使用套接字的文件传输服务器/客户端

牛枫

2023-03-14

问题内容：

我正在尝试在服务器和客户端之间进行文件传输，但是工作非常糟糕。基本上需要发生的是：
1）客户端将txt文件发送到服务器（我称为“ quotidiani.txt”）
2）服务器将其保存在另一个txt文件中（“ receive.txt”）
3）服务器运行脚本上对其进行修改并以其他名称保存（“ output.txt”）的脚本
。4）服务器将文件发送回客户端，客户端以相同的名称（final.txt）保存文件（在同一套接字上）

问题是读取的第一个文件（quotidiani.txt）只是一小部分，然后出现一些错误。我希望有人能帮助我理解和纠正我的错误。

这是我的代码：

client.c：

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <signal.h>
#include <ctype.h>          
#include <arpa/inet.h>
#include <netdb.h>

#define PORT 20000
#define LENGTH 512


void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
    /* Variable Definition */
    int sockfd; 
    int nsockfd;
    char revbuf[LENGTH]; 
    struct sockaddr_in remote_addr;

    /* Get the Socket file descriptor */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor! (errno = %d)\n",errno);
        exit(1);
    }

    /* Fill the socket address struct */
    remote_addr.sin_family = AF_INET; 
    remote_addr.sin_port = htons(PORT); 
    inet_pton(AF_INET, "127.0.0.1", &remote_addr.sin_addr); 
    bzero(&(remote_addr.sin_zero), 8);

    /* Try to connect the remote */
    if (connect(sockfd, (struct sockaddr *)&remote_addr, sizeof(struct sockaddr)) == -1)
    {
        fprintf(stderr, "ERROR: Failed to connect to the host! (errno = %d)\n",errno);
        exit(1);
    }
    else 
        printf("[Client] Connected to server at port %d...ok!\n", PORT);

    /* Send File to Server */
    //if(!fork())
    //{
        char* fs_name = "/home/aryan/Desktop/quotidiani.txt";
        char sdbuf[LENGTH]; 
        printf("[Client] Sending %s to the Server... ", fs_name);
        FILE *fs = fopen(fs_name, "r");
        if(fs == NULL)
        {
            printf("ERROR: File %s not found.\n", fs_name);
            exit(1);
        }

        bzero(sdbuf, LENGTH); 
        int fs_block_sz; 
        while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs)) > 0)
        {
            if(send(sockfd, sdbuf, fs_block_sz, 0) < 0)
            {
                fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
                break;
            }
            bzero(sdbuf, LENGTH);
        }
        printf("Ok File %s from Client was Sent!\n", fs_name);
    //}

    /* Receive File from Server */
    printf("[Client] Receiveing file from Server and saving it as final.txt...");
    char* fr_name = "/home/aryan/Desktop/progetto/final.txt";
    FILE *fr = fopen(fr_name, "a");
    if(fr == NULL)
        printf("File %s Cannot be opened.\n", fr_name);
    else
    {
        bzero(revbuf, LENGTH); 
        int fr_block_sz = 0;
        while((fr_block_sz = recv(sockfd, revbuf, LENGTH, 0)) > 0)
        {
            int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
            if(write_sz < fr_block_sz)
            {
                error("File write failed.\n");
            }
            bzero(revbuf, LENGTH);
            if (fr_block_sz == 0 || fr_block_sz != 512) 
            {
                break;
            }
        }
        if(fr_block_sz < 0)
        {
            if (errno == EAGAIN)
            {
                printf("recv() timed out.\n");
            }
            else
            {
                fprintf(stderr, "recv() failed due to errno = %d\n", errno);
            }
        }
        printf("Ok received from server!\n");
        fclose(fr);
    }
    close (sockfd);
    printf("[Client] Connection lost.\n");
    return (0);
}

服务器

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <signal.h>
#include <ctype.h>          
#include <arpa/inet.h>
#include <netdb.h>

#define PORT 20000 
#define BACKLOG 5
#define LENGTH 512

void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main ()
{
    /* Defining Variables */
    int sockfd; 
    int nsockfd; 
    int num;
    int sin_size; 
    struct sockaddr_in addr_local; /* client addr */
    struct sockaddr_in addr_remote; /* server addr */
    char revbuf[LENGTH]; // Receiver buffer

    /* Get the Socket file descriptor */
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1 )
    {
        fprintf(stderr, "ERROR: Failed to obtain Socket Descriptor. (errno = %d)\n", errno);
        exit(1);
    }
    else 
        printf("[Server] Obtaining socket descriptor successfully.\n");

    /* Fill the client socket address struct */
    addr_local.sin_family = AF_INET; // Protocol Family
    addr_local.sin_port = htons(PORT); // Port number
    addr_local.sin_addr.s_addr = INADDR_ANY; // AutoFill local address
    bzero(&(addr_local.sin_zero), 8); // Flush the rest of struct

    /* Bind a special Port */
    if( bind(sockfd, (struct sockaddr*)&addr_local, sizeof(struct sockaddr)) == -1 )
    {
        fprintf(stderr, "ERROR: Failed to bind Port. (errno = %d)\n", errno);
        exit(1);
    }
    else 
        printf("[Server] Binded tcp port %d in addr 127.0.0.1 sucessfully.\n",PORT);

    /* Listen remote connect/calling */
    if(listen(sockfd,BACKLOG) == -1)
    {
        fprintf(stderr, "ERROR: Failed to listen Port. (errno = %d)\n", errno);
        exit(1);
    }
    else
        printf ("[Server] Listening the port %d successfully.\n", PORT);

    int success = 0;
    while(success == 0)
    {
        sin_size = sizeof(struct sockaddr_in);

        /* Wait a connection, and obtain a new socket file despriptor for single connection */
        if ((nsockfd = accept(sockfd, (struct sockaddr *)&addr_remote, &sin_size)) == -1) 
        {
            fprintf(stderr, "ERROR: Obtaining new Socket Despcritor. (errno = %d)\n", errno);
            exit(1);
        }
        else 
            printf("[Server] Server has got connected from %s.\n", inet_ntoa(addr_remote.sin_addr));

        /*Receive File from Client */
        char* fr_name = "/home/aryan/Desktop/receive.txt";
        FILE *fr = fopen(fr_name, "a");
        if(fr == NULL)
            printf("File %s Cannot be opened file on server.\n", fr_name);
        else
        {
            bzero(revbuf, LENGTH); 
            int fr_block_sz = 0;
            while((fr_block_sz = recv(nsockfd, revbuf, LENGTH, 0)) > 0) 
            {
                int write_sz = fwrite(revbuf, sizeof(char), fr_block_sz, fr);
                if(write_sz < fr_block_sz)
                {
                    error("File write failed on server.\n");
                }
                bzero(revbuf, LENGTH);
                if (fr_block_sz == 0 || fr_block_sz != 512) 
                {
                    break;
                }
            }
            if(fr_block_sz < 0)
            {
                if (errno == EAGAIN)
                {
                    printf("recv() timed out.\n");
                }
                else
                {
                    fprintf(stderr, "recv() failed due to errno = %d\n", errno);
                    exit(1);
                }
            }
            printf("Ok received from client!\n");
            fclose(fr); 
        }

        /* Call the Script */
        system("cd ; chmod +x script.sh ; ./script.sh");

        /* Send File to Client */
        //if(!fork())
        //{
            char* fs_name = "/home/aryan/Desktop/output.txt";
            char sdbuf[LENGTH]; // Send buffer
            printf("[Server] Sending %s to the Client...", fs_name);
            FILE *fs = fopen(fs_name, "r");
            if(fs == NULL)
            {
                fprintf(stderr, "ERROR: File %s not found on server. (errno = %d)\n", fs_name, errno);
                exit(1);
            }

            bzero(sdbuf, LENGTH); 
            int fs_block_sz; 
            while((fs_block_sz = fread(sdbuf, sizeof(char), LENGTH, fs))>0)
            {
                if(send(nsockfd, sdbuf, fs_block_sz, 0) < 0)
                {
                    fprintf(stderr, "ERROR: Failed to send file %s. (errno = %d)\n", fs_name, errno);
                    exit(1);
                }
                bzero(sdbuf, LENGTH);
            }
            printf("Ok sent to client!\n");
            success = 1;
            close(nsockfd);
            printf("[Server] Connection with Client closed. Server will wait now...\n");
            while(waitpid(-1, NULL, WNOHANG) > 0);
        //}
    }
}

问题答案：

一些注释没有特定的顺序：

您浪费了太多机会去了解确切的错误：
```
if(listen(sockfd,BACKLOG) == -1)
```
{
printf(“ERROR: Failed to listen Port %d.\n”, PORT);
return (0);
}

此块绝对应包含a
perror("listen")或类似名称。当错误详细信息将通过进行报告时，始终包含perror()或包含strerror()在每个错误处理块中errno。具有确切的故障原因将为您节省编程时间，并且在事情将来无法按预期运行时为您和您的用户节省时间。

您的错误处理需要进一步标准化：
```
if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1 )
```
{
printf(“ERROR: Failed to obtain Socket Descriptor.\n”);
return (0);
}

这应该不是 return 0，因为这将标志着该外壳的程序运行完成没有错误。您应该return 1（或使用EXIT_SUCCESS和EXIT_FAILURE）发出异常退出信号。

     else 
    printf("[Server] Server has got connected from %s.\n", inet_ntoa(addr_remote.sin_addr));

 /*Receive File from Client */

在前面的代码块中，您遇到了错误情况，但仍然继续执行。这是获得非常不良行为的快速方法。这应该重新启动主服务器循环或退出子进程或类似的过程。（取决于您是否保留多进程服务器。）

    if(!fork())
{

前面的代码块忘记了fork() 失败的原因 。fork()会并且确实会失败-尤其是在大学中常见的共享托管环境中-
因此您应该为来自失败，孩子，父母的完整而复杂的三个可能的返回值做好准备fork()。

看来您正在fork()不加选择地使用；您的客户端和服务器都非常简单，它们的运行方式意味着不能同时为多个客户端提供服务。您可能应该严格遵循每个流程，至少要等到算法完全调试好并找出某种方式同时运行多个客户端为止。我希望这是您现在遇到的问题的根源。
您需要使用函数来封装细节。编写一个函数以连接到服务器，编写一个函数以发送文件，编写一个函数以写入文件，等等。编写一个函数以处理复杂的部分写入。（我特别建议writen从Unix环境书的源代码中的 “ 高级编程”中窃取该功能。文件lib/writen.c。）如果正确编写了这些功能，则可以在客户端和服务器中重新使用它们。（有点像将它们放入utils.c并像那样编译程序gcc -o server server.c utils.c。）

具有较小的功能，每个功能都可以做一件事情，这样您就可以一次专注于少量的代码，并为每个功能编写很少的测试，这将帮助您缩小仍需要改进的代码部分的范围。

使用套接字的文件传输服务器/客户端

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