2

我正在尝试使用sendmsg和recvmsg函数（C 语言）通过 unix 域套接字发送和接收消息。

过程非常简单：

  • 服务器使用sendmsg向客户端发送一个字符串（必须使用struct msghdr）；
  • 字符串在 main (argv[1]) 中作为参数传递；
  • 客户端使用recvmsg接收字符串；
  • 客户端将字符串打印到标准输出。

我有以下问题：

1 - 当服务器发送字符串“test”时：

$ ./server test

2 - 客户端正确打印：

$ ./client
print data received > test

但，

1- 当字符串更大（> 7 个字符）时，例如“hello_world”：

$ ./server hello_world

2 - 客户端打印奇怪的字符（好像没有'\0'）：

$ ./client
print data received > hello_woh?!#

问题与消息的长度有关吗？

如何定义消息的长度以便正确打印？

编辑：服务器源代码：

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>

#define SOCK_PATH "/tmp/usocket"

int send_msg_to_client(int socketfd, char* data) {

  struct msghdr msg;
  struct iovec iov;
  int s;

  memset(&msg, 0, sizeof(msg));
  memset(&iov, 0, sizeof(iov));

  msg.msg_name = NULL;
  msg.msg_namelen = 0;
  iov.iov_base = data;
  // replace sizeof(data) by strlen(data)+1
  iov.iov_len = strlen(data)+1;
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;
  msg.msg_control = NULL;
  msg.msg_controllen = 0;
  msg.msg_flags = 0;

  printf("msg: %s\n", (char *) iov.iov_base);

  s = sendmsg(socketfd, &msg, 0);

  if(s < 0){
    perror("sendmsg");
    return 0;
  }

  return s;
}


int main(int argc, char* argv[])
{

        if (argc != 2) {
          printf("Usage: $ %s <data>\n",argv[0]);
          return 0;
        }

    int s, s2, len, slen;
    socklen_t t;
    struct sockaddr_un local, remote;
    char* data = argv[1];

    printf("print data: %s\n",data);

    if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    memset(&local, 0, sizeof(local));
    local.sun_family = AF_UNIX;
    strcpy(local.sun_path, SOCK_PATH);

    unlink(local.sun_path);

    len = strlen(local.sun_path) + sizeof(local.sun_family);
    if (bind(s, (struct sockaddr *)&local, len) == -1) {
        perror("bind");
        exit(1);
    }

    if (listen(s, 5) == -1) {
        perror("listen");
        exit(1);
    }

    printf("Waiting for a connection...\n");

    t = sizeof(remote);
    if ((s2 = accept(s, (struct sockaddr *)&remote, &t)) == -1) {
        perror("accept");
        exit(1);
    }

    printf("Connected.\n");

    slen = send_msg_to_client(s2, data);

    if(slen < 0)
        perror("send");

    printf("sent data length: %d\n", slen);

    close(s2);

    return 0;
}

编辑：客户端源代码：

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>

#define SOCK_PATH "/tmp/usocket"
#define MAX 100

int recv_msg_from_server(int socketfd, char data[MAX]) {

  struct msghdr msg;
  struct iovec iov;
  int s;

  memset(&msg, 0, sizeof(msg));
  memset(&iov, 0, sizeof(iov));

  msg.msg_name = NULL;
  msg.msg_namelen = 0;
  iov.iov_base = data;
  //replace sizeof(data) by MAX
  iov.iov_len = MAX;
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;
  msg.msg_control = NULL;
  msg.msg_controllen = 0;
  msg.msg_flags = 0;


  s = recvmsg(socketfd, &msg, 0);

  if(s < 0){
    perror("recvmsg");
    return 0;
  }

  return s;
}


int main(void)
{
    int s, len, slen;
    struct sockaddr_un remote;
    char data[MAX];

    if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
            perror("socket");
            exit(1);
        }

    printf("Trying to connect...\n");

    memset(&remote, 0, sizeof(remote));

    remote.sun_family = AF_UNIX;
    strcpy(remote.sun_path, SOCK_PATH);
    len = strlen(remote.sun_path) + sizeof(remote.sun_family);

    if (connect(s, (struct sockaddr *)&remote, len) == -1) {
            perror("connect");
            exit(1);
        }

    printf("Connected.\n");

    slen = recv_msg_from_server(s, data);

    if (slen < 0) {
        perror("recvmsg");
    }

    //data[MAX] = '\0';
    printf("print data received > %s\n", data);

    close(s);

    return 0;
}
4

1 回答 1

2

乍一看，您似乎正在将有效载荷 ( iov.iov_len)的长度设置sizeof(data)为sizeof(char*). 假设您在 64 位机器上运行它，这个大小是 8 个字节，这解释了为什么它确实适用于较短的字符串。

你可能想成功strlen(data) + 1。

于 2013-10-23T21:22:17.840 回答