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()
{ } 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, "\nmulti_timer_cb: timeout_ms %ld", timeout_ms); /* cancel running timer */
timer.cancel(); if ( timeout_ms > )
{
/* 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 ;
} /* 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);
}
}
} 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, "\nevent_cb: socket=%d action=%d \nERROR=%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, "\nevent_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 <= )
{
fprintf(MSG_OUT, "\nlast transfer done, kill timeout");
timer.cancel();
}
else
{
int action_continue = (tcp_socket->mask) & action;
if (action_continue)
{
fprintf(MSG_OUT, "\ncontinue 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, "\ntimer_cb: "); CURLMcode rc;
rc = curl_multi_socket_action(g->multi, CURL_SOCKET_TIMEOUT, , &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, "\nsetsock: socket=%d, act=%d ", s, act);
assert(tcp_socket->sock.native_handle() == s); if ( act == CURL_POLL_IN )
{
fprintf(MSG_OUT, "\nwatching 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, "\nwatching 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, "\nwatching 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, "\nmulti_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,
"\nsocket 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, "\nsocket closed already before remove CURL_POLL_REMOVE event. bug???", s);
//*actionp = what;
return ;
}
else
{
fprintf(MSG_OUT, "\nwe don't know how to create asio::ip::tcp::socket without this fd's protocol family, please recompiled libcurl without c-ares\n");
fprintf(MSG_OUT, "\nsocket %d is a c-ares socket, ignoring", s);
return ; // 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, "\n");
fprintf(MSG_OUT, "\nremsock: socket=%d", s);
}
else
{
fprintf(MSG_OUT,
"\nChanging 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 ;
} /* 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 + ); strncpy(pBuffer, (const char *)ptr, written);
pBuffer [written] = '\0'; fprintf(MSG_OUT, "\nfetch %u bytes\n", 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, "\nProgress: %s (%g/%g)", conn->url, dlnow, dltotal);
fprintf(MSG_OUT, "\nProgress: %s (%g)", conn->url, ult); return ;
} /* 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 */
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, "\nERROR: Returning CURL_SOCKET_BAD to signal error");
}
else
{
sockfd = tcp_socket->sock.native_handle();
fprintf(MSG_OUT, "\nOpened 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 + == socket_map.size());
}
} return sockfd;
} /* CURLOPT_CLOSESOCKETFUNCTION */
static int closesocket_cb(void *clientp, curl_socket_t item)
{
fprintf(MSG_OUT, "\nclosesocket : %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 = ;
// 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 ;
} /* 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(, sizeof(ConnInfo));
memset(conn, , sizeof(ConnInfo));
conn->error[]='\0'; conn->easy = curl_easy_init(); if ( !conn->easy )
{
fprintf(MSG_OUT, "\ncurl_easy_init() failed, exiting!");
exit();
}
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,
"\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, , 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 = ; 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, "\ndone.\n");
return ;
}