在Linux上使用TCP進行文件傳輸

Question

我在Linux上嘗試TCP文件傳輸。 建立連接后，服務器應將“send.txt”發送給客戶端，客戶端接收該文件並將其保存為“receive.txt”。 然后連接中斷。

正確的輸入和輸出應該是：

服務器終端：

$./server &
[server] obtain socket descriptor successfully.
[server] bind tcp port 5000 in addr 0.0.0.0 successfully.
[server] listening the port 5000 successfully.
[server] server has got connect from 127.0.0.1.
[server] send send.txt to the client…ok!
[server] connection closed.

客戶終端：

$./client 
[client] connected to server at port 5000…ok!
[client] receive file sent by server to receive.txt…ok!
[client] connection lost.

服務器和客戶端都應該在進程后退出。

但是我現在得到了什么

$ ./server &
[server] obtain socket descriptor successfully.
[server] bind tcp port 5000 in addr 0.0.0.0 sucessfully.
[server] listening the port 5000 sucessfully.
[server] server has got connect from 127.0.0.1.
[server] send send.txt to the client...ok!
[server] connection closed.

/*Here the server doesn't exit*/

$ ./client
[client] connected to server at port 5000...ok!

/*Here the client doesn't exit*/

此外，生成EMPTY“receive.txt”。

我的代碼首先是為傳輸簡單的字符串而編寫的，並且它正常工作。 所以我猜問題在於文件傳輸部分。

我的代碼如下：

server.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>
#define PORT 5000 // The port which is communicate with server
#define BACKLOG 10
#define LENGTH 512 // Buffer length
int main ()
{
    int sockfd; // Socket file descriptor
    int nsockfd; // New Socket file descriptor
    int num;
    int sin_size; // to store struct size
    struct sockaddr_in addr_local;
    struct sockaddr_in addr_remote;
    /* Get the Socket file descriptor */
    if( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1 )
    {
        printf ("ERROR: Failed to obtain Socket Descriptor.\n");
        return (0);
    }
    else printf ("[server] obtain socket descriptor successfully.\n");
    /* Fill the local 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 )
    {
        printf ("ERROR: Failed to bind Port %d.\n",PORT);
        return (0);
    }
    else printf("[server] bind tcp port %d in addr 0.0.0.0 sucessfully.\n",PORT);
    /* Listen remote connect/calling */
    if(listen(sockfd,BACKLOG) == -1)
    {
        printf ("ERROR: Failed to listen Port %d.\n", PORT);
        return (0);
    }
    else printf ("[server] listening the port %d sucessfully.\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) 
            printf ("ERROR: Obtain new Socket Despcritor error.\n");
        else printf ("[server] server has got connect from %s.\n", inet_ntoa(addr_remote.sin_addr));
        /* Child process */
        if(!fork())
        {
            char* f_name = "send.txt";
            char sdbuf[LENGTH]; // Send buffer
            printf("[server] send %s to the client...", f_name);
            FILE *fp = fopen(f_name, "r");
            if(fp == NULL)
            {
                printf("ERROR: File %s not found.\n", f_name);
                exit(1);
            }
            bzero(sdbuf, LENGTH);
            int f_block_sz;
            while((f_block_sz = fread(sdbuf, sizeof(char), LENGTH, fp))>0)
            {
                if(send(nsockfd, sdbuf, f_block_sz, 0) < 0)
                {
                    printf("ERROR: Failed to send file %s.\n", f_name);
                    break;
                }
                bzero(sdbuf, LENGTH);
            }
            printf("ok!\n");
            success = 1;
            close(nsockfd);
            printf("[server] connection closed.\n");
            while(waitpid(-1, NULL, WNOHANG) > 0);
        }
    }
}

client.c

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#define PORT 5000
#define LENGTH 512 // Buffer length
int main(int argc, char *argv[])
{
    int sockfd; // Socket file descriptor
    char revbuf[LENGTH]; // Receiver buffer
    struct sockaddr_in remote_addr; 
    /* Get the Socket file descriptor */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        printf("ERROR: Failed to obtain Socket Descriptor!\n");
        return (0);
    }
    /* 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)
    {
        printf ("ERROR: Failed to connect to the host!\n");
        return (0);
    }
    else printf("[client] connected to server at port %d...ok!\n", PORT);
    //printf ("OK: Have connected to %s\n",argv[1]);
    printf("[client] receive file sent by server to receive.txt...");
    char* f_name = "receive.txt";
    FILE *fp = fopen(f_name, "a");
    if(fp == NULL) printf("File %s cannot be opened.\n", f_name);
    else
    {
        bzero(revbuf, LENGTH);
        int f_block_sz = 0;
        int success = 0;
        while(success == 0)
        {
            while(f_block_sz = recv(sockfd, revbuf, LENGTH, 0))
            {
                if(f_block_sz < 0)
                {
                    printf("Receive file error.\n");
                    break;
                }
                int write_sz = fwrite(revbuf, sizeof(char), f_block_sz, fp);
                if(write_sz < f_block_sz)
                {
                    printf("File write failed.\n");
                    break;
                }
                bzero(revbuf, LENGTH);
            }
            printf("ok!\n");
            success = 1;
            fclose(fp);
        }
    }
    close (sockfd);
    printf("[client] connection lost.\n");
    return (0);
}

非常感謝你！

Answer 1

您需要將代碼添加到f_block_sz代碼中。 recv()有一些可靠的返回值：

• <0 - 錯誤， errno錯誤號（ errno.h ）
• 0 - 連接已關閉
• >0 - 數據讀取，字節數

你需要處理第二種情況。 添加else案例：

else if(f_block_sz)
{
  break;
}

因此，當服務器關閉連接時，循環將被破壞，並且您的代碼將打印您[client] connection lost並退出。

Answer 2

您還有另一個問題，即您的服務器程序是多進程的，並且每次獲取傳入連接時都會分叉。 父級保持活動狀態以接受新連接，子級處理連接。 子進程的退出不足以導致父進程退出。

如果您只想處理一個連接，請不要使用fork。

如果您希望繼續當前的設置，則需要將子進程更改為使用_exit而不是exit並讓父進程處理SIGCHLD信號（在子進程退出時收到）。

即。

#include <signal.h>

void terminate(int signal) {
    // close sockfd -- you will need to make it global
    // or have terminate alter some global variable that main can monitor to 
    // detect when it is meant to exit
    exit(0); // don't exit if you choose the second option
}

int main() {

    signal(SIGCHLD, terminate);

    ...

}