mirror of https://bitbucket.org/ausocean/av.git
111 lines
2.8 KiB
Go
111 lines
2.8 KiB
Go
/*
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NAME
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parse.go
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DESCRIPTION
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parse.go provides functionality for parsing RTP packets.
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AUTHOR
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Saxon A. Nelson-Milton <saxon@ausocean.org>
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LICENSE
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Copyright (C) 2019 the Australian Ocean Lab (AusOcean)
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This is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package rtp
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import (
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"encoding/binary"
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"errors"
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)
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const badVer = "incompatible RTP version"
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// Marker returns the state of the RTP marker bit, and an error if parsing fails.
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func Marker(d []byte) (bool, error) {
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if len(d) < defaultHeadSize {
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panic("invalid RTP packet length")
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}
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if version(d) != rtpVer {
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return false, errors.New(badVer)
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}
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return d[1]&0x80 != 0, nil
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}
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// Payload returns the payload from an RTP packet provided the version is
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// compatible, otherwise an error is returned.
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func Payload(d []byte) ([]byte, error) {
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err := checkPacket(d)
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if err != nil {
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return nil, err
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}
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extLen := 0
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if hasExt(d) {
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extLen = 4 + 4*(int(binary.BigEndian.Uint16(d[optionalFieldIdx+4*csrcCount(d)+2:])))
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}
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payloadIdx := optionalFieldIdx + 4*csrcCount(d) + extLen
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return d[payloadIdx:], nil
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}
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// SSRC returns the source identifier from an RTP packet. An error is return if
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// the packet is not valid.
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func SSRC(d []byte) (uint32, error) {
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err := checkPacket(d)
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if err != nil {
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return 0, err
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}
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return binary.BigEndian.Uint32(d[8:]), nil
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}
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// Sequence returns the sequence number of an RTP packet. An error is returned
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// if the packet is not valid.
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func Sequence(d []byte) (uint16, error) {
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err := checkPacket(d)
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if err != nil {
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return 0, err
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}
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return binary.BigEndian.Uint16(d[2:]), nil
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}
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// checkPacket checks the validity of the packet, firstly by checking size and
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// then also checking that version is compatible with these utilities.
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func checkPacket(d []byte) error {
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if len(d) < defaultHeadSize {
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return errors.New("invalid RTP packet length")
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}
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if version(d) != rtpVer {
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return errors.New(badVer)
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}
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return nil
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}
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// hasExt returns true if an extension is present in the RTP packet.
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func hasExt(d []byte) bool {
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return (d[0] & 0x10 >> 4) == 1
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}
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// csrcCount returns the number of CSRC fields.
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func csrcCount(d []byte) int {
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return int(d[0] & 0x0f)
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}
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// version returns the version of the RTP packet.
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func version(d []byte) int {
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return int(d[0] & 0xc0 >> 6)
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}
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