unix socket send() 成功，但 recv() 失败

Question

我正在使用 unix 域套接字编写一个简单的客户端服务器程序，但我的客户端程序中的 recv() 调用有问题。

程序执行如下：

服务器设置套接字并等待连接
客户端连接并发送一个字符串
服务器接收字符串，并将字符串发送回客户端（如回显）
客户端 recv() 调用失败，返回 "resource temporarily unavailable"
客户端退出
服务器等待另一个连接

我还尝试在我的客户端中使用 poll() 调用来等待服务器的响应。然而，在这种情况下，recv() 调用只会收到一个 0，这意味着连接已在服务器端关闭，但实际上并没有。

我已经用尽了 google 这个错误，但我遇到的任何修复似乎都适用于我的代码。

我在下面包含了我的客户端（注释掉了 poll() 代码）和服务器代码。

我可能遗漏了一些明显的东西...但是任何见解都将不胜感激！

服务器代码：

    /*
 *  testServer.c
 *
 */

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <termios.h>
#include <fcntl.h>
#include <poll.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <linux/spi/spidev.h>
#include <linux/sockios.h>
#include <errno.h>

#define SOCK_PATH "/var/run/ts.serv" 

void handleSockIO(int *sockDesc);

int main ()
{
    int sock;
    struct sockaddr_un sock_addr;
    int len, p;
    struct pollfd poll_fd[1];

    printf("[TS] testServer Started.\r\n");

    if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) 
    {
        perror("[TS]wr_sock creation");
    }
    else 
    {
        printf("[TS] Created socket descriptor.\r\n");
    }


    sock_addr.sun_family = AF_UNIX;
    strcpy(sock_addr.sun_path, SOCK_PATH);
    unlink(sock_addr.sun_path);

    len = strlen(sock_addr.sun_path) + sizeof(sock_addr.sun_family);

    if (bind(sock, (struct sockaddr *)&sock_addr, len) == -1) 
    {
        perror("[TS]sock bind failed\r\n");
    }
    else 
    {
        printf("[TS] Bound socket to sock_addr.\r\n");
    }

    if (listen(sock, 5) == -1) 
    {
        perror("[TS] sock listen fail");
    }
    else 
    {
        printf("[TS] Socket now listening.\r\n");
    }

    poll_fd[0].fd = sock;
    poll_fd[0].events = POLLIN;

    printf("[TS] Waiting for a connection...\r\n");

    while (1) 
    {
        p = poll(poll_fd, 1, 1); //Wait for 1 ms for data

        if (p == -1) 
        {
            perror("[TS] Poll");
        } 
        else if (p == 0) 
        {
            //printf("Timeout occurred!\n"); 
        } 
        else 
        {
            if (poll_fd[0].revents & POLLIN)//Data available to read without blocking
            { 
                printf("[TS] Data available on sock..\r\n");
                handleSockIO(&sock);

                printf("[TS] Waiting for another connection...\r\n");
            }
        }
    }//While(1)

    return 0;
}

void handleSockIO(int *sockDesc)
{
    int ioSock, n;
    socklen_t t;
    struct sockaddr_un remote_addr;
    char str[15];

    memset(str, ' ', sizeof(str));

    t = sizeof(remote_addr);

    if ((ioSock = accept(*sockDesc, (struct sockaddr *)&remote_addr, &t)) == -1) 
    {
        perror("accept failed\r\n");
    }
    else 
    {
        printf("[TS] Receiving...\r\n");

        n = recv(ioSock, str, sizeof(str), 0);

        if (n < 0) 
            printf("[TS] recvfrom failed: %s\r\n", strerror(errno));
        else if(n == 0)
        {
            printf("[TS] Received %d on ioSock...\r\n", n);
        }
        else if(n > 0)
        {
            printf("[TS] Received: %s, which is %d long.\r\n", str, strlen(str));

            printf("[TS] Echoing response...\r\n");

            if (send(ioSock, str, n, 0) == -1) //Echo str back
            {
                printf("[TS] send failed: %s\r\n", strerror(errno));
            }
            else 
            {
                printf("[TS] Send successful\r\n");
            }

            //============Wait to close IO descriptor=================
            int r;
            char temp[1]; //Arbitrary buffer to satisfy recv()
            do 
            {
                printf("[TS] Waiting for client to close connection...\r\n");
                r = recv(ioSock, temp, sizeof(temp), 0);

                if (r == 0)
                {
                    printf("[TS] Client closed connection, closing ioSock...\r\n");
                    close(ioSock);
                }
            } while (r != 0);

            //========================================================
        }//if(n>0) else...
    }       
}

客户代码：

 /*
 *  testClient.c
 *
 */

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <termios.h>
#include <fcntl.h>
#include <poll.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <linux/sockios.h>
#include <errno.h>

#define CHAR_BUF_SIZE 15
#define SEND_STRING "Hello!"
#define SOCK_PATH "/var/run/ts.serv" 

int main ()
{
    char str[CHAR_BUF_SIZE] = {0};
    int c, len, n, p;
    int s; // s will hold a socket descriptor returned by socket()
    struct sockaddr_un serv_addr;
    struct pollfd poll_fd[1];

    printf("[TC] testClient Started.\r\n");

    //===============SOCKET SETUP===============================

    if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) 
    {
        printf("[TC] Socket failed: %s\r\n", strerror(errno));
    }

    memset(&serv_addr, '0', sizeof(serv_addr));

    serv_addr.sun_family = AF_UNIX;
    strcpy(serv_addr.sun_path, SOCK_PATH);

    len = strlen(serv_addr.sun_path) + sizeof(serv_addr.sun_family);

    //==========================================================

    //  printf("[TC]Trying to connect to TS socket...\r\n");

    //===============RESPONSE POLL SETUP========================

    poll_fd[0].fd = s;
    poll_fd[0].events = POLLIN;

    //==========================================================

    printf("[TC] Connecting to SOCK_PATH...\r\n");

    c = connect(s, (struct sockaddr *)&serv_addr, len);

    if (c == -1)
    {
        printf("[TC] Connection failed: %s\r\n", strerror(errno));
    }
    else 
    {
        printf("[TC] Connected. Sending string....\r\n");

        if (send(s, SEND_STRING, strlen(SEND_STRING), 0) == -1) 
        {
            printf("[TC] send() failed: %s\r\n", strerror(errno));
        }
        else 
        { 
            printf("[TC] Send on SOCK_PATH successful.\r\n");
            //Sending complete------------------------------------------------
            //Wait for response...

            printf("[TC] Waiting for server response...\r\n");

//          p = poll(poll_fd, 1, -1); //Wait for a response
//          
//          if (p == -1) 
//          {
//              perror("[TC] Poll");
//          } 
//          else 
//          {
//              if(poll_fd[0].revents & POLLIN)
//              {
                    n = recv(s, str, sizeof(str), 0);

                    if (n < 0) 
                    {
                        printf("[TC] Receive on SOCK_PATH failed: %s\r\n", 
                               strerror(errno));
                    }
                    else if(n == 0)
                    {
                        printf("[TC] %d Received on SOCK_PATH.\r\n", n);
                    }
                    else if(n > 0)
                    {
                        printf("[TC] Received %d from SOCK_PATH: %s\r\n", 
                               n, str);
                    }
//              }
//          }
        }//if(send())
    }//if(connect())

    printf("[TC] Transction complete, closing connection and exiting.\r\n");

    close(s);

    return 0;
}

Answer 1

len = sizeof(serv_addr) 而不是 len = strlen(serv_addr.sun_path) + sizeof(serv_addr.sun_family) 应该可以解决您的问题。也不要忽略编译器警告，例如 n = recv(s, str, strlen(str), 0)，其中 n 声明为 int 并且 ssize_t 由 recv 返回。它将帮助您避免以后的错误。

unix socket send() 成功，但 recv() 失败

unix socket send() succeeds, but recv() fails

c

sockets

unix

send

recv