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http3: return the context cancellation error from RoundTrip #4203

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merged 1 commit into from
Dec 21, 2023
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http3: return the context cancellation error from RoundTrip #4203

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http3: return the context cancellation error from RoundTrip
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@marten-seemann
marten-seemann committed Dec 13, 2023
commit 7c2ca28e4fb89e0217b7f5efd70a290f16d3d6c9
9 changes: 9 additions & 0 deletions http3/client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
}
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2 changes: 1 addition & 1 deletion http3/client_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -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())
})
})
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15 changes: 15 additions & 0 deletions integrationtests/self/http_test.go
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Expand Up @@ -299,6 +299,21 @@ 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))
})

Comment on lines +302 to +316
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@jhump jhump Dec 13, 2023 •
edited
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Another useful test would be to verify receipt of deadline exceeded, which looks very similar to this case.

	It("handles context deadline exceeded", func() {
		mux.HandleFunc("/cancel", func(w http.ResponseWriter, r *http.Request) {
			<-r.Context().Done()
		})

		ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, fmt.Sprintf("https://localhost:%d/cancel", port), nil)
		Expect(err).ToNot(HaveOccurred())

		_, err = client.Do(req)
		Expect(err).To(HaveOccurred())
		Expect(err).To(MatchError(context.DeadlineExceeded))
	})

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A test case for the body-read error wouldn't be much different:

	It("handles context cancellations when reading body", func() {
		mux.HandleFunc("/cancel", func(w http.ResponseWriter, r *http.Request) {
			w.WriteHeader(http.StatusOK)
			<-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)

		resp, err = client.Do(req)
		Expect(err).ToNot(HaveOccurred())
		_, err = resp.Body.Read(make([]byte, 1024))
		Expect(err).To(HaveOccurred())
		Expect(err).To(MatchError(context.Canceled))
	})

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A test case for the body-read error wouldn't be much different:

That's a much bigger change. The Go documentation for the request context says:

For an outgoing client request, the context controls the entire lifetime of a request and its response: obtaining a connection, sending the request, and reading the response headers and body.

So you're right, the body needs to return the context error as well. Currently, we don't even pass the context to the body, and it's not clear to me how to correctly respect the context without spawning a new Go routine, since the Stream.Read call is blocking call.

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I suggest doing this in a follow-up PR. I'll open a new issue.

It("cancels requests", func() {
handlerCalled := make(chan struct{})
mux.HandleFunc("/cancel", func(w http.ResponseWriter, r *http.Request) {
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