http3: return the context cancellation error from RoundTrip (#4203)

http3/client.go

@@ -254,6 +254,15 @@ func (c *client) maxHeaderBytes() uint64 {
 
 // RoundTripOpt executes a request and returns a response
 func (c *client) RoundTripOpt(req *http.Request, opt RoundTripOpt) (*http.Response, error) {
+	rsp, err := c.roundTripOpt(req, opt)
+	if err != nil && req.Context().Err() != nil {
+		// if the context was canceled, return the context cancellation error
+		err = req.Context().Err()
+	}
+	return rsp, err
+}
+
+func (c *client) roundTripOpt(req *http.Request, opt RoundTripOpt) (*http.Response, error) {
 	if authorityAddr("https", hostnameFromRequest(req)) != c.hostname {
 		return nil, fmt.Errorf("http3 client BUG: RoundTripOpt called for the wrong client (expected %s, got %s)", c.hostname, req.Host)
 	}

http3/client_test.go

@@ -922,7 +922,7 @@ var _ = Describe("Client", func() {
 							return 0, errors.New("test done")
 						})
 						_, err := cl.RoundTripOpt(req, roundTripOpt)
-						Expect(err).To(MatchError("test done"))
+						Expect(err).To(MatchError(context.Canceled))
 						Eventually(done).Should(BeClosed())
 					})
 				})

integrationtests/self/http_test.go

@@ -319,6 +319,21 @@ var _ = Describe("HTTP tests", func() {
 		Expect(string(body)).To(Equal("Hello, World!\n"))
 	})
 
+	It("handles context cancellations", func() {
+		mux.HandleFunc("/cancel", func(w http.ResponseWriter, r *http.Request) {
+			<-r.Context().Done()
+		})
+
+		ctx, cancel := context.WithCancel(context.Background())
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, fmt.Sprintf("https://localhost:%d/cancel", port), nil)
+		Expect(err).ToNot(HaveOccurred())
+		time.AfterFunc(50*time.Millisecond, cancel)
+
+		_, err = client.Do(req)
+		Expect(err).To(HaveOccurred())
+		Expect(err).To(MatchError(context.Canceled))
+	})
+
 	It("cancels requests", func() {
 		handlerCalled := make(chan struct{})
 		mux.HandleFunc("/cancel", func(w http.ResponseWriter, r *http.Request) {