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Source file src/net/http/requestwrite_test.go

Documentation: net/http

  // Copyright 2010 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package http
  
  import (
  	"bufio"
  	"bytes"
  	"errors"
  	"fmt"
  	"io"
  	"io/ioutil"
  	"net"
  	"net/url"
  	"strings"
  	"testing"
  	"time"
  )
  
  type reqWriteTest struct {
  	Req  Request
  	Body interface{} // optional []byte or func() io.ReadCloser to populate Req.Body
  
  	// Any of these three may be empty to skip that test.
  	WantWrite string // Request.Write
  	WantProxy string // Request.WriteProxy
  
  	WantError error // wanted error from Request.Write
  }
  
  var reqWriteTests = []reqWriteTest{
  	// HTTP/1.1 => chunked coding; no body; no trailer
  	0: {
  		Req: Request{
  			Method: "GET",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "www.techcrunch.com",
  				Path:   "/",
  			},
  			Proto:      "HTTP/1.1",
  			ProtoMajor: 1,
  			ProtoMinor: 1,
  			Header: Header{
  				"Accept":           {"text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"},
  				"Accept-Charset":   {"ISO-8859-1,utf-8;q=0.7,*;q=0.7"},
  				"Accept-Encoding":  {"gzip,deflate"},
  				"Accept-Language":  {"en-us,en;q=0.5"},
  				"Keep-Alive":       {"300"},
  				"Proxy-Connection": {"keep-alive"},
  				"User-Agent":       {"Fake"},
  			},
  			Body:  nil,
  			Close: false,
  			Host:  "www.techcrunch.com",
  			Form:  map[string][]string{},
  		},
  
  		WantWrite: "GET / HTTP/1.1\r\n" +
  			"Host: www.techcrunch.com\r\n" +
  			"User-Agent: Fake\r\n" +
  			"Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n" +
  			"Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7\r\n" +
  			"Accept-Encoding: gzip,deflate\r\n" +
  			"Accept-Language: en-us,en;q=0.5\r\n" +
  			"Keep-Alive: 300\r\n" +
  			"Proxy-Connection: keep-alive\r\n\r\n",
  
  		WantProxy: "GET http://www.techcrunch.com/ HTTP/1.1\r\n" +
  			"Host: www.techcrunch.com\r\n" +
  			"User-Agent: Fake\r\n" +
  			"Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n" +
  			"Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7\r\n" +
  			"Accept-Encoding: gzip,deflate\r\n" +
  			"Accept-Language: en-us,en;q=0.5\r\n" +
  			"Keep-Alive: 300\r\n" +
  			"Proxy-Connection: keep-alive\r\n\r\n",
  	},
  	// HTTP/1.1 => chunked coding; body; empty trailer
  	1: {
  		Req: Request{
  			Method: "GET",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "www.google.com",
  				Path:   "/search",
  			},
  			ProtoMajor:       1,
  			ProtoMinor:       1,
  			Header:           Header{},
  			TransferEncoding: []string{"chunked"},
  		},
  
  		Body: []byte("abcdef"),
  
  		WantWrite: "GET /search HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Transfer-Encoding: chunked\r\n\r\n" +
  			chunk("abcdef") + chunk(""),
  
  		WantProxy: "GET http://www.google.com/search HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Transfer-Encoding: chunked\r\n\r\n" +
  			chunk("abcdef") + chunk(""),
  	},
  	// HTTP/1.1 POST => chunked coding; body; empty trailer
  	2: {
  		Req: Request{
  			Method: "POST",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "www.google.com",
  				Path:   "/search",
  			},
  			ProtoMajor:       1,
  			ProtoMinor:       1,
  			Header:           Header{},
  			Close:            true,
  			TransferEncoding: []string{"chunked"},
  		},
  
  		Body: []byte("abcdef"),
  
  		WantWrite: "POST /search HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Connection: close\r\n" +
  			"Transfer-Encoding: chunked\r\n\r\n" +
  			chunk("abcdef") + chunk(""),
  
  		WantProxy: "POST http://www.google.com/search HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Connection: close\r\n" +
  			"Transfer-Encoding: chunked\r\n\r\n" +
  			chunk("abcdef") + chunk(""),
  	},
  
  	// HTTP/1.1 POST with Content-Length, no chunking
  	3: {
  		Req: Request{
  			Method: "POST",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "www.google.com",
  				Path:   "/search",
  			},
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			Header:        Header{},
  			Close:         true,
  			ContentLength: 6,
  		},
  
  		Body: []byte("abcdef"),
  
  		WantWrite: "POST /search HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Connection: close\r\n" +
  			"Content-Length: 6\r\n" +
  			"\r\n" +
  			"abcdef",
  
  		WantProxy: "POST http://www.google.com/search HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Connection: close\r\n" +
  			"Content-Length: 6\r\n" +
  			"\r\n" +
  			"abcdef",
  	},
  
  	// HTTP/1.1 POST with Content-Length in headers
  	4: {
  		Req: Request{
  			Method: "POST",
  			URL:    mustParseURL("http://example.com/"),
  			Host:   "example.com",
  			Header: Header{
  				"Content-Length": []string{"10"}, // ignored
  			},
  			ContentLength: 6,
  		},
  
  		Body: []byte("abcdef"),
  
  		WantWrite: "POST / HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Content-Length: 6\r\n" +
  			"\r\n" +
  			"abcdef",
  
  		WantProxy: "POST http://example.com/ HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Content-Length: 6\r\n" +
  			"\r\n" +
  			"abcdef",
  	},
  
  	// default to HTTP/1.1
  	5: {
  		Req: Request{
  			Method: "GET",
  			URL:    mustParseURL("/search"),
  			Host:   "www.google.com",
  		},
  
  		WantWrite: "GET /search HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"\r\n",
  	},
  
  	// Request with a 0 ContentLength and a 0 byte body.
  	6: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 0, // as if unset by user
  		},
  
  		Body: func() io.ReadCloser { return ioutil.NopCloser(io.LimitReader(strings.NewReader("xx"), 0)) },
  
  		WantWrite: "POST / HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Transfer-Encoding: chunked\r\n" +
  			"\r\n0\r\n\r\n",
  
  		WantProxy: "POST / HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Transfer-Encoding: chunked\r\n" +
  			"\r\n0\r\n\r\n",
  	},
  
  	// Request with a 0 ContentLength and a nil body.
  	7: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 0, // as if unset by user
  		},
  
  		Body: func() io.ReadCloser { return nil },
  
  		WantWrite: "POST / HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Content-Length: 0\r\n" +
  			"\r\n",
  
  		WantProxy: "POST / HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Content-Length: 0\r\n" +
  			"\r\n",
  	},
  
  	// Request with a 0 ContentLength and a 1 byte body.
  	8: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 0, // as if unset by user
  		},
  
  		Body: func() io.ReadCloser { return ioutil.NopCloser(io.LimitReader(strings.NewReader("xx"), 1)) },
  
  		WantWrite: "POST / HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Transfer-Encoding: chunked\r\n\r\n" +
  			chunk("x") + chunk(""),
  
  		WantProxy: "POST / HTTP/1.1\r\n" +
  			"Host: example.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"Transfer-Encoding: chunked\r\n\r\n" +
  			chunk("x") + chunk(""),
  	},
  
  	// Request with a ContentLength of 10 but a 5 byte body.
  	9: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 10, // but we're going to send only 5 bytes
  		},
  		Body:      []byte("12345"),
  		WantError: errors.New("http: ContentLength=10 with Body length 5"),
  	},
  
  	// Request with a ContentLength of 4 but an 8 byte body.
  	10: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 4, // but we're going to try to send 8 bytes
  		},
  		Body:      []byte("12345678"),
  		WantError: errors.New("http: ContentLength=4 with Body length 8"),
  	},
  
  	// Request with a 5 ContentLength and nil body.
  	11: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 5, // but we'll omit the body
  		},
  		WantError: errors.New("http: Request.ContentLength=5 with nil Body"),
  	},
  
  	// Request with a 0 ContentLength and a body with 1 byte content and an error.
  	12: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 0, // as if unset by user
  		},
  
  		Body: func() io.ReadCloser {
  			err := errors.New("Custom reader error")
  			errReader := &errorReader{err}
  			return ioutil.NopCloser(io.MultiReader(strings.NewReader("x"), errReader))
  		},
  
  		WantError: errors.New("Custom reader error"),
  	},
  
  	// Request with a 0 ContentLength and a body without content and an error.
  	13: {
  		Req: Request{
  			Method:        "POST",
  			URL:           mustParseURL("/"),
  			Host:          "example.com",
  			ProtoMajor:    1,
  			ProtoMinor:    1,
  			ContentLength: 0, // as if unset by user
  		},
  
  		Body: func() io.ReadCloser {
  			err := errors.New("Custom reader error")
  			errReader := &errorReader{err}
  			return ioutil.NopCloser(errReader)
  		},
  
  		WantError: errors.New("Custom reader error"),
  	},
  
  	// Verify that DumpRequest preserves the HTTP version number, doesn't add a Host,
  	// and doesn't add a User-Agent.
  	14: {
  		Req: Request{
  			Method:     "GET",
  			URL:        mustParseURL("/foo"),
  			ProtoMajor: 1,
  			ProtoMinor: 0,
  			Header: Header{
  				"X-Foo": []string{"X-Bar"},
  			},
  		},
  
  		WantWrite: "GET /foo HTTP/1.1\r\n" +
  			"Host: \r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"X-Foo: X-Bar\r\n\r\n",
  	},
  
  	// If no Request.Host and no Request.URL.Host, we send
  	// an empty Host header, and don't use
  	// Request.Header["Host"]. This is just testing that
  	// we don't change Go 1.0 behavior.
  	15: {
  		Req: Request{
  			Method: "GET",
  			Host:   "",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "",
  				Path:   "/search",
  			},
  			ProtoMajor: 1,
  			ProtoMinor: 1,
  			Header: Header{
  				"Host": []string{"bad.example.com"},
  			},
  		},
  
  		WantWrite: "GET /search HTTP/1.1\r\n" +
  			"Host: \r\n" +
  			"User-Agent: Go-http-client/1.1\r\n\r\n",
  	},
  
  	// Opaque test #1 from golang.org/issue/4860
  	16: {
  		Req: Request{
  			Method: "GET",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "www.google.com",
  				Opaque: "/%2F/%2F/",
  			},
  			ProtoMajor: 1,
  			ProtoMinor: 1,
  			Header:     Header{},
  		},
  
  		WantWrite: "GET /%2F/%2F/ HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n\r\n",
  	},
  
  	// Opaque test #2 from golang.org/issue/4860
  	17: {
  		Req: Request{
  			Method: "GET",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "x.google.com",
  				Opaque: "//y.google.com/%2F/%2F/",
  			},
  			ProtoMajor: 1,
  			ProtoMinor: 1,
  			Header:     Header{},
  		},
  
  		WantWrite: "GET http://y.google.com/%2F/%2F/ HTTP/1.1\r\n" +
  			"Host: x.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n\r\n",
  	},
  
  	// Testing custom case in header keys. Issue 5022.
  	18: {
  		Req: Request{
  			Method: "GET",
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "www.google.com",
  				Path:   "/",
  			},
  			Proto:      "HTTP/1.1",
  			ProtoMajor: 1,
  			ProtoMinor: 1,
  			Header: Header{
  				"ALL-CAPS": {"x"},
  			},
  		},
  
  		WantWrite: "GET / HTTP/1.1\r\n" +
  			"Host: www.google.com\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"ALL-CAPS: x\r\n" +
  			"\r\n",
  	},
  
  	// Request with host header field; IPv6 address with zone identifier
  	19: {
  		Req: Request{
  			Method: "GET",
  			URL: &url.URL{
  				Host: "[fe80::1%en0]",
  			},
  		},
  
  		WantWrite: "GET / HTTP/1.1\r\n" +
  			"Host: [fe80::1]\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"\r\n",
  	},
  
  	// Request with optional host header field; IPv6 address with zone identifier
  	20: {
  		Req: Request{
  			Method: "GET",
  			URL: &url.URL{
  				Host: "www.example.com",
  			},
  			Host: "[fe80::1%en0]:8080",
  		},
  
  		WantWrite: "GET / HTTP/1.1\r\n" +
  			"Host: [fe80::1]:8080\r\n" +
  			"User-Agent: Go-http-client/1.1\r\n" +
  			"\r\n",
  	},
  }
  
  func TestRequestWrite(t *testing.T) {
  	for i := range reqWriteTests {
  		tt := &reqWriteTests[i]
  
  		setBody := func() {
  			if tt.Body == nil {
  				return
  			}
  			switch b := tt.Body.(type) {
  			case []byte:
  				tt.Req.Body = ioutil.NopCloser(bytes.NewReader(b))
  			case func() io.ReadCloser:
  				tt.Req.Body = b()
  			}
  		}
  		setBody()
  		if tt.Req.Header == nil {
  			tt.Req.Header = make(Header)
  		}
  
  		var braw bytes.Buffer
  		err := tt.Req.Write(&braw)
  		if g, e := fmt.Sprintf("%v", err), fmt.Sprintf("%v", tt.WantError); g != e {
  			t.Errorf("writing #%d, err = %q, want %q", i, g, e)
  			continue
  		}
  		if err != nil {
  			continue
  		}
  
  		if tt.WantWrite != "" {
  			sraw := braw.String()
  			if sraw != tt.WantWrite {
  				t.Errorf("Test %d, expecting:\n%s\nGot:\n%s\n", i, tt.WantWrite, sraw)
  				continue
  			}
  		}
  
  		if tt.WantProxy != "" {
  			setBody()
  			var praw bytes.Buffer
  			err = tt.Req.WriteProxy(&praw)
  			if err != nil {
  				t.Errorf("WriteProxy #%d: %s", i, err)
  				continue
  			}
  			sraw := praw.String()
  			if sraw != tt.WantProxy {
  				t.Errorf("Test Proxy %d, expecting:\n%s\nGot:\n%s\n", i, tt.WantProxy, sraw)
  				continue
  			}
  		}
  	}
  }
  
  func TestRequestWriteTransport(t *testing.T) {
  	t.Parallel()
  
  	matchSubstr := func(substr string) func(string) error {
  		return func(written string) error {
  			if !strings.Contains(written, substr) {
  				return fmt.Errorf("expected substring %q in request: %s", substr, written)
  			}
  			return nil
  		}
  	}
  
  	noContentLengthOrTransferEncoding := func(req string) error {
  		if strings.Contains(req, "Content-Length: ") {
  			return fmt.Errorf("unexpected Content-Length in request: %s", req)
  		}
  		if strings.Contains(req, "Transfer-Encoding: ") {
  			return fmt.Errorf("unexpected Transfer-Encoding in request: %s", req)
  		}
  		return nil
  	}
  
  	all := func(checks ...func(string) error) func(string) error {
  		return func(req string) error {
  			for _, c := range checks {
  				if err := c(req); err != nil {
  					return err
  				}
  			}
  			return nil
  		}
  	}
  
  	type testCase struct {
  		method string
  		clen   int64 // ContentLength
  		body   io.ReadCloser
  		want   func(string) error
  
  		// optional:
  		init         func(*testCase)
  		afterReqRead func()
  	}
  
  	tests := []testCase{
  		{
  			method: "GET",
  			want:   noContentLengthOrTransferEncoding,
  		},
  		{
  			method: "GET",
  			body:   ioutil.NopCloser(strings.NewReader("")),
  			want:   noContentLengthOrTransferEncoding,
  		},
  		{
  			method: "GET",
  			clen:   -1,
  			body:   ioutil.NopCloser(strings.NewReader("")),
  			want:   noContentLengthOrTransferEncoding,
  		},
  		// A GET with a body, with explicit content length:
  		{
  			method: "GET",
  			clen:   7,
  			body:   ioutil.NopCloser(strings.NewReader("foobody")),
  			want: all(matchSubstr("Content-Length: 7"),
  				matchSubstr("foobody")),
  		},
  		// A GET with a body, sniffing the leading "f" from "foobody".
  		{
  			method: "GET",
  			clen:   -1,
  			body:   ioutil.NopCloser(strings.NewReader("foobody")),
  			want: all(matchSubstr("Transfer-Encoding: chunked"),
  				matchSubstr("\r\n1\r\nf\r\n"),
  				matchSubstr("oobody")),
  		},
  		// But a POST request is expected to have a body, so
  		// no sniffing happens:
  		{
  			method: "POST",
  			clen:   -1,
  			body:   ioutil.NopCloser(strings.NewReader("foobody")),
  			want: all(matchSubstr("Transfer-Encoding: chunked"),
  				matchSubstr("foobody")),
  		},
  		{
  			method: "POST",
  			clen:   -1,
  			body:   ioutil.NopCloser(strings.NewReader("")),
  			want:   all(matchSubstr("Transfer-Encoding: chunked")),
  		},
  		// Verify that a blocking Request.Body doesn't block forever.
  		{
  			method: "GET",
  			clen:   -1,
  			init: func(tt *testCase) {
  				pr, pw := io.Pipe()
  				tt.afterReqRead = func() {
  					pw.Close()
  				}
  				tt.body = ioutil.NopCloser(pr)
  			},
  			want: matchSubstr("Transfer-Encoding: chunked"),
  		},
  	}
  
  	for i, tt := range tests {
  		if tt.init != nil {
  			tt.init(&tt)
  		}
  		req := &Request{
  			Method: tt.method,
  			URL: &url.URL{
  				Scheme: "http",
  				Host:   "example.com",
  			},
  			Header:        make(Header),
  			ContentLength: tt.clen,
  			Body:          tt.body,
  		}
  		got, err := dumpRequestOut(req, tt.afterReqRead)
  		if err != nil {
  			t.Errorf("test[%d]: %v", i, err)
  			continue
  		}
  		if err := tt.want(string(got)); err != nil {
  			t.Errorf("test[%d]: %v", i, err)
  		}
  	}
  }
  
  type closeChecker struct {
  	io.Reader
  	closed bool
  }
  
  func (rc *closeChecker) Close() error {
  	rc.closed = true
  	return nil
  }
  
  // TestRequestWriteClosesBody tests that Request.Write closes its request.Body.
  // It also indirectly tests NewRequest and that it doesn't wrap an existing Closer
  // inside a NopCloser, and that it serializes it correctly.
  func TestRequestWriteClosesBody(t *testing.T) {
  	rc := &closeChecker{Reader: strings.NewReader("my body")}
  	req, err := NewRequest("POST", "http://foo.com/", rc)
  	if err != nil {
  		t.Fatal(err)
  	}
  	buf := new(bytes.Buffer)
  	if err := req.Write(buf); err != nil {
  		t.Error(err)
  	}
  	if !rc.closed {
  		t.Error("body not closed after write")
  	}
  	expected := "POST / HTTP/1.1\r\n" +
  		"Host: foo.com\r\n" +
  		"User-Agent: Go-http-client/1.1\r\n" +
  		"Transfer-Encoding: chunked\r\n\r\n" +
  		chunk("my body") +
  		chunk("")
  	if buf.String() != expected {
  		t.Errorf("write:\n got: %s\nwant: %s", buf.String(), expected)
  	}
  }
  
  func chunk(s string) string {
  	return fmt.Sprintf("%x\r\n%s\r\n", len(s), s)
  }
  
  func mustParseURL(s string) *url.URL {
  	u, err := url.Parse(s)
  	if err != nil {
  		panic(fmt.Sprintf("Error parsing URL %q: %v", s, err))
  	}
  	return u
  }
  
  type writerFunc func([]byte) (int, error)
  
  func (f writerFunc) Write(p []byte) (int, error) { return f(p) }
  
  // TestRequestWriteError tests the Write err != nil checks in (*Request).write.
  func TestRequestWriteError(t *testing.T) {
  	failAfter, writeCount := 0, 0
  	errFail := errors.New("fake write failure")
  
  	// w is the buffered io.Writer to write the request to. It
  	// fails exactly once on its Nth Write call, as controlled by
  	// failAfter. It also tracks the number of calls in
  	// writeCount.
  	w := struct {
  		io.ByteWriter // to avoid being wrapped by a bufio.Writer
  		io.Writer
  	}{
  		nil,
  		writerFunc(func(p []byte) (n int, err error) {
  			writeCount++
  			if failAfter == 0 {
  				err = errFail
  			}
  			failAfter--
  			return len(p), err
  		}),
  	}
  
  	req, _ := NewRequest("GET", "http://example.com/", nil)
  	const writeCalls = 4 // number of Write calls in current implementation
  	sawGood := false
  	for n := 0; n <= writeCalls+2; n++ {
  		failAfter = n
  		writeCount = 0
  		err := req.Write(w)
  		var wantErr error
  		if n < writeCalls {
  			wantErr = errFail
  		}
  		if err != wantErr {
  			t.Errorf("for fail-after %d Writes, err = %v; want %v", n, err, wantErr)
  			continue
  		}
  		if err == nil {
  			sawGood = true
  			if writeCount != writeCalls {
  				t.Fatalf("writeCalls constant is outdated in test")
  			}
  		}
  		if writeCount > writeCalls || writeCount > n+1 {
  			t.Errorf("for fail-after %d, saw unexpectedly high (%d) write calls", n, writeCount)
  		}
  	}
  	if !sawGood {
  		t.Fatalf("writeCalls constant is outdated in test")
  	}
  }
  
  // dumpRequestOut is a modified copy of net/http/httputil.DumpRequestOut.
  // Unlike the original, this version doesn't mutate the req.Body and
  // try to restore it. It always dumps the whole body.
  // And it doesn't support https.
  func dumpRequestOut(req *Request, onReadHeaders func()) ([]byte, error) {
  
  	// Use the actual Transport code to record what we would send
  	// on the wire, but not using TCP.  Use a Transport with a
  	// custom dialer that returns a fake net.Conn that waits
  	// for the full input (and recording it), and then responds
  	// with a dummy response.
  	var buf bytes.Buffer // records the output
  	pr, pw := io.Pipe()
  	defer pr.Close()
  	defer pw.Close()
  	dr := &delegateReader{c: make(chan io.Reader)}
  
  	t := &Transport{
  		Dial: func(net, addr string) (net.Conn, error) {
  			return &dumpConn{io.MultiWriter(&buf, pw), dr}, nil
  		},
  	}
  	defer t.CloseIdleConnections()
  
  	// Wait for the request before replying with a dummy response:
  	go func() {
  		req, err := ReadRequest(bufio.NewReader(pr))
  		if err == nil {
  			if onReadHeaders != nil {
  				onReadHeaders()
  			}
  			// Ensure all the body is read; otherwise
  			// we'll get a partial dump.
  			io.Copy(ioutil.Discard, req.Body)
  			req.Body.Close()
  		}
  		dr.c <- strings.NewReader("HTTP/1.1 204 No Content\r\nConnection: close\r\n\r\n")
  	}()
  
  	_, err := t.RoundTrip(req)
  	if err != nil {
  		return nil, err
  	}
  	return buf.Bytes(), nil
  }
  
  // delegateReader is a reader that delegates to another reader,
  // once it arrives on a channel.
  type delegateReader struct {
  	c chan io.Reader
  	r io.Reader // nil until received from c
  }
  
  func (r *delegateReader) Read(p []byte) (int, error) {
  	if r.r == nil {
  		r.r = <-r.c
  	}
  	return r.r.Read(p)
  }
  
  // dumpConn is a net.Conn that writes to Writer and reads from Reader.
  type dumpConn struct {
  	io.Writer
  	io.Reader
  }
  
  func (c *dumpConn) Close() error                       { return nil }
  func (c *dumpConn) LocalAddr() net.Addr                { return nil }
  func (c *dumpConn) RemoteAddr() net.Addr               { return nil }
  func (c *dumpConn) SetDeadline(t time.Time) error      { return nil }
  func (c *dumpConn) SetReadDeadline(t time.Time) error  { return nil }
  func (c *dumpConn) SetWriteDeadline(t time.Time) error { return nil }
  

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