posix udp poll based example

net.cpp

#include <arpa/inet.h>
#include <sys/poll.h>
#include <sys/socket.h>

#include <stdio.h>
#include <string.h>

#include <unistd.h>

static struct {
    sockaddr local;
    int socket;

    sockaddr * remote_list;
    int remote_count;
} intern;

int init_net( int port )
{
    int ret;

    intern.remote_list = new sockaddr[ 32 ];

    static sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons( port );
    addr.sin_addr.s_addr = htonl( INADDR_ANY );

    memcpy( &intern.local, &addr, sizeof( sockaddr_in ) );

    intern.socket = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );

    if ( intern.socket == -1 ) {
        fprintf( stderr, "socket() failed\n" );
        return 1;
    }

    ret = bind( intern.socket, &intern.local, sizeof( sockaddr ) );

    if ( ret == -1 ) {
        fprintf( stderr, "bind() failed\n" );
        return 1;
    }

    return 0;
}

int add_net_remote( const char * ip, int port )
{
    static sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_port = htons( port );
    addr.sin_addr.s_addr = inet_addr( ip );

    int id = intern.remote_count++;
    memcpy( intern.remote_list + id, &addr, sizeof( sockaddr_in ) );

    return id;
}

void terminate_net()
{
    close( intern.socket );
}

int poll_packet( char * buffer, int size, int * source )
{
    pollfd info;
    info.fd = intern.socket;
    info.events = POLLIN;

    int ret = poll( &info, 1, 0 );

    if ( ret == -1 ) {
        fprintf( stderr, "poll() failed\n" );
        return -1;
    }

    if ( ret == 0 ) {
        // no events
        return 0;
    }

    socklen_t addr_len = sizeof( sockaddr );

    sockaddr addr;

    int len = recvfrom( intern.socket, buffer, size, 0, &addr, &addr_len );

    // find remote
    for ( int i = 0; i < intern.remote_count; i++ ) {
        if ( memcmp( &addr, intern.remote_list + i, sizeof( sockaddr ) ) ==
             0 ) {
            *source = i;
            return len;
        }
    }

    // new remote
    int id = intern.remote_count++;
    memcpy( intern.remote_list + id, &addr, sizeof( sockaddr ) );
    *source = id;

    return len;
}

int send_packet( int dest, const void * buffer, int size )
{
    int ret = sendto(
        intern.socket,
        buffer,
        size,
        0,
        intern.remote_list + dest,
        sizeof( sockaddr )
    );

    if ( ret == -1 ) {
        fprintf( stderr, "sendto() failed\n" );
    }

    return ret;
}

net.hpp

#pragma once

/// @param port
/// @return 0 on success
int init_net( int port );

void terminate_net();

/// @param ip
/// @param port
/// @return remote id
int add_net_remote( const char * ip, int port );

/// @param buffer
/// @param size
/// @param source remote id of the packet's source
/// @return bytes recieved
int poll_packet( char * buffer, int size, int * source );


/// @param dest remote id of packet's destination
/// @param buffer
/// @param size
/// @return bytes sent
int send_packet( int dest, const void * buffer, int size );