使用asio搭建服务器

1. 背景介绍1.1 什么是asio使用了linux、asio、protobuf等大量开源项目，开发过程共也借鉴了其他一些开源项目。asio由Christopher M. Kohlhoff大牛从2003年着手开发，2006年申请加入C++ tr1,2008年3月份加入boost1.35.0，按照boost与C++标准库的发展惯例，预测很快会加入C++标准库中。其中的async调用方式已经作为非常重要的新特性，加入到C++0x标准库。1.2 asio的相关资料asio官方提供了及其详细的文档、例子、教程，没有必要再累赘地将其转述一遍。如果有朋友对英文有些吃力，网上也早有很多翻译版。这里提供一些官方的文档资料：非boost版本的asio —— http://think-async.com/与boost::asio的主要区别就是名字空间是boost::asio还是asio。boost::asio —— http://www.boost.org/doc/libs/1520/doc/html/boost_asio.html申请加入tr2时的申报材料 —— 猛击此处下载高清pdfproactor模式的首篇论文 —— 猛击此处下载高清pdf使用asio的大型开源网络项目sip —— https://svn.resiprocate.org/rep/resiprocate/main2. 源码参考由于代码使用了一点其他的工具，所以并没有想让读者能够编译通过。但是对从头开始搭建服务器的朋友来说，一定是一份非常有价值的参考。2.1 作为Client的模块这部分供作为Client去连接其他服务器时使用。给出的源码中有三个类：TcpConnection, BizConnection, Client. 其中TcpConnection 提供了与协议无关的tcp连接，异步操作的结果以虚函数方式供派生类使用BizConnection 继承自TcpConnection，使用具体的协议解析报文Client使用BizConnection，并提供了等待具体某条消息的wait_for、心跳、延迟等功能2.1.1 tcpconnection.h#ifndef TCPCONNECTION_H#define TCPCONNECTION_H/** * @author [e-mail] */#include <asio.hpp>#include <asio/deadline_timer.hpp>#include <boost/shared_ptr.hpp>#include <boost/enable_shared_from_this.hpp>#include <boost/timer.hpp>#include <sstream>#include "safehandler.h"class TcpConnection        : public boost::enable_shared_from_this<TcpConnection>        , private boost::noncopyable{public:    typedef std::vector<uint8_t> DataBuffer;    typedef boost::shared_ptr<TcpConnection> TcpPtr;    static TcpPtr create(asio::io_service& io_service, const string& name){return TcpPtr(new TcpConnection(io_service, name));}    virtual ~TcpConnection();    void start(const string& ip, const string& port);    void start(unsigned ip, uint16_t port);    void start(const string& ip, uint16_t port);    void stop();    bool isConnected() {return m_socket.is_open();}    /// Getters and Setters    void setName(const string& name) {m_name = name;}    const string& getName() {return m_name;}    void setHeadLength(uint32_t size) {m_headLength = size;}    uint32_t getHeadLength() {return m_headLength;}    void setConnectTimeoutSec(uint32_t sec) {m_connectTimeoutSec = sec;}    uint32_t getConnectTimeoutSec() {return m_connectTimeoutSec;}    const string& getip() {return m_ip;}    uint16_t getport() {return m_port;}    string getFarpointInfo() { stringstream ss; ss << m_name << " " << m_ip << ":" << m_port << " "; return ss.str(); }protected:    explicit TcpConnection(asio::io_service& io_service, const string& name);    /// Provide for derived class    void connect(asio::ip::tcp::endpoint endpoint);    void receiveHead();    void receiveBody(uint32_t bodyLength);    void send(const void *data, uint32_t length);    /// Class override callbacks    virtual void onConnectSuccess() { assert(false); }    virtual void onConnectFailure(const asio::error_code& e) { (void)e; assert(false); }    virtual void onReceiveHeadSuccess(DataBuffer& data) { (void)data; assert(false); }    virtual void onReceiveBodySuccess(DataBuffer& data) { (void)data; assert(false); }    virtual void onReceiveFailure(const asio::error_code& e) { (void)e; assert(false); }    virtual void onSendSuccess() { assert(false); }    virtual void onSendFailure(const asio::error_code& e) { (void)e; assert(false); }    virtual void onTimeoutFailure(const asio::error_code& e) { (void)e; assert(false); }    virtual void onCommonError(uint32_t ec, const string& em) { (void)ec; (void)em; assert(false); }private:    void checkDeadline(const asio::error_code& e);    void handleConnect(const asio::error_code &e);    void handleReceiveHead(const asio::error_code& e);    void handleReceiveBody(const asio::error_code& e);    void handleSend(const asio::error_code& e);    typedef TcpConnection this_type;    asio::ip::tcp::socket m_socket;    asio::deadline_timer m_deadline;    bool m_stopped;    DataBuffer m_readBuf;    string m_name;    boost::shared_ptr<Probe> m_probe;    uint32_t m_headLength;    uint32_t m_connectTimeoutSec;    string m_ip;    uint16_t m_port;};#endif // TCPCONNECTION_H2.1.2 tcpconnection.cpp#include "stdafx.h"#include "tcpconnection.h"using asio::ip::tcp;TcpConnection::TcpConnection(asio::io_service &io_service, const string& name)    : m_socket(io_service)    , m_deadline(io_service)    , m_stopped(false)    , m_name(name)    , m_probe(new Probe)    , m_headLength(10)    , m_connectTimeoutSec(5)    , m_ip("")    , m_port(0){}TcpConnection::~TcpConnection(){    stop();}void TcpConnection::start(const string &ip, const string &port){    start(ip, atoi(port.c_str()));}void TcpConnection::start(unsigned ip, uint16_t port){    connect(tcp::endpoint(asio::ip::address_v4(ip), port));}void TcpConnection::start(const string &ip, uint16_t port){    asio::ip::address_v4 addr_v4 = asio::ip::address_v4::from_string(ip);    connect(tcp::endpoint(addr_v4, port));}void TcpConnection::stop(){    if (!m_stopped) {        m_stopped = true;        try {            m_readBuf.clear();            asio::error_code ignored;            m_socket.shutdown(tcp::socket::shutdown_both, ignored);            m_socket.close(ignored);            m_deadline.cancel();        } catch (const asio::system_error& err) {            FATAL("asio::system_error em %s", err.what());        }    }}void TcpConnection::connect(tcp::endpoint endpoint){    m_stopped = false;    m_ip = endpoint.address().to_string();    m_port = endpoint.port();    INFO("Trying connect %s:%u ...%s", STR(m_ip), m_port, STR(m_name));    m_deadline.expires_from_now(boost::posix_time::seconds(m_connectTimeoutSec));    m_socket.async_connect(endpoint, boost::bind(&TcpConnection::handleConnect, shared_from_this(), asio::placeholders::error));    m_deadline.async_wait(SafeHandler1<this_type, const asio::error_code&>(&this_type::checkDeadline, this, m_probe));}void TcpConnection::receiveHead(){    m_readBuf.resize(m_headLength);    asio::async_read(m_socket, asio::buffer(&m_readBuf[0], m_headLength),                     boost::bind(&TcpConnection::handleReceiveHead, shared_from_this(), asio::placeholders::error));}void TcpConnection::receiveBody(uint32_t bodyLength){    if (!m_stopped){        if ((bodyLength <= MAX_BUFFER_SIZE) && (bodyLength > 0)) {            m_readBuf.resize(bodyLength + m_headLength);            asio::async_read(m_socket, asio::buffer(&m_readBuf[m_headLength], bodyLength),                             boost::bind(&TcpConnection::handleReceiveBody, shared_from_this(), asio::placeholders::error));        } else {            onCommonError(S_FATAL, "illegal bodyLength to call receiveBody");        }    } else {        onCommonError(S_ERROR, "illegal to call receiveBody while tcp is not connected");    }}void TcpConnection::send(const void* data, uint32_t length){    if (!m_stopped) {        if (length <= MAX_BUFFER_SIZE) {            asio::async_write(m_socket, asio::const_buffers_1(data, length),                              boost::bind(&TcpConnection::handleSend, shared_from_this(), asio::placeholders::error));        } else {            onCommonError(S_ERROR, "too big length to call send");        }    } else {        onCommonError(S_ERROR, "illegal to call send while tcp is not connected");    }}/** * @brief TcpConnection::checkDeadline * @param e * case1: m_stopped == true which means user canceled * case2: m_deadline.expires_at() <= asio::deadline_timer::traits_type::now() *          Check whether the deadline has passed. We compare the deadline against            the current time since a new asynchronous operation may have moved the            deadline before this actor had a chance to run. */void TcpConnection::checkDeadline(const asio::error_code& e){    if (!m_stopped) {        if (m_deadline.expires_at() <= asio::deadline_timer::traits_type::now()) {            onTimeoutFailure(e);        }    }}void TcpConnection::handleConnect(const asio::error_code &e){    if (!m_stopped) {        if (!e) {            m_deadline.cancel();            onConnectSuccess();        } else {            onConnectFailure(e);        }    } else {        INFO("%s %s %u user's canceled by stop()", STR(m_name), STR(m_ip), m_port);    }}void TcpConnection::handleReceiveHead(const asio::error_code &e){    if (!m_stopped) {        if (!e) {            onReceiveHeadSuccess(m_readBuf);        } else if (isConnected()){            onReceiveFailure(e);        }    } else {        INFO("%s %s %u user's canceled by stop()", STR(m_name), STR(m_ip), m_port);    }}void TcpConnection::handleReceiveBody(const asio::error_code &e){    if (!m_stopped) {        if (!e) {            onReceiveBodySuccess(m_readBuf);        } else if (isConnected()){            onReceiveFailure(e);        }    } else {        INFO("%s %s %u user's canceled by stop()", STR(m_name), STR(m_ip), m_port);    }}void TcpConnection::handleSend(const asio::error_code &e){    if (!m_stopped) {        if (!e) {            //onSendSuccess();        } else if (isConnected()){            onSendFailure(e);        }    } else {        INFO("%s %s %u user's canceled by stop()", STR(m_name), STR(m_ip), m_port);    }}2.1.3 bizconnection.h#ifndef BIZCONNECTION_H#define BIZCONNECTION_H/** * @author [e-mail] */#include <asio.hpp>#include <cstdio>#include <stdexcept>#include "sigslot/sigslot.h"#include "tcpconnection.h"class BizConnection        : public TcpConnection{public:    typedef boost::shared_ptr<BizConnection> BizPtr;    static BizPtr create(asio::io_service& io_service, const string& name = string(""))    {        return BizPtr(new BizConnection(io_service, name));    }    void sendBizMsg(uint32_t uri, const BizPackage& pkg);    sigslot::signal0<> BizConnected;    sigslot::signal2<uint32_t, const string&> BizError;    sigslot::signal0<> BizClosed;    sigslot::signal1<BizPackage&> BizMsgArrived;protected:    explicit BizConnection(asio::io_service& io_service, const string& name);    /// Implement callbacks in base class    virtual void onConnectSuccess();    virtual void onConnectFailure(const asio::error_code& e);    virtual void onReceiveHeadSuccess(DataBuffer& data);    virtual void onReceiveBodySuccess(DataBuffer& data);    virtual void onReceiveFailure(const asio::error_code& e);    virtual void onSendSuccess();    virtual void onSendFailure(const asio::error_code& e);    virtual void onTimeoutFailure(const asio::error_code &e);    virtual void onCommonError(uint32_t ec, const string &em);    static void initNeedErrorSet();    static std::set<uint32_t> m_needError;private:    inline bool peekLength(void* data, uint32_t length, uint32_t& outputi32);    void handleError(const string& from, uint32_t ec, const asio::error_code& e = asio::error_code());};inline bool BizConnection::peekLength(void* data, uint32_t length, uint32_t& outputi32){    if (length >= 4) {        memcpy(&outputi32, data, sizeof(uint32_t));        return true;    } else {        return false;    }}#endif // BIZCONNECTION_H2.1.4 bizconnection.cpp#include "stdafx.h"#include "bizconnection.h"#include "tcpconnection.h"std::set<uint32_t> BizConnection::m_needError;BizConnection::BizConnection(asio::io_service &io_service, const string& name)    : TcpConnection(io_service, name){}void BizConnection::sendBizMsg(unsigned uri, const BizPackage &pkg){    /// TODO: usually this BizPackage contains the buffer of stream data to be sent to farpoint    /// You should implement this by retriving buffer in BizPackage then call TcpConnection::send();}void BizConnection::onConnectSuccess(){    receiveHead();    BizConnected.emit();}void BizConnection::onConnectFailure(const asio::error_code &e){    if (e == asio::error::operation_aborted) {        INFO("%s %s %u operation aborted... %s", STR(getName()), STR(getip()), getport(), STR(e.message()));    }    else if ((e == asio::error::already_connected) || (e == asio::error::already_open) || (e == asio::error::already_started)) {        WARN("%s %s %u alread connected... %s", STR(getName()), STR(getip()), getport(), STR(e.message()));    } else {        handleError("onConnectFailure", S_FATAL, e);    }}void BizConnection::onReceiveHeadSuccess(TcpConnection::DataBuffer &data){    uint32_t pkglen = 0;    if (peekLength(data.data(), data.size(), pkglen)) {        receiveBody(pkglen - getHeadLength());    } else {        handleError("peekLength", S_FATAL);    }}void BizConnection::onReceiveBodySuccess(TcpConnection::DataBuffer &data){    /// This is simply an example, actually it's user's duty to unmarshal buffer to package.    BizPackage msg;    BizPackage.unserializeFrom(data);    BizMsgArrived.emit(msg);    receiveHead();}void BizConnection::onReceiveFailure(const asio::error_code &e){    if ((e == asio::error::operation_aborted)) {        INFO("%s operation_aborted... %s", STR(getFarpointInfo()), STR(e.message()));    } else {        handleError("onReceiveFailure", S_FATAL, e);    }}void BizConnection::onSendSuccess(){    /// Leave it blank}void BizConnection::onSendFailure(const asio::error_code &e){    if ((e == asio::error::operation_aborted)) {        INFO("%s operation_aborted... %s", STR(getFarpointInfo()), STR(e.message()));    } else {        handleError("onSendFailure", S_FATAL, e);    }}void BizConnection::onTimeoutFailure(const asio::error_code &e){    if ((e == asio::error::operation_aborted)) {        INFO("%s operation_aborted... %s", STR(getFarpointInfo()), STR(e.message()));    } else {        handleError("onTimeoutFailure", S_FATAL);    }}void BizConnection::onCommonError(uint32_t ec, const string &em){    handleError(em, ec);}void BizConnection::handleError(const string& from, uint32_t ec, const asio::error_code &e/* = asio::error_code()*/){    stringstream ss;    ss << getFarpointInfo() << " " << from;    if (e) {        ss << " asio " << e.value() << " " << e.message();    }    BizError.emit(ec, ss.str());}2.1.5 client.h#ifndef CLIENT_H#define CLIENT_H/** * @author [e-mail] */#include "bizconnection.h"#include "handler.h"#include "safehandler.h"#include <asio.hpp>#include <boost/timer.hpp>class Client        : public sigslot::has_slots<>{protected:    BizConnection::BizPtr m_pBizConnection;public:    typedef void (Client::*RequestPtr)(BizPackage&);    typedef std::map<uint32_t, RequestPtr> RequestMap;    typedef void (Client::*NotifyPtr)(BizPackage&);    typedef std::map<uint32_t, NotifyPtr> NotifyMap;    explicit Client(const string& name = string(""));    /// 继承类需要实现的提供外部的方法    virtual void startServer() = 0;    virtual bool sendToServer(YProto &proto) = 0;    virtual void stopServer() {clearWaitforTimer(); m_pBizConnection->stop();}protected:    /// 继承类需要实现的初始化函数    virtual void initRequestMap() {assert(false);}    virtual void initNotifyMap() {assert(false);}    virtual void initSignal();    /// 继承类需要实现的钩子函数，用于处理网络事件    virtual void onBizMsgArrived(core::Request& msg) = 0;    virtual void onBizError(uint32_t ec, const string& em);    virtual void onBizConnected() = 0;    /// 继承类可以使用的工具方法    /// 1. 心跳类    void setKeepAliveSec(uint32_t sec) {m_keepAliveSec = sec;}    uint32_t getKeepAliveSec() {return m_keepAliveSec;}    void startKeepAlive();    void keepAlive(const asio::error_code& e);    virtual void onKeepAlive() {assert(false);}    /// 2. 登陆状态类    void setHasLogin(bool b) {m_hasLogin = b;}    bool getHasLogin() {return m_hasLogin;}    bool isOnline() { return (m_pBizConnection->isConnected() && m_hasLogin);}    /// 3. 消息保存类    template <typename Handler>    bool savePendingCommand(Handler handler)    {        if(m_pendingCmd.size() < MaxPendingCommandCount) {            m_pendingCmd.push_back(Command(handler));            return true;        }        return false;    }    void sendPendingCommand()    {        if (isOnline()) {            vector<Command>::iterator it = m_pendingCmd.begin();            for(; it != m_pendingCmd.end(); ++it) {                (*it)();            }            m_pendingCmd.clear();        }    }    /// 4. 延迟处理类    typedef void (Client::*HoldonCallback)();    void holdonSeconds(uint32_t sec, HoldonCallback func);    void holdonHandler(HoldonCallback func, const asio::error_code &e);    /// 5. waitfor 工具 处理异步消息超时    typedef boost::shared_ptr<asio::deadline_timer> SharedTimerPtr;    typedef boost::scoped_ptr<asio::deadline_timer> ScopedTimerPtr;    typedef boost::shared_ptr<Probe> SharedProbe;    typedef map<uint32_t, SharedTimerPtr> Uri2Timer;            /// 等待收到的包uri --> 这个时间timer    void waitfor(uint32_t uri, uint32_t sec);                   /// 在发送req的时候调用，sec 秒数 uri 等待收到的uri    void waitforTimeout(uint32_t uri, const asio::error_code& e); /// 所有waitfor超时都会自动回调这个函数    virtual void onWaitforTimeout(uint32_t uri) {(void)uri; assert(false);}         /// 继承类覆盖这个钩子函数来进行错误处理    void waitforReceived(uint32_t uri);                         /// 当响应函数handler被回调时，记得调用waitforReceived做清理工作    void eraseWaitforTimer(uint32_t uri);    void clearWaitforTimer();    /// 继承类可以使用的工具成员：心跳 探针 请求阻塞    typedef std::set<uint32_t> BlockReq;    BlockReq m_block;    SharedProbe m_probe;    ScopedTimerPtr m_timer;    uint32_t m_keepAliveSec;    bool m_hasLogin;    vector<Command> m_pendingCmd;    static const uint32_t MaxPendingCommandCount = 20;    ScopedTimerPtr m_holdonTimer;    Uri2Timer m_uri2timer;};#define BIND_REQ(m, uri, callback) \    m[static_cast<uint32_t>(uri)] = static_cast<RequestPtr>(callback);#define BIND_NOTIFY(m, uri, callback) \    m[static_cast<uint32_t>(uri)] = static_cast<NotifyPtr>(callback);#endif // CLIENT_H2.1.6 client.cpp#include "stdafx.h"#include "client.h"Client::Client(const string& name)    : m_pBizConnection(BizConnection::create(ioService::instance(), name))    , m_probe(new Probe)    , m_keepAliveSec(10)    , m_hasLogin(false){}void Client::initSignal(){    m_pBizConnection->BizError.connect(this, &Client::onBizError);    m_pBizConnection->BizMsgArrived.connect(this, &Client::onBizMsgArrived);    m_pBizConnection->BizConnected.connect(this, &Client::onBizConnected);}void Client::onBizError(uint32_t ec, const string &em){    m_facade.serverError.emit(ec, em);}void Client::startKeepAlive(){    m_timer.reset(new asio::deadline_timer(m_facade.io_service_ref));    m_timer->expires_from_now(boost::posix_time::seconds(m_keepAliveSec));    m_timer->async_wait(SafeHandler1<Client, const asio::error_code&>(&Client::keepAlive, this, m_probe));}void Client::keepAlive(const asio::error_code &e){    if (e != asio::error::operation_aborted) {        FINE("%u send ping to %s %s:%u", m_facade.m_pInfo->uid, STR(m_pBizConnection->getName()), STR(m_pBizConnection->getip()), m_pBizConnection->getport());        onKeepAlive();        m_timer->expires_from_now(boost::posix_time::seconds(m_keepAliveSec ));        m_timer->async_wait(SafeHandler1<Client, const asio::error_code&>(&Client::keepAlive, this, m_probe));    }}void Client::holdonSeconds(uint32_t sec, HoldonCallback func){    m_holdonTimer.reset(new asio::deadline_timer(m_facade.io_service_ref));    m_holdonTimer->expires_from_now(boost::posix_time::seconds(sec));    SafeHandler1Bind1<Client, HoldonCallback, const asio::error_code&> h(&Client::holdonHandler, this, func, m_probe);    m_holdonTimer->async_wait(h);}void Client::holdonHandler(HoldonCallback func, const asio::error_code &e){    if (!e) {        if (m_holdonTimer != NULL)            m_holdonTimer->cancel();        (this->*func)();    } else {         WARN("error: %s", STR(e.message()));    }}void Client::waitfor(uint32_t uri, uint32_t sec){    SharedTimerPtr t(new asio::deadline_timer(m_facade.io_service_ref));    t->expires_from_now(boost::posix_time::seconds(sec));    t->async_wait(SafeHandler1Bind1<Client, uint32_t, const asio::error_code&>(                      &Client::waitforTimeout, this, uri, m_probe));    m_uri2timer[uri] = t;}void Client::waitforTimeout(uint32_t uri, const asio::error_code &e){    if (e != asio::error::operation_aborted) {        FATAL("%s waitfor uri %u timeout", STR(m_pBizConnection->getName()), uri);        eraseWaitforTimer(uri);        onWaitforTimeout(uri);    }}void Client::waitforReceived(uint32_t uri){    eraseWaitforTimer(uri);}void Client::eraseWaitforTimer(uint32_t uri){    Uri2Timer::iterator it = m_uri2timer.find(uri);    if (it != m_uri2timer.end()) {        SharedTimerPtr& t = it->second;        if (t) {            asio::error_code e;            t->cancel(e);            t.reset();        }        m_uri2timer.erase(it);    }}void Client::clearWaitforTimer(){    Uri2Timer::iterator it = m_uri2timer.begin();    for (; it != m_uri2timer.end(); ++it) {        SharedTimerPtr& t = it->second;        if (t) {            asio::error_code e;            t->cancel(e);            t.reset();        }    }    m_uri2timer.clear();}2.2 作为server模块作为server模块由于涉及公司的业务比较多，这里剥离出一个作为crossdomain服务器的部分，功能很简单：flash客户端通过socket请求crossdomain配置文件，server返回给定的字符串。这里使用了比较著名的pimpl模式，将实现完全隐藏在cpp文件中。2.2.1 crossdomain.h#ifndef CROSSDOMAIN_H#define CROSSDOMAIN_H#include <string>#include <boost/shared_ptr.hpp>#include <asio.hpp>/** * @author [e-mail] */class CrossDomain{private:    struct Server;    boost::shared_ptr<Server> m_pserver;    CrossDomain(asio::io_service& io_service, const std::string& local_port);    static CrossDomain* s_instance;public:    static void create(asio::io_service& io_service, const std::string& local_port)    {        s_instance = new CrossDomain(io_service, local_port);    }    static CrossDomain* instance();    void start_server();};#endif // CROSSDOMAIN_H2.2.2 crossdomain.cpp#include "stdafx.h"#include "crossdomain.h"using asio::ip::tcp;using boost::uint8_t;CrossDomain* CrossDomain::s_instance = NULL;struct CrossDomainImpl : public boost::enable_shared_from_this<CrossDomainImpl>{public:    static const unsigned MaxReadSize = 22;    typedef boost::shared_ptr<CrossDomainImpl> CrossDomainImplPtr;    static CrossDomainImplPtr create(asio::io_service& io_service) {        return CrossDomainImplPtr(new CrossDomainImpl(io_service));    }    tcp::socket& get_socket() {        return m_socket;    }    void start() {        start_read_some();    }    ~CrossDomainImpl() {        close();    }    void close() {        if (m_socket.is_open()) {            m_socket.close();        }    }private:    CrossDomainImpl(asio::io_service& io_service)        : m_socket(io_service)    {    }    void start_read_some() {        m_socket.async_read_some(asio::buffer(m_readbuf, MaxReadSize),            boost::bind(&CrossDomainImpl::handle_read_some, shared_from_this(), asio::placeholders::error()));    }    void handle_read_some(const asio::error_code& err) {        if (!err) {            string str(m_readbuf);            string reply("invalid");            if (str == "<policy-file-request/>") {                reply = "anything you wanna send back to client...";            }            asio::async_write(m_socket, asio::buffer(ref),                    boost::bind(&CrossDomainImpl::handle_write, shared_from_this(), asio::placeholders::error));        }    }    void handle_write(const asio::error_code& error) {        FINE("CrossDomain handle_write, gonna close");        close();    }    tcp::socket m_socket;    char m_readbuf[MaxReadSize];};struct CrossDomain::Server{private:    CrossDomain *m_facade;    tcp::acceptor m_acceptor;    bool m_listened;    string m_local_port;public:    Server(asio::io_service& io_service, const string &local_port)        : m_acceptor(io_service)        , m_listened(false)        , m_local_port(local_port)    {        // intend to leave it blank    }    ~Server() {        if (m_acceptor.is_open()) {            INFO("close server acceptor");            m_acceptor.close();        }    }    void start_server() {        FINE("CrossDomain start_server....");        if (!m_listened) {            FINE("Try to listen...");            try {                tcp::endpoint ep(tcp::endpoint(tcp::v4(), atoi(m_local_port.c_str())));                m_acceptor.open(ep.protocol());                m_acceptor.bind(ep);                m_acceptor.listen();            } catch (const asio::system_error& ec) {                WARN("Port %s already in use! Fail to listen...", STR(m_local_port));                return;            } catch (...) {                WARN("Unknown error while trying to listen...");                return;            }            m_listened = true;            FINE("Listen port %s succesfully!", STR(m_local_port));        }        CrossDomainImpl::CrossDomainImplPtr new_server_impl = CrossDomainImpl::create(m_acceptor.get_io_service());        m_acceptor.async_accept(new_server_impl->get_socket(),            boost::bind(&Server::handle_accept, this, new_server_impl, asio::placeholders::error));    }private:    void handle_accept(CrossDomainImpl::CrossDomainImplPtr pserver_impl, const asio::error_code& err) {        FINE("CrossDomain handle_accpet....");        if (!err) {            FINE("CrossDomain everything ok, start...");            pserver_impl->start();    // start this server            start_server();           // waiting for another Tuna Connection        } else {            pserver_impl->close();        }    }};CrossDomain::CrossDomain(asio::io_service &io_service, const std::string &local_port)    : m_pserver(new Server(io_service, local_port)){}CrossDomain *CrossDomain::instance(){    if (!s_instance) {        return NULL;    }    return s_instance;}void CrossDomain::start_server(){    m_pserver->start_server();}3. 使用asio的陷阱上边代码其实有几点漏洞：3.1 std::vector<uint_8>不适合作为buffervector<uint8_t>不适合做buffer的原因是，sgi的内存分配器会以2倍的形式增长vector的内存，例如这个buffer要求100K，但当前vector的capability只有90K，那么sgi默认内存分配器会将vector的capability增长到180K。注意capability与size的区别。这就导致vector的内存占用依赖最大buffer的size，这是很危险的。推荐使用boost的circular_buffer作为buffer，能有效避免内存碎片、隐式内存泄露等问题。3.2 asio::const_buffer拷贝构造函数没有深拷贝const_buffer系列静态buffer只能从mutable_buffermerge过来，但是从const_buffer的拷贝构造函数源码能看到，他并不对buffer做深拷贝。所以试图将其放到队列或者容器中，期待产生buffer的拷贝，是错误的。3.3. async_write可能会拆包发送例如先调用async_write发送一个100K的大包，再马上调用async_write发送一个8字节的ping包，非常可能出现问题。async_write函数的实现是循环调用async_write_some，对于大包会将其拆分成几个小报文。如果此时收到用户一个新的async_write调用，非常可能将小包夹在大包的几个部分中间发送，导致接收端出现异常。解决的办法可以直接操作async_write_some，代替async_write。但更方便的办法是创建一个发送队列。实际上asio会准确地将发送成功的通知发送给用户，例如刚刚100K的打包，直到所有100K全部发送完成，才会调用handle回调。因此可以在发送时将报文入队列，回调函数里将报文出队列，发送下一个小报时判断队列是否为空，如果非空说明100K的包还没有发完。示例代码如下：///发送时入队列void TcpConnection::send(const void* data, uint32_t length){    if (!m_stopped) {        if (length <= MAX_BUFFER_SIZE) {            const char* begin = (const char*)data;            vector<char> vec(begin, begin + length);            bool isLastComplete = m_bufQueue.empty();            m_bufQueue.push_back(vec);            /// 如果没有残余的包，就直接发送            if (isLastComplete) {                vector<char>& b(m_bufQueue.front());                send(b);            }        } else {            onCommonError(S_ERROR, "too big length to call send");        }    } else {        onCommonError(S_ERROR, "illegal to call send while tcp is not connected");    }}void TcpConnection::send(const std::vector<char>& vec){    if (!m_stopped) {        asio::async_write(m_socket, asio::buffer(&vec[0], vec.size()), asio::transfer_all(),                           boost::bind(&TcpConnection::handleSend, shared_from_this(), asio::placeholders::error));    } else {        onCommonError(S_ERROR, "illegal to call send while tcp is not connected");    }}///回调函数将之前的buffer出队列，同时检查是否有后来的包void TcpConnection::handleSend(const asio::error_code &e){    if (!m_stopped) {        if (!e) {            m_bufQueue.pop_front();            if (!m_bufQueue.empty()) {                std::vector<char>& b(m_bufQueue.front());                send(b);            }            //onSendSuccess();        } else if (isConnected()){            onSendFailure(e);        }    } else {        INFO("%s %s %u user's canceled by stop()", STR(m_name), STR(m_ip), m_port);    }}