net/http/httptest: fill ContentLength in recorded Response

This change fills the ContentLength field in the http.Response returned by
ResponseRecorder.Result.

Fixes #16952.

Change-Id: I9c49b1bf83e3719b5275b03a43aff5033156637d
Reviewed-on: https://go-review.googlesource.com/28302Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/httptest/recorder.go

@@ -8,6 +8,8 @@ import (
 	"bytes"
 	"io/ioutil"
 	"net/http"
+	"strconv"
+	"strings"
 )
 
 // ResponseRecorder is an implementation of http.ResponseWriter that
@@ -162,6 +164,7 @@ func (rw *ResponseRecorder) Result() *http.Response {
 	if rw.Body != nil {
 		res.Body = ioutil.NopCloser(bytes.NewReader(rw.Body.Bytes()))
 	}
+	res.ContentLength = parseContentLength(res.Header.Get("Content-Length"))
 
 	if trailers, ok := rw.snapHeader["Trailer"]; ok {
 		res.Trailer = make(http.Header, len(trailers))
@@ -186,3 +189,20 @@ func (rw *ResponseRecorder) Result() *http.Response {
 	}
 	return res
 }
+
+// parseContentLength trims whitespace from s and returns -1 if no value
+// is set, or the value if it's >= 0.
+//
+// This a modified version of same function found in net/http/transfer.go. This
+// one just ignores an invalid header.
+func parseContentLength(cl string) int64 {
+	cl = strings.TrimSpace(cl)
+	if cl == "" {
+		return -1
+	}
+	n, err := strconv.ParseInt(cl, 10, 64)
+	if err != nil {
+		return -1
+	}
+	return n
+}

src/net/http/httptest/recorder_test.go

@@ -94,6 +94,14 @@ func TestRecorder(t *testing.T) {
 			return nil
 		}
 	}
+	hasContentLength := func(length int64) checkFunc {
+		return func(rec *ResponseRecorder) error {
+			if got := rec.Result().ContentLength; got != length {
+				return fmt.Errorf("ContentLength = %d; want %d", got, length)
+			}
+			return nil
+		}
+	}
 
 	tests := []struct {
 		name   string
@@ -141,7 +149,7 @@ func TestRecorder(t *testing.T) {
 				w.(http.Flusher).Flush() // also sends a 200
 				w.WriteHeader(201)
 			},
-			check(hasStatus(200), hasFlush(true)),
+			check(hasStatus(200), hasFlush(true), hasContentLength(-1)),
 		},
 		{
 			"Content-Type detection",
@@ -244,6 +252,16 @@ func TestRecorder(t *testing.T) {
 				hasNotHeaders("X-Bar"),
 			),
 		},
+		{
+			"setting Content-Length header",
+			func(w http.ResponseWriter, r *http.Request) {
+				body := "Some body"
+				contentLength := fmt.Sprintf("%d", len(body))
+				w.Header().Set("Content-Length", contentLength)
+				io.WriteString(w, body)
+			},
+			check(hasStatus(200), hasContents("Some body"), hasContentLength(9)),
+		},
 	}
 	r, _ := http.NewRequest("GET", "http://foo.com/", nil)
 	for _, tt := range tests {