net/http: refactor testing of Request.Body on 0 ContentLength

Code movement only, to look more like the equivalent http2 code, and
to make an upcoming fix look more obvious.

Updates #16002 (to be fixed once this code is in)

Change-Id: Iaa4f965be14e98f9996e7c4624afe6e19bed1a80
Reviewed-on: https://go-review.googlesource.com/30087
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

src/net/http/request.go

@@ -1215,3 +1215,42 @@ func (r *Request) isReplayable() bool {
 	}
 	return false
 }
+
+// bodyAndLength reports the request's body and content length, with
+// the difference from r.ContentLength being that 0 means actually
+// zero, and -1 means unknown.
+func (r *Request) bodyAndLength() (body io.Reader, contentLen int64) {
+	body = r.Body
+	if body == nil {
+		return nil, 0
+	}
+	if r.ContentLength != 0 {
+		return body, r.ContentLength
+	}
+	// Don't try to sniff the bytes if they're using a custom
+	// transfer encoding (or specified chunked themselves), and
+	// don't sniff if they're not using HTTP/1.1 and can't chunk
+	// anyway.
+	if len(r.TransferEncoding) != 0 || !r.ProtoAtLeast(1, 1) {
+		return body, -1
+	}
+
+	// Test to see if it's actually zero or just unset.
+	var buf [1]byte
+	n, err := io.ReadFull(body, buf[:])
+	if err != nil && err != io.EOF {
+		return errorReader{err}, -1
+	}
+
+	if n == 1 {
+		// Oh, guess there is data in this Body Reader after all.
+		// The ContentLength field just wasn't set.
+		// Stich the Body back together again, re-attaching our
+		// consumed byte.
+		// TODO(bradfitz): switch to stitchByteAndReader
+		return io.MultiReader(bytes.NewReader(buf[:]), body), -1
+	}
+
+	// Body is actually empty.
+	return nil, 0
+}

src/net/http/transfer.go

@@ -59,38 +59,18 @@ func newTransferWriter(r interface{}) (t *transferWriter, err error) {
 			return nil, fmt.Errorf("http: Request.ContentLength=%d with nil Body", rr.ContentLength)
 		}
 		t.Method = valueOrDefault(rr.Method, "GET")
-		t.Body = rr.Body
-		t.BodyCloser = rr.Body
-		t.ContentLength = rr.ContentLength
 		t.Close = rr.Close
 		t.TransferEncoding = rr.TransferEncoding
 		t.Trailer = rr.Trailer
 		atLeastHTTP11 = rr.ProtoAtLeast(1, 1)
-		if t.Body != nil && len(t.TransferEncoding) == 0 && atLeastHTTP11 {
-			if t.ContentLength == 0 {
-				// Test to see if it's actually zero or just unset.
-				var buf [1]byte
-				n, rerr := io.ReadFull(t.Body, buf[:])
-				if rerr != nil && rerr != io.EOF {
-					t.ContentLength = -1
-					t.Body = errorReader{rerr}
-				} else if n == 1 {
-					// Oh, guess there is data in this Body Reader after all.
-					// The ContentLength field just wasn't set.
-					// Stich the Body back together again, re-attaching our
-					// consumed byte.
-					t.ContentLength = -1
-					t.Body = io.MultiReader(bytes.NewReader(buf[:]), t.Body)
-				} else {
-					// Body is actually empty.
-					t.Body = nil
-					t.BodyCloser = nil
-				}
+
+		t.Body, t.ContentLength = rr.bodyAndLength()
+		if t.Body != nil {
+			t.BodyCloser = rr.Body
 		}
-			if t.ContentLength < 0 {
+		if t.ContentLength < 0 && len(t.TransferEncoding) == 0 && atLeastHTTP11 {
 			t.TransferEncoding = []string{"chunked"}
 		}
-		}
 	case *Response:
 		t.IsResponse = true
 		if rr.Request != nil {