boost::asio 使用 libcurl

curl 使用 asio 的官方样例 http://curl.haxx.se/libcurl/c/asiohiper.html， 但这个例子用起来有很明细的 bug，asio 异步IO 只注册一次，也就是第一次 aync_read 之后对socket的读都是由 超时 驱动的。自己把样例改了下。

curl 和 asio 组合的时候相比（select， libevent， libuv）非常复杂。绝不仅仅是多了下面2个 socket 创建和关闭的回调函数。

CURLOPT_OPENSOCKETFUNCTION 创建套接字

CURLOPT_CLOSESOCKETFUNCTION  关闭套接字

 

 

还有下面这些坑：

 

1. 通过 CURLMOPT_SOCKETFUNCTION 的回调函数 remove 套接字的读写事件，有时候会发生在 CURLOPT_CLOSESOCKETFUNCTION 回调执行之后

 

2. curl 使用 c-ares 做域名解析时候， c-ares 的套接字也会传给 CURLMOPT_SOCKETFUNCTION 的回调函数。 此处要根据已有 文件描述符 创建 asio socket，并监听。 但是缺少创建 asio socket 需要知道协议类型，所以这里不能创建socket以注册IO事件，只能等定时器超时后去读 c-ares 的套接字。 所以请重新编译 curl 禁用 c-ares

 

3. asio 的异步IO函数，需要在每次读之后都 作下判断，如果 CURLMOPT_SOCKETFUNCTION 的回调函数 没有放弃此类事件的关注，则需要继续注册 asio 异步IO事件

 

4. windows 平台上，如果网站连接超时。只会触发 CURLOPT_CLOSESOCKETFUNCTION 回调被执行， 但不会触发 CURLMOPT_SOCKETFUNCTION 的回调函数。所以需要在 CURLOPT_CLOSESOCKETFUNCTION 回调 中调用 asio 的 cancel 取消已经注册的异步IO事件。 而取消 异步IO 会直到下次运行 io_service.run() 再触发 asio 异步IO 的回调函数，并通过 boost::system::error_code 指示回调被取消了。导致 asio socket 生命周期必须撑到  CURLOPT_CLOSESOCKETFUNCTION 回调之后

 

 

结论：

1.windows 平台上为了更好的可维护性，还是用 select 比较好，（定义一个足够大的 FD_SETSIZE——win下默认是 64，太小。而 linux 下这个值是不能调整的。）如果你嫌 select 轮询过多 socket 时性能低，你就上多线程和select的组合，每个线程 select 自己的socket。

2.如果要代码更好的跨平台，windows只是测试，需要在Linux、BSD上有更好的性能，这时可以使用 liev 库（win下官方 libcurl 样例是跑不了，需要参考我另外一篇文章自定义 重写 libev 的 EV_WIN32_HANDLE_TO_FD）

3.不要为了用 IOCP 而选 asio 来驱动 curl，这带来巨大的代码复杂性。

 

 

最后附上能在 windows 和 linux 跑的样例 (以 curl 7.39 、 asio 1.56为例)：

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ | |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 2012, Daniel Stenberg, <daniel@haxx.se>, 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 <string.h>
#include <iostream>
 
#include <curl/curl.h>
#include <boost/asio.hpp>
#include <boost/bind.hpp>

 
#define MSG_OUT stdout  
 
/* boost::asio related objects
 * using global variables for simplicity
 */ 
boost::asio::io_service io_service;
boost::asio::deadline_timer timer(io_service);

typedef struct _SocketInfo
{
    _SocketInfo(boost::asio::io_service &io)
        : sock(io),
          mask(0)
    {

    }

    boost::asio::ip::tcp::socket sock;
    int mask; // is used to store current action 
} SocketInfo;
typedef boost::shared_ptr<SocketInfo> socket_ptr;

// windows 上连接超时， eventcb 会一直挂起。需要在 closesocket 回调中取消所有异步事件
// 取消异步事件又会导致， eventcb 在 closesocket 回调 之后被调用。
// 所以不能简单的在 closesocket 回调 中释放 socket_ptr 的资源。所以这里得用 shared_ptr
std::map<curl_socket_t, socket_ptr> 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);
 
/* Update the event timer after curl_multi library calls */ 
static int multi_timer_cb(CURLM *multi, long timeout_ms, GlobalInfo *g)
{
  fprintf(MSG_OUT, "
multi_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, "
ERROR: %s returns %s", where, s);
      /* ignore this error */ 
      return;
    }
    fprintf(MSG_OUT, "
ERROR: %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, "
REMAINING: %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, "
DONE: %s => (%d) %s", eff_url, res, conn->error);
      curl_multi_remove_handle(g->multi, easy);
      free(conn->url);
      curl_easy_cleanup(easy);
      free(conn);
    }
  }
}

static void setsock(socket_ptr &tcp_socket, curl_socket_t s, CURL*e, int act, GlobalInfo*g);
 
/* Called by asio when there is an action on a socket */ 
static void event_cb(GlobalInfo *g, socket_ptr &tcp_socket, curl_socket_t s, CURL*e, int action, const boost::system::error_code &err)
{
    CURLMcode rc;

    assert(tcp_socket->sock.native_handle() == s);

    if (err)
    {
        fprintf(MSG_OUT, "
event_cb: socket=%d action=%d 
ERROR=%s", s, action, err.message().c_str());
        rc = curl_multi_socket_action(g->multi, tcp_socket->sock.native_handle(), CURL_CSELECT_ERR, &g->still_running);
    }
    else
    {
        fprintf(MSG_OUT, "
event_cb: socket=%d action=%d", s, action);
        rc = curl_multi_socket_action(g->multi, tcp_socket->sock.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, "
last transfer done, kill timeout");
        timer.cancel();
    }
    else
    {
        int action_continue = (tcp_socket->mask) & action;
        if (action_continue)
        {
            fprintf(MSG_OUT, "
continue read or write: %d", action_continue);
            setsock(tcp_socket, s, e, action_continue, g); // continue read or write
        }
    }
}
 
/* Called by asio when our timeout expires */ 
static void timer_cb(const boost::system::error_code & error, GlobalInfo *g)
{
  if ( !error)
  {
    fprintf(MSG_OUT, "
timer_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);
  }
}
 
static void setsock(socket_ptr &tcp_socket, curl_socket_t s, CURL*e, int act, GlobalInfo*g)
{
  fprintf(MSG_OUT, "
setsock: socket=%d, act=%d ", s, act);
  assert(tcp_socket->sock.native_handle() == s);
 
  if ( act == CURL_POLL_IN )
  {
    fprintf(MSG_OUT, "
watching for socket to become readable");
 
    tcp_socket->sock.async_read_some(boost::asio::null_buffers(),
                             boost::bind(&event_cb, g,
                               tcp_socket, s, e,
                               act, _1));
  }
  else if ( act == CURL_POLL_OUT )
  {
    fprintf(MSG_OUT, "
watching for socket to become writable");
 
    tcp_socket->sock.async_write_some(boost::asio::null_buffers(),
                              boost::bind(&event_cb, g,
                                tcp_socket, s, e,
                                act, _1));
  }
  else if ( act == CURL_POLL_INOUT )
  {
    fprintf(MSG_OUT, "
watching for socket to become readable & writable");
 
    tcp_socket->sock.async_read_some(boost::asio::null_buffers(),
                             boost::bind(&event_cb, g,
                               tcp_socket, s, e,
                               CURL_POLL_IN, _1));
 
    tcp_socket->sock.async_write_some(boost::asio::null_buffers(),
                              boost::bind(&event_cb, g,
                                tcp_socket, s, e,
                                CURL_POLL_OUT, _1));
  }
}
 
/* CURLMOPT_SOCKETFUNCTION */ 
static int multi_sock_cb(CURL *e, curl_socket_t s, int what, void *cbp, void *sockp)
{
  fprintf(MSG_OUT, "
multi_sock_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,
          "
socket callback: s=%d e=%p what=%s ", s, e, whatstr[what]);

  std::map<curl_socket_t, socket_ptr>::iterator it = socket_map.find(s);

  if ( it == socket_map.end() )
  {
      if(actionp)
      {
          fprintf(MSG_OUT, "
socket closed already before remove CURL_POLL_REMOVE event. bug???", s);
          //*actionp = what;
          return 0;
      }
      else
      {
          fprintf(MSG_OUT, "
we don't know how to create asio::ip::tcp::socket without this fd's protocol family, please recompiled libcurl without c-ares
");
          fprintf(MSG_OUT, "
socket %d is a c-ares socket, ignoring", s);
          return 0; // don't poll this fd, will cause c-ares read dns response until timeout
      }

  }

  socket_ptr &tcp_socket = it->second;

  if ( !actionp )
  {
      actionp = &(tcp_socket->mask);

      curl_multi_assign(g->multi, s, actionp);
  }
 
  if ( what == CURL_POLL_REMOVE )
  {
    fprintf(MSG_OUT, "
");
    fprintf(MSG_OUT, "
remsock: socket=%d", s);
  }
  else
  {
      fprintf(MSG_OUT,
              "
Changing action from %s to %s",
              whatstr[*actionp], whatstr[what]);
      setsock(tcp_socket, s, e, what & (~*actionp), g); // only add new instrest
  }

done:
  *actionp = what;
  return 0;
}
 
 
/* CURLOPT_WRITEFUNCTION */ 
static size_t write_cb(void *ptr, size_t size, size_t nmemb, void *data)
{
 
  size_t written = size * nmemb;
  char* pBuffer = (char*)malloc(written + 1);
 
  strncpy(pBuffer, (const char *)ptr, written);
  pBuffer [written] = '';
 
  fprintf(MSG_OUT, "
fetch %u bytes
", written);
  //fprintf(MSG_OUT, "%s", pBuffer);
 
  free(pBuffer);
 
  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, "
Progress: %s (%g/%g)", conn->url, dlnow, dltotal);
  fprintf(MSG_OUT, "
Progress: %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, "
opensocket :");
 
  curl_socket_t sockfd = CURL_SOCKET_BAD;
 
  /* restrict to ipv4 */ 
  if (purpose == CURLSOCKTYPE_IPCXN && address->family == AF_INET)
  {
    /* create a tcp socket object */ 
    SocketInfo *tcp_socket = new SocketInfo(io_service);
 
    /* open it and get the native handle*/ 
    boost::system::error_code ec;
    tcp_socket->sock.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, "
ERROR: Returning CURL_SOCKET_BAD to signal error");
    }
    else
    {
      sockfd = tcp_socket->sock.native_handle();
      fprintf(MSG_OUT, "
Opened socket %d", sockfd);
 
      /* save it for monitoring */
      size_t size = socket_map.size();
      socket_map.insert(std::pair<curl_socket_t, socket_ptr>(sockfd, socket_ptr(tcp_socket)));
      assert(size + 1 == socket_map.size());
    }
  }
 
  return sockfd;
}
 
/* CURLOPT_CLOSESOCKETFUNCTION */ 
static int closesocket_cb(void *clientp, curl_socket_t item)
{
  fprintf(MSG_OUT, "
closesocket : %d", item);
 
  std::map<curl_socket_t, socket_ptr>::iterator it = socket_map.find(item);
 
  if ( it != socket_map.end() )
  {
    assert(it->second->sock.native_handle() == item);
    it->second->mask = 0;
    // close or cancel will cancel any asynchronous send, receive or connect operations 
    // Caution: on Windows platform, if connect host timeout, the event_cb will pending forever. Must be canceled manually
    it->second->sock.cancel(); 
    socket_map.erase(it);
  }
  else
      assert(false);
 
  return 0;
}
 
/* Create a new easy handle, and add it to the global curl_multi */ 
static void new_conn(const char *url, GlobalInfo *g )
{
  ConnInfo *conn;
  CURLMcode rc;
 
  conn = (ConnInfo *)calloc(1, sizeof(ConnInfo));
  memset(conn, 0, sizeof(ConnInfo));
  conn->error[0]='';
 
  conn->easy = curl_easy_init();
 
  if ( !conn->easy )
  {
    fprintf(MSG_OUT, "
curl_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, 3L);
  curl_easy_setopt(conn->easy, CURLOPT_LOW_SPEED_LIMIT, 10L);
  curl_easy_setopt(conn->easy, CURLOPT_CONNECTTIMEOUT, 16L); // timeout for the connect phase 
 
  /* 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_cb);
 
  fprintf(MSG_OUT,
          "
Adding 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, multi_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);
 
  for (int idx = 1; idx < argc; ++idx)
  {
      new_conn(argv[idx], &g);  /* add a URL */ 
  }
 
  /* enter io_service run loop */ 
  io_service.run();
 
  curl_multi_cleanup(g.multi);
 
  fprintf(MSG_OUT, "
done.
");
  return 0;
}