Web server example written on C language (Mac OS)

main.h

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

// global constants
#define PORT 8080  // port to connect on
#define LISTENQ 10 // number of connections

int list_s; // listening socket

// clean up listening socket on ctrl-c
void cleanup(int sig)
{
    printf("Cleaning up connections and exiting.\n");

    // try to close the listening socket
    if (close(list_s) < 0)
    {
        fprintf(stderr, "Error calling close()\n");
        exit(EXIT_FAILURE);
    }

    // exit with success
    exit(EXIT_SUCCESS);
}

int main()
{
    int conn_s;
    struct sockaddr_in servaddr;

    char send_buffer[1025];

    // set up signal handler for ctrl-c
    (void)signal(SIGINT, cleanup);

    // socket create and verification
    if ((list_s = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        fprintf(stderr, "Error creating listening socket.\n");
        exit(EXIT_FAILURE);
    }

    // set all bytes in socket address structure to zero
    memset(&servaddr, 0, sizeof(servaddr));

    // assign IP, PORT
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(PORT);

    // binding newly created socket to given IP and verification
    if (bind(list_s, (struct sockaddr *)&servaddr, sizeof(servaddr)) != 0)
    {
        fprintf(stderr, "Error calling bind()\n");
        exit(EXIT_FAILURE);
    }

    // now server is ready to listen and verification
    if ((listen(list_s, LISTENQ)) == -1)
    {
        fprintf(stderr, "Error Listening\n");
        exit(EXIT_FAILURE);
    }

    // Size of the address
    int addrlen = sizeof(servaddr);

    memset(send_buffer, 0, sizeof(send_buffer));
    snprintf(send_buffer, sizeof(send_buffer), "HTTP/1.1 200 OK\nContent-Type: text/html\nContent-Length: 21\n\n<b>Hello, world!</b>\n");

    // Have the child loop infinetly dealing with a connection then getting the next one in the queue
    while (1)
    {
        // Accept a connection
        conn_s = accept(list_s, (struct sockaddr *)&servaddr, (socklen_t *)&addrlen);

        // If something went wrong with accepting the connection deal with it
        if (conn_s == -1)
        {
            fprintf(stderr, "Error accepting connection\n");
            exit(EXIT_FAILURE);
        }

        // buffer 1M
        char buffer[1024*1024] = {0};
        long valread = read( conn_s , buffer, 1024*1024);

        write(conn_s, send_buffer, strlen(send_buffer));

        // Close the connection now were done
        close(conn_s);
    }
}