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。