net/http: fix duplicate status code in Response.Write

Fixes #3636

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/6203094

src/pkg/net/http/response.go

@@ -202,9 +202,12 @@ func (r *Response) Write(w io.Writer) error {
 			text = "status code " + strconv.Itoa(r.StatusCode)
 		}
 	}
-	io.WriteString(w, "HTTP/"+strconv.Itoa(r.ProtoMajor)+".")
-	io.WriteString(w, strconv.Itoa(r.ProtoMinor)+" ")
-	io.WriteString(w, strconv.Itoa(r.StatusCode)+" "+text+"\r\n")
+	protoMajor, protoMinor := strconv.Itoa(r.ProtoMajor), strconv.Itoa(r.ProtoMinor)
+	statusCode := strconv.Itoa(r.StatusCode) + " "
+	if strings.HasPrefix(text, statusCode) {
+		text = text[len(statusCode):]
+	}
+	io.WriteString(w, "HTTP/"+protoMajor+"."+protoMinor+" "+statusCode+text+"\r\n")
 
 	// Process Body,ContentLength,Close,Trailer
 	tw, err := newTransferWriter(r)

src/pkg/net/http/response_test.go

@@ -14,6 +14,7 @@ import (
 	"io/ioutil"
 	"net/url"
 	"reflect"
+	"strings"
 	"testing"
 )
 
@@ -444,3 +445,17 @@ func TestLocationResponse(t *testing.T) {
 		}
 	}
 }
+
+func TestResponseStatusStutter(t *testing.T) {
+	r := &Response{
+		Status:     "123 some status",
+		StatusCode: 123,
+		ProtoMajor: 1,
+		ProtoMinor: 3,
+	}
+	var buf bytes.Buffer
+	r.Write(&buf)
+	if strings.Contains(buf.String(), "123 123") {
+		t.Errorf("stutter in status: %s", buf.String())
+	}
+}

src/pkg/net/http/transfer.go

@@ -71,7 +71,9 @@ func newTransferWriter(r interface{}) (t *transferWriter, err error) {
 			}
 		}
 	case *Response:
-		t.Method = rr.Request.Method
+		if rr.Request != nil {
+			t.Method = rr.Request.Method
+		}
 		t.Body = rr.Body
 		t.BodyCloser = rr.Body
 		t.ContentLength = rr.ContentLength
@@ -79,7 +81,7 @@ func newTransferWriter(r interface{}) (t *transferWriter, err error) {
 		t.TransferEncoding = rr.TransferEncoding
 		t.Trailer = rr.Trailer
 		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
-		t.ResponseToHEAD = noBodyExpected(rr.Request.Method)
+		t.ResponseToHEAD = noBodyExpected(t.Method)
 	}
 
 	// Sanitize Body,ContentLength,TransferEncoding