http2: simplify TestServerWindowUpdateOnBodyClose

This test closes a handler's request mid-test by poking into
the server internals. There's no reason I can see to do this,
when the handler can just call req.Body.Close to achieve the
same effect.

Change the test to use the public API.

Change-Id: I4f14939e951c4d8f07abd9d3c2f30c2004f87dad
Reviewed-on: https://go-review.googlesource.com/c/net/+/701001
Reviewed-by: Nicholas Husin <husin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Nicholas Husin <nsh@golang.org>
Auto-Submit: Nicholas Husin <nsh@golang.org>

http2/server_test.go

diff --git a/http2/server_test.go b/http2/server_test.go
index ec5b305..cd6e771 100644
--- a/http2/server_test.go
+++ b/http2/server_test.go
@@ -4290,8 +4290,7 @@
 func testServerWindowUpdateOnBodyClose(t testing.TB) {
 	const windowSize = 65535 * 2
 	content := make([]byte, windowSize)
-	blockCh := make(chan bool)
-	errc := make(chan error, 1)
+	errc := make(chan error)
 	st := newServerTester(t, func(w http.ResponseWriter, r *http.Request) {
 		buf := make([]byte, 4)
 		n, err := io.ReadFull(r.Body, buf)
@@ -4303,8 +4302,7 @@
 			errc <- fmt.Errorf("too few bytes read: %d", n)
 			return
 		}
-		blockCh <- true
-		<-blockCh
+		r.Body.Close()
 		errc <- nil
 	}, func(s *Server) {
 		s.MaxUploadBufferPerConnection = windowSize
@@ -4323,9 +4321,9 @@
 		EndHeaders: true,
 	})
 	st.writeData(1, false, content[:windowSize/2])
-	<-blockCh
-	st.stream(1).body.CloseWithError(io.EOF)
-	blockCh <- true
+	if err := <-errc; err != nil {
+		t.Fatal(err)
+	}
 
 	// Wait for flow control credit for the portion of the request written so far.
 	increments := windowSize / 2
@@ -4345,10 +4343,6 @@
 	// Writing data after the stream is reset immediately returns flow control credit.
 	st.writeData(1, false, content[windowSize/2:])
 	st.wantWindowUpdate(0, windowSize/2)
-
-	if err := <-errc; err != nil {
-		t.Error(err)
-	}
 }
 
 func TestNoErrorLoggedOnPostAfterGOAWAY(t *testing.T) {