//*****************************************************************************
//
// listener.cc
//
// by solthae
// Simple server code that allows for remote connections.
// Can have various uses (honeypot, listener, mud server, etc.).
// I've hardcoded it to run on localhost with no specific service being run,
// in hopes that those wishing to mod it for multiple clients, specific
// services, etc. will follow up and learn more on their own.
//
// Compile: g++ -o listener listener.cc
//
// Usage: ./listener 2600 &
//
// This will leave a process running as seen with 'ps,' listening for 
// connections on port 2600.
//*****************************************************************************

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

// error() reports an error then exits program
void error(const char *err) {
	perror(err);
	exit (1);
}

int main(int argc, char **argv) {
	int z;
	int x;
	struct sockaddr_in serverAddress;  // AF_INET family
	struct sockaddr_in clientAddress;  // AF_INET family
	unsigned short portNumber;
	FILE *rStream = NULL;              // Read stream
	FILE *wStream = NULL;              // Write stream
	int s;                             // Socket
	int c;                             // Client socket
	char buf[4096];                    // IO buffer
	socklen_t addrlen;                 // For accept(2) when using g++

	// Check for correct argument usage
	if (argc != 2) {
		fprintf(stderr, "Usage: %s <port number>\n", argv[0]);
		exit (1);
	}

	// Assign supplied argument as port number
	portNumber = atoi(argv[1]);

	// Create a TCP/IP socket to use
	if ((s = socket(PF_INET, SOCK_STREAM, 0)) == -1 )
			error("socket(2)");
	
	// Fill in local address structure, that'd be our server address
	memset(&serverAddress, 0, sizeof(serverAddress));  // Clear out struct
	serverAddress.sin_family = AF_INET;                // Internet address family
	serverAddress.sin_addr.s_addr = htonl(INADDR_ANY); // Any incoming interface
	serverAddress.sin_port = htons(portNumber);        // Local port to use

	// Bind to server address
	if ((z = bind(s, (struct sockaddr *) &serverAddress, sizeof(serverAddress))) == -1)
		error("bind(2)");

	// Make it a listening socket
	if ((z = listen(s, 10)) == -1)
		error("listen(2)");

	// The server loop
	for (;;) {
		// Wait for a connection
		addrlen = sizeof(clientAddress);

		if ((c = accept(s, (struct sockaddr *) &clientAddress, &addrlen)) == -1)
			error("accept(2)");

		// The read stream is where the clients requests are going to be coming in
		// through (don't mix them up)
		// Create read stream
		if (!(rStream = fdopen(c, "r"))) {
			close(c);
			continue;
		}

		// The write stream in where you are going to print you message (like requests)
		// to the client (don't mix them up)
		// Create write stream
		if (!(wStream = fdopen(dup(c), "w"))) {
			fclose(rStream);
			continue;
		}

		// Set both streams to line buffered mode
		setlinebuf(rStream);
		setlinebuf(wStream);

		printf("-------------------------------------\n");
		printf("- Put a telnet message here for fun -\n");
		printf("-------------------------------------\n");

		//	*** NOTE TO READERS ***
		// This is the main workhorse of the code.
		// This takes requests from the client through the read stream rStream.
		// You then can process these 'requests' (i.e., send text, etc.)
		// as a 'char buf[]' (i.e., string).
		//
		// Below:
		// Process 1 echo's sent command.
		// Process 2 prints 'stringlen'.
		// Process 3 goes through 'buf' one-by-one printing the chars.
		// Enjoy making creative ways to process 'buf' from different clients.
		//
		// Process clients requests
		while (fgets(buf, sizeof buf, rStream)) {
			printf("\nEcho: %s", buf);          // Process 1
			printf("\nSize: %d", strlen(buf));  // Process 2

			for (x = 0; x < strlen(buf); x++)
				printf("\n%c", buf[x]);
		}

		// Close client's connection
		fclose(wStream);
		shutdown(fileno(rStream), SHUT_RDWR);
		fclose(rStream);

	}

	// If control gets here there's a problem with time/space
	return 0;
}