net/http: populate ContentLength in HEAD responses

Also fixes a necessary TODO in the process.

Fixes #4126

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6869053

src/pkg/net/http/client_test.go

@@ -527,3 +527,38 @@ func TestClientWithIncorrectTLSServerName(t *testing.T) {
 		t.Errorf("wanted error mentioning 127.0.0.1 and badserver; got error: %v", err)
 	}
 }
+
+// Verify Response.ContentLength is populated. http://golang.org/issue/4126
+func TestClientHeadContentLength(t *testing.T) {
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		if v := r.FormValue("cl"); v != "" {
+			w.Header().Set("Content-Length", v)
+		}
+	}))
+	defer ts.Close()
+	tests := []struct {
+		suffix string
+		want   int64
+	}{
+		{"/?cl=1234", 1234},
+		{"/?cl=0", 0},
+		{"", -1},
+	}
+	for _, tt := range tests {
+		req, _ := NewRequest("HEAD", ts.URL+tt.suffix, nil)
+		res, err := DefaultClient.Do(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if res.ContentLength != tt.want {
+			t.Errorf("Content-Length = %d; want %d", res.ContentLength, tt.want)
+		}
+		bs, err := ioutil.ReadAll(res.Body)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(bs) != 0 {
+			t.Errorf("Unexpected content: %q", bs)
+		}
+	}
+}

src/pkg/net/http/response.go

@@ -49,7 +49,7 @@ type Response struct {
 	Body io.ReadCloser
 
 	// ContentLength records the length of the associated content.  The
-	// value -1 indicates that the length is unknown.  Unless RequestMethod
+	// value -1 indicates that the length is unknown.  Unless Request.Method
 	// is "HEAD", values >= 0 indicate that the given number of bytes may
 	// be read from Body.
 	ContentLength int64
@@ -178,7 +178,7 @@ func (r *Response) ProtoAtLeast(major, minor int) bool {
 //  StatusCode
 //  ProtoMajor
 //  ProtoMinor
-//  RequestMethod
+//  Request.Method
 //  TransferEncoding
 //  Trailer
 //  Body

src/pkg/net/http/response_test.go

@@ -193,7 +193,7 @@ var respTests = []respTest{
 			Request:       dummyReq("HEAD"),
 			Header:        Header{},
 			Close:         true,
-			ContentLength: 0,
+			ContentLength: -1,
 		},
 
 		"",

src/pkg/net/http/server.go

@@ -614,7 +614,7 @@ func (w *response) finishRequest() {
 	// HTTP/1.0 clients keep their "keep-alive" connections alive, and for
 	// HTTP/1.1 clients is just as good as the alternative: sending a
 	// chunked response and immediately sending the zero-length EOF chunk.
-	if w.written == 0 && w.header.get("Content-Length") == "" {
+	if w.written == 0 && w.header.get("Content-Length") == "" && w.req.Method != "HEAD" {
 		w.header.Set("Content-Length", "0")
 	}
 	// If this was an HTTP/1.0 request with keep-alive and we sent a

src/pkg/net/http/transfer.go

@@ -294,10 +294,19 @@ func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
 		return err
 	}
 
-	t.ContentLength, err = fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
+	realLength, err := fixLength(isResponse, t.StatusCode, t.RequestMethod, t.Header, t.TransferEncoding)
 	if err != nil {
 		return err
 	}
+	if isResponse && t.RequestMethod == "HEAD" {
+		if n, err := parseContentLength(t.Header.get("Content-Length")); err != nil {
+			return err
+		} else {
+			t.ContentLength = n
+		}
+	} else {
+		t.ContentLength = realLength
+	}
 
 	// Trailer
 	t.Trailer, err = fixTrailer(t.Header, t.TransferEncoding)
@@ -310,7 +319,7 @@ func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
 	// See RFC2616, section 4.4.
 	switch msg.(type) {
 	case *Response:
-		if t.ContentLength == -1 &&
+		if realLength == -1 &&
 			!chunked(t.TransferEncoding) &&
 			bodyAllowedForStatus(t.StatusCode) {
 			// Unbounded body.
@@ -323,11 +332,11 @@ func readTransfer(msg interface{}, r *bufio.Reader) (err error) {
 	switch {
 	case chunked(t.TransferEncoding):
 		t.Body = &body{Reader: newChunkedReader(r), hdr: msg, r: r, closing: t.Close}
-	case t.ContentLength >= 0:
+	case realLength >= 0:
 		// TODO: limit the Content-Length. This is an easy DoS vector.
-		t.Body = &body{Reader: io.LimitReader(r, t.ContentLength), closing: t.Close}
+		t.Body = &body{Reader: io.LimitReader(r, realLength), closing: t.Close}
 	default:
-		// t.ContentLength < 0, i.e. "Content-Length" not mentioned in header
+		// realLength < 0, i.e. "Content-Length" not mentioned in header
 		if t.Close {
 			// Close semantics (i.e. HTTP/1.0)
 			t.Body = &body{Reader: r, closing: t.Close}
@@ -434,9 +443,9 @@ func fixLength(isResponse bool, status int, requestMethod string, header Header,
 	// Logic based on Content-Length
 	cl := strings.TrimSpace(header.get("Content-Length"))
 	if cl != "" {
-		n, err := strconv.ParseInt(cl, 10, 64)
-		if err != nil || n < 0 {
-			return -1, &badStringError{"bad Content-Length", cl}
+		n, err := parseContentLength(cl)
+		if err != nil {
+			return -1, err
 		}
 		return n, nil
 	} else {
@@ -641,3 +650,18 @@ func (b *body) Close() error {
 	}
 	return nil
 }
+
+// parseContentLength trims whitespace from s and returns -1 if no value
+// is set, or the value if it's >= 0.
+func parseContentLength(cl string) (int64, error) {
+	cl = strings.TrimSpace(cl)
+	if cl == "" {
+		return -1, nil
+	}
+	n, err := strconv.ParseInt(cl, 10, 64)
+	if err != nil || n < 0 {
+		return 0, &badStringError{"bad Content-Length", cl}
+	}
+	return n, nil
+
+}

src/pkg/net/http/transport.go

@@ -604,10 +604,7 @@ func (pc *persistConn) readLoop() {
 			alive = false
 		}
 
-		// TODO(bradfitz): this hasBody conflicts with the defition
-		// above which excludes HEAD requests.  Is this one
-		// incomplete?
-		hasBody := resp != nil && resp.ContentLength != 0
+		hasBody := resp != nil && rc.req.Method != "HEAD" && resp.ContentLength != 0
 		var waitForBodyRead chan bool
 		if hasBody {
 			lastbody = resp.Body

src/pkg/net/http/transport_test.go

@@ -464,7 +464,7 @@ func TestTransportHeadResponses(t *testing.T) {
 		if e, g := "123", res.Header.Get("Content-Length"); e != g {
 			t.Errorf("loop %d: expected Content-Length header of %q, got %q", i, e, g)
 		}
-		if e, g := int64(0), res.ContentLength; e != g {
+		if e, g := int64(123), res.ContentLength; e != g {
 			t.Errorf("loop %d: expected res.ContentLength of %v, got %v", i, e, g)
 		}
 	}