client: pass the provided ctx to backoff.RetryNotify

If we hit a connection error in any of the ..WithContext functions, we
end up blocked in the backoff.RetryNotify loop. This loop can use a
context, but it needs to be bound to the BackOff provided when
RetryNotify is called.

Added a test case `TestSubscribeWithContextAbortRetrier` to
demonstrate the problem and verify the fix.

Fixes r3labs#131.

client.go

@@ -109,15 +109,7 @@ func (c *Client) SubscribeWithContext(ctx context.Context, stream string, handle
 			}
 		}
 	}
-
-	// Apply user specified reconnection strategy or default to standard NewExponentialBackOff() reconnection method
-	var err error
-	if c.ReconnectStrategy != nil {
-		err = backoff.RetryNotify(operation, c.ReconnectStrategy, c.ReconnectNotify)
-	} else {
-		err = backoff.RetryNotify(operation, backoff.NewExponentialBackOff(), c.ReconnectNotify)
-	}
-	return err
+	return c.retryNotify(ctx, operation)
 }
 
 // SubscribeChan sends all events to the provided channel
@@ -183,14 +175,7 @@ func (c *Client) SubscribeChanWithContext(ctx context.Context, stream string, ch
 
 	go func() {
 		defer c.cleanup(ch)
-		// Apply user specified reconnection strategy or default to standard NewExponentialBackOff() reconnection method
-		var err error
-		if c.ReconnectStrategy != nil {
-			err = backoff.RetryNotify(operation, c.ReconnectStrategy, c.ReconnectNotify)
-		} else {
-			err = backoff.RetryNotify(operation, backoff.NewExponentialBackOff(), c.ReconnectNotify)
-		}
-
+		err := c.retryNotify(ctx, operation)
 		// channel closed once connected
 		if err != nil && !connected {
 			errch <- err
@@ -201,6 +186,18 @@ func (c *Client) SubscribeChanWithContext(ctx context.Context, stream string, ch
 	return err
 }
 
+func (c *Client) retryNotify(ctx context.Context, operation func() error) error {
+	var bk backoff.BackOff
+	// Apply user specified reconnection strategy or default to standard NewExponentialBackOff() reconnection method
+	if c.ReconnectStrategy != nil {
+		bk = c.ReconnectStrategy
+	} else {
+		bk = backoff.NewExponentialBackOff()
+	}
+	bk = backoff.WithContext(bk, ctx)
+	return backoff.RetryNotify(operation, bk, c.ReconnectNotify)
+}
+
 func (c *Client) startReadLoop(reader *EventStreamReader) (chan *Event, chan error) {
 	outCh := make(chan *Event)
 	erChan := make(chan error)

client_test.go

@@ -422,3 +422,29 @@ func TestSubscribeWithContextDone(t *testing.T) {
 
 	assert.Equal(t, n1, n2)
 }
+
+func TestSubscribeWithContextAbortRetrier(t *testing.T) {
+	// Run a server that only responds with HTTP errors which will put the client into the
+	// backoff.RetryNotify loop.
+	const status = http.StatusBadGateway
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		t.Log(r.Method, r.URL.String(), http.StatusText(status))
+		w.WriteHeader(status)
+	}))
+	defer srv.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	c := NewClient(srv.URL)
+	c.ReconnectNotify = backoff.Notify(func(err error, d time.Duration) {
+		t.Logf("ReconnectNotify err: %v, duration: %s", err, d.String())
+		// The client has processed the HTTP server error from above, so cancel the context
+		// for the SubscribeWithContext call.
+		cancel()
+	})
+
+	err := c.SubscribeWithContext(ctx, "test", func(msg *Event) {
+		t.Fatal("Received event when none was expected:", msg)
+	})
+	require.Error(t, err)
+	assert.Regexp(t, `could not connect to stream: `+http.StatusText(status), err.Error())
+}