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>

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 }
 		}

src/net/http/request_test.go

@@ -498,10 +498,14 @@ func TestNewRequestContentLength(t *testing.T) {
 		{bytes.NewBuffer([]byte("1234")), 4},
 		{strings.NewReader("12345"), 5},
 		{strings.NewReader(""), 0},
-		// Not detected:
-		{struct{ io.Reader }{strings.NewReader("xyz")}, -1},
-		{io.NewSectionReader(strings.NewReader("x"), 0, 6), -1},
-		{readByte(io.NewSectionReader(strings.NewReader("xy"), 0, 6)), -1},
+		{NoBody, 0},
+
+		// Not detected. During Go 1.8 we tried to make these set to -1, but
+		// due to Issue 18117, we keep these returning 0, even though they're
+		// unknown.
+		{struct{ io.Reader }{strings.NewReader("xyz")}, 0},
+		{io.NewSectionReader(strings.NewReader("x"), 0, 6), 0},
+		{readByte(io.NewSectionReader(strings.NewReader("xy"), 0, 6)), 0},
 	}
 	for i, tt := range tests {
 		req, err := NewRequest("POST", "http://localhost/", tt.r)
@@ -511,9 +515,6 @@ func TestNewRequestContentLength(t *testing.T) {
 		if req.ContentLength != tt.want {
 			t.Errorf("test[%d]: ContentLength(%T) = %d; want %d", i, tt.r, req.ContentLength, tt.want)
 		}
-		if (req.ContentLength == 0) != (req.Body == NoBody) {
-			t.Errorf("test[%d]: ContentLength = %d but Body non-nil is %v", i, req.ContentLength, req.Body != nil)
-		}
 	}
 }
 
@@ -825,16 +826,6 @@ func TestNewRequestGetBody(t *testing.T) {
 	}
 }
 
-func TestNewRequestNoBody(t *testing.T) {
-	req, err := NewRequest("GET", "http://foo.com/", NoBody)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if req.ContentLength != 0 {
-		t.Errorf("ContentLength = %d; want 0", req.ContentLength)
-	}
-}
-
 func testMissingFile(t *testing.T, req *Request) {
 	f, fh, err := req.FormFile("missing")
 	if f != nil {

src/net/http/requestwrite_test.go

@@ -581,12 +581,14 @@ func (rc *closeChecker) Close() error {
 // inside a NopCloser, and that it serializes it correctly.
 func TestRequestWriteClosesBody(t *testing.T) {
 	rc := &closeChecker{Reader: strings.NewReader("my body")}
-	req, _ := NewRequest("POST", "http://foo.com/", rc)
-	if req.ContentLength != -1 {
-		t.Errorf("got req.ContentLength %d, want -1", req.ContentLength)
+	req, err := NewRequest("POST", "http://foo.com/", rc)
+	if err != nil {
+		t.Fatal(err)
 	}
 	buf := new(bytes.Buffer)
-	req.Write(buf)
+	if err := req.Write(buf); err != nil {
+		t.Error(err)
+	}
 	if !rc.closed {
 		t.Error("body not closed after write")
 	}