linux SIGPIPE信号

客户端与服务器端建立好TCP连接，如果此时服务器端关闭对应的socket，从而发送FIN报文给客户端，但是客户端仍然在对应的socket上发送数据，此时当服务器收到客户端的第一个write时，服务器发送RST报文告诉客户端自己的socket已经关闭，如果此时客户端仍然write数据给服务器，则客户端底层会触发发送SIGPIPE信号，该信号默认是终止进程，如果不想被终止，则修改信号处理函数。
tcpserver.c

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <strings.h>
#include "readn.h"


void str_echo(int fd)
{
    int n;
    char recvline[MAXLINE];
again:
    while((n = read(fd,recvline,MAXLINE))>0) {
        writen(fd,recvline,n);
    }
    if(n < 0 && errno == EINTR) {
        goto again;
    }else if (n < 0) {
        printf("read error\n");
    }
}
void sig_proc(int signo)
{
    int status;
    pid_t pid;
    if(signo == SIGCHLD) {
       while((pid = wait(&status)) > 0)
           printf("pid %d terminated\n",pid);
       printf("exit.....pid=%d,selfpid=%d,ppid=%d\n",pid,getpid(),getppid());
    }
}
int main(int argc,char *argv[])
{
    int ret = 0;
    int listen_fd;
    int conn_fd;
    struct sockaddr_in server_addr;
    struct sockaddr_in client_addr;
    pid_t pid;
    socklen_t len;

    listen_fd = socket(AF_INET,SOCK_STREAM,0);

    if(listen_fd < 0) {
        printf("socket error\n");
        return -1;
    }

    bzero(&server_addr,sizeof(struct sockaddr_in));

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(10000);
    //server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    ret = inet_pton(AF_INET,"127.0.0.1",&server_addr.sin_addr.s_addr);
    if(ret < 0) {
        printf("inet_pton error\n");
        close(listen_fd);
        return ret;
    }else if(ret == 0) {
        printf("the second parameter of inet_addr is null\n");
    }

    if(bind(listen_fd,(struct sockaddr*)&server_addr,sizeof(struct sockaddr)) == -1) {
            printf("bind error\n");
            close(listen_fd);
            return -1;
    }


    if(listen(listen_fd,1024) == -1) {
        printf("listen error\n");
        close(listen_fd);
        return -1;
    }
    signal(SIGCHLD,sig_proc);

    for(;;) {
        len = sizeof(client_addr);
        conn_fd = accept(listen_fd,(struct sockaddr*)&client_addr,&len);
        if(conn_fd < 0) {
            printf("accept error,errno=%d\n",errno);
            if(errno == EINTR)
                continue;
            return -1;
        }

        pid = fork();

        if(pid < 0) {
            printf("fork error\n");
            return -1;
        }else if(pid == 0) {
            close(listen_fd);
            /*TODO::handle on conn_fd*/
            str_echo(conn_fd);
            exit(0);
        }
        close(conn_fd);
   }

    return 0;
}

tcpclient.c

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <string.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <errno.h>
#include <signal.h>
#include "readn.h"
void str_cli(FILE *fp,int fd)
{
    int ret;
    char sendline[1024], recvline[1024];
    while(fgets(sendline,1024,fp)) {
        writen(fd,sendline,1);
        sleep(1);
        ret = writen(fd,sendline+1,strlen(sendline)-1);
        if(ret < 0)
            printf("writen error in str_cli,ret = %d,errno=%d\n",ret,errno);
        memset(recvline,0,sizeof(recvline));
        if(0 == readline(fd,recvline,sizeof(recvline))) {
            printf("server terminated\n");
            return;
        }
        fputs(recvline,stdout);
    }
}

void sig_pipe(int signo)
{
    printf("catch sigpipe\n");
}

int main(int argc,char* argv[])
{
    int fd;
    struct sockaddr_in server_addr;
    int ret = 0;

    fd = socket(AF_INET,SOCK_STREAM,0);

    if(fd < 0) {
        printf("socket error\n");
        return -1;
    }

    bzero(&server_addr,sizeof(struct sockaddr_in));

    server_addr.sin_family = AF_INET;
    ret = inet_pton(AF_INET,"127.0.0.1",&server_addr.sin_addr);

    if(ret < 0) {
        printf("inet_pton error\n");
        return -1;
    }else if(ret == 0) {
        printf("the second parameter of inet_pton is NULL\n");
    }
    server_addr.sin_port = htons(10000);

    ret = connect(fd,(struct sockaddr*)&server_addr,sizeof(struct sockaddr));
    if(ret < 0) {
        printf("connect error\n");
        return -1;
    }
    signal(SIGPIPE,sig_pipe);
    str_cli(stdin,fd);

    return 0;
}

编译运行：
[e-mail]:~/test/socket>gcc -g readn.c tcpclient.c -o tcpclient -Wall
[e-mail]:~/test/socket>gcc -g readn.c tcpserver.c -o tcpserver -Wall

1)运行服务器
  ./tcpserver
2)运行客户端
 ./tcpclient
3)在客户端敲入任一字符，客户端可以回显
4)使用ps命令查找服务器子进程ID，并kill之
 [e-mail]:~/codes/ipv6_8_12>ps -t pts/4 -o pid,ppid,tty,stat,args,wchan
  PID  PPID TT       STAT COMMAND                     WCHAN
20573 31168 pts/4    S+   ./tcpserver                 inet_csk_accept
20578 20573 pts/4    S+   ./tcpserver                 sk_wait_data
31168 31167 pts/4    Ss   -bash                       wait
kill服务器子进程
kill -9  20578 
5)在客户端输入任一字符，客户端进程由于收到SIGPIPE信号而退出。
abc                            -----输入abc
catch sigpipe
writen error in str_cli,ret = -1,errno=32
server terminated