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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：
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。
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：
/*************************************************************************** * _ _ ____ _ * 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_ptrstd::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 > 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); } }}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 <= 0 ) { 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, 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, "\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 0; } 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 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, "\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 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] = ‘\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 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 */ 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 + 1 == 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 = 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]=‘\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, 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, 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, "\ndone.\n"); return 0;}
boost::asio 使用 libcurl
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