/*
 * Proxy.c
 *  This program is a Basic HTTP proxy which receives the HTTP Requests from the web browser
 *  and forward it to the desired web server. After receiving the response from the web server
 *  it forward it to the web browser of the client.
 *  The proxy listens on port 8001
 *  Created on: Jan 23, 2018
 */

/* Standard libraries */
#include <stdio.h>
#include <stdlib.h>

/* Libraries for socket programming */
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

/* Library for parsing strings */
#include <string.h>
#include <strings.h>

/* h_addr?! */
#include <netdb.h>

/* Clean exit! */
#include <signal.h>

int lstn_sock;

/* The function will run after catching Ctrl+c in terminal */
void catcher(int sig) {
	close(lstn_sock);
	printf("catcher with signal  %d\n", sig);
	exit(0);

}

int main() {

	/* For catching Crtl+c in terminal */
	signal(SIGINT, catcher);
	int lstn_port = 8001;

	/* Initializing the Address */
	struct sockaddr_in addr_proxy;
	addr_proxy.sin_family = AF_INET;
	addr_proxy.sin_addr.s_addr = htonl(INADDR_ANY);
	addr_proxy.sin_port = htons(lstn_port);
	printf("Address Initialization: done.\n");

	/* Creating the listening socket for proxy */
	lstn_sock = socket(AF_INET, SOCK_STREAM, 0);
	if (lstn_sock < 0) {
		printf("Error in socket() call.\n");
		exit(-1);
	} else {
		printf("Listening Socket creation: done.\n");
	}

	/* Binding the socket to address and port */
	int bind_status;
	bind_status = bind(lstn_sock, (struct sockaddr *) &addr_proxy,
			sizeof(struct sockaddr_in));
	if (bind_status < 0) {
		printf("Error in bind() call.\n");
		exit(-1);
	} else {
		printf("Binding: done.\n");
	}

	/* Listening on binded port number */
	int lstn_status;
	lstn_status = listen(lstn_sock, 10);
	if (lstn_status < 0) {
		printf("Error in listen() call.\n");
		exit(-1);
	}
	/* Infinite while loop for listening accepting connection requests */
	while (1) {
		/* Accepting connection requests */
		int data_sock;
		data_sock = accept(lstn_sock, NULL, NULL);
		if (data_sock < 0) {
			printf("Error in accept() call");
			exit(-1);
		} else {
			printf("Accepting connection request: done.\n");
		}

		/* Receiving HTTP message from the client */
		char c_message_in[1024];
		char s_message_out[1024];
		int c_recv_status;
		c_recv_status = recv(data_sock, c_message_in, sizeof(c_message_in), 0);
		if (c_recv_status < 0) {
			printf("Error in recv() call for client recv message\n");
			exit(-1);
		} else {
			printf("############################################\n");
			printf("## HTTP message received from the client. ##\n ");
			printf("############################################\n");
		}

		/* Preserving the HTTP request for sending it to the web server later */
		strcpy(s_message_out, c_message_in);

		/* Parsing the HTTP message to extract the HOST name of the desired web server */
		char host[1024];
		char URL[1024];
		char PATH[1024];
		int i;

		// find and parse the GET request, isolating the URL for later use
		char *pathname = strtok(c_message_in, "\r\n");
		printf("Found HTTP request: %s\n", pathname);
		if (sscanf(pathname, "GET http://%s", URL) == 1)
			printf("URL = %s\n", URL);

		// seperate the hostname from the pathname
		for (i = 0; i < strlen(URL); i++) {
			if (URL[i] == '/') {
				strncpy(host, URL, i); //copy out the hostname
				host[i] = '\0';
				break;
			}
		}

		bzero(PATH, 500); //to clear junk at the beginning of this buffer. don't know why its there
		for (; i < strlen(URL); i++) {
			strcat(PATH, &URL[i]); //copy out the path
			break;
		}
		printf("******************************\n");
		printf("First Half(host): %s\n", host); //firstHalf is the hostname
		printf("Second Half(path): %s\n", PATH); //secondHalf is the path
		printf("******************************\n");

		/* Creating the TCP socket for connecting to the desired web server */
		// Address initialization
		struct sockaddr_in addr_server;
		struct hostent *server;

		// Getting web server's Address by its host name
		server = gethostbyname(host);
		if (server == NULL)
			printf("Error in gethostbyname() call.\n");
		else
			printf("Web server = %s\n", server->h_name);

		// Initialize socket structure
		bzero((char *) &addr_server, sizeof(addr_server));
		addr_server.sin_family = AF_INET;
		bcopy((char *) server->h_addr, (char *) &addr_server.sin_addr.s_addr, server->h_length);
		addr_server.sin_port = htons(80);

		// Creating the socket
		int web_sock = socket(AF_INET, SOCK_STREAM, 0);
		if (web_sock < 0) {
			printf(
					"Error in socket() call for creating --proxy-WebServer-- socket.\n");
		} else {
			printf("###############################################\n");
			printf("## --proxy-WebServer-- socket creation: done ##\n");
			printf("###############################################\n");
		}

		// Connecting to the web server's socket
		int connect_status;
		connect_status = connect(web_sock, (struct sockaddr *) &addr_server,
				sizeof(addr_server));
		if (connect_status < 0) {
			printf(
					"Error in connect() call for connecting to the web server's socket.\n");
			exit(-1);
		} else {
			printf("Web server's socket connection establishment: done\n ");
		}

		/* Sending the HTTP request of the client to the web server */
		int web_send_status;
		web_send_status = send(web_sock, s_message_out, sizeof(c_message_in),
				0);
		if (web_send_status < 0) {
			printf(
					" Error in send() call for sending HTTP request to the web server.\n ");
			exit(-1);
		} else {
			printf("##############################################\n");
			printf("## Sending HTTP request to the server: done ##\n");
			printf("##############################################\n");
		}

		/* Receiving the HTTP response from the web server */
		char w_message_in[10000];
		int web_recv_status;
		web_recv_status = recv(web_sock, w_message_in, sizeof(w_message_in), 0);
		if (web_recv_status < 0) {
			printf(
					" Error in recv() call for receiving web server's HTTP response.\n ");
			exit(-1);
		} else {
			printf("################################################\n");
			printf("## Receiving web server's HTTP response: done ##\n");
			printf("################################################\n");
		}
		/* Closing the socket connection with the web server */
		close(web_sock);
		/* Sending the HTTP response to the client */
		int c_send_status;
		c_send_status = send(data_sock, w_message_in, sizeof(w_message_in), 0);
		if (c_send_status < 0) {
			printf(
					"Error in send() call for sending HTTP response to the client.\n");
			exit(-1);
		} else {
			printf("###############################################\n");
			printf("## Sending HTTP response to the client: done ##\n");
			printf("###############################################\n");
		}
		/* Closing the socket connection with the client */
		close(data_sock);
		printf("data socket is closed.\n");
	}
	close(lstn_sock);
	printf("lstn_sock is closed.\n");
	return 0;

}