mirror of https://bitbucket.org/ausocean/av.git
70 lines
1.8 KiB
Go
70 lines
1.8 KiB
Go
/*
|
|
NAME
|
|
parse.go
|
|
|
|
DESCRIPTION
|
|
parse.go provides functionality for parsing RTP packets.
|
|
|
|
AUTHOR
|
|
Saxon A. Nelson-Milton <saxon@ausocean.org>
|
|
|
|
LICENSE
|
|
Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
|
|
|
|
This is free software: you can redistribute it and/or modify them
|
|
under the terms of the GNU General Public License as published by the
|
|
Free Software Foundation, either version 3 of the License, or (at your
|
|
option) any later version.
|
|
|
|
It is distributed in the hope that it will be useful, but WITHOUT
|
|
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
|
|
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
|
|
for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
in gpl.txt. If not, see [GNU licenses](http://www.gnu.org/licenses).
|
|
*/
|
|
|
|
package rtp
|
|
|
|
import (
|
|
"encoding/binary"
|
|
"errors"
|
|
)
|
|
|
|
const badVer = "incompatible RTP version"
|
|
|
|
// Payload returns the payload from an RTP packet provided the version is
|
|
// compatible, otherwise an error is returned.
|
|
func Payload(d []byte) ([]byte, error) {
|
|
if version(d) != rtpVer {
|
|
return nil, errors.New(badVer)
|
|
}
|
|
extLen := 0
|
|
if hasExt(d) {
|
|
extLen = 4 + 4*(int(binary.BigEndian.Uint16(d[optionalFieldIdx+4*csrcCount(d)+2:])))
|
|
}
|
|
payloadIdx := optionalFieldIdx + 4*csrcCount(d) + extLen
|
|
return d[payloadIdx:], nil
|
|
}
|
|
|
|
// hasExt returns true if an extension is present in the RTP packet. The version
|
|
// must be compatible otherwise we panic.
|
|
func hasExt(d []byte) bool {
|
|
if (d[0] & 0x10 >> 4) == 1 {
|
|
return true
|
|
}
|
|
return false
|
|
}
|
|
|
|
// csrcCount returns the number of CSRC fields. If the version is not compatible
|
|
// we panic.
|
|
func csrcCount(d []byte) int {
|
|
return int(d[0] & 0x0f)
|
|
}
|
|
|
|
// version returns the version of the RTP packet.
|
|
func version(d []byte) int {
|
|
return int(d[0] & 0xc0 >> 6)
|
|
}
|