http: fix Content-Range and Content-Length in response

RFC2616 sections 4.4 and 14.16:
  * Cannot use Content-Length with non-identity Transfer-Encoding
  * Content-Range response is "bytes x-y/z" not "x-y/z"

R=rsc
CC=golang-dev
https://golang.org/cl/4018041

src/pkg/http/fs.go

@@ -166,7 +166,7 @@ func serveFile(w ResponseWriter, r *Request, name string, redirect bool) {
 		}
 		size = ra.length
 		code = StatusPartialContent
-		w.SetHeader("Content-Range", fmt.Sprintf("%d-%d/%d", ra.start, ra.start+ra.length, d.Size))
+		w.SetHeader("Content-Range", fmt.Sprintf("bytes %d-%d/%d", ra.start, ra.start+ra.length-1, d.Size))
 	}
 
 	w.SetHeader("Accept-Ranges", "bytes")

src/pkg/http/fs_test.go

@@ -134,7 +134,7 @@ func TestServeFile(t *testing.T) {
 		if rt.code == StatusRequestedRangeNotSatisfiable {
 			continue
 		}
-		h := fmt.Sprintf("%d-%d/%d", rt.start, rt.end, testFileLength)
+		h := fmt.Sprintf("bytes %d-%d/%d", rt.start, rt.end-1, testFileLength)
 		if rt.r == "" {
 			h = ""
 		}

src/pkg/http/server.go

@@ -229,6 +229,10 @@ func (w *response) WriteHeader(code int) {
 		w.header["Transfer-Encoding"] = "", false
 		w.chunking = false
 	}
+	// Cannot use Content-Length with non-identity Transfer-Encoding.
+	if w.chunking {
+		w.header["Content-Length"] = "", false
+	}
 	if !w.req.ProtoAtLeast(1, 0) {
 		return
 	}