GODRIVER-1849 Add new WaitQueueTimeoutError to wrap context error (#568)

Author: Benjamin Rewis

x/mongo/driver/topology/CMAP_spec_test.go

@@ -160,7 +160,7 @@ func runCMAPTest(t *testing.T, testFileName string) {
 			for len(testInfo.backgroundThreadErrors) > 0 {
 				bgErr := <-testInfo.backgroundThreadErrors
 				errs = append(errs, bgErr)
-				if bgErr != nil && strings.ToLower(test.Error.Message) == bgErr.Error() {
+				if bgErr != nil && strings.Contains(bgErr.Error(), strings.ToLower(test.Error.Message)) {
 					erroredCorrectly = true
 					break
 				}

x/mongo/driver/topology/errors.go

@@ -1,6 +1,8 @@
 package topology
 
-import "fmt"
+import (
+	"fmt"
+)
 
 // ConnectionError represents a connection error.
 type ConnectionError struct {
@@ -25,3 +27,20 @@ func (e ConnectionError) Error() string {
 func (e ConnectionError) Unwrap() error {
 	return e.Wrapped
 }
+
+// WaitQueueTimeoutError represents a timeout when requesting a connection from the pool
+type WaitQueueTimeoutError struct {
+	Wrapped error
+}
+
+func (w WaitQueueTimeoutError) Error() string {
+	errorMsg := "timed out while checking out a connection from connection pool"
+	if w.Wrapped != nil {
+		return fmt.Sprintf("%s: %s", errorMsg, w.Wrapped.Error())
+	}
+	return errorMsg
+}
+
+func (w WaitQueueTimeoutError) Unwrap() error {
+	return w.Wrapped
+}

x/mongo/driver/topology/pool.go

@@ -31,9 +31,6 @@ var ErrConnectionClosed = ConnectionError{ConnectionID: "<closed>", message: "co
 // ErrWrongPool is return when a connection is returned to a pool it doesn't belong to.
 var ErrWrongPool = PoolError("connection does not belong to this pool")
 
-// ErrWaitQueueTimeout is returned when the request to get a connection from the pool timesout when on the wait queue
-var ErrWaitQueueTimeout = PoolError("timed out while checking out a connection from connection pool")
-
 // PoolError is an error returned from a Pool method.
 type PoolError string
 
@@ -340,7 +337,10 @@ func (p *pool) get(ctx context.Context) (*connection, error) {
 				Reason:  event.ReasonTimedOut,
 			})
 		}
-		return nil, ErrWaitQueueTimeout
+		errWaitQueueTimeout := WaitQueueTimeoutError{
+			Wrapped: ctx.Err(),
+		}
+		return nil, errWaitQueueTimeout
 	}
 
 	// This loop is so that we don't end up with more than maxPoolSize connections if p.conns.Maintain runs between

x/mongo/driver/topology/pool_test.go

@@ -689,6 +689,40 @@ func TestPool(t *testing.T) {
 			noerr(t, err)
 		})
 	})
+	t.Run("wait queue timeout error", func(t *testing.T) {
+		cleanup := make(chan struct{})
+		addr := bootstrapConnections(t, 1, func(nc net.Conn) {
+			<-cleanup
+			_ = nc.Close()
+		})
+		d := newdialer(&net.Dialer{})
+		pc := poolConfig{
+			Address:     address.Address(addr.String()),
+			MaxPoolSize: 1,
+		}
+		p, err := newPool(pc, WithDialer(func(Dialer) Dialer { return d }))
+		noerr(t, err)
+		err = p.connect()
+		noerr(t, err)
+
+		// get first connection.
+		_, err = p.get(context.Background())
+		noerr(t, err)
+
+		// Set a short timeout and get again.
+		ctx, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
+		defer cancel()
+		_, err = p.get(ctx)
+		assert.NotNil(t, err, "expected a WaitQueueTimeout; got nil")
+
+		// Assert that error received is WaitQueueTimeoutError with context deadline exceeded.
+		wqtErr, ok := err.(WaitQueueTimeoutError)
+		assert.True(t, ok, "expected a WaitQueueTimeoutError; got %v", err)
+		assert.True(t, wqtErr.Unwrap() == context.DeadlineExceeded,
+			"expected a timeout error; got %v", wqtErr)
+
+		close(cleanup)
+	})
 }
 
 type sleepDialer struct {