http2: catch panics server-side, respect RST_STREAM on the Transport side

Tests in https://go-review.googlesource.com/#/c/17683/5/src/net/http/serve_test.go:
TestHandlerPanicNil_h2 and TestHandlerPanic_h2, to be re-enabled
after the copy to the main repo.

Updates golang/go#13555 (fixes the bug after the copy to the main repo)

Change-Id: I7aa3e55fb21b576ea4f94c7ed41d1ebd750ef951
Reviewed-on: https://go-review.googlesource.com/17823
Reviewed-by: Ian Lance Taylor <iant@golang.org>

http2/server.go

@@ -47,6 +47,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -615,6 +616,7 @@ func (sc *serverConn) stopShutdownTimer() {
 }
 
 func (sc *serverConn) notePanic() {
+	// Note: this is for serverConn.serve panicking, not http.Handler code.
 	if testHookOnPanicMu != nil {
 		testHookOnPanicMu.Lock()
 		defer testHookOnPanicMu.Unlock()
@@ -837,6 +839,11 @@ func (sc *serverConn) startFrameWrite(wm frameWriteMsg) {
 	go sc.writeFrameAsync(wm)
 }
 
+// errHandlerPanicked is the error given to any callers blocked in a read from
+// Request.Body when the main goroutine panics. Since most handlers read in the
+// the main ServeHTTP goroutine, this will show up rarely.
+var errHandlerPanicked = errors.New("http2: handler panicked")
+
 // wroteFrame is called on the serve goroutine with the result of
 // whatever happened on writeFrameAsync.
 func (sc *serverConn) wroteFrame(res frameWriteResult) {
@@ -851,6 +858,10 @@ func (sc *serverConn) wroteFrame(res frameWriteResult) {
 
 	closeStream := endsStream(wm.write)
 
+	if _, ok := wm.write.(handlerPanicRST); ok {
+		sc.closeStream(st, errHandlerPanicked)
+	}
+
 	// Reply (if requested) to the blocked ServeHTTP goroutine.
 	if ch := wm.done; ch != nil {
 		select {
@@ -1530,9 +1541,25 @@ func (sc *serverConn) newWriterAndRequest() (*responseWriter, *http.Request, err
 
 // Run on its own goroutine.
 func (sc *serverConn) runHandler(rw *responseWriter, req *http.Request, handler func(http.ResponseWriter, *http.Request)) {
-	defer rw.handlerDone()
-	// TODO: catch panics like net/http.Server
+	didPanic := true
+	defer func() {
+		if didPanic {
+			e := recover()
+			// Same as net/http:
+			const size = 64 << 10
+			buf := make([]byte, size)
+			buf = buf[:runtime.Stack(buf, false)]
+			sc.writeFrameFromHandler(frameWriteMsg{
+				write:  handlerPanicRST{rw.rws.stream.id},
+				stream: rw.rws.stream,
+			})
+			sc.logf("http2: panic serving %v: %v\n%s", sc.conn.RemoteAddr(), e, buf)
+			return
+		}
+		rw.handlerDone()
+	}()
 	handler(rw, req)
+	didPanic = false
 }
 
 func handleHeaderListTooLong(w http.ResponseWriter, r *http.Request) {
@@ -1920,9 +1947,6 @@ func (w *responseWriter) write(lenData int, dataB []byte, dataS string) (n int,
 
 func (w *responseWriter) handlerDone() {
 	rws := w.rws
-	if rws == nil {
-		panic("handlerDone called twice")
-	}
 	rws.handlerDone = true
 	w.Flush()
 	w.rws = nil

http2/transport.go

@@ -584,6 +584,8 @@ func (cc *ClientConn) RoundTrip(req *http.Request) (*http.Response, error) {
 		case <-requestCancel(req):
 			cs.abortRequestBodyWrite()
 			return nil, errRequestCanceled
+		case <-cs.peerReset:
+			return nil, cs.resetErr
 		case err := <-bodyCopyErrc:
 			if err != nil {
 				return nil, err

http2/write.go

@@ -95,6 +95,16 @@ func (w *writeData) writeFrame(ctx writeContext) error {
 	return ctx.Framer().WriteData(w.streamID, w.endStream, w.p)
 }
 
+// handlerPanicRST is the message sent from handler goroutines when
+// the handler panics.
+type handlerPanicRST struct {
+	StreamID uint32
+}
+
+func (hp handlerPanicRST) writeFrame(ctx writeContext) error {
+	return ctx.Framer().WriteRSTStream(hp.StreamID, ErrCodeInternal)
+}
+
 func (se StreamError) writeFrame(ctx writeContext) error {
 	return ctx.Framer().WriteRSTStream(se.StreamID, se.Code)
 }