server_for_send.cpp

 #include <errno.h>  
#include <sys/types.h>  
#include <sys/socket.h>  
#include <netinet/in.h>  
#include <unistd.h>
#include <arpa/inet.h>
#include <bits/stdc++.h>  
   
#define LENGTH_OF_LISTEN_QUEUE     20    
#define BUFFER_SIZE                1024    
#define FILE_NAME_MAX_SIZE         512    

int main(int argc, char **argv)    
{    
    // 设置一个socket地址结构server_addr,代表服务器internet的地址和端口
    struct sockaddr_in   server_addr;
    bzero(&server_addr, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = htons(INADDR_ANY);
    //如果输入方法不对，则进行提示
    if( argc != 2){
        printf("usage: ./server_for_send <port>\n");
        exit(0);
    }
    //设置端口
    int port=atoi(argv[1]);
    server_addr.sin_port = htons(port);
    
    // create a stream socket
    // 创建用于internet的流协议(TCP)socket，用server_socket代表服务器向客户端提供服务的接口
    int server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket < 0)
    {
        printf("Create Socket Failed!\n");
        exit(1);
    }
    
    // 把socket和socket地址结构绑定
    if (bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)))
    {
        printf("Server Bind Port Failed!\n");
        exit(1);
    }
    
    // server_socket用于监听
    if (listen(server_socket, LENGTH_OF_LISTEN_QUEUE))
    {
        printf("Server Listen Failed!\n");
        exit(1);
    }
    
    // 服务器端一直运行用以持续为客户端提供服务
    while(1)
    {
        // 定义客户端的socket地址结构client_addr，当收到来自客户端的请求后，调用accept
        // 接受此请求，同时将client端的地址和端口等信息写入client_addr中
        struct sockaddr_in client_addr;
        socklen_t          length = sizeof(client_addr);

        // 接受一个从client端到达server端的连接请求,将客户端的信息保存在client_addr中
        // 如果没有连接请求，则一直等待直到有连接请求为止，这是accept函数的特性，可以
        // 用select()来实现超时检测
        // accpet返回一个新的socket,这个socket用来与此次连接到server的client进行通信
        // 这里的new_server_socket代表了这个通信通道
        int new_server_socket = accept(server_socket, (struct sockaddr*)&client_addr, &length);
        if (new_server_socket < 0)
        {
            printf("Server Accept Failed!\n");
            break;
        }
        //定义buffer
        char buffer[BUFFER_SIZE];
        bzero(buffer, sizeof(buffer));
        length = recv(new_server_socket, buffer, BUFFER_SIZE, 0);
        if (length < 0)
        {
            printf("Server Recieve Data Failed!\n");
            break;
        }

        char file_name[FILE_NAME_MAX_SIZE + 1];
        bzero(file_name, sizeof(file_name));
        strncpy(file_name, buffer,
                strlen(buffer) > FILE_NAME_MAX_SIZE ? FILE_NAME_MAX_SIZE : strlen(buffer));
        //读取文件
        FILE *fp = fopen(file_name, "rb");
        if (fp == NULL)
        {   //如果读取失败，则提示
            printf("File:\t%s Not Found!\n", file_name);
        }
        else
        {
            //发送数据
            bzero(buffer, BUFFER_SIZE);
            int file_block_length = 0;
            while( (file_block_length = fread(buffer, sizeof(char), BUFFER_SIZE, fp)) > 0)
            {
                printf("file_block_length = %d\n", file_block_length);

                // 发送buffer中的字符串到new_server_socket,实际上就是发送给客户端
                if (send(new_server_socket, buffer, file_block_length, 0) < 0)
                {
                    printf("Send File:\t%s Failed!\n", file_name);
                    break;
                }
                //清空buffer
                bzero(buffer, sizeof(buffer));
            }
            fclose(fp);
            printf("File:\t%s Transfer Finished!\n", file_name);
        }

        close(new_server_socket);
    }
    
    close(server_socket);
    
    return 0;
}