correctly handle panicking http.Handler

fixes #290

h2quic/response_writer.go

@@ -38,6 +38,9 @@ func (w *responseWriter) Header() http.Header {
 }
 
 func (w *responseWriter) WriteHeader(status int) {
+	if w.headerWritten {
+		return
+	}
 	w.headerWritten = true
 
 	var headers bytes.Buffer
@@ -68,9 +71,3 @@ func (w *responseWriter) Write(p []byte) (int, error) {
 	}
 	return w.dataStream.Write(p)
 }
-
-func (w *responseWriter) finish() {
-	if !w.headerWritten {
-		w.WriteHeader(200)
-	}
-}

h2quic/response_writer_test.go

@@ -79,14 +79,9 @@ var _ = Describe("Response Writer", func() {
 		}))
 	})
 
-	It("writes a 200 in finish if nothing was called", func() {
-		w.finish()
-		Expect(headerStream.Bytes()).To(Equal([]byte{0x0, 0x0, 0x1, 0x1, 0x4, 0x0, 0x0, 0x0, 0x5, 0x88})) // 0x88 is 200
-	})
-
-	It("doesn't do anything in finish if data was written before", func() {
+	It("does not WriteHeader() twice", func() {
 		w.WriteHeader(200)
-		w.finish()
+		w.WriteHeader(500)
 		Expect(headerStream.Bytes()).To(Equal([]byte{0x0, 0x0, 0x1, 0x1, 0x4, 0x0, 0x0, 0x0, 0x5, 0x88})) // 0x88 is 200
 	})
 })

h2quic/server.go

@@ -7,6 +7,7 @@ import (
 	"io/ioutil"
 	"net"
 	"net/http"
+	"runtime"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -166,8 +167,25 @@ func (s *Server) handleRequest(session streamCreator, headerStream utils.Stream,
 		if handler == nil {
 			handler = http.DefaultServeMux
 		}
-		handler.ServeHTTP(responseWriter, req)
-		responseWriter.finish()
+		panicked := false
+		func() {
+			defer func() {
+				if p := recover(); p != nil {
+					// Copied from net/http/server.go
+					const size = 64 << 10
+					buf := make([]byte, size)
+					buf = buf[:runtime.Stack(buf, false)]
+					utils.Errorf("http: panic serving: %v\n%s", p, buf)
+					panicked = true
+				}
+			}()
+			handler.ServeHTTP(responseWriter, req)
+		}()
+		if panicked {
+			responseWriter.WriteHeader(500)
+		} else {
+			responseWriter.WriteHeader(200)
+		}
 		if responseWriter.dataStream != nil {
 			responseWriter.dataStream.Close()
 		}

h2quic/server_test.go

@@ -98,6 +98,22 @@ var _ = Describe("H2 server", func() {
 			}).Should(Equal([]byte{0x0, 0x0, 0x1, 0x1, 0x4, 0x0, 0x0, 0x0, 0x5, 0x88})) // 0x88 is 200
 		})
 
+		It("correctly handles a panicking handler", func() {
+			s.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				panic("foobar")
+			})
+			headerStream.Write([]byte{
+				0x0, 0x0, 0x11, 0x1, 0x5, 0x0, 0x0, 0x0, 0x5,
+				// Taken from https://http2.github.io/http2-spec/compression.html#request.examples.with.huffman.coding
+				0x82, 0x86, 0x84, 0x41, 0x8c, 0xf1, 0xe3, 0xc2, 0xe5, 0xf2, 0x3a, 0x6b, 0xa0, 0xab, 0x90, 0xf4, 0xff,
+			})
+			err := s.handleRequest(session, headerStream, &sync.Mutex{}, hpackDecoder, h2framer)
+			Expect(err).NotTo(HaveOccurred())
+			Eventually(func() []byte {
+				return headerStream.Buffer.Bytes()
+			}).Should(Equal([]byte{0x0, 0x0, 0x1, 0x1, 0x4, 0x0, 0x0, 0x0, 0x5, 0x8e})) // 0x82 is 500
+		})
+
 		It("does not close the dataStream when end of stream is not set", func() {
 			var handlerCalled bool
 			s.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {