net/http: log handler panic before closing HTTP connection

Fix originally from rogpeppe in 5414048 but was rolled
back due to test breakage.

This CL makes the test more robust to order of operations.

Fixes #2480 again.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5536072

src/pkg/net/http/serve_test.go

@@ -904,17 +904,13 @@ func testHandlerPanic(t *testing.T, withHijack bool) {
 		panic("intentional death for testing")
 	}))
 	defer ts.Close()
-	_, err := Get(ts.URL)
-	if err == nil {
-		t.Logf("expected an error")
-	}
 
 	// Do a blocking read on the log output pipe so its logging
 	// doesn't bleed into the next test.  But wait only 5 seconds
 	// for it.
-	done := make(chan bool)
+	done := make(chan bool, 1)
 	go func() {
-		buf := make([]byte, 1024)
+		buf := make([]byte, 4<<10)
 		_, err := pr.Read(buf)
 		pr.Close()
 		if err != nil {
@@ -922,6 +918,12 @@ func testHandlerPanic(t *testing.T, withHijack bool) {
 		}
 		done <- true
 	}()
+
+	_, err := Get(ts.URL)
+	if err == nil {
+		t.Logf("expected an error")
+	}
+
 	select {
 	case <-done:
 		return

src/pkg/net/http/server.go

@@ -569,14 +569,15 @@ func (c *conn) serve() {
 		if err == nil {
 			return
 		}
-		if c.rwc != nil { // may be nil if connection hijacked
-			c.rwc.Close()
-		}
 
 		var buf bytes.Buffer
 		fmt.Fprintf(&buf, "http: panic serving %v: %v\n", c.remoteAddr, err)
 		buf.Write(debug.Stack())
 		log.Print(buf.String())
+
+		if c.rwc != nil { // may be nil if connection hijacked
+			c.rwc.Close()
+		}
 	}()
 
 	if tlsConn, ok := c.rwc.(*tls.Conn); ok {