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Boost.Asio C++ 网络编程之十:基于TCP的异步服务端

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       这个流程图是相当复杂的:从Boost.Asio出来你可以看到4个箭头指向on_accept,on_read,on_write和on_check_ping。这也就意味着你永远不知道哪个异步调用是下一个完成的调用,但是你可以确定的是它是这4个操作中的一个。

基于TCP的异步服务端

1.流程图

2.实现

#ifdef WIN32
#define _WIN32_WINNT 0x0501
#include <stdio.h>
#endif
#include <iostream> 
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
using namespace boost::asio;
using namespace boost::posix_time;
io_service service;

class talk_to_client;
typedef boost::shared_ptr<talk_to_client> client_ptr;
typedef std::vector<client_ptr> array;
array clients;

#define MEM_FN(x)       boost::bind(&self_type::x, shared_from_this())
#define MEM_FN1(x,y)    boost::bind(&self_type::x, shared_from_this(),y)
#define MEM_FN2(x,y,z)  boost::bind(&self_type::x, shared_from_this(),y,z)

void update_clients_changed();

/** simple connection to server:
- logs in just with username (no password)
- all connections are initiated by the client: client asks, server answers
- server disconnects any client that hasn't pinged for 5 seconds

Possible client requests:
- gets a list of all connected clients
- ping: the server answers either with "ping ok" or "ping client_list_changed"
*/
class talk_to_client : public boost::enable_shared_from_this<talk_to_client>
    , boost::noncopyable {
    typedef talk_to_client self_type;
    talk_to_client() : sock_(service), started_(false),
        timer_(service), clients_changed_(false) {
    }
public:
    typedef boost::system::error_code error_code;
    typedef boost::shared_ptr<talk_to_client> ptr;

    void start() {
        started_ = true;
        clients.push_back(shared_from_this());
        last_ping = boost::posix_time::microsec_clock::local_time();
        do_read();
    }
    static ptr new_() {
        ptr new_(new talk_to_client);
        return new_;
    }
    void stop() {
        if (!started_) return;
        started_ = false;
        sock_.close();

        ptr self = shared_from_this();
        array::iterator it = std::find(clients.begin(), clients.end(), self);
        clients.erase(it);
        update_clients_changed();
    }
    bool started() const { return started_; }
    ip::tcp::socket & sock() { return sock_; }
    std::string username() const { return username_; }
    void set_clients_changed() { clients_changed_ = true; }
private:
    void on_read(const error_code & err, size_t bytes) {
        if (err) stop();
        if (!started()) return;
        // process the msg
        std::string msg(read_buffer_, bytes);
        if (msg.find("login ") == 0) on_login(msg);
        else if (msg.find("ping") == 0) on_ping();
        else if (msg.find("ask_clients") == 0) on_clients();
        else std::cerr << "invalid msg " << msg << std::endl;
    }

    void on_login(const std::string & msg) {
        std::istringstream in(msg);
        in >> username_ >> username_;
        std::cout << username_ << " logged in" << std::endl;
        do_write("login ok\n");
        update_clients_changed();
    }
    void on_ping() {
        do_write(clients_changed_ ? "ping client_list_changed\n" : "ping ok\n");
        clients_changed_ = false;
    }
    void on_clients() {
        std::string msg;
        for (array::const_iterator b = clients.begin(), e = clients.end(); b != e; ++b)
            msg += (*b)->username() + " ";
        do_write("clients " + msg + "\n");
    }

    void do_ping() {
        do_write("ping\n");
    }
    void do_ask_clients() {
        do_write("ask_clients\n");
    }

    void on_check_ping() {
        boost::posix_time::ptime now = boost::posix_time::microsec_clock::local_time();
        if ((now - last_ping).total_milliseconds() > 5000) {
            std::cout << "stopping " << username_ << " - no ping in time" << std::endl;
            stop();
        }
        last_ping = boost::posix_time::microsec_clock::local_time();
    }
    void post_check_ping() {
        timer_.expires_from_now(boost::posix_time::millisec(5000));
        timer_.async_wait(MEM_FN(on_check_ping));
    }

    void on_write(const error_code & err, size_t bytes) {
        do_read();
    }
    void do_read() {
        async_read(sock_, buffer(read_buffer_),
            MEM_FN2(read_complete, _1, _2), MEM_FN2(on_read, _1, _2));
        post_check_ping();
    }
    void do_write(const std::string & msg) {
        if (!started()) return;
        std::copy(msg.begin(), msg.end(), write_buffer_);
        sock_.async_write_some(buffer(write_buffer_, msg.size()),
            MEM_FN2(on_write, _1, _2));
    }
    size_t read_complete(const boost::system::error_code & err, size_t bytes) {
        if (err) return 0;
        bool found = std::find(read_buffer_, read_buffer_ + bytes, '\n') < read_buffer_ + bytes;
        return found ? 0 : 1;
    }
private:
    ip::tcp::socket sock_;
    enum { max_msg = 1024 };
    char read_buffer_[max_msg];
    char write_buffer_[max_msg];
    bool started_;
    std::string username_;
    deadline_timer timer_;
    boost::posix_time::ptime last_ping;
    bool clients_changed_;
};

void update_clients_changed() {
    for (array::iterator b = clients.begin(), e = clients.end(); b != e; ++b)
        (*b)->set_clients_changed();
}

ip::tcp::acceptor acceptor(service, ip::tcp::endpoint(ip::tcp::v4(), 8001));

void handle_accept(talk_to_client::ptr client, const boost::system::error_code & err) {
    client->start();
    talk_to_client::ptr new_client = talk_to_client::new_();
    acceptor.async_accept(new_client->sock(), boost::bind(handle_accept, new_client, _1));
}

int main(int argc, char* argv[]) {
    talk_to_client::ptr client = talk_to_client::new_();
    acceptor.async_accept(client->sock(), boost::bind(handle_accept, client, _1));
    service.run();
}

我们已经学到了怎么写一些基础的客户端/服务端应用。我们已经避免了一些诸如内存泄漏死锁的低级错误。所有的编码都是框架式的,这样你就可以根据你自己的需求对它们进行扩展。