Simple nodejs HTTP server with exceptions & URL handling

serv.js

#!/usr/bin/env node
// [email protected]
// http://jessie.z.je/serv.js
// Sun May 15 01:38:52 CEST 2016
// Missing modules? npm install <name>
//
// user@libcrack:~$ url="http://127.0.0.1:3003"
// user@libcrack:~$ for i in {0..9}; do msg "$url/$i"; curl -s "$url/$i"; done
// [*] http://127.0.0.1:3003/0
// [*] http://127.0.0.1:3003/1
// [*] http://127.0.0.1:3003/2
// [*] http://127.0.0.1:3003/3
// [*] http://127.0.0.1:3003/4
// [*] http://127.0.0.1:3003/5
// [*] http://127.0.0.1:3003/6
// [*] http://127.0.0.1:3003/7
// [*] http://127.0.0.1:3003/8
// [*] http://127.0.0.1:3003/9
//
// user@libcrack:~$ ./serv.js
// [0.0.0.0:3003] HTTP Server started at 0.0.0.0:3003
// [127.0.0.1] ======================================
// [127.0.0.1] New client (1) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=55851
// [127.0.0.1] Requested path /0
// [127.0.0.1] Received invalid value "0" != "55851"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (2) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=56965
// [127.0.0.1] Requested path /1
// [127.0.0.1] Received invalid value "1" != "56965"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (3) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=55787
// [127.0.0.1] Requested path /2
// [127.0.0.1] Received invalid value "2" != "55787"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (4) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=54941
// [127.0.0.1] Requested path /3
// [127.0.0.1] Received invalid value "3" != "54941"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (5) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=54929
// [127.0.0.1] Requested path /4
// [127.0.0.1] Received invalid value "4" != "54929"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (6) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=57177
// [127.0.0.1] Requested path /5
// [127.0.0.1] Received invalid value "5" != "57177"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (7) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=56099
// [127.0.0.1] Requested path /6
// [127.0.0.1] Received invalid value "6" != "56099"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (8) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=56172
// [127.0.0.1] Requested path /7
// [127.0.0.1] Received invalid value "7" != "56172"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (9) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=55545
// [127.0.0.1] Requested path /8
// [127.0.0.1] Received invalid value "8" != "55545"
// [127.0.0.1] ======================================
// [127.0.0.1] New client (10) from 127.0.0.1
// [127.0.0.1] val=0
// [127.0.0.1] val=0080
// [127.0.0.1] val=6400
// [127.0.0.1] val=56949
// [127.0.0.1] Requested path /9
// [127.0.0.1] Received invalid value "9" != "56949"

const url = require("url");
const http = require("http");
const crypto = require("crypto");
const system = require("system");

var tmout = 5000;
var lport = 3003;
// var lhost = "127.0.0.1";
var lhost = "0.0.0.0";
var totalClients = 0;

// XXX TypeError: Cannot read property 'length' of undefined
//
// // Pase arguments
// if (system.args.length < 2) {
//     console.log("\nUsage: "+ system.args[0] + "<ip>:<port>");
//     console.log("  ip   : listener IP address");
//     console.log("  port : listener TCP port number");
//     console.log("");
//     console.log("\n  example: " + system.args[0] + "0.0.0.0:3000\n")
//     exit(1);
// } else {
//     lport = system.args[1].split(":")[0];
//     lhost = system.args[1].split(":")[1];
// }

// --- Get random value (the lol way) -------
// @param s: input string
// @returns: sha256 hash of param s
function getRandom(s) {
    return crypto.createHash("sha256").
    update(s).digest("binary")[0];
}

// --- Get client address -------------------
// @param req: HTTP client request
// @returns: HTTP client IP address
//var getClientAddr = function(req) {
function getClientAddr(req) {
    return (req.headers["x-forwarded-for"] || "").split(",")[0] || req.connection.remoteAddress;
};

// --- 404 not found handler ----------------
// @param res: HTTP server response
// @returns: none
// var handle404 = function (res) {
function handle404(res) {
    res.writeHead(404, {
        "Content-Type": "text/plain"
    });
    res.write("404 Not Found\r\n");
    res.end();
}

// --- HTTP server dispatch callback --------
// handleReqResp = function (req, res){...});
// server = http.createServer(handleReqResp);
var server = http.createServer(function(req, res) {

    res.writeHead(200, {
        "Content-Type": "text/plain"
    });

    var flag = "8===============D";
    var rawip = getClientAddr(req);
    var secret = "105b2f2c9b32f99d8df";
    var ip = new Number(rawip.replace(/\./g, ""));
    var binip = ip.toString(2);
    var val = 0;

    var log = function(msg) {
        console.log("[" + rawip + "] " + msg);
    }

    totalClients += 1;

    log("========================================");
    log("New client (" + totalClients + ") from " + rawip);
    log("val=" + val);

    for (var i = 1; i <= binip.length; i++) {
        var x = getRandom(secret + binip.slice(0, i));
        if (x < 100) {
            val += x;
        }
    }
    log("val=" + val);

    val *= val;
    log("val=" + val);

    for (var i = 1; i <= 1000; i++) {
        val += Math.floor(Math.random() * 100);
    }
    log("val=" + val);

    // This line of code  caused the below exception to be thrown:
    //     res.end("THIS IS THE FLAG ON THE ACTUAL SERVER");
    //
    // _http_outgoing.js:542
    //     throw new TypeError('First argument must be a string or Buffer');
    //     ^
    // Solution: check if val is empty/null/invalid

    var path = url.parse(req.url).pathname;
    var uval = path.slice(0, 0) + path.slice(1, path.length);
    log("Requested path " + path);

    if (uval == "") {
        log("Received empty value");
        res.end();
    } else if (uval == val) {
        log("Received valid value \"" + uval + "\" == \"" + val + "\"");
        log("Sending flag \"" + flag + "\" to " + rawip);
        res.write(flag + "\r\n");
        res.end();
    } else {
        log("Received invalid value \"" + uval + "\" != \"" + val + "\"");
        res.end();
    }

    // XXX: req.url.slice(req.url.indexOf('/') fails when path is empty
    //
    // console.log("req.url.slice(req.url.indexOf('/') + 1 = " +
    //         req.url.slice(req.url.indexOf("/") + 1));
    //
    // if (req.url.slice(req.url.indexOf("/") + 1) == val) {
    //     console.log("Sending flag to " + rawip);
    //     res.write("THIS IS THE FLAG ON THE ACTUAL SERVER\r\n");
    //     res.end();
    // } else {
    //    console.log("Sending val=" + val + " to " + rawip);
    //    res.write("null\r\n");
    //    res.end(val);
    // }

});

// --- HTTP server listener -----------------
server.listen(lport, lhost, function() {
    console.log("[" + lhost + ":" + lport + "] " +
        "HTTP Server started at " + lhost + ":" + lport);
});

// --- HTTP server exception handler --------
server.on("error", function(e) {
    if (e.code == "EADDRINUSE") {
        console.log("[" + lhost + ":" + lport + "] " +
            "Address " + lhost + ":" + lport + " in use");
        console.log("[" + lhost + ":" + lport + "] " +
            "Waiting " + tmout / 1000 + " seconds for a free slot");

        setTimeout(function() {
            server.close();
            server.listen(lport, lhost);
        }, tmout);
    }
});