Example program to demonstrate the usage of curl multi interface with boost::asio

1.cpp

boost::asio::io_service io_service;
boost::asio::deadline_timer timer(io_service);

2.cpp

curl_multi_setopt(g.multi, CURLMOPT_TIMERFUNCTION, multi_timer_cb);
curl_multi_setopt(g.multi, CURLMOPT_TIMERDATA, &g);

3.cpp

/* Update the event timer after curl_multi library calls */
static int multi_timer_cb(CURLM *multi, long timeout_ms, GlobalInfo *g)
{
  fprintf(MSG_OUT, "\nmulti_timer_cb: timeout_ms %ld", timeout_ms);

  /* cancel running timer */
  timer.cancel();

  if ( timeout_ms > 0 )
  {
    /* update timer */
    timer.expires_from_now(boost::posix_time::millisec(timeout_ms));
    timer.async_wait(boost::bind(&timer_cb, _1, g));
  }
  else
  {
    /* call timeout function immediately */
    boost::system::error_code error; /*success*/
    timer_cb(error, g);
  }

  return 0;
}

4.cpp

/* Called by asio when our timeout expires */
static void timer_cb(const boost::system::error_code & error, GlobalInfo *g)
{
  if ( !error)
  {
    fprintf(MSG_OUT, "\ntimer_cb: ");

    CURLMcode rc;
    rc = curl_multi_socket_action(g->multi, CURL_SOCKET_TIMEOUT, 0, &g->still_running);

    mcode_or_die("timer_cb: curl_multi_socket_action", rc);
    check_multi_info(g);
  }
}

5.cpp

curl_multi_setopt(g.multi, CURLMOPT_SOCKETFUNCTION, sock_cb);
curl_multi_setopt(g.multi, CURLMOPT_SOCKETDATA, &g);

6.cpp

/* call this function to get a socket */
curl_easy_setopt(conn->easy, CURLOPT_OPENSOCKETFUNCTION, opensocket);

/* call this function to close a socket */
curl_easy_setopt(conn->easy, CURLOPT_CLOSESOCKETFUNCTION, closesocket);

7.cpp

/* CURLOPT_OPENSOCKETFUNCTION */
static curl_socket_t opensocket(void *clientp,
                                curlsocktype purpose,
                                struct curl_sockaddr *address)
{
  fprintf(MSG_OUT, "\nopensocket :");

  curl_socket_t sockfd = CURL_SOCKET_BAD;

  /* restrict to ipv4 */
  if (purpose == CURLSOCKTYPE_IPCXN && address->family == AF_INET)
  {
    /* create a tcp socket object */
    boost::asio::ip::tcp::socket *tcp_socket = new boost::asio::ip::tcp::socket(io_service);

    /* open it and get the native handle*/
    boost::system::error_code ec;
    tcp_socket->open(boost::asio::ip::tcp::v4(), ec);

    if (ec)
    {
      //An error occurred
      std::cout << std::endl << "Couldn't open socket [" << ec << "][" << ec.message() << "]";
      fprintf(MSG_OUT, "\nERROR: Returning CURL_SOCKET_BAD to signal error");
    }
    else
    {
      sockfd = tcp_socket->native_handle();
      fprintf(MSG_OUT, "\nOpened socket %d", sockfd);

      /* save it for monitoring */
      socket_map.insert(std::pair<curl_socket_t, boost::asio::ip::tcp::socket *>(sockfd, tcp_socket));
    }
  }

  return sockfd;
}

8.cpp

/* CURLMOPT_SOCKETFUNCTION */
static int sock_cb(CURL *e, curl_socket_t s, int what, void *cbp, void *sockp)
{
  fprintf(MSG_OUT, "\nsock_cb: socket=%d, what=%d, sockp=%p", s, what, sockp);

  GlobalInfo *g = (GlobalInfo*) cbp;
  int *actionp = (int*) sockp;
  const char *whatstr[]={ "none", "IN", "OUT", "INOUT", "REMOVE"};

  fprintf(MSG_OUT,
          "\nsocket callback: s=%d e=%p what=%s ", s, e, whatstr[what]);

  if ( what == CURL_POLL_REMOVE )
  {
    fprintf(MSG_OUT, "\n");
    remsock(actionp, g);
  }
  else
  {
    if ( !actionp )
    {
      fprintf(MSG_OUT, "\nAdding data: %s", whatstr[what]);
      addsock(s, e, what, g);
    }
    else
    {
      fprintf(MSG_OUT,
              "\nChanging action from %s to %s",
              whatstr[*actionp], whatstr[what]);
      setsock(actionp, s, e, what, g);
    }
  }
  return 0;
}

9.cpp

/* Called by asio when there is an action on a socket */
static void event_cb(const boost::system::error_code error, GlobalInfo * g, boost::asio::ip::tcp::socket * tcp_socket, int action)
{
    if (!error)
    {
        fprintf(MSG_OUT, "\nevent_cb: action=%d", action);

        CURLMcode rc;
        rc = curl_multi_socket_action(g->multi, tcp_socket->native_handle(), action, &g->still_running);

        mcode_or_die("event_cb: curl_multi_socket_action", rc);
        check_multi_info(g);

        if ( g->still_running <= 0 )
        {
            fprintf(MSG_OUT, "\nlast transfer done, kill timeout");
            timer.cancel();
        }
        else
        {
            watch_socket(action, tcp_socket, g);
        }
    }
}

asiohiper.cpp

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 2012, Daniel Stenberg, <[email protected]>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at http://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/

/*
 * file: asiohiper.cpp
 * Example program to demonstrate the use of multi socket interface
 * with boost::asio
 *
 * This program is in c++ and uses boost::asio instead of libevent/libev.
 * Requires boost::asio, boost::bind and boost::system
 *
 * This is an adaptation of libcurl's "hiperfifo.c" and "evhiperfifo.c"
 * sample programs. This example implements a subset of the functionality from
 * hiperfifo.c, for full functionality refer hiperfifo.c or evhiperfifo.c
 *
 * Written by Lijo Antony based on hiperfifo.c by Jeff Pohlmeyer
 *
 * When running, the program creates an easy handle for a URL and
 * uses the curl_multi API to fetch it.
 *
 * Note:
 *  For the sake of simplicity, URL is hard coded to "www.google.com"
 *
 * This is purely a demo app, all retrieved data is simply discarded by the write
 * callback.
 */


#include <curl/curl.h>
#include <boost/asio.hpp>
#include <boost/bind.hpp>

#define MSG_OUT stdout /* Send info to stdout, change to stderr if you want */

/* boost::asio related objects
 * using global variables for simplicity
 */
boost::asio::io_service io_service;
boost::asio::deadline_timer timer(io_service);
std::map<curl_socket_t, boost::asio::ip::tcp::socket *> socket_map;

/* Global information, common to all connections */
typedef struct _GlobalInfo
{
  CURLM *multi;
  int still_running;
} GlobalInfo;

/* Information associated with a specific easy handle */
typedef struct _ConnInfo
{
  CURL *easy;
  char *url;
  GlobalInfo *global;
  char error[CURL_ERROR_SIZE];
} ConnInfo;

static void timer_cb(const boost::system::error_code & error, GlobalInfo *g);
static void watch_socket(int act, boost::asio::ip::tcp::socket *tcp_socket, GlobalInfo *g);

/* Update the event timer after curl_multi library calls */
static int multi_timer_cb(CURLM *multi, long timeout_ms, GlobalInfo *g)
{
  fprintf(MSG_OUT, "\nmulti_timer_cb: timeout_ms %ld", timeout_ms);

  /* cancel running timer */
  timer.cancel();

  if ( timeout_ms > 0 )
  {
    /* update timer */
    timer.expires_from_now(boost::posix_time::millisec(timeout_ms));
    timer.async_wait(boost::bind(&timer_cb, _1, g));
  }
  else
  {
    /* call timeout function immediately */
    boost::system::error_code error; /*success*/
    timer_cb(error, g);
  }

  return 0;
}

/* Die if we get a bad CURLMcode somewhere */
static void mcode_or_die(const char *where, CURLMcode code)
{
  if ( CURLM_OK != code )
  {
    const char *s;
    switch ( code )
    {
    case CURLM_CALL_MULTI_PERFORM: s="CURLM_CALL_MULTI_PERFORM"; break;
    case CURLM_BAD_HANDLE:         s="CURLM_BAD_HANDLE";         break;
    case CURLM_BAD_EASY_HANDLE:    s="CURLM_BAD_EASY_HANDLE";    break;
    case CURLM_OUT_OF_MEMORY:      s="CURLM_OUT_OF_MEMORY";      break;
    case CURLM_INTERNAL_ERROR:     s="CURLM_INTERNAL_ERROR";     break;
    case CURLM_UNKNOWN_OPTION:     s="CURLM_UNKNOWN_OPTION";     break;
    case CURLM_LAST:               s="CURLM_LAST";               break;
    default: s="CURLM_unknown";
      break;
    case     CURLM_BAD_SOCKET:         s="CURLM_BAD_SOCKET";
      fprintf(MSG_OUT, "\nERROR: %s returns %s", where, s);
      /* ignore this error */
      return;
    }
    fprintf(MSG_OUT, "\nERROR: %s returns %s", where, s);
    exit(code);
  }
}

/* Check for completed transfers, and remove their easy handles */
static void check_multi_info(GlobalInfo *g)
{
  char *eff_url;
  CURLMsg *msg;
  int msgs_left;
  ConnInfo *conn;
  CURL *easy;
  CURLcode res;

  fprintf(MSG_OUT, "\nREMAINING: %d", g->still_running);

  while ((msg = curl_multi_info_read(g->multi, &msgs_left)))
  {
    if (msg->msg == CURLMSG_DONE)
    {
      easy = msg->easy_handle;
      res = msg->data.result;
      curl_easy_getinfo(easy, CURLINFO_PRIVATE, &conn);
      curl_easy_getinfo(easy, CURLINFO_EFFECTIVE_URL, &eff_url);
      fprintf(MSG_OUT, "\nDONE: %s => (%d) %s", eff_url, res, conn->error);
      curl_multi_remove_handle(g->multi, easy);
      free(conn->url);
      curl_easy_cleanup(easy);
      free(conn);
    }
  }
}

/* Called by asio when there is an action on a socket */
static void event_cb(const boost::system::error_code error, GlobalInfo * g, boost::asio::ip::tcp::socket * tcp_socket, int action)
{
    if (!error)
    {
        fprintf(MSG_OUT, "\nevent_cb: action=%d", action);

        CURLMcode rc;
        rc = curl_multi_socket_action(g->multi, tcp_socket->native_handle(), action, &g->still_running);

        mcode_or_die("event_cb: curl_multi_socket_action", rc);
        check_multi_info(g);

        if ( g->still_running <= 0 )
        {
            fprintf(MSG_OUT, "\nlast transfer done, kill timeout");
            timer.cancel();
        }
        else
        {
            watch_socket(action, tcp_socket, g);
        }
    }
}

/* Called by asio when our timeout expires */
static void timer_cb(const boost::system::error_code & error, GlobalInfo *g)
{
  if ( !error)
  {
    fprintf(MSG_OUT, "\ntimer_cb: ");

    CURLMcode rc;
    rc = curl_multi_socket_action(g->multi, CURL_SOCKET_TIMEOUT, 0, &g->still_running);

    mcode_or_die("timer_cb: curl_multi_socket_action", rc);
    check_multi_info(g);
  }
}

/* Clean up any data */
static void remsock(int *f, GlobalInfo *g)
{
  fprintf(MSG_OUT, "\nremsock: ");

  if ( f )
  {
    free(f);
  }
}

static void setsock(int *fdp, curl_socket_t s, CURL*e, int act, GlobalInfo*g)
{
  fprintf(MSG_OUT, "\nsetsock: socket=%d, act=%d, fdp=%p", s, act, fdp);

  std::map<curl_socket_t, boost::asio::ip::tcp::socket *>::iterator it = socket_map.find(s);

  if ( it == socket_map.end() )
  {
    fprintf(MSG_OUT, "\nsocket %d is a c-ares socket, ignoring", s);
    return;
  }

  boost::asio::ip::tcp::socket * tcp_socket = it->second;

  *fdp = act;
  watch_socket(act, tcp_socket, g);
}

static void watch_socket(int act, boost::asio::ip::tcp::socket *tcp_socket, GlobalInfo *g)
{
    if (tcp_socket->is_open())
    {
        tcp_socket->cancel();

        if (act == CURL_POLL_IN)
        {
            fprintf(MSG_OUT, "\nwatching for socket to become readable");

            tcp_socket->async_read_some(boost::asio::null_buffers(),
                                      boost::bind(&event_cb,
                                          _1,
                                          g,
                                          tcp_socket,
                                          act));
        }
        else if (act == CURL_POLL_OUT)
        {
            fprintf(MSG_OUT, "\nwatching for socket to become writable");

            tcp_socket->async_write_some(boost::asio::null_buffers(),
                                      boost::bind(&event_cb,
                                          _1,
                                          g,
                                          tcp_socket,
                                          act));
        }
        else if (act == CURL_POLL_INOUT)
        {
            fprintf(MSG_OUT, "\nwatching for socket to become readable & writable");

            tcp_socket->async_read_some(boost::asio::null_buffers(),
                                      boost::bind(&event_cb,
                                          _1,
                                          g,
                                          tcp_socket,
                                          act));

            tcp_socket->async_write_some(boost::asio::null_buffers(),
                                      boost::bind(&event_cb,
                                          _1,
                                          g,
                                          tcp_socket,
                                          act));
        }
    }
}


static void addsock(curl_socket_t s, CURL *easy, int action, GlobalInfo *g)
{
  int *fdp = (int *)calloc(sizeof(int), 1); /* fdp is used to store current action */

  setsock(fdp, s, easy, action, g);
  curl_multi_assign(g->multi, s, fdp);
}

/* CURLMOPT_SOCKETFUNCTION */
static int sock_cb(CURL *e, curl_socket_t s, int what, void *cbp, void *sockp)
{
  fprintf(MSG_OUT, "\nsock_cb: socket=%d, what=%d, sockp=%p", s, what, sockp);

  GlobalInfo *g = (GlobalInfo*) cbp;
  int *actionp = (int*) sockp;
  const char *whatstr[]={ "none", "IN", "OUT", "INOUT", "REMOVE"};

  fprintf(MSG_OUT,
          "\nsocket callback: s=%d e=%p what=%s ", s, e, whatstr[what]);

  if ( what == CURL_POLL_REMOVE )
  {
    fprintf(MSG_OUT, "\n");
    remsock(actionp, g);
  }
  else
  {
    if ( !actionp )
    {
      fprintf(MSG_OUT, "\nAdding data: %s", whatstr[what]);
      addsock(s, e, what, g);
    }
    else
    {
      fprintf(MSG_OUT,
              "\nChanging action from %s to %s",
              whatstr[*actionp], whatstr[what]);
      setsock(actionp, s, e, what, g);
    }
  }
  return 0;
}


/* CURLOPT_WRITEFUNCTION */
static size_t write_cb(void *ptr, size_t size, size_t nmemb, void *data)
{
  size_t written = size * nmemb;
  /* Do something meaningful with the data */
  fprintf(MSG_OUT, ".");
  return written;
}


/* CURLOPT_PROGRESSFUNCTION */
static int prog_cb (void *p, double dltotal, double dlnow, double ult,
                    double uln)
{
  ConnInfo *conn = (ConnInfo *)p;
  (void)ult;
  (void)uln;

  fprintf(MSG_OUT, "\nProgress: %s (%g/%g)", conn->url, dlnow, dltotal);
  fprintf(MSG_OUT, "\nProgress: %s (%g)", conn->url, ult);

  return 0;
}

/* CURLOPT_OPENSOCKETFUNCTION */
static curl_socket_t opensocket(void *clientp,
                                curlsocktype purpose,
                                struct curl_sockaddr *address)
{
  fprintf(MSG_OUT, "\nopensocket :");

  curl_socket_t sockfd = CURL_SOCKET_BAD;

  /* restrict to ipv4 */
  if (purpose == CURLSOCKTYPE_IPCXN && address->family == AF_INET)
  {
    /* create a tcp socket object */
    boost::asio::ip::tcp::socket *tcp_socket = new boost::asio::ip::tcp::socket(io_service);

    /* open it and get the native handle*/
    boost::system::error_code ec;
    tcp_socket->open(boost::asio::ip::tcp::v4(), ec);

    if (ec)
    {
      //An error occurred
      std::cout << std::endl << "Couldn't open socket [" << ec << "][" << ec.message() << "]";
      fprintf(MSG_OUT, "\nERROR: Returning CURL_SOCKET_BAD to signal error");
    }
    else
    {
      sockfd = tcp_socket->native_handle();
      fprintf(MSG_OUT, "\nOpened socket %d", sockfd);

      /* save it for monitoring */
      socket_map.insert(std::pair<curl_socket_t, boost::asio::ip::tcp::socket *>(sockfd, tcp_socket));
    }
  }

  return sockfd;
}

/* CURLOPT_CLOSESOCKETFUNCTION */
static int closesocket(void *clientp, curl_socket_t item)
{
  fprintf(MSG_OUT, "\nclosesocket : %d", item);

  std::map<curl_socket_t, boost::asio::ip::tcp::socket *>::iterator it = socket_map.find(item);

  if ( it != socket_map.end() )
  {
    delete it->second;
    socket_map.erase(it);
  }

  return 0;
}

/* Create a new easy handle, and add it to the global curl_multi */
static void new_conn(char *url, GlobalInfo *g )
{
  ConnInfo *conn;
  CURLMcode rc;

  conn = (ConnInfo *)calloc(1, sizeof(ConnInfo));
  memset(conn, 0, sizeof(ConnInfo));
  conn->error[0]='\0';

  conn->easy = curl_easy_init();

  if ( !conn->easy )
  {
    fprintf(MSG_OUT, "\ncurl_easy_init() failed, exiting!");
    exit(2);
  }
  conn->global = g;
  conn->url = strdup(url);
  curl_easy_setopt(conn->easy, CURLOPT_URL, conn->url);
  curl_easy_setopt(conn->easy, CURLOPT_WRITEFUNCTION, write_cb);
  curl_easy_setopt(conn->easy, CURLOPT_WRITEDATA, &conn);
  curl_easy_setopt(conn->easy, CURLOPT_VERBOSE, 1L);
  curl_easy_setopt(conn->easy, CURLOPT_ERRORBUFFER, conn->error);
  curl_easy_setopt(conn->easy, CURLOPT_PRIVATE, conn);
  curl_easy_setopt(conn->easy, CURLOPT_NOPROGRESS, 1L);
  curl_easy_setopt(conn->easy, CURLOPT_PROGRESSFUNCTION, prog_cb);
  curl_easy_setopt(conn->easy, CURLOPT_PROGRESSDATA, conn);
  curl_easy_setopt(conn->easy, CURLOPT_LOW_SPEED_TIME, 60L);
  curl_easy_setopt(conn->easy, CURLOPT_LOW_SPEED_LIMIT, 10L);

  /* call this function to get a socket */
  curl_easy_setopt(conn->easy, CURLOPT_OPENSOCKETFUNCTION, opensocket);

  /* call this function to close a socket */
  curl_easy_setopt(conn->easy, CURLOPT_CLOSESOCKETFUNCTION, closesocket);

  fprintf(MSG_OUT,
          "\nAdding easy %p to multi %p (%s)", conn->easy, g->multi, url);
  rc = curl_multi_add_handle(g->multi, conn->easy);
  mcode_or_die("new_conn: curl_multi_add_handle", rc);

  /* note that the add_handle() will set a time-out to trigger very soon so
     that the necessary socket_action() call will be called by this app */
}

int main(int argc, char **argv)
{
  GlobalInfo g;
  CURLMcode rc;
  (void)argc;
  (void)argv;

  memset(&g, 0, sizeof(GlobalInfo));
  g.multi = curl_multi_init();

  curl_multi_setopt(g.multi, CURLMOPT_SOCKETFUNCTION, sock_cb);
  curl_multi_setopt(g.multi, CURLMOPT_SOCKETDATA, &g);
  curl_multi_setopt(g.multi, CURLMOPT_TIMERFUNCTION, multi_timer_cb);
  curl_multi_setopt(g.multi, CURLMOPT_TIMERDATA, &g);

  new_conn((char *)"http://us.download.nvidia.com/XFree86/Linux-x86_64/331.79/NVIDIA-Linux-x86_64-331.79.run", &g);  /* add a URL */

  /* enter io_service run loop */
  io_service.run();

  curl_multi_cleanup(g.multi);

  fprintf(MSG_OUT, "\ndone.\n");
  return 0;
}

As a quick fix, I copied 219-250 into the event_cb, 174, else {}. Seems to work at a first glance.

@jonface Thanks for pointing that out.