GODRIVER-372 Add Ping method to mongo.Client

Author: chasinglogic

mongo/client.go

@@ -109,6 +109,22 @@ func (c *Client) Disconnect(ctx context.Context) error {
 	return c.topology.Disconnect(ctx)
 }
 
+// Ping verifies that the client can connect to the topology.
+// If readPreference is nil then will use the client's default read
+// preference.
+func (c *Client) Ping(ctx context.Context, rp *readpref.ReadPref) error {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+
+	if rp == nil {
+		rp = c.readPreference
+	}
+
+	_, err := c.topology.SelectServer(ctx, description.ReadPrefSelector(rp))
+	return err
+}
+
 // StartSession starts a new session.
 func (c *Client) StartSession(opts ...sessionopt.Session) (*Session, error) {
 	if c.topology.SessionPool == nil {

mongo/client_internal_test.go

@@ -406,3 +406,31 @@ func TestClient_CausalConsistency(t *testing.T) {
 	require.True(t, sess.Consistent)
 	sess.EndSession(ctx)
 }
+
+func TestClient_Ping_DefaultReadPreference(t *testing.T) {
+	cs := testutil.ConnString(t)
+	c, err := NewClient(cs.String())
+	require.NoError(t, err)
+	require.NotNil(t, c)
+
+	err = c.Connect(ctx)
+	require.NoError(t, err)
+
+	err = c.Ping(ctx, nil)
+	require.NoError(t, err)
+}
+
+func TestClient_Ping_InvalidHost(t *testing.T) {
+	dur, err := time.ParseDuration("1ms")
+	require.NoError(t, err)
+
+	c, err := NewClientWithOptions("mongodb://nohost:27017", clientopt.ServerSelectionTimeout(dur))
+	require.NoError(t, err)
+	require.NotNil(t, c)
+
+	err = c.Connect(ctx)
+	require.NoError(t, err)
+
+	err = c.Ping(ctx, nil)
+	require.NotNil(t, err)
+}