c - SCTP客户端和服务器在读取对方发送的消息时遇到错误

Question

我正在使用 Linux SCTP 套接字 API 实现一个简单的 SCTP 客户端和服务器。客户端和服务器都使用一对一的套接字样式。连接到服务器后，客户端向服务器发送 hello 消息，服务器用 hello 消息进行响应。这是服务器和客户端的代码:

服务器.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/sctp.h>
#include "common.h"

int main(int argc, char *argv[])
{
    int srvr_sock;
    struct sockaddr_in srv_addr;
    struct sockaddr_in clnt_addr;
    struct sctp_sndrcvinfo sndrcvinfo;
    struct sctp_event_subscribe event;
    socklen_t addr_sz;
    char snd_buf[] = "Hello from server";
    char rcv_buf[1024] = {0};
    int new_fd;
    int flags;
    int rd_sz;
    int ret;

    /* One-to-one style */
    /* Create socket */
    srvr_sock = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
    if (srvr_sock < 0)
    {
        perror("Open srvr_sock");
        exit(EXIT_FAILURE);
    }

    /* Bind to server address */
    memset(&srv_addr, 0, sizeof(srv_addr));
    srv_addr.sin_family = AF_INET;
    srv_addr.sin_port = htons(SERVER_PORT_NUM);
    srv_addr.sin_addr.s_addr = inet_addr(SERVER_IP_ADDR_1);
    ret = bind(srvr_sock, (struct sockaddr *) &srv_addr, sizeof(srv_addr));
    if (ret < 0)
    {
        perror("Bind srvr_sock");
        exit(EXIT_FAILURE);
    }

    /* Enable all events */
    event.sctp_data_io_event = 1;
    event.sctp_association_event = 1;
    event.sctp_address_event = 1;
    event.sctp_send_failure_event = 1;
    event.sctp_peer_error_event = 1;
    event.sctp_shutdown_event = 1;
    event.sctp_partial_delivery_event = 1;
    event.sctp_adaptation_layer_event = 1;
    if (setsockopt(srvr_sock, IPPROTO_SCTP, SCTP_EVENTS, &event,
        sizeof(event)) != 0)
    {
        perror("setsockopt failed");
        exit(EXIT_FAILURE);
    }

    /* Listen */
    ret = listen(srvr_sock, 5);
    if (ret < 0)
    {
        perror("Listen on srvr_sock");
        exit(EXIT_FAILURE);
    }

    /* Server loop */
    while (1)
    {
        printf("Waiting for new connection...\n");
        new_fd = accept(srvr_sock, (struct sockaddr *)&clnt_addr, &addr_sz);
        if (new_fd < 0)
        {
            perror("Failed to accept client connection");
            continue;
        }

        memset(rcv_buf, 0, sizeof(rcv_buf));
        rd_sz = sctp_recvmsg(new_fd, (void *)rcv_buf, sizeof(rcv_buf),
                            (struct sockaddr *) NULL,
                            0,
                            &sndrcvinfo,
                            &flags);
        if (rd_sz <= 0)
        {
            continue;
        }

        if (flags & MSG_NOTIFICATION)
        {
            printf("Notification received. rd_sz=%d\n", rd_sz);
        }
        printf("New client connected\n");
        printf("Received %d bytes from client: %s\n", rd_sz, rcv_buf);

        /* Send hello to client */
        ret = sctp_sendmsg(new_fd, /* sd */
                           (void *) snd_buf, /* msg */
                           strlen(snd_buf), /* len */
                           NULL, /* to */
                           0, /* to len */
                           0, /* ppid */
                           0, /* flags */
                           STREAM_ID_1, /* stream_no */
                           0, /* TTL */
                           0 /* context */); 
        if (ret < 0)
        {
            perror("Error when send data to client");
        }
        else
        {
            printf("Send %d bytes to client\n", ret);
        }

        if (close(new_fd) < 0)
        {
            perror("Close socket failed");
        }
    }
    close(srvr_sock);

    return 0;
}

客户端.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/sctp.h>
#include "common.h"

int main(int argc, char *argv[])
{
    int conn_fd;
    struct sockaddr_in srvr_addr;
    struct sctp_sndrcvinfo sndrcvinfo;
    socklen_t addr_sz = sizeof(struct sockaddr_in);
    int flags;
    char rcv_buf[1024] = {0};
    char snd_buf[] = "Hello from client";
    int rcv_cnt;
    int ret;

    /* One-to-one style */
    /* Create socket */
    conn_fd = socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);
    if (conn_fd < 0)
    {
        perror("Create socket conn_fd");
        exit(EXIT_FAILURE);
    }

    /* Specify the peer endpoint to which we'll connect */
    memset(&srvr_addr, 0, sizeof(srvr_addr));
    srvr_addr.sin_family = AF_INET;
    srvr_addr.sin_port = htons(SERVER_PORT_NUM);
    srvr_addr.sin_addr.s_addr = inet_addr(SERVER_IP_ADDR_1);

    /* Connect */
    ret = connect(conn_fd, (struct sockaddr *)&srvr_addr, sizeof(srvr_addr));
    if (ret < 0)
    {
        perror("Connect failed");
        exit(EXIT_FAILURE);
    }
    printf("Connected to server\n");

    /* Send hello to server */
    ret = sctp_sendmsg(conn_fd, (void *)snd_buf, strlen(snd_buf),
                        (struct sockaddr *) &srvr_addr, sizeof(srvr_addr), 0,
                        0, STREAM_ID_1, 0, 0);
    if (ret < 0)
    {
        perror("Send to server failed");
        close(conn_fd);
        exit(EXIT_FAILURE);
    }
    else
    {
        printf("Send %d bytes to server\n", ret);
    }

    /* Read message from server */
    rcv_cnt = sctp_recvmsg(conn_fd, (void *)rcv_buf, sizeof(rcv_buf),
            (struct sockaddr *) &srvr_addr, &addr_sz,
            &sndrcvinfo, &flags);
    if (rcv_cnt <= 0)
    {
        printf("Socket error or EOF\n");
    }
    else if (flags & MSG_NOTIFICATION)
    {
        printf("Notification received. rcv_cnt=%d\n", rcv_cnt);
    }
    else
    {
        printf("Received %d bytes from server: %s\n", rcv_cnt, rcv_buf);
    }

    /* close socket */
    close(conn_fd);

    return 0;
}

common.h

#define SERVER_PORT_NUM     16789
#define SERVER_IP_ADDR_1    "192.168.56.102"
#define STREAM_ID_1         1

客户端和服务器运行在同一子网的 2 个 Debian 虚拟机上，客户端 IP 为 192.168.56.101，服务器 IP 为 192.168.56.102。

当我启动服务器然后运行客户端时，大多数情况下客户端会失败并显示以下输出:

./client
Connected to server
Send to server failed: Cannot assign requested address

但是服务器显示它已读取从客户端发送的数据并已响应服务器问候消息:

 ./server
Waiting for new connection...
Notification received. rd_sz=20
New client connected
Received 20 bytes from client: ▒
Send 17 bytes to client
Waiting for new connection...

在这种情况下，从客户端接收到的数据也已损坏。

我多次尝试运行客户端，有时会成功:

$ ./client
Connected to server
Send 17 bytes to server
Received 17 bytes from server: Hello from server

在这种情况下，服务器仍然显示相同的日志消息。

为什么客户端大部分时间都会失败，而只有几次成功？结果似乎对我来说是不可预测的。另外为什么服务器读取的数据在服务器的输出中被损坏？

Answer 1

尝试绑定(bind)客户端套接字。在 client.c 中，在套接字创建和连接之前放置:

cli_addr.sin_family = AF_INET;
cli_addr.sin_port = 0;
cli_addr.sin_addr.s_addr = inet_addr(INADDR_ANY); /* or inet_addr("192.168.56.101"); 
for multiple ip addresses or network cards */
ret = bind(conn_fd, (struct sockaddr *) &cli_addr, sizeof(cli_addr));
if (ret < 0)
{
  perror("Bind client_sock");
  exit(EXIT_FAILURE);
}