boost asio 学习(八) 网络基础二进制写发送和接收

http://www.gamedev.net/blog/950/entry-2249317-a-guide-to-getting-
started-with-boostasio?pg=9

8. Networking basics: binary protocol sending and receiving (TCP)

现在我们了解了boost::asio库和一些简单的tcp网络知识。现在进行一些简单的网路底层封装.通过使用这些分装。我们能重复使用并且将
注意力集中在程序逻辑而不是一再编写网络通讯代码。
重要注意事项:代码完全是出于教育目的。不要在商业系统中使用。
另外使用这个网络封装代码的开销是需要考虑的。比如说，大量的vector与list的分配。bind与shared_ptr指针的开销。这也是这个代码
仅用来作为教育用途的原因。

有多重类型的函数用来发送和接收。我们基于协议选择不同的类型。
我们的例子中使用async_write and async_read_some.
使用async_write的原因是函数写入所有的数据，而无需担心部分发送的问题。同样的，我们使用async_read_some作为通用函数去读取数
据因为我们没有特定的协议用来接收。

现在我们学习一个完整的使用IO函数的例子。我们扩展7-C的例子。

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#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <boost/lexical_cast.hpp>
#include <boost/cstdint.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <iostream>
#include <string>
 
boost::mutex global_stream_lock;
 
void WorkerThread( boost::shared_ptr< boost::asio::io_service > io_service )
{
    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] Thread Start" << std::endl;
    global_stream_lock.unlock();
 
    while( true )
    {
        try
        {
            boost::system::error_code ec;
            io_service->run( ec );
            if( ec )
            {
                global_stream_lock.lock();
                std::cout << "[" << boost::this_thread::get_id()
                    << "] Error: " << ec << std::endl;
                global_stream_lock.unlock();
            }
            break;
        }
        catch( std::exception & ex )
        {
            global_stream_lock.lock();
            std::cout << "[" << boost::this_thread::get_id()
                << "] Exception: " << ex.what() << std::endl;
            global_stream_lock.unlock();
        }
    }
 
    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] Thread Finish" << std::endl;
    global_stream_lock.unlock();
}
 
struct ClientContext : public boost::enable_shared_from_this< ClientContext >
{
    boost::asio::ip::tcp::socket m_socket;
     
    std::vector< boost::uint8_t > m_recv_buffer;
    size_t m_recv_buffer_index;
 
    std::list< std::vector< boost::uint8_t > > m_send_buffer;
 
    ClientContext( boost::asio::io_service & io_service )
        : m_socket( io_service ), m_recv_buffer_index( 0 )
    {
        m_recv_buffer.resize( 4096 );
    }
 
    ~ClientContext()
    {
    }
 
    void Close()
    {
        boost::system::error_code ec;
        m_socket.shutdown( boost::asio::ip::tcp::socket::shutdown_both, ec );
        m_socket.close( ec );
    }
 
    void OnSend( const boost::system::error_code & ec, std::list< std::vector< boost::uint8_t > >::iterator itr )
    {
        if( ec )
        {
            global_stream_lock.lock();
            std::cout << "[" << boost::this_thread::get_id()
                << "] Error: " << ec << std::endl;
            global_stream_lock.unlock();
 
            Close();
        }
        else
        {
            global_stream_lock.lock();
            std::cout << "[" << boost::this_thread::get_id()
                << "] Sent " << (*itr).size() << " bytes." << std::endl;
            global_stream_lock.unlock();
        }
        m_send_buffer.erase( itr );
 
        // Start the next pending send
        if( !m_send_buffer.empty() )
        {
            boost::asio::async_write( 
                m_socket, 
                boost::asio::buffer( m_send_buffer.front() ), 
                boost::bind( 
                    &ClientContext::OnSend, 
                    shared_from_this(), 
                    boost::asio::placeholders::error, 
                    m_send_buffer.begin()
                )
            );
        }
    }
 
    void Send( const void * buffer, size_t length )
    {
        bool can_send_now = false;
 
        std::vector< boost::uint8_t > output;
        std::copy( (const boost::uint8_t *)buffer, (const boost::uint8_t *)buffer + length, std::back_inserter( 
 
output ) );
 
        // Store if this is the only current send or not
        can_send_now = m_send_buffer.empty();
 
        // Save the buffer to be sent
        m_send_buffer.push_back( output );
 
        // Only send if there are no more pending buffers waiting!
        if( can_send_now )
        {
            // Start the next pending send
            boost::asio::async_write( 
                m_socket, 
                boost::asio::buffer( m_send_buffer.front() ), 
                boost::bind( 
                    &ClientContext::OnSend, 
                    shared_from_this(), 
                    boost::asio::placeholders::error, 
                    m_send_buffer.begin()
                )
            );
        }
    }
 
    void OnRecv( const boost::system::error_code & ec, size_t bytes_transferred )
    {
        if( ec )
        {
            global_stream_lock.lock();
            std::cout << "[" << boost::this_thread::get_id()
                << "] Error: " << ec << std::endl;
            global_stream_lock.unlock();
 
            Close();
        }
        else
        {
            // Increase how many bytes we have saved up
            m_recv_buffer_index += bytes_transferred;
 
            // Debug information
            global_stream_lock.lock();
            std::cout << "[" << boost::this_thread::get_id()
                << "] Recv " << bytes_transferred << " bytes." << std::endl;
            global_stream_lock.unlock();
 
            // Dump all the data
            global_stream_lock.lock();
            for( size_t x = 0; x < m_recv_buffer_index; ++x )
            {
                std::cout << std::hex << std::setfill( '0' ) << 
                    std::setw( 2 ) << (int)m_recv_buffer[ x ] << " ";
                if( ( x + 1 ) % 16 == 0 )
                {
                    std::cout << std::endl;
                }
            }
            std::cout << std::endl << std::dec;
            global_stream_lock.unlock();
 
            // Discard all the data (virtually, not physically!)
            m_recv_buffer_index = 0;
 
            // Start the next recv cycle
            Recv();
        }
    }
 
    void Recv()
    {
        m_socket.async_read_some( 
            boost::asio::buffer( 
                &m_recv_buffer[ m_recv_buffer_index ], 
                m_recv_buffer.size() - m_recv_buffer_index ), 
            boost::bind( &ClientContext::OnRecv, shared_from_this(), _1, _2 )
        );
    }
};
 
void OnAccept( const boost::system::error_code & ec, boost::shared_ptr< ClientContext > client )
{
    if( ec )
    {
        global_stream_lock.lock();
        std::cout << "[" << boost::this_thread::get_id()
            << "] Error: " << ec << std::endl;
        global_stream_lock.unlock();
    }
    else
    {
        global_stream_lock.lock();
        std::cout << "[" << boost::this_thread::get_id()
            << "] Accepted!" << std::endl;
        global_stream_lock.unlock();
 
        // 2 bytes message size, followed by the message
        client->Send( "\x02\x00Hi", 6 );
        client->Recv();
    }
}
 
int main( int argc, char * argv[] )
{
    boost::shared_ptr< boost::asio::io_service > io_service(
        new boost::asio::io_service
        );
    boost::shared_ptr< boost::asio::io_service::work > work(
        new boost::asio::io_service::work( *io_service )
        );
    boost::shared_ptr< boost::asio::io_service::strand > strand(
        new boost::asio::io_service::strand( *io_service )
        );
 
    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] Press [return] to exit." << std::endl;
    global_stream_lock.unlock();
 
    // 1 worker thread so we do not have to deal with thread safety issues
    boost::thread_group worker_threads;
    for( int x = 0; x < 1; ++x )
    {
        worker_threads.create_thread( boost::bind( &WorkerThread, io_service ) );
    }
 
    boost::shared_ptr< boost::asio::ip::tcp::acceptor > acceptor(
        new boost::asio::ip::tcp::acceptor( *io_service )
        );
    boost::shared_ptr< ClientContext > client(
        new ClientContext( *io_service )
        );
 
    try
    {
        boost::asio::ip::tcp::resolver resolver( *io_service );
        boost::asio::ip::tcp::resolver::query query( 
            "127.0.0.1", 
            boost::lexical_cast< std::string >( 7777 )
            );
        boost::asio::ip::tcp::endpoint endpoint = *resolver.resolve( query );
        acceptor->open( endpoint.protocol() );
        acceptor->set_option( boost::asio::ip::tcp::acceptor::reuse_address( false ) );
        acceptor->bind( endpoint );
        acceptor->listen( boost::asio::socket_base::max_connections );
        acceptor->async_accept( client->m_socket, boost::bind( OnAccept, _1, client ) );
 
        global_stream_lock.lock();
        std::cout << "Listening on: " << endpoint << std::endl;
        global_stream_lock.unlock();
    }
    catch( std::exception & ex )
    {
        global_stream_lock.lock();
        std::cout << "[" << boost::this_thread::get_id()
            << "] Exception: " << ex.what() << std::endl;
        global_stream_lock.unlock();
    }
 
    std::cin.get();
 
    boost::system::error_code ec;
    acceptor->close( ec );
 
    io_service->stop();
 
    worker_threads.join_all();
 
    return 0;
}

这个例子中，我们添加了ClientContext 类。它用来存储所有传入连接的上下文的具体结构。类封装了必须的io接收发送的函数。例子中
，服务器将发送一个具体的信息给传入连接。我们没配置一个具体的客户端去测试，仅仅使用简单的telnet即可。任意数据发送到服务器
将被输出到命令行。
同上一个例子不同的是，每个连接都需要自己的上下文。上下文应包含socket 发送接收缓存以及其他用户数据。另外，例子不是线程安装
的，所以我们限制在一个线程运行。我们将稍后讨论这个问题。现在，对于socket的读写将选择正确的api函数以避免发生问题.

为了正确的使用，我们必须确认上下文和缓存在函数的生存的整个期间都是有效的。这个例子中，我们使用一个vector list来发送，使用一个vector来接收缓存。根据我们实现的协议，我们可能需要做一些小小的改动。比如说，如果我们想处理流中的包。这种情况下，我们将希望使用async_read读取头结构然后使用async_read读取具体尺寸的数据。

在大型程序中，一次只处理一个包的缺点就是效率低下。假设我们有1003字节信息在流中。我们将执行读取包这个逻辑100次。而我们使用async_read_some，效率会更高。