fix: respect context cancellation in httpClient.Do (#1971)

Co-authored-by: Pedram Pourmohammad <pedram.pourmohamad@gmail.com>
Co-authored-by: Kemal Akkoyun <kakkoyun@users.noreply.github.com>

Author: kakkoyun

api/client.go

@@ -141,21 +141,21 @@ func (c *httpClient) Do(ctx context.Context, req *http.Request) (*http.Response,
 	}
 
 	var body []byte
-	done := make(chan error, 1)
+	done := make(chan struct{})
+	var readErr error
 	go func() {
+		defer close(done)
 		var buf bytes.Buffer
-		_, err := buf.ReadFrom(resp.Body)
+		_, readErr = buf.ReadFrom(resp.Body)
 		body = buf.Bytes()
-		done <- err
 	}()
 
 	select {
 	case <-ctx.Done():
 		resp.Body.Close()
-		<-done
 		return resp, nil, ctx.Err()
-	case err = <-done:
+	case <-done:
 		resp.Body.Close()
-		return resp, body, err
+		return resp, body, readErr
 	}
 }

api/client_test.go

@@ -164,6 +164,54 @@ func TestDoContextCancellation(t *testing.T) {
 	}
 }
 
+func TestDoContextCancellationSlowServer(t *testing.T) {
+	serverDone := make(chan struct{})
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		if f, ok := w.(http.Flusher); ok {
+			f.Flush()
+		}
+		<-serverDone
+	}))
+	defer func() {
+		close(serverDone)
+		ts.Close()
+	}()
+
+	client, err := NewClient(Config{
+		Address: ts.URL,
+	})
+	if err != nil {
+		t.Fatalf("failed to create client: %v", err)
+	}
+
+	req, err := http.NewRequest(http.MethodGet, 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 !errors.Is(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 > 500*time.Millisecond {
+		t.Errorf("client.Do did not return promptly on cancellation: took %v", elapsed)
+	}
+
+	if resp != nil && resp.Body != nil {
+		resp.Body.Close()
+	}
+}
+
 // Serve any http request with a response of N KB of spaces.
 type serveSpaces struct {
 	sizeKB int