av/protocol/rtp/client.go

/*
NAME
  client.go

DESCRIPTION
  client.go provides an RTP client.

AUTHOR
  Saxon A. Nelson-Milton <saxon@ausocean.org>

LICENSE
  This is Copyright (C) 2019 the Australian Ocean Lab (AusOcean).

  It 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 http://www.gnu.org/licenses.
*/

package rtp

import (
	"net"
	"sync"
)

// Client describes an RTP client that can receive an RTP stream and implements
// io.Reader.
type Client struct {
	r        *PacketReader
	ssrc     uint32
	mu       sync.Mutex
	sequence uint16
	cycles   uint16
}

// NewClient returns a pointer to a new Client.
//
// addr is the address of form <ip>:<port> that we expect to receive
// RTP at.
func NewClient(addr string) (*Client, error) {
	c := &Client{r: &PacketReader{}}

	a, err := net.ResolveUDPAddr("udp", addr)
	if err != nil {
		return nil, err
	}

	c.r.PacketConn, err = net.ListenUDP("udp", a)
	if err != nil {
		return nil, err
	}
	return c, nil
}

// SSRC returns the identified for the source from which the RTP packets being
// received are coming from.
func (c *Client) SSRC() uint32 {
	return c.ssrc
}

// Read implements io.Reader.
func (c *Client) Read(p []byte) (int, error) {
	n, err := c.r.Read(p)
	if err != nil {
		return n, err
	}
	if c.ssrc == 0 {
		c.ssrc, _ = SSRC(p[:n])
	}
	s, _ := Sequence(p[:n])
	c.setSequence(s)
	return n, err
}

// setSequence sets the most recently received sequence number, and updates the
// cycles count if the sequence number has rolled over.
func (c *Client) setSequence(s uint16) {
	c.mu.Lock()
	if s < c.sequence {
		c.cycles++
	}
	c.sequence = s
	c.mu.Unlock()
}

// Sequence returns the most recent RTP packet sequence number received.
func (c *Client) Sequence() uint16 {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.sequence
}

// Cycles returns the number of RTP sequence number cycles that have been received.
func (c *Client) Cycles() uint16 {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.cycles
}

// PacketReader provides an io.Reader interface to an underlying UDP PacketConn.
type PacketReader struct {
	net.PacketConn
}

// Read implements io.Reader.
func (r PacketReader) Read(b []byte) (int, error) {
	n, _, err := r.PacketConn.ReadFrom(b)
	return n, err
}