/*********************************************************************************
 *      Copyright:  (C) 2025 LingYun IoT System Studio
 *                  All rights reserved.
 *
 *       Filename:  socketd.c
 *    Description:  This file is TCP socket server example program.
 *
 *        Version:  1.0.0(10/20/2025)
 *         Author:  Guo Wenxue <guowenxue@gmail.com>
 *      ChangeLog:  1, Release initial version on "10/20/2025 09:48:51 PM"
 *
 ********************************************************************************/

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <getopt.h>
#include <ctype.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <sys/wait.h>

#define BACKLOG              13

int         g_stop = 0; /* program stop or not */

void sig_handler(int signum)
{
    switch(signum)
    {
        case SIGTERM:
            printf("SIGTERM signal detected(kill/killall)\n");
            break;

        case SIGSEGV:
            printf("SIGSEGV signal detected(segmentation fault)\n");
            break;

        case SIGPIPE:
            printf("SIGPIPE signal detected(socket error)\n");
            break;

        case SIGINT:
            printf("SIGINT signal detected(Ctrl+C)\n");
            break;

        case SIGCHLD:
            printf("SIGCHLD signal detected(child exit)\n");
            waitpid(-1, NULL, WNOHANG);
            break;

        default:
            break;
    }

    g_stop = 1;
}

void print_usage(char *progname)
{
    printf("%s usage: \n", progname);
    printf("  -p(--port): sepcify listen port.\n");
    printf("  -h(--Help): print this help information.\n");

    return ;
}

int main(int argc, char **argv)
{
    int                     rv = -1;
    int                     listen_fd,  client_fd = -1;
    int                     port = 10086;
    struct sockaddr_in      serv_addr;
    struct sockaddr_in      cli_addr;
    socklen_t               addr_len = sizeof(cli_addr);
    int                     reuse = 1;

    int                     debug = 0;
    struct rlimit           limit;
    pid_t                   pid;

    int                     ch;
    struct option           opts[] = {
        {"debug", no_argument, NULL, 'd'},
        {"port", required_argument, NULL, 'p'},
        {"help", no_argument, NULL, 'h'},
        {NULL, 0, NULL, 0}
    };

    /* parser command line input arguments */
    while( (ch=getopt_long(argc, argv, "dp:h", opts, NULL)) != -1 )
    {
        switch(ch)
        {
            case 'd':
                debug = 1;
                break;

            case 'p':
                port=atoi(optarg);
                break;

            case 'h':
                print_usage(argv[0]);
                return 0;
        }
    }

    /* set Max. fd limit */
    getrlimit(RLIMIT_NOFILE, &limit);
    limit.rlim_cur = limit.rlim_max;
    setrlimit(RLIMIT_NOFILE, &limit);

    if( !debug )
    {
        daemon(0, 0);
    }

    /* install signal */
    signal(SIGTERM, sig_handler);  /* capture kill/killall signal */
    signal(SIGSEGV, sig_handler);  /* capture segmentation fault signal */
    signal(SIGPIPE, sig_handler);  /* capture socket error signal */
    signal(SIGINT,  sig_handler);  /* capture Ctrl+C signal */
    signal(SIGCHLD, sig_handler);  /* capture child exit signal */

    /* create TCP socket */
    listen_fd = socket(AF_INET, SOCK_STREAM, 0);
    if(listen_fd < 0 )
    {
        printf("create socket failure: %s\n", strerror(errno));
        return -1;
    }

    /* resolve the "Address already in use" error when using bind() */
    setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse));

    /* bind socket server information */
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(port);
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    if( bind(listen_fd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0 )
    {
        printf("create socket failure: %s\n", strerror(errno));
        return -2;
    }
    printf("socket[%d] bind on port[%d] for all IP address ok\n", listen_fd, port);

    /* start listen socket */
    listen(listen_fd, BACKLOG);

    while( !g_stop )
    {
        /* accept new incoming socket client  */
        printf("\nStart waiting and accept new client connect...\n");
        client_fd = accept(listen_fd, (struct sockaddr*)&cli_addr, &addr_len);
        if(client_fd < 0)
        {
            printf("accept new socket failure: %s\n", strerror(errno));
            return -2;
        }
        printf("Accept new client[%s:%d] with fd [%d]\n", inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port), client_fd);

        pid = fork();
        if( pid < 0 ) /* fork() failed */
        {
            printf("fork() create child process failure: %s\n", strerror(errno));
            close(client_fd);
            continue;
        }
        else if( pid > 0 ) /* parent process */
        {
            /* close client fd and goes to accept new client again */
            close(client_fd);
            continue;
        }
        else /* child process */
        {
            int                  i;
            char                 buf[1024];

            /* close the listen socket fd, parent will handle it */
            close(listen_fd);

            printf("Child process start to commuicate with socket client...\n");
            while(1)
            {
                /* receive data from socket client */
                memset(buf, 0, sizeof(buf));
                rv=read(client_fd, buf, sizeof(buf));
                if( rv < 0 )
                {
                    printf("Read data from client sockfd[%d] failure: %s\n", client_fd, strerror(errno));
                    close(client_fd);
                    exit(0);
                }
                else if( rv == 0)
                {
                    printf("Socket[%d] get disconnected\n", client_fd);
                    close(client_fd);
                    exit(1);
                }
                else if( rv > 0 )
                {
                    printf("Read %d bytes data from client: %s\n", rv, buf);
                }

                /* convert letter from lowercase to uppercase */
                for(i=0; i<rv; i++)
                {
                    buf[i]=toupper(buf[i]);
                }

                /* write back data to socket client */
                rv=write(client_fd, buf, rv);
                if(rv < 0)
                {
                    printf("Write to client by sockfd[%d] failure: %s\n", client_fd, strerror(errno));
                    close(client_fd);
                    exit(1);
                }
            } /* Child process loop */
        }
    }

    close(listen_fd);
    return 0;
}