C++ Socket发送大消息未完成：仅发143080字节后失败

我编写了一个C++函数send_full_msg，尝试发送205453字节的消息，但该函数仅发送143080字节后，send()调用连续多次返回-1，最终触发超时退出。Python测试客户端通过循环接收，仅收到143080字节，无法获取完整消息。尝试禁用Socket发送超时、调整发送块大小（8000/16000字节）均未解决问题；且无论消息大小如何（如207801字节），始终仅能发送143080字节。相关代码、运行日志及函数调用方式如下：

禁用超时代码 #

setsockopt(sock_fd, SOL_SOCKET,SO_SNDTIMEO,(const char*)&time_val_struct,sizeof(time_val_struct));

C++发送函数 #

size_t network::send_full_msg(int sock_fd, char *write_buf, size_t write_buf_length, std::chrono::microseconds timeout)
{
    debug_log log("network_interface", "send_full_msg");
    try{

        log.msg("Preparing to send an entire message through. msg size is...." + to_string(write_buf_length));

        const size_t chunk_size = 16000;        //每次发送16000字节
        fcntl(sock_fd, F_SETFL, O_NONBLOCK); //设置socket为非阻塞模式

        log.msg("Set socket non blocking..." + to_string(write_buf_length));

        struct timeval time_val_struct;
        time_val_struct.tv_sec = 0;
        time_val_struct.tv_usec = 0;
        setsockopt(sock_fd, SOL_SOCKET,SO_SNDTIMEO,(const char*)&time_val_struct,sizeof(time_val_struct));
        log.msg("Turned off socket timeout..." + to_string(write_buf_length));


        size_t pos_in_buf = 0; //起始位置，每次发送后递增
        ssize_t size_sent = 0; //send调用返回的发送字节数

        int num_neg_count=0;
        auto start_time = chrono::high_resolution_clock::now();

        while (pos_in_buf < write_buf_length)
        {
            auto current_time = chrono::high_resolution_clock::now();
            auto duration = chrono::duration_cast<chrono::microseconds>(current_time - start_time);

            if (duration > timeout || num_neg_count>3) //超时或连续3次发送失败则退出
            {
                log.msg("Timeout exceeded");
                break;
            }

            size_t remaining_buf_size = write_buf_length - pos_in_buf; //剩余待发送字节数
            size_t bytes_to_write = remaining_buf_size > chunk_size ? chunk_size : remaining_buf_size; //本次要发送的字节数
            size_sent = send(sock_fd, write_buf+pos_in_buf, bytes_to_write, 0);

            log.msg("Sent bytes..." + to_string(size_sent));
            log.msg("Pos in buf..." + to_string(pos_in_buf));
            log.msg("Bytes to write..." + to_string(bytes_to_write));
            
            if (size_sent < 0)
            {
                num_neg_count++; //连续失败计数加1
                this_thread::sleep_for(chrono::microseconds(100)); //等待100微秒后重试
                continue;
            }else{
                num_neg_count = 0; //重置失败计数
                pos_in_buf += size_sent;
            }
            
        }

        log.msg("Total data length sent was: " + to_string(pos_in_buf));
        if(pos_in_buf == 0)
            return -1; //无数据发送，返回错误

        return pos_in_buf; //返回实际发送的总字节数
    }catch(exception &e){
        cout << " Exception in network socket " << e.what() << endl;
        return -1;
    }
}

运行日志 #

[ network_interface/send_full_msg ] Preparing to send an entire message through. msg size is....205453
[ network_interface/send_full_msg ] Set socket non blocking...205453
[ network_interface/send_full_msg ] Turned off socket timeout
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...0
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...16000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...32000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...48000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...64000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...80000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...96000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...16000
[ network_interface/send_full_msg ] Pos in buf...112000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...15080
[ network_interface/send_full_msg ] Pos in buf...128000
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...-1
[ network_interface/send_full_msg ] Pos in buf...143080
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...-1
[ network_interface/send_full_msg ] Pos in buf...143080
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...-1
[ network_interface/send_full_msg ] Pos in buf...143080
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Sent bytes...-1
[ network_interface/send_full_msg ] Pos in buf...143080
[ network_interface/send_full_msg ] Bytes to write...16000
[ network_interface/send_full_msg ] Timeout exceeded
[ network_interface/send_full_msg ] Total data length sent was: 143080

函数调用方式 #

send_full_msg(client_fd, const_char<char*>(response.c_str()), response.length(), chrono::microseconds((int)5e6);

内容的提问来源于stack exchange，提问作者Dwight Kulkarni