net/http: add test that panic in a handler signals an error to the client

Change-Id: Iba40edc9ddad62534b06c5af20bbc3dd3dc14d0a
Reviewed-on: https://go-review.googlesource.com/21881
Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/clientserver_test.go

@@ -1123,6 +1123,34 @@ func testBogusStatusWorks(t *testing.T, h2 bool) {
 	}
 }
 
+func TestInterruptWithPanic_h1(t *testing.T) { testInterruptWithPanic(t, h1Mode) }
+func TestInterruptWithPanic_h2(t *testing.T) { testInterruptWithPanic(t, h2Mode) }
+func testInterruptWithPanic(t *testing.T, h2 bool) {
+	log.SetOutput(ioutil.Discard) // is noisy otherwise
+	defer log.SetOutput(os.Stderr)
+
+	const msg = "hello"
+	defer afterTest(t)
+	cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
+		io.WriteString(w, msg)
+		w.(Flusher).Flush()
+		panic("no more")
+	}))
+	defer cst.close()
+	res, err := cst.c.Get(cst.ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+	slurp, err := ioutil.ReadAll(res.Body)
+	if string(slurp) != msg {
+		t.Errorf("client read %q; want %q", slurp, msg)
+	}
+	if err == nil {
+		t.Errorf("client read all successfully; want some error")
+	}
+}
+
 type noteCloseConn struct {
 	net.Conn
 	closeFunc func()