, create the next
   530  		// request hop and replace req.
   531  		if len(reqs) > 0 {
   532  			loc := resp.Header.Get("Location")
   533  			if loc == "" {
   534  				resp.closeBody()
   535  				return nil, uerr(fmt.Errorf("%d response missing Location header", resp.StatusCode))
   536  			}
   537  			u, err := req.URL.Parse(loc)
   538  			if err != nil {
   539  				resp.closeBody()
   540  				return nil, uerr(fmt.Errorf("failed to parse Location header %q: %v", loc, err))
   541  			}
   542  			host := ""
   543  			if req.Host != "" && req.Host != req.URL.Host {
   544  				// If the caller specified a custom Host header and the
   545  				// redirect location is relative, preserve the Host header
   546  				// through the redirect. See issue #22233.
   547  				if u, _ := url.Parse(loc); u != nil && !u.IsAbs() {
   548  					host = req.Host
   549  				}
   550  			}
   551  			ireq := reqs[0]
   552  			req = &Request{
   553  				Method:   redirectMethod,
   554  				Response: resp,
   555  				URL:      u,
   556  				Header:   make(Header),
   557  				Host:     host,
   558  				Cancel:   ireq.Cancel,
   559  				ctx:      ireq.ctx,
   560  			}
   561  			if includeBody && ireq.GetBody != nil {
   562  				req.Body, err = ireq.GetBody()
   563  				if err != nil {
   564  					resp.closeBody()
   565  					return nil, uerr(err)
   566  				}
   567  				req.ContentLength = ireq.ContentLength
   568  			}
   569  
   570  			// Copy original headers before setting the Referer,
   571  			// in case the user set Referer on their first request.
   572  			// If they really want to override, they can do it in
   573  			// their CheckRedirect func.
   574  			copyHeaders(req)
   575  
   576  			// Add the Referer header from the most recent
   577  			// request URL to the new one, if it's not https->http:
   578  			if ref := refererForURL(reqs[len(reqs)-1].URL, req.URL); ref != "" {
   579  				req.Header.Set("Referer", ref)
   580  			}
   581  			err = c.checkRedirect(req, reqs)
   582  
   583  			// Sentinel error to let users select the
   584  			// previous response, without closing its
   585  			// body. See Issue 10069.
   586  			if err == ErrUseLastResponse {
   587  				return resp, nil
   588  			}
   589  
   590  			// Close the previous response's body. But
   591  			// read at least some of the body so if it's
   592  			// small the underlying TCP connection will be
   593  			// re-used. No need to check for errors: if it
   594  			// fails, the Transport won't reuse it anyway.
   595  			const maxBodySlurpSize = 2 << 10
   596  			if resp.ContentLength == -1 || resp.ContentLength <= maxBodySlurpSize {
   597  				io.CopyN(ioutil.Discard, resp.Body, maxBodySlurpSize)
   598  			}
   599  			resp.Body.Close()
   600  
   601  			if err != nil {
   602  				// Special case for Go 1 compatibility: return both the response
   603  				// and an error if the CheckRedirect function failed.
   604  				// See https://golang.org/issue/3795
   605  				// The resp.Body has already been closed.
   606  				ue := uerr(err)
   607  				ue.(*url.Error).URL = loc
   608  				return resp, ue
   609  			}
   610  		}
   611  
   612  		reqs = append(reqs, req)
   613  		var err error
   614  		var didTimeout func() bool
   615  		if resp, didTimeout, err = c.send(req, deadline); err != nil {
   616  			// c.send() always closes req.Body
   617  			reqBodyClosed = true
   618  			if !deadline.IsZero() && didTimeout() {
   619  				err = &httpError{
   620  					err:     err.Error() + " (Client.Timeout exceeded while awaiting headers)",
   621  					timeout: true,
   622  				}
   623  			}
   624  			return nil, uerr(err)
   625  		}
   626  
   627  		var shouldRedirect bool
   628  		redirectMethod, shouldRedirect, includeBody = redirectBehavior(req.Method, resp, reqs[0])
   629  		if !shouldRedirect {
   630  			return resp, nil
   631  		}
   632  
   633  		req.closeBody()
   634  	}
   635  }
   636  
   637  // makeHeadersCopier makes a function that copies headers from the
   638  // initial Request, ireq. For every redirect, this function must be called
   639  // so that it can copy headers into the upcoming Request.
   640  func (c *Client) makeHeadersCopier(ireq *Request) func(*Request) {
   641  	// The headers to copy are from the very initial request.
   642  	// We use a closured callback to keep a reference to these original headers.
   643  	var (
   644  		ireqhdr  = ireq.Header.clone()
   645  		icookies map[string][]*Cookie
   646  	)
   647  	if c.Jar != nil && ireq.Header.Get("Cookie") != "" {
   648  		icookies = make(map[string][]*Cookie)
   649  		for _, c := range ireq.Cookies() {
   650  			icookies[c.Name] = append(icookies[c.Name], c)
   651  		}
   652  	}
   653  
   654  	preq := ireq // The previous request
   655  	return func(req *Request) {
   656  		// If Jar is present and there was some initial cookies provided
   657  		// via the request header, then we may need to alter the initial
   658  		// cookies as we follow redirects since each redirect may end up
   659  		// modifying a pre-existing cookie.
   660  		//
   661  		// Since cookies already set in the request header do not contain
   662  		// information about the original domain and path, the logic below
   663  		// assumes any new set cookies override the original cookie
   664  		// regardless of domain or path.
   665  		//
   666  		// See https://golang.org/issue/17494
   667  		if c.Jar != nil && icookies != nil {
   668  			var changed bool
   669  			resp := req.Response // The response that caused the upcoming redirect
   670  			for _, c := range resp.Cookies() {
   671  				if _, ok := icookies[c.Name]; ok {
   672  					delete(icookies, c.Name)
   673  					changed = true
   674  				}
   675  			}
   676  			if changed {
   677  				ireqhdr.Del("Cookie")
   678  				var ss []string
   679  				for _, cs := range icookies {
   680  					for _, c := range cs {
   681  						ss = append(ss, c.Name+"="+c.Value)
   682  					}
   683  				}
   684  				sort.Strings(ss) // Ensure deterministic headers
   685  				ireqhdr.Set("Cookie", strings.Join(ss, "; "))
   686  			}
   687  		}
   688  
   689  		// Copy the initial request's Header values
   690  		// (at least the safe ones).
   691  		for k, vv := range ireqhdr {
   692  			if shouldCopyHeaderOnRedirect(k, preq.URL, req.URL) {
   693  				req.Header[k] = vv
   694  			}
   695  		}
   696  
   697  		preq = req // Update previous Request with the current request
   698  	}
   699  }
   700  
   701  func defaultCheckRedirect(req *Request, via []*Request) error {
   702  	if len(via) >= 10 {
   703  		return errors.New("stopped after 10 redirects")
   704  	}
   705  	return nil
   706  }
   707  
   708  // Post issues a POST to the specified URL.
   709  //
   710  // Caller should close resp.Body when done reading from it.
   711  //
   712  // If the provided body is an io.Closer, it is closed after the
   713  // request.
   714  //
   715  // Post is a wrapper around DefaultClient.Post.
   716  //
   717  // To set custom headers, use NewRequest and DefaultClient.Do.
   718  //
   719  // See the Client.Do method documentation for details on how redirects
   720  // are handled.
   721  func Post(url string, contentType string, body io.Reader) (resp *Response, err error) {
   722  	return DefaultClient.Post(url, contentType, body)
   723  }
   724  
   725  // Post issues a POST to the specified URL.
   726  //
   727  // Caller should close resp.Body when done reading from it.
   728  //
   729  // If the provided body is an io.Closer, it is closed after the
   730  // request.
   731  //
   732  // To set custom headers, use NewRequest and Client.Do.
   733  //
   734  // See the Client.Do method documentation for details on how redirects
   735  // are handled.
   736  func (c *Client) Post(url string, contentType string, body io.Reader) (resp *Response, err error) {
   737  	req, err := NewRequest("POST", url, body)
   738  	if err != nil {
   739  		return nil, err
   740  	}
   741  	req.Header.Set("Content-Type", contentType)
   742  	return c.Do(req)
   743  }
   744  
   745  // PostForm issues a POST to the specified URL, with data's keys and
   746  // values URL-encoded as the request body.
   747  //
   748  // The Content-Type header is set to application/x-www-form-urlencoded.
   749  // To set other headers, use NewRequest and DefaultClient.Do.
   750  //
   751  // When err is nil, resp always contains a non-nil resp.Body.
   752  // Caller should close resp.Body when done reading from it.
   753  //
   754  // PostForm is a wrapper around DefaultClient.PostForm.
   755  //
   756  // See the Client.Do method documentation for details on how redirects
   757  // are handled.
   758  func PostForm(url string, data url.Values) (resp *Response, err error) {
   759  	return DefaultClient.PostForm(url, data)
   760  }
   761  
   762  // PostForm issues a POST to the specified URL,
   763  // with data's keys and values URL-encoded as the request body.
   764  //
   765  // The Content-Type header is set to application/x-www-form-urlencoded.
   766  // To set other headers, use NewRequest and Client.Do.
   767  //
   768  // When err is nil, resp always contains a non-nil resp.Body.
   769  // Caller should close resp.Body when done reading from it.
   770  //
   771  // See the Client.Do method documentation for details on how redirects
   772  // are handled.
   773  func (c *Client) PostForm(url string, data url.Values) (resp *Response, err error) {
   774  	return c.Post(url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
   775  }
   776  
   777  // Head issues a HEAD to the specified URL. If the response is one of
   778  // the following redirect codes, Head follows the redirect, up to a
   779  // maximum of 10 redirects:
   780  //
   781  //    301 (Moved Permanently)
   782  //    302 (Found)
   783  //    303 (See Other)
   784  //    307 (Temporary Redirect)
   785  //    308 (Permanent Redirect)
   786  //
   787  // Head is a wrapper around DefaultClient.Head
   788  func Head(url string) (resp *Response, err error) {
   789  	return DefaultClient.Head(url)
   790  }
   791  
   792  // Head issues a HEAD to the specified URL. If the response is one of the
   793  // following redirect codes, Head follows the redirect after calling the
   794  // Client's CheckRedirect function:
   795  //
   796  //    301 (Moved Permanently)
   797  //    302 (Found)
   798  //    303 (See Other)
   799  //    307 (Temporary Redirect)
   800  //    308 (Permanent Redirect)
   801  func (c *Client) Head(url string) (resp *Response, err error) {
   802  	req, err := NewRequest("HEAD", url, nil)
   803  	if err != nil {
   804  		return nil, err
   805  	}
   806  	return c.Do(req)
   807  }
   808  
   809  // cancelTimerBody is an io.ReadCloser that wraps rc with two features:
   810  // 1) on Read error or close, the stop func is called.
   811  // 2) On Read failure, if reqDidTimeout is true, the error is wrapped and
   812  //    marked as net.Error that hit its timeout.
   813  type cancelTimerBody struct {
   814  	stop          func() // stops the time.Timer waiting to cancel the request
   815  	rc            io.ReadCloser
   816  	reqDidTimeout func() bool
   817  }
   818  
   819  func (b *cancelTimerBody) Read(p []byte) (n int, err error) {
   820  	n, err = b.rc.Read(p)
   821  	if err == nil {
   822  		return n, nil
   823  	}
   824  	b.stop()
   825  	if err == io.EOF {
   826  		return n, err
   827  	}
   828  	if b.reqDidTimeout() {
   829  		err = &httpError{
   830  			err:     err.Error() + " (Client.Timeout exceeded while reading body)",
   831  			timeout: true,
   832  		}
   833  	}
   834  	return n, err
   835  }
   836  
   837  func (b *cancelTimerBody) Close() error {
   838  	err := b.rc.Close()
   839  	b.stop()
   840  	return err
   841  }
   842  
   843  func shouldCopyHeaderOnRedirect(headerKey string, initial, dest *url.URL) bool {
   844  	switch CanonicalHeaderKey(headerKey) {
   845  	case "Authorization", "Www-Authenticate", "Cookie", "Cookie2":
   846  		// Permit sending auth/cookie headers from "foo.com"
   847  		// to "sub.foo.com".
   848  
   849  		// Note that we don't send all cookies to subdomains
   850  		// automatically. This function is only used for
   851  		// Cookies set explicitly on the initial outgoing
   852  		// client request. Cookies automatically added via the
   853  		// CookieJar mechanism continue to follow each
   854  		// cookie's scope as set by Set-Cookie. But for
   855  		// outgoing requests with the Cookie header set
   856  		// directly, we don't know their scope, so we assume
   857  		// it's for *.domain.com.
   858  
   859  		ihost := canonicalAddr(initial)
   860  		dhost := canonicalAddr(dest)
   861  		return isDomainOrSubdomain(dhost, ihost)
   862  	}
   863  	// All other headers are copied:
   864  	return true
   865  }
   866  
   867  // isDomainOrSubdomain reports whether sub is a subdomain (or exact
   868  // match) of the parent domain.
   869  //
   870  // Both domains must already be in canonical form.
   871  func isDomainOrSubdomain(sub, parent string) bool {
   872  	if sub == parent {
   873  		return true
   874  	}
   875  	// If sub is "foo.example.com" and parent is "example.com",
   876  	// that means sub must end in "."+parent.
   877  	// Do it without allocating.
   878  	if !strings.HasSuffix(sub, parent) {
   879  		return false
   880  	}
   881  	return sub[len(sub)-len(parent)-1] == '.'
   882  }
   883  

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