fix race condition in WritePacketRTP() (#334)

client_format.go

@@ -2,6 +2,7 @@ package gortsplib
 
 import (
 	"fmt"
+	"io"
 	"time"
 
 	"github.com/pion/rtcp"
@@ -14,6 +15,28 @@ import (
 	"github.com/bluenviron/gortsplib/v3/pkg/rtpreorderer"
 )
 
+// workaround until this gets tagged:
+// https://github.com/pion/rtp/pull/234
+func rtpPacketMarshalToSafe(p *rtp.Packet, buf []byte) (n int, err error) {
+	n, err = p.Header.MarshalTo(buf)
+	if err != nil {
+		return 0, err
+	}
+
+	// Make sure the buffer is large enough to hold the packet.
+	if n+len(p.Payload)+int(p.PaddingSize) > len(buf) {
+		return 0, io.ErrShortBuffer
+	}
+
+	m := copy(buf[n:], p.Payload)
+
+	if p.Header.Padding {
+		buf[n+m+int(p.PaddingSize-1)] = p.PaddingSize
+	}
+
+	return n + m + int(p.PaddingSize), nil
+}
+
 type clientFormat struct {
 	c               *Client
 	cm              *clientMedia
@@ -76,7 +99,7 @@ func (ct *clientFormat) stop() {
 
 func (ct *clientFormat) writePacketRTPWithNTP(pkt *rtp.Packet, ntp time.Time) error {
 	byts := make([]byte, udpMaxPayloadSize)
-	n, err := pkt.MarshalTo(byts)
+	n, err := rtpPacketMarshalToSafe(pkt, byts)
 	if err != nil {
 		return err
 	}