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fix: client prompt return on context cancellation #1729

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fix: client prompt return on context cancellation #1729

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24 changes: 8 additions & 16 deletions api/client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -131,34 +131,26 @@ func (c *httpClient) Do(ctx context.Context, req *http.Request) (*http.Response,
req = req.WithContext(ctx)
}
resp, err := c.client.Do(req)
defer func() {
if resp != nil {
resp.Body.Close()
}
}()

if err != nil {
return nil, nil, err
}

var body []byte
done := make(chan struct{})
done := make(chan error, 1)
go func() {
var buf bytes.Buffer
_, err = buf.ReadFrom(resp.Body)
_, err := buf.ReadFrom(resp.Body)
body = buf.Bytes()
close(done)
done <- err
}()

select {
case <-ctx.Done():
resp.Body.Close()
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This assumes that close will somehow cancel _, err := buf.ReadFrom(resp.Body). Is it true? How?

Can we have a unit tests that perhaps shows this? 🤔

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Yes, calling resp.Body.Close() will close the underlying connection, which unblocks any pending read and returns an error.

see unit test, if okay i will add this to client_test.go

func TestDoContextCancellation(t *testing.T) {
	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("partial"))
		if f, ok := w.(http.Flusher); ok {
			f.Flush()
		}

		time.Sleep(500 * time.Millisecond) // simulate delay
		w.Write([]byte(" remaining"))
	}))
	defer ts.Close()

	client, err := NewClient(Config{
		Address: ts.URL,
	})
	if err != nil {
		t.Fatalf("failed to create client: %v", err)
	}

	req, err := http.NewRequest("GET", ts.URL, nil)
	if err != nil {
		t.Fatalf("failed to create request: %v", err)
	}

	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
	defer cancel()

	start := time.Now()
	resp, body, err := client.Do(ctx, req)
	elapsed := time.Since(start)

	if err != context.DeadlineExceeded {
		t.Errorf("expected error %v, got: %v", context.DeadlineExceeded, err)
	}
	if body != nil {
		t.Errorf("expected no body due to cancellation, got: %q", string(body))
	}
	if elapsed > 200*time.Millisecond {
		t.Errorf("Do did not return promptly on cancellation: took %v", elapsed)
	}

	if resp != nil && resp.Body != nil {
		resp.Body.Close()
	}
}

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@bwplotka could you take a look 👀

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Sorry for lag!

Yea, looks like this behaviour is documented also in HTTP docs:

	// Body must allow Read to be called concurrently with Close.
	// In particular, calling Close should unblock a Read waiting
	// for input. <--- this one.
	Body io.ReadCloser

It would be epic to have this test yes! However instead of 500ms delay, I would block it with <-t.Context.Done() or something. This will ensure we get Do returning without Go test timeout.

Thanks!

<-done
err = resp.Body.Close()
if err == nil {
err = ctx.Err()
}
case <-done:
return resp, nil, ctx.Err()
case err = <-done:
resp.Body.Close()
return resp, body, err
}

return resp, body, err
}
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