net/http/httputil: fix DumpRequestOut with ContentLength & false body param

Fixes #6471

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/14920050

src/pkg/net/http/httputil/dump.go

@@ -45,13 +45,27 @@ 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 }
 
+type neverEnding byte
+
+func (b neverEnding) Read(p []byte) (n int, err error) {
+	for i := range p {
+		p[i] = byte(b)
+	}
+	return len(p), nil
+}
+
 // DumpRequestOut is like DumpRequest but includes
 // headers that the standard http.Transport adds,
 // such as User-Agent.
 func DumpRequestOut(req *http.Request, body bool) ([]byte, error) {
 	save := req.Body
+	dummyBody := false
 	if !body || req.Body == nil {
 		req.Body = nil
+		if req.ContentLength != 0 {
+			req.Body = ioutil.NopCloser(io.LimitReader(neverEnding('x'), req.ContentLength))
+			dummyBody = true
+		}
 	} else {
 		var err error
 		save, req.Body, err = drainBody(req.Body)
@@ -99,7 +113,19 @@ func DumpRequestOut(req *http.Request, body bool) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	return buf.Bytes(), nil
+	dump := buf.Bytes()
+
+	// If we used a dummy body above, remove it now.
+	// TODO: if the req.ContentLength is large, we allocate memory
+	// unnecessarily just to slice it off here.  But this is just
+	// a debug function, so this is acceptable for now. We could
+	// discard the body earlier if this matters.
+	if dummyBody {
+		if i := bytes.Index(dump, []byte("\r\n\r\n")); i >= 0 {
+			dump = dump[:i+4]
+		}
+	}
+	return dump, nil
 }
 
 // delegateReader is a reader that delegates to another reader,

src/pkg/net/http/httputil/dump_test.go

@@ -20,6 +20,7 @@ type dumpTest struct {
 
 	WantDump    string
 	WantDumpOut string
+	NoBody      bool // if true, set DumpRequest{,Out} body to false
 }
 
 var dumpTests = []dumpTest{
@@ -83,6 +84,31 @@ var dumpTests = []dumpTest{
 			"User-Agent: Go 1.1 package http\r\n" +
 			"Accept-Encoding: gzip\r\n\r\n",
 	},
+
+	// Request with Body, but Dump requested without it.
+	{
+		Req: http.Request{
+			Method: "POST",
+			URL: &url.URL{
+				Scheme: "http",
+				Host:   "post.tld",
+				Path:   "/",
+			},
+			ContentLength: 6,
+			ProtoMajor:    1,
+			ProtoMinor:    1,
+		},
+
+		Body: []byte("abcdef"),
+
+		WantDumpOut: "POST / HTTP/1.1\r\n" +
+			"Host: post.tld\r\n" +
+			"User-Agent: Go 1.1 package http\r\n" +
+			"Content-Length: 6\r\n" +
+			"Accept-Encoding: gzip\r\n\r\n",
+
+		NoBody: true,
+	},
 }
 
 func TestDumpRequest(t *testing.T) {
@@ -105,7 +131,7 @@ func TestDumpRequest(t *testing.T) {
 
 		if tt.WantDump != "" {
 			setBody()
-			dump, err := DumpRequest(&tt.Req, true)
+			dump, err := DumpRequest(&tt.Req, !tt.NoBody)
 			if err != nil {
 				t.Errorf("DumpRequest #%d: %s", i, err)
 				continue
@@ -118,7 +144,7 @@ func TestDumpRequest(t *testing.T) {
 
 		if tt.WantDumpOut != "" {
 			setBody()
-			dump, err := DumpRequestOut(&tt.Req, true)
+			dump, err := DumpRequestOut(&tt.Req, !tt.NoBody)
 			if err != nil {
 				t.Errorf("DumpRequestOut #%d: %s", i, err)
 				continue