net/http: reject HTTP/1.1 Content-Length with sign in response

Enforces section 14.13 of RFC 2616 so that Content-Length header
values with a sign such as "+5" will be rejected.

Updates #39017

Change-Id: Icce9f00d03c8475fe704b33f9bed9089ff8802f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/234817
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/net/http/httptest/recorder.go

@@ -226,9 +226,9 @@ func parseContentLength(cl string) int64 {
 	if cl == "" {
 		return -1
 	}
-	n, err := strconv.ParseInt(cl, 10, 64)
+	n, err := strconv.ParseUint(cl, 10, 63)
 	if err != nil {
 		return -1
 	}
-	return n
+	return int64(n)
 }

src/net/http/httptest/recorder_test.go

@@ -310,3 +310,39 @@ func TestRecorder(t *testing.T) {
 		})
 	}
 }
+
+// issue 39017 - disallow Content-Length values such as "+3"
+func TestParseContentLength(t *testing.T) {
+	tests := []struct {
+		cl   string
+		want int64
+	}{
+		{
+			cl:   "3",
+			want: 3,
+		},
+		{
+			cl:   "+3",
+			want: -1,
+		},
+		{
+			cl:   "-3",
+			want: -1,
+		},
+		{
+			// max int64, for safe conversion before returning
+			cl:   "9223372036854775807",
+			want: 9223372036854775807,
+		},
+		{
+			cl:   "9223372036854775808",
+			want: -1,
+		},
+	}
+
+	for _, tt := range tests {
+		if got := parseContentLength(tt.cl); got != tt.want {
+			t.Errorf("%q:\n\tgot=%d\n\twant=%d", tt.cl, got, tt.want)
+		}
+	}
+}

src/net/http/transfer.go

@@ -1039,11 +1039,11 @@ func parseContentLength(cl string) (int64, error) {
 	if cl == "" {
 		return -1, nil
 	}
-	n, err := strconv.ParseInt(cl, 10, 64)
-	if err != nil || n < 0 {
+	n, err := strconv.ParseUint(cl, 10, 63)
+	if err != nil {
 		return 0, badStringError("bad Content-Length", cl)
 	}
-	return n, nil
+	return int64(n), nil
 
 }
 

src/net/http/transfer_test.go

@@ -326,3 +326,39 @@ func TestParseTransferEncoding(t *testing.T) {
 		}
 	}
 }
+
+// issue 39017 - disallow Content-Length values such as "+3"
+func TestParseContentLength(t *testing.T) {
+	tests := []struct {
+		cl      string
+		wantErr error
+	}{
+		{
+			cl:      "3",
+			wantErr: nil,
+		},
+		{
+			cl:      "+3",
+			wantErr: badStringError("bad Content-Length", "+3"),
+		},
+		{
+			cl:      "-3",
+			wantErr: badStringError("bad Content-Length", "-3"),
+		},
+		{
+			// max int64, for safe conversion before returning
+			cl:      "9223372036854775807",
+			wantErr: nil,
+		},
+		{
+			cl:      "9223372036854775808",
+			wantErr: badStringError("bad Content-Length", "9223372036854775808"),
+		},
+	}
+
+	for _, tt := range tests {
+		if _, gotErr := parseContentLength(tt.cl); !reflect.DeepEqual(gotErr, tt.wantErr) {
+			t.Errorf("%q:\n\tgot=%v\n\twant=%v", tt.cl, gotErr, tt.wantErr)
+		}
+	}
+}

src/net/http/transport_test.go

@@ -6222,3 +6222,22 @@ func TestIssue32441(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+// Issue 39017. Ensure that HTTP/1 transports reject Content-Length headers
+// that contain a sign (eg. "+3"), per RFC 2616, Section 14.13.
+func TestTransportRejectsSignInContentLength(t *testing.T) {
+	cst := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		w.Header().Set("Content-Length", "+3")
+		w.Write([]byte("abc"))
+	}))
+	defer cst.Close()
+
+	c := cst.Client()
+	res, err := c.Get(cst.URL)
+	if err == nil || res != nil {
+		t.Fatal("Expected a non-nil error and a nil http.Response")
+	}
+	if got, want := err.Error(), `bad Content-Length "+3"`; !strings.Contains(got, want) {
+		t.Fatalf("Error mismatch\nGot: %q\nWanted substring: %q", got, want)
+	}
+}