net/http: revert change making NewRequest set ContentLength -1

The introduction of NoBody and related body-peeking bug fixes also
added a "cleanup" of sorts to make NewRequest set the returned
Requests's ContentLength to -1 when it didn't know it.

Using -1 to mean unknown is what the documentation says, but then
people apparently(?) depended on it being zero so they could do this:

    req, _ := http.NewRequest("POST", url, someNonNilReaderWithUnkownSize)
    req.Body = nil
    res, err := http.DefaultClient.Do(req)

... and expect it to work.

After https://golang.org/cl/31445 the contrived(?) code above stopped
working, since Body was nil and ContentLength was -1, which has been
disallowed since Go 1.0.

So this restores the old behavior of NewRequest, not setting it to -1.
That part of the fix isn't required as of https://golang.org/cl/31726
(which added NoBody)

I still don't know whether this bug is hypothetical or actually
affected people in practice.

Let's assume it's real for now.

Fixes #18117

Change-Id: I42400856ee92a1a4999b5b4668bef97d885fbb53
Reviewed-on: https://go-review.googlesource.com/33801
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/net/http/request.go b/src/net/http/request.go
index 2d65ca3c8a..81763007c4 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -785,9 +785,11 @@ func NewRequest(method, urlStr string, body io.Reader) (*Request, error) {
 				return ioutil.NopCloser(&r), nil
 			}
 		default:
-			if body != NoBody {
-				req.ContentLength = -1 // unknown
-			}
+			// This is where we'd set it to -1 (at least
+			// if body != NoBody) to mean unknown, but
+			// that broke people during the Go 1.8 testing
+			// period. People depend on it being 0 I
+			// guess. Maybe retry later. See Issue 18117.
 		}
 		// For client requests, Request.ContentLength of 0
 		// means either actually 0, or unknown. The only way
@@ -797,7 +799,7 @@ func NewRequest(method, urlStr string, body io.Reader) (*Request, error) {
 		// so we use a well-known ReadCloser variable instead
 		// and have the http package also treat that sentinel
 		// variable to mean explicitly zero.
-		if req.ContentLength == 0 {
+		if req.GetBody != nil && req.ContentLength == 0 {
 			req.Body = NoBody
 			req.GetBody = func() (io.ReadCloser, error) { return NoBody, nil }
 		}