allow calling PLAY twice (#128)

internal/client/client.go

@@ -770,14 +770,17 @@ func (c *Client) handleRequest(req *base.Request) error {
 		}
 
 	case base.PLAY:
+		// play can be sent twice, allow calling it even if we're already playing
 		err := c.checkState(map[state]struct{}{
 			statePrePlay: {},
+			statePlay:    {},
 		})
 		if err != nil {
 			c.writeResError(cseq, base.StatusBadRequest, err)
 			return errStateTerminate
 		}
 
+		if c.state == statePrePlay {
 			basePath, ok := req.URL.BasePath()
 			if !ok {
 				c.writeResError(cseq, base.StatusBadRequest, fmt.Errorf("unable to find base path (%s)", req.URL))
@@ -796,6 +799,7 @@ func (c *Client) handleRequest(req *base.Request) error {
 				c.writeResError(cseq, base.StatusBadRequest, fmt.Errorf("no tracks have been setup"))
 				return errStateTerminate
 			}
+		}
 
 		// write response before setting state
 		// otherwise, in case of TCP connections, RTP packets could be sent
@@ -807,7 +811,11 @@ func (c *Client) handleRequest(req *base.Request) error {
 				"Session": base.HeaderValue{sessionId},
 			},
 		})
+
+		if c.state == statePrePlay {
 			return errStatePlay
+		}
+		return nil
 
 	case base.RECORD:
 		err := c.checkState(map[state]struct{}{