GODRIVER-1439 Only close connections for heartbeat errors (#261)

Author: Divjot Arora

x/mongo/driver/topology/connection.go

@@ -103,12 +103,19 @@ func (c *connection) connect(ctx context.Context) {
 
 	if c.config.tlsConfig != nil {
 		tlsConfig := c.config.tlsConfig.Clone()
-		c.nc, err = configureTLS(ctx, c.nc, c.addr, tlsConfig)
+
+		// store the result of configureTLS in a separate variable than c.nc to avoid overwriting c.nc with nil in
+		// error cases.
+		tlsNc, err := configureTLS(ctx, c.nc, c.addr, tlsConfig)
 		if err != nil {
+			if c.nc != nil {
+				_ = c.nc.Close()
+			}
 			atomic.StoreInt32(&c.connected, disconnected)
 			c.connectErr = ConnectionError{Wrapped: err, init: true}
 			return
 		}
+		c.nc = tlsNc
 	}
 
 	c.bumpIdleDeadline()

x/mongo/driver/topology/server.go

@@ -540,15 +540,16 @@ func (s *Server) heartbeat(conn *connection) (description.Server, *connection) {
 			if err == nil {
 				tmpDesc := op.Result(s.address)
 				descPtr = &tmpDesc
+			} else {
+				// close the connection here rather than in the error check below to avoid calling Close on a net.Conn
+				// that wasn't successfully created
+				_ = conn.close()
 			}
 		}
 
 		// we do a retry if the server is connected, if succeed return new server desc (see below)
 		if err != nil {
 			saved = err
-			if conn != nil && conn.nc != nil {
-				conn.nc.Close()
-			}
 			conn = nil
 			if _, ok := err.(ConnectionError); ok {
 				s.pool.drain()