http: ignore Transfer-Encoding on HEAD responses

Amazon S3 sends Transfer-Encoding "chunked"
on its 404 responses to HEAD requests for
missing objects.

We weren't ignoring the Transfer-Encoding
and were thus interpretting the subsequent
response headers as a chunk header from the
previous responses body (but a HEAD response
can't have a body)

R=rsc, adg
CC=golang-dev
https://golang.org/cl/4346050

src/pkg/http/response_test.go

@@ -164,6 +164,28 @@ var respTests = []respTest{
 		"Body here\n",
 	},
 
+	// Chunked response in response to a HEAD request (the "chunked" should
+	// be ignored, as HEAD responses never have bodies)
+	{
+		"HTTP/1.0 200 OK\r\n" +
+			"Transfer-Encoding: chunked\r\n" +
+			"\r\n",
+
+		Response{
+			Status:        "200 OK",
+			StatusCode:    200,
+			Proto:         "HTTP/1.0",
+			ProtoMajor:    1,
+			ProtoMinor:    0,
+			RequestMethod: "HEAD",
+			Header:        Header{},
+			Close:         true,
+			ContentLength: 0,
+		},
+
+		"",
+	},
+
 	// Status line without a Reason-Phrase, but trailing space.
 	// (permitted by RFC 2616)
 	{

src/pkg/http/transfer.go

@@ -215,7 +215,7 @@ func readTransfer(msg interface{}, r *bufio.Reader) (err os.Error) {
 	}
 
 	// Transfer encoding, content length
-	t.TransferEncoding, err = fixTransferEncoding(t.Header)
+	t.TransferEncoding, err = fixTransferEncoding(t.RequestMethod, t.Header)
 	if err != nil {
 		return err
 	}
@@ -289,13 +289,20 @@ func readTransfer(msg interface{}, r *bufio.Reader) (err os.Error) {
 func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
 
 // Sanitize transfer encoding
-func fixTransferEncoding(header Header) ([]string, os.Error) {
+func fixTransferEncoding(requestMethod string, header Header) ([]string, os.Error) {
 	raw, present := header["Transfer-Encoding"]
 	if !present {
 		return nil, nil
 	}
 
 	header["Transfer-Encoding"] = nil, false
+
+	// Head responses have no bodies, so the transfer encoding
+	// should be ignored.
+	if requestMethod == "HEAD" {
+		return nil, nil
+	}
+
 	encodings := strings.Split(raw[0], ",", -1)
 	te := make([]string, 0, len(encodings))
 	// TODO: Even though we only support "identity" and "chunked"

src/pkg/http/transport_test.go

@@ -296,6 +296,35 @@ func TestTransportHeadResponses(t *testing.T) {
 	}
 }
 
+// TestTransportHeadChunkedResponse verifies that we ignore chunked transfer-encoding
+// on responses to HEAD requests.
+func TestTransportHeadChunkedResponse(t *testing.T) {
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		if r.Method != "HEAD" {
+			panic("expected HEAD; got " + r.Method)
+		}
+		w.Header().Set("Transfer-Encoding", "chunked") // client should ignore
+		w.Header().Set("x-client-ipport", r.RemoteAddr)
+		w.WriteHeader(200)
+	}))
+	defer ts.Close()
+
+	tr := &Transport{DisableKeepAlives: false}
+	c := &Client{Transport: tr}
+
+	res1, err := c.Head(ts.URL)
+	if err != nil {
+		t.Fatalf("request 1 error: %v", err)
+	}
+	res2, err := c.Head(ts.URL)
+	if err != nil {
+		t.Fatalf("request 2 error: %v", err)
+	}
+	if v1, v2 := res1.Header.Get("x-client-ipport"), res2.Header.Get("x-client-ipport"); v1 != v2 {
+		t.Errorf("ip/ports differed between head requests: %q vs %q", v1, v2)
+	}
+}
+
 func TestTransportNilURL(t *testing.T) {
 	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
 		fmt.Fprintf(w, "Hi")