/*********************************************************************************
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* Copyright: (C) 2025 LingYun IoT System Studio
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* All rights reserved.
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*
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* Filename: socketd.c
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* Description: This file is TCP socket server example program.
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*
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* Version: 1.0.0(10/20/2025)
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* Author: Guo Wenxue <guowenxue@gmail.com>
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* ChangeLog: 1, Release initial version on "10/20/2025 09:48:51 PM"
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*
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********************************************************************************/
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#include <stdio.h>
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#include <string.h>
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#include <errno.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <signal.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include <getopt.h>
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#include <ctype.h>
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#include <sys/time.h>
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#include <sys/resource.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#define BACKLOG 13
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int g_stop = 0; /* program stop or not */
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void sig_handler(int signum)
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{
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switch(signum)
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{
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case SIGTERM:
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printf("SIGTERM signal detected(kill/killall)\n");
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break;
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case SIGSEGV:
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printf("SIGSEGV signal detected(segmentation fault)\n");
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break;
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case SIGPIPE:
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printf("SIGPIPE signal detected(socket error)\n");
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break;
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case SIGINT:
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printf("SIGINT signal detected(Ctrl+C)\n");
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break;
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case SIGCHLD:
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printf("SIGCHLD signal detected(child exit)\n");
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waitpid(-1, NULL, WNOHANG);
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break;
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default:
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break;
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}
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g_stop = 1;
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}
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void print_usage(char *progname)
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{
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printf("%s usage: \n", progname);
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printf(" -p(--port): sepcify listen port.\n");
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printf(" -h(--Help): print this help information.\n");
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return ;
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}
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int main(int argc, char **argv)
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{
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int rv = -1;
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int listen_fd, client_fd = -1;
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int port = 10086;
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struct sockaddr_in serv_addr;
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struct sockaddr_in cli_addr;
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socklen_t addr_len = sizeof(cli_addr);
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int reuse = 1;
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int debug = 0;
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struct rlimit limit;
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pid_t pid;
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int ch;
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struct option opts[] = {
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{"debug", no_argument, NULL, 'd'},
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{"port", required_argument, NULL, 'p'},
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{"help", no_argument, NULL, 'h'},
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{NULL, 0, NULL, 0}
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};
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/* parser command line input arguments */
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while( (ch=getopt_long(argc, argv, "dp:h", opts, NULL)) != -1 )
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{
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switch(ch)
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{
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case 'd':
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debug = 1;
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break;
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case 'p':
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port=atoi(optarg);
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break;
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case 'h':
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print_usage(argv[0]);
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return 0;
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}
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}
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/* set Max. fd limit */
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getrlimit(RLIMIT_NOFILE, &limit);
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limit.rlim_cur = limit.rlim_max;
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setrlimit(RLIMIT_NOFILE, &limit);
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if( !debug )
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{
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daemon(0, 0);
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}
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/* install signal */
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signal(SIGTERM, sig_handler); /* capture kill/killall signal */
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signal(SIGSEGV, sig_handler); /* capture segmentation fault signal */
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signal(SIGPIPE, sig_handler); /* capture socket error signal */
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signal(SIGINT, sig_handler); /* capture Ctrl+C signal */
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signal(SIGCHLD, sig_handler); /* capture child exit signal */
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/* create TCP socket */
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listen_fd = socket(AF_INET, SOCK_STREAM, 0);
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if(listen_fd < 0 )
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{
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printf("create socket failure: %s\n", strerror(errno));
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return -1;
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}
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/* resolve the "Address already in use" error when using bind() */
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setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse));
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/* bind socket server information */
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memset(&serv_addr, 0, sizeof(serv_addr));
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serv_addr.sin_family = AF_INET;
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serv_addr.sin_port = htons(port);
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serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
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if( bind(listen_fd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0 )
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{
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printf("create socket failure: %s\n", strerror(errno));
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return -2;
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}
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printf("socket[%d] bind on port[%d] for all IP address ok\n", listen_fd, port);
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/* start listen socket */
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listen(listen_fd, BACKLOG);
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while( !g_stop )
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{
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/* accept new incoming socket client */
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printf("\nStart waiting and accept new client connect...\n");
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client_fd = accept(listen_fd, (struct sockaddr*)&cli_addr, &addr_len);
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if(client_fd < 0)
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{
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printf("accept new socket failure: %s\n", strerror(errno));
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return -2;
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}
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printf("Accept new client[%s:%d] with fd [%d]\n", inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port), client_fd);
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pid = fork();
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if( pid < 0 ) /* fork() failed */
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{
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printf("fork() create child process failure: %s\n", strerror(errno));
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close(client_fd);
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continue;
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}
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else if( pid > 0 ) /* parent process */
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{
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/* close client fd and goes to accept new client again */
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close(client_fd);
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continue;
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}
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else /* child process */
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{
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int i;
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char buf[1024];
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/* close the listen socket fd, parent will handle it */
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close(listen_fd);
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printf("Child process start to commuicate with socket client...\n");
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while(1)
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{
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/* receive data from socket client */
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memset(buf, 0, sizeof(buf));
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rv=read(client_fd, buf, sizeof(buf));
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if( rv < 0 )
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{
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printf("Read data from client sockfd[%d] failure: %s\n", client_fd, strerror(errno));
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close(client_fd);
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exit(0);
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}
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else if( rv == 0)
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{
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printf("Socket[%d] get disconnected\n", client_fd);
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close(client_fd);
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exit(1);
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}
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else if( rv > 0 )
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{
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printf("Read %d bytes data from client: %s\n", rv, buf);
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}
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/* convert letter from lowercase to uppercase */
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for(i=0; i<rv; i++)
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{
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buf[i]=toupper(buf[i]);
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}
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/* write back data to socket client */
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rv=write(client_fd, buf, rv);
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if(rv < 0)
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{
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printf("Write to client by sockfd[%d] failure: %s\n", client_fd, strerror(errno));
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close(client_fd);
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exit(1);
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}
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} /* Child process loop */
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}
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}
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close(listen_fd);
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return 0;
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}
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