C语言 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，服务器以 hello 消息响应。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=%dn", rd_sz);
}
printf("New client connectedn");
printf("Received %d bytes from client: %sn", 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 clientn", 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 servern");
/* 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 servern", 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 EOFn");
}
else if (flags & MSG_NOTIFICATION)
{
printf("Notification received. rcv_cnt=%dn", rcv_cnt);
}
else
{
printf("Received %d bytes from server: %sn", rcv_cnt, rcv_buf);
}
/* close socket */
close(conn_fd);
return 0;
}

普通.h

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

客户端和服务器在同一子网中的 2 个 Debian VM 上运行，客户端的 IP 是 192.168.56.101，服务器的 IP 是 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，从客户端接收的数据也会损坏。

我尝试多次运行客户端，有时它会成功：

$ ./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，而只成功几次？结果对我来说似乎是不可预测的。还有为什么服务器读取的数据在服务器的输出中损坏了？

Answer 1

尝试绑定客户端套接字。 在套接字之间的client.c中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);
}