/*
 * http://linux.m2osw.com/c-implementation-udp-clientserver
 *
 * UDPServer.cpp
 *
 *  Created on: 29.06.2016
 *      Author: Tobias Frust
 */

// ========================= SEVER =========================

/** \brief Initialize a UDP server object.
 *
 * This function initializes a UDP server object making it ready to
 * receive messages.
 *
 * The server address and port are specified in the constructor so
 * if you need to receive messages from several different addresses
 * and/or port, you'll have to create a server for each.
 *
 * The address is a string and it can represent an IPv4 or IPv6
 * address.
 *
 * Note that this function calls connect() to connect the socket
 * to the specified address. To accept data on different UDP addresses
 * and ports, multiple UDP servers must be created.
 *
 * \note
 * The socket is open in this process. If you fork() or exec() then the
 * socket will be closed by the operating system.
 *
 * \warning
 * We only make use of the first address found by getaddrinfo(). All
 * the other addresses are ignored.
 *
 * \exception udp_client_server_runtime_error
 * The udp_client_server_runtime_error exception is raised when the address
 * and port combinaison cannot be resolved or if the socket cannot be
 * opened.
 *
 * \param[in] addr  The address we receive on.
 * \param[in] port  The port we receive from.
 */

#include "UDPServer.h"

#include <string.h>
#include <unistd.h>

#ifndef SOCK_CLOEXEC
#define SOCK_CLOEXEC 0
#endif

UDPServer::UDPServer(const std::string& addr, int port)
    : f_port(port)
    , f_addr(addr)
{
    char decimal_port[16];
    snprintf(decimal_port, sizeof(decimal_port), "%d", f_port);
    decimal_port[sizeof(decimal_port) / sizeof(decimal_port[0]) - 1] = '\0';
    struct addrinfo hints;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;
    hints.ai_protocol = IPPROTO_UDP;
    int r(getaddrinfo(addr.c_str(), decimal_port, &hints, &f_addrinfo));
    if(r != 0 || f_addrinfo == NULL)
    {
        throw udp_client_server_runtime_error(("invalid address or port for UDP socket: \"" + addr + ":" + decimal_port + "\"").c_str());
    }
    f_socket = socket(f_addrinfo->ai_family, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
    if(f_socket == -1)
    {
        freeaddrinfo(f_addrinfo);
        throw udp_client_server_runtime_error(("could not create UDP socket for: \"" + addr + ":" + decimal_port + "\"").c_str());
    }
    r = bind(f_socket, f_addrinfo->ai_addr, f_addrinfo->ai_addrlen);
    if(r != 0)
    {
        freeaddrinfo(f_addrinfo);
        close(f_socket);
        throw udp_client_server_runtime_error(("could not bind UDP socket with: \"" + addr + ":" + decimal_port + "\"").c_str());
    }
}

/** \brief Clean up the UDP server.
 *
 * This function frees the address info structures and close the socket.
 */
UDPServer::~UDPServer()
{
    freeaddrinfo(f_addrinfo);
    close(f_socket);
}

/** \brief The socket used by this UDP server.
 *
 * This function returns the socket identifier. It can be useful if you are
 * doing a select() on many sockets.
 *
 * \return The socket of this UDP server.
 */
int UDPServer::get_socket() const
{
    return f_socket;
}

/** \brief The port used by this UDP server.
 *
 * This function returns the port attached to the UDP server. It is a copy
 * of the port specified in the constructor.
 *
 * \return The port of the UDP server.
 */
int UDPServer::get_port() const
{
    return f_port;
}

/** \brief Return the address of this UDP server.
 *
 * This function returns a verbatim copy of the address as passed to the
 * constructor of the UDP server (i.e. it does not return the canonalized
 * version of the address.)
 *
 * \return The address as passed to the constructor.
 */
std::string UDPServer::get_addr() const
{
    return f_addr;
}

/** \brief Wait on a message.
 *
 * This function waits until a message is received on this UDP server.
 * There are no means to return from this function except by receiving
 * a message. Remember that UDP does not have a connect state so whether
 * another process quits does not change the status of this UDP server
 * and thus it continues to wait forever.
 *
 * Note that you may change the type of socket by making it non-blocking
 * (use the get_socket() to retrieve the socket identifier) in which
 * case this function will not block if no message is available. Instead
 * it returns immediately.
 *
 * \param[in] msg  The buffer where the message is saved.
 * \param[in] max_size  The maximum size the message (i.e. size of the \p msg buffer.)
 *
 * \return The number of bytes read or -1 if an error occurs.
 */
int UDPServer::recv(char *msg, size_t max_size)
{
    return ::recv(f_socket, msg, max_size, 0);
}

/** \brief Wait for data to come in.
 *
 * This function waits for a given amount of time for data to come in. If
 * no data comes in after max_wait_ms, the function returns with -1 and
 * errno set to EAGAIN.
 *
 * The socket is expected to be a blocking socket (the default,) although
 * it is possible to setup the socket as non-blocking if necessary for
 * some other reason.
 *
 * This function blocks for a maximum amount of time as defined by
 * max_wait_ms. It may return sooner with an error or a message.
 *
 * \param[in] msg  The buffer where the message will be saved.
 * \param[in] max_size  The size of the \p msg buffer in bytes.
 * \param[in] max_wait_ms  The maximum number of milliseconds to wait for a message.
 *
 * \return -1 if an error occurs or the function timed out, the number of bytes received otherwise.
 */
int UDPServer::timed_recv(char *msg, size_t max_size, int max_wait_ms)
{
    fd_set s;
    FD_ZERO(&s);
    FD_SET(f_socket, &s);
    struct timeval timeout;
    timeout.tv_sec = max_wait_ms / 1000;
    timeout.tv_usec = (max_wait_ms % 1000) * 1000;
    int retval = select(f_socket + 1, &s, &s, &s, &timeout);
    if(retval == -1)
    {
        // select() set errno accordingly
        return -1;
    }
    if(retval > 0)
    {
        // our socket has data
        return ::recv(f_socket, msg, max_size, 0);
    }

    // our socket has no data
    errno = EAGAIN;
    return -1;
}