/*******************************************************************************
*
* single_document_webserver.c
*        
* AUTHOR:
*   Dan Harkless                                                    <opensource@
*   http://harkless.org/dan/software/                              harkless.org>
* 
* COPYRIGHT:
*   This file is Copyright (C) 2000 by Dan Harkless, and is released under the
*   GNU General Public License <http://www.gnu.org/copyleft/gpl.html>.
*
* USAGE:
*   % single_document_webserver <HTML_file> [<port>]
*
* EXAMPLE:
*   % single_document_webserver under_construction.html 8080
*                                                                            
* DESCRIPTION:                                                               
*   A very simple webserver that just outputs a fixed HTML file for every HTTP
*   request it gets.  This can be useful if you need to output some kind of
*   "under construction" or "we are experiencing technical difficulties" type of
*   page but can't or don't want to use a full-blown webserver.  Note that if
*   you refer to any graphics in your HTML file, they'll need to be absolute
*   URLs to images served by another machine.
*
*   By default this program binds to port 80, but you can specify an alternate
*   port if desired.  The port is bound to on all interfaces / addresses,
*   which may or may not be what you want on multi-homed hosts.
*
* COMPILATION:
*   AIX/...:  % cc single_document_webserver.c -o single_document_webserver
*   Solaris:  % cc single_document_webserver.c -lsocket \
*               -o single_document_webserver
*
* DATE        MODIFICATION
* ==========  ==================================================================
* 2000-09-19  Original.
*                                                                            
*******************************************************************************/


#include <sys/types.h>   /* must precede <sys/stat.h> */

#include <sys/stat.h>    /* must precede <fcntl.h> */

#include <errno.h>       /* for errno */
#include <fcntl.h>       /* for O_RDONLY */
#include <netinet/in.h>  /* for struct sockaddr_in, etc. */
#include <stdio.h>       /* for fprintf(), etc. */
#include <stdlib.h>      /* for EXIT_FAILURE, etc. */
#include <string.h>      /* for strerror(), etc. */
#include <sys/socket.h>  /* for socket(), etc. */
#include <unistd.h>      /* for close() */


#define HTTP_HEADER      "HTTP/1.0 200 OK\nContent-Type: text/html\n\n"
#define MAX_LISTEN_QUEUE 1024  /* arbitrary but should always be OK */


char*  our_program_name_global;


void  die(char*  failed_syscall) {
    fprintf(stderr, "%s: %s(): %s.  Aborting.\n",
	    our_program_name_global, failed_syscall, strerror(errno));

    exit(EXIT_FAILURE);
}


int  main(int  argc, char**  argv) {
    char*               HTML_filename;
    char*               last_slash_in_argv_0 = strrchr(argv[0], '/');
    int                 HTML_fd, listen_fd, port;
    struct sockaddr_in  server_address;

    if (last_slash_in_argv_0 == NULL)
	our_program_name_global = argv[0];
    else
	our_program_name_global = last_slash_in_argv_0 + 1;
	
    if (argc < 2 || argc > 3) {
	fputs("Usage: single_document_webserver <HTML_file> [<port>]\n",
	      stderr);
	return EXIT_FAILURE;
    }

    HTML_filename = argv[1];

    HTML_fd = open(HTML_filename, O_RDONLY);
    if (HTML_fd < 0)
	die("open");

    if (argc == 3)
	port = atoi(argv[2]);
    else
	port = 80;

    listen_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (listen_fd < 0)
	die("socket");

    memset(&server_address, 0, sizeof(server_address));
    server_address.sin_addr.s_addr = htonl(INADDR_ANY);
    server_address.sin_family = AF_INET;
    server_address.sin_port = htons(port);

    if (bind(listen_fd, (struct sockaddr*)&server_address,
	     sizeof(server_address)) < 0)
	die("bind");

    if (listen(listen_fd, MAX_LISTEN_QUEUE) < 0)
	die("listen");

    while (1) {
	char  buffer[BUFSIZ];
	char  char_1_back=' ', char_2_back=' ', char_3_back=' ', this_char=' ';
	int   accept_fd = accept(listen_fd, (struct sockaddr*)NULL, NULL);
	int   result;

	if (accept_fd < 0)
	    die("accept");

	/* Eat HTTP commands. */
	do {
	    /* Read byte-by-byte to ease detection of "\r\n\r\n". */
	    result = read(accept_fd, buffer, 1);
	    if (result < 0)
		die("read");
	    else if (result == 0)
		break;  /* client closed connection before "\r\n\r\n" */
	    
	    char_3_back = char_2_back;
	    char_2_back = char_1_back;
	    char_1_back = this_char;

	    this_char = buffer[0];
	}
	while (!(char_3_back == '\r' && char_2_back == '\n' &&
		 char_1_back == '\r' && this_char == '\n'));

	if (result != 0) {
	    /* Output the HTTP header. */
	    if (write(accept_fd, HTTP_HEADER, sizeof(HTTP_HEADER) - 1) < 0)
		die("write");
	    
	    /* Rewind the HTML file. */
	    if (lseek(HTML_fd, 0, SEEK_SET) == -1)  /* "< 0" not cool here */
		die("lseek");
	    
	    /* Output the HTML file. */
	    do {
		result = read(HTML_fd, buffer, BUFSIZ);
		if (result < 0)
		    die("read");
		
		if (write(accept_fd, buffer, result) < 0)
		    die("write");
	    }
	    while (result > 0);
	}

	/* Close this network connection. */
	if (close(accept_fd) < 0)
	    die("close");
    }

    return EXIT_SUCCESS;  /* never reached -- here to make the compiler happy */
}