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>

1 files changed, 39 insertions, 0 deletions

diff --git a/src/net/http/request.go b/src/net/http/request.go
index b191d519f2..21e25b08ef 100644
--- a/src/net/http/request.go
+++ b/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
+}