fix transport header parsing with dahua rtsp server (#121)

pkg/headers/transport.go

@@ -201,17 +201,8 @@ func (h *Transport) Read(v base.HeaderValue) error {
 			h.ServerPorts = ports
 
 		case "ssrc":
-			// replace initial spaces
-			var b strings.Builder
-			b.Grow(len(v))
-			i := 0
-			for ; i < len(v) && v[i] == ' '; i++ {
-				b.WriteByte('0')
-			}
-			b.WriteString(v[i:])
-			v = b.String()
+			v = strings.TrimLeft(v, " ")
 
-			// add initial zeros
 			if (len(v) % 2) != 0 {
 				v = "0" + v
 			}

pkg/headers/transport_test.go

@@ -181,6 +181,23 @@ var casesTransport = []struct {
 			}(),
 		},
 	},
+	{
+		"dahua rtsp server ssrc with initial spaces",
+		base.HeaderValue{`RTP/AVP/TCP;unicast;interleaved=0-1;ssrc=     D93FF`},
+		base.HeaderValue{`RTP/AVP/TCP;unicast;interleaved=0-1;ssrc=000D93FF`},
+		Transport{
+			Protocol: TransportProtocolTCP,
+			Delivery: func() *TransportDelivery {
+				v := TransportDeliveryUnicast
+				return &v
+			}(),
+			InterleavedIDs: &[2]int{0, 1},
+			SSRC: func() *uint32 {
+				v := uint32(0xD93FF)
+				return &v
+			}(),
+		},
+	},
 }
 
 func TestTransportRead(t *testing.T) {