unix 套接字数据报：服务器接收到无效字符

Posted 2023-02-16

【中文标题】unix 套接字数据报：服务器接收到无效字符

【英文标题】：unix socket datagram: server receive invalid characters

【发布时间】：2021-02-04 09:47:28

【问题描述】：

我正在尝试创建一个 Unix 套接字数据报示例。客户端可以顺利发送和接收消息。服务器可以这样做，以防缓冲区长度小于SOCKET_BUFFER_SIZE，否则服务器的输出会在接收的缓冲区中显示一些无效字符。

客户代码

#include "ud_hdr.h"

#define IN_BUF_SIZE     200

int main(int argc, char **argv)

    struct sockaddr_un  svr_addr, cli_addr;
    int                 sfd, i;
    ssize_t             num_rw;
    socklen_t           svr_addr_len;
    char                sock_buf[SOCK_BUF_SIZE];
    char                in_buf[IN_BUF_SIZE];

    // Create sockets:
    sfd = socket(AF_UNIX, SOCK_DGRAM, 0);
    if (sfd == -1) 
        printf("Error line|%d|: %s", __LINE__, strerror(errno));
        exit(EXIT_FAILURE);
    

    // ! In Unix domain, the client needs to assign an address to its socket
    // ! if it wants to RECEIVE datagrams sent by server.
    memset(&cli_addr, 0, sizeof(struct sockaddr_un));
    cli_addr.sun_family = AF_UNIX;
    snprintf(cli_addr.sun_path, sizeof(cli_addr.sun_path), \
            "/tmp/dxduc/ud_cli.%ld", (long)getpid());
    if (bind(sfd, (struct sockaddr *) &cli_addr, sizeof(struct sockaddr_un)) == -1) 
        printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
        exit(EXIT_FAILURE);
    

    // Construct server's address:
    memset(&svr_addr, 0, sizeof(struct sockaddr_un));
    svr_addr.sun_family = AF_UNIX;
    strncpy(svr_addr.sun_path, SOCKET_SV_PATH, sizeof(svr_addr.sun_path) - 1);

    printf("Client is ready to run\n");
    while (1) 
        printf("Enter new msg: ");
        fflush(stdout); // * clear the output buffer and move the buffered data to output (a.k.a console in this case)
        memset(in_buf, 0, sizeof(in_buf));
        memset(sock_buf, 0, sizeof(sock_buf));
        num_rw = read(STDIN_FILENO, in_buf, IN_BUF_SIZE);

        // Remove '\n' and '\r' in input:
        for (i = 0; i < IN_BUF_SIZE; i++) 
            // if ((in_buf[i] == '\r') || (in_buf[i] == '\n')) 
            if (in_buf[i] == '\n') 
                in_buf[i] = 0x0;
            
        

        printf("Msg to server: |%s|, len = %ld, num_rw = %ld\n", in_buf, strlen(in_buf), num_rw);
        svr_addr_len = sizeof(struct sockaddr_un);
        if (num_rw > 0) 
            // Send msg to server:
            if (sendto(sfd, in_buf, strlen(in_buf), 0, (struct sockaddr *) &svr_addr, svr_addr_len) != strlen(in_buf)) 
                printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
                exit(EXIT_FAILURE);
            
         else if (num_rw == 0) 
            printf("Nothing to send to server\n");
            continue;
         else if (num_rw == -1) 
            printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
            exit(EXIT_FAILURE);
        

        // Read response from server
        num_rw = recvfrom(sfd, sock_buf, SOCK_BUF_SIZE, 0, (struct sockaddr *) &svr_addr, &svr_addr_len);
        if (num_rw == -1) 
            printf("Error line|%d|, %s", __LINE__, strerror(errno));
            exit(EXIT_FAILURE);
         else 
            printf("Receive from server: |%s|, len=%ld, num_rw=%ld\n", sock_buf, strlen(sock_buf), num_rw);
        
    

服务器的代码

#include "ud_hdr.h"

int main(int argc, char **argv)

    struct sockaddr_un  svr_addr, cli_addr;
    int                 sfd, i;
    ssize_t             num_rw;
    socklen_t           cli_addr_len;
    char                buf[SOCK_BUF_SIZE];

    // Create socket:
    sfd = socket(AF_UNIX, SOCK_DGRAM, 0);
    if (sfd == -1) 
        printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
        exit(EXIT_FAILURE);
    

    // Verify socket's name path:
    if (strlen(SOCKET_SV_PATH) > (sizeof(svr_addr.sun_path) - 1)) 
        printf("Error line|%d|: invalid socket name", __LINE__);
        exit(EXIT_FAILURE);
    

    // Remove any existing file having the same namepath with server's:
    if ((remove(SOCKET_SV_PATH) == -1) && (errno != ENOENT)) 
        printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
        exit(EXIT_FAILURE);
    

    // Bind the socket to desired addr:
    memset(&svr_addr, 0, sizeof(struct sockaddr_un));
    svr_addr.sun_family = AF_UNIX;
    strncpy(svr_addr.sun_path, SOCKET_SV_PATH, sizeof(svr_addr.sun_path) - 1);

    if (bind(sfd, (struct sockaddr *)&svr_addr, sizeof(struct sockaddr_un)) == -1) 
        printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
        exit(EXIT_FAILURE);
    

    while (1) 
        // Receive data from client:
        memset(buf, 0, sizeof(buf));
        cli_addr_len = sizeof (struct sockaddr_un);
        num_rw = recvfrom(sfd, buf, SOCK_BUF_SIZE, 0, (struct sockaddr *) &cli_addr, &cli_addr_len);

        if (num_rw == -1) 
            printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
            exit(EXIT_FAILURE);
        

        printf("Server received %ld bytes from %s, ret_buf=|%s|, len=%ld\n", (long)num_rw, cli_addr.sun_path, buf, strlen(buf));

        // Uppercase received characters:
        for (i = 0; i < num_rw; i++) 
            buf[i] = toupper((unsigned char)buf[i]);
        

        // Send back uppercase-ed characters to client:
        printf("Send back to client: |%s|, len=%ld\n", buf, strlen(buf));
        if (sendto(sfd, buf, strlen(buf), 0, (struct sockaddr *) &cli_addr, cli_addr_len) != strlen(buf)) 
            printf("Error line|%d|: %s\n", __LINE__, strerror(errno));
            exit(EXIT_FAILURE);
        
    

头文件

#ifndef _UD_HDR_H_
#define _UD_HDR_H_

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>

#include <errno.h>
#include <unistd.h>
#include <ctype.h>

// * The Makefile should have created /tmp/dxduc before run this program
#define SOCKET_SV_PATH      "/tmp/dxduc/ud_basic"
#define SOCK_BUF_SIZE            10

#endif // _UD_HDR_H_

这就是我得到的

# Client
Client is ready to run
Enter new msg: stack  
Msg to server: |stack|, len = 5, num_rw = 6
Receive from server: |STACK|, len=5, num_rw=5
Enter new msg: ***
Msg to server: |***|, len = 13, num_rw = 14
Receive from server: |STACKOVERF|, len=10, num_rw=10

#Server
Server received 5 bytes from /tmp/dxduc/ud_cli.2385, ret_buf=|stack|, len=5
Send back to client: |STACK|, len=5
Server received 10 bytes from /tmp/dxduc/ud_cli.2385, ret_buf=|stackoverf�  |, len=14
Send back to client: |STACKOVERF�   |, len=14

奇怪的是客户端收到了预期的消息，尽管服务器在发送之前没有正确格式化消息。

这是我的预期输出

# Client
Client is ready to run
Enter new msg: stack  
Msg to server: |stack|, len = 5, num_rw = 6
Receive from server: |STACK|, len=5, num_rw=5
Enter new msg: ***
Msg to server: |***|, len = 13, num_rw = 14
Receive from server: |STACKOVERF|, len=10, num_rw=10

#Server
Server received 5 bytes from /tmp/dxduc/ud_cli.2385, ret_buf=|stack|, len=5
Send back to client: |STACK|, len=5
Server received 10 bytes from /tmp/dxduc/ud_cli.2385, ret_buf=|stackoverf|, len=10
Send back to client: |STACKOVERF|, len=14

我该如何解决？

【问题讨论】：

你的缓冲区可能不是零终止的

@dvhh 你说的是哪个缓冲区？客户端准备发送到服务器的缓冲区？

@dvhh 没有“可能”。 sendto(sfd, in_buf, strlen(in_buf), 0, (struct sockaddr *) &svr_addr, svr_addr_len) 不会发送正确的 C 字符串，因为它将 not 以零结尾。

@AndrewHenle 我知道如何解决这个问题，谢谢

【参考方案1】：

您的 SOCK_BUF_SIZE 为 10，您收到 10 个字节（在您的客户端中）。它会覆盖您的 0 字节。 你应该使用

char sock_buf[SOCK_BUF_SIZE+1];