c++ - 简单的客户端/服务器在传输中丢失线路 (boost/Windows)

Question

第一个环境数据:Windows 7, c:\boost (1.55.0), Microsoft Visual C++ 2010 Express (SP1)

这是您能想到的最简单的客户端/服务器功能版本，使用换行结束行作为传输方式(请忽略缺少限制和超时!)

服务器等待客户端发送"f\n"，然后将本地文本文件中修剪过的行发回给客户端。最后一行仅包含一个点 (.)，表示传输结束(忽略文件中可以有一个点的事实。)

问题是什么？

服务器上的输出显示所有线路都被发送回客户端。然而，客户端显示缺少一些行。

我看不出传输丢失数据的可能性在哪里。

这是功能齐全的服务器代码。构建它，并在没有参数的情况下在服务器上运行。

#define _CRT_SECURE_NO_WARNINGS

#include "stdafx.h"
#include <iostream>
#include <boost/asio.hpp>

void writeln( boost::asio::ip::tcp::socket& socket, const std::string& text )
{
    std::cout << "writeln " << text << "\n" ;
    boost::system::error_code error ;
    boost::asio::write( socket, boost::asio::buffer( text + "\n", text.length() + 1 ), boost::asio::transfer_all(), error );
}

bool readln( boost::asio::ip::tcp::socket& socket, std::string& text )
{
    try
    {
        boost::asio::streambuf response ;
        boost::asio::read_until( socket, response, "\n" ) ;

        std::istream response_stream( &response ) ;
        std::getline( response_stream, text ) ;

        if ( text != "." )
            return true ;
    }
    catch( const std::exception& e )
    {
        std::cerr << e.what() << "\n" ;
    }

    return false ;
}

static char* trim( char* line )
{
    size_t len = strlen( line ) ;

    while ( len > 0 && ( line[ len - 1 ] == ' ' || line[ len - 1 ] == '\t' || line[ len - 1 ] == '\n' || line[ len - 1 ] == '\r' ))
        len-- ;

    line[ len ] = 0 ;

    return line ;
}

static void f( boost::asio::ip::tcp::socket& socket )
{
    std::string fname = "c:\\f.txt" ;
    FILE* f = fopen( fname.c_str(), "r" ) ;
    if ( f != NULL )
    {
        char line[ 1024 ] ;

        while ( fgets( line, sizeof( line ), f ) != NULL )
            writeln( socket, trim( line )) ;

        fclose( f ) ;
    }
}

int main( int argc, char* argv[])
{
    try
    {
        boost::asio::io_service        io_service ;
        boost::asio::ip::tcp::acceptor acceptor( io_service, boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), 8080 )) ;

        for (;;)
        {
            boost::asio::ip::tcp::socket socket( io_service ) ;
            std::string                  cmd ;

            acceptor.accept( socket ) ;
            while ( readln( socket, cmd ))
            {
                std::cout << cmd << "\n" ;
                if ( cmd == "f" )
                    f( socket ) ;

                writeln( socket, "." ) ;
            }
        }
    }
    catch( const std::exception& e )
    {
        std::cerr << e.what() << "\n" ;
    }

    return 0 ;
}

这是客户端的代码。调用 prog 127.0.0.1 f 查看结果。

#include "stdafx.h"
#include <boost/asio.hpp>
#include <iostream>

void writeln( boost::asio::ip::tcp::socket& socket, const std::string& text )
{
    boost::system::error_code error ;
    boost::asio::write( socket, boost::asio::buffer( text + "\n", text.length() + 1 ), boost::asio::transfer_all(), error );
}

bool readln( boost::asio::ip::tcp::socket& socket, std::string& text )
{
    try
    {
        boost::asio::streambuf response ;
        boost::asio::read_until( socket, response, "\n" ) ;
        std::istream response_stream( &response ) ;
        std::getline( response_stream, text ) ;
        std::cout << "readln " << text << "\n" ;
        if ( text != "." )
            return true ;
    }
    catch( const std::exception& e )
    {
        std::cerr << e.what() << "\n" ;
    }

    return false ;
}

int main( int argc, char* argv[])
{
    if ( argc > 2 )
        try
        {
            boost::asio::io_service      io_service ;
            boost::asio::ip::tcp::socket socket( io_service ) ;
            std::string                  text ;

            socket.connect( boost::asio::ip::tcp::endpoint( boost::asio::ip::address::from_string( argv[ 1 ]), 8080 )) ;

            writeln( socket, argv[ 2 ]) ;

            while ( readln( socket, text ))
                std::cout << text << "\n" ;

            return 0 ;
        }
        catch( const std::exception& e )
        {
            std::cerr << e.what() << "\n" ;
            return 1 ;
        }
}

Answer 1

客户端版本的bool readln( boost::asio::ip::tcp::socket& socket, std::string& text ) 函数不正确。使用缓冲的 io，吃得比应该吃的多。

这不是最好的版本，而是代替客户当前的代码:

    while ( readln( socket, text ))
        std::cout << text << "\n" ;

它可以做到:

    boost::asio::streambuf response ;

    for(;;)
    {
        boost::asio::read_until( socket, response, "\n" ) ;
        std::istream response_stream( &response ) ;
        std::getline( response_stream, text ) ;
        if ( text == "." )
            break ;
        std::cout << text << "\n" ;
    }