MCSignOnDoor in D

MCSOD.d

/*
* MCSignOnDoor rewrite in D by jkcclemens <jkc.clemens@royaldev.org>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
module org.royaldev.mcsod.MCSOD;

import std.stdio: writeln, writefln;
import std.c.stdlib: exit;
import std.conv: to;
import std.socket: Socket, SocketException, SocketType, AddressFamily, InternetAddress;
import std.getopt: getopt, config;

string host = "localhost";
short port = 25565;
string motd = "Server is down.";
int onlinePlayers = 0;
int maxPlayers = 20;

MCSOD mcsod = null;

extern(C) private void shutdown(int value) {
    if (mcsod !is null) mcsod.shutdown();
    exit(1);
}

private void main(string[] args) {
    version (Posix) { // posix support only; windows should learn to be a legit OS
        import core.sys.posix.signal: sigset, SIGINT;
        sigset(SIGINT, &shutdown);
    }
    bool help = false;
    getopt(
        args,
        config.caseSensitive,
        config.bundling,
        config.passThrough,
        "h|help", &help,
        "H|host", &host,
        "p|port", &port,
        "m|motd", &motd,
        "o|online-players", &onlinePlayers,
        "P|max-players", &maxPlayers
    );
    if (help) {
        writeln("Usage: ", args[0], " [-H host] [-p port] [-m motd] [-o onlinePlayers] [-P maxPlayers]");
        writeln("-H | --host\n\tSets the hostname to bind to.\n\tDefaults to \"localhost\"");
        writeln("-p | --port\n\tSets the port to bind to.\n\tDefaults to 25565");
        writeln("-m | --motd\n\tSets the Message of the Day to display.\n\tDefaults to \"Server is down.\"");
        writeln("-o | --online-players\n\tSets the amount of online players to display.\n\tDefaults to 0.");
        writeln("-P | --max-players\n\tSets the maximum amount of players to display.\n\tDefaults to 20.");
        exit(0);
    }
    mcsod = new MCSOD();
}

public class MCSOD {

    Socket s = null;
    Socket c = null;

    public this() {
        try {
            s = new Socket(AddressFamily.INET, SocketType.STREAM);
            s.bind(new InternetAddress(host, port));
        } catch (SocketException s) {
            writeln("Couldn't connect!");
            exit(1);
        }
        s.listen(100);
        while (true) {
            c = s.accept();
            writeln("Connection from ", c.remoteAddress().toAddrString(), ":", c.remoteAddress().toPortString(), ".");
            while (c.isAlive()) {
                int length = fromVarint(c);
                if (length < 1) {
                    c.close();
                    continue;
                }
                int packetID = fromVarint(c);
                if (packetID != 0) {
                    writefln("Invalid packet ID: %s", packetID);
                    c.close();
                    continue;
                }
                int protocolVersion = fromVarint(c);
                if (protocolVersion != 4) {
                    writefln("Invalid protocol version: %s", protocolVersion);
                    c.close();
                    continue;
                }
                int stringLength = fromVarint(c);
                if (stringLength < 1) c.close();
                if (c.receive(new byte[stringLength]) != stringLength) { // read out host string
                    c.close();
                    continue;
                }
                if (c.receive(new byte[2]) != 2) { // read two bytes for port
                    c.close();
                    continue;
                }
                int nextState = fromVarint(c);
                if (nextState != 1) {
                    writefln("Invalid next state: %s", nextState);
                    c.close();
                    continue;
                }
                if (fromVarint(c) != 1) {
                    c.close();
                    continue;
                }
                packetID = fromVarint(c);
                if (packetID != 0) {
                    writefln("Invalid packet ID: %s", packetID);
                    c.close();
                    continue;
                }
                char[] json =
                "{" ~
                    "\"version\": {" ~
                        "\"name\": \"Offline\"," ~
                        "\"protocol\": 4" ~
                    "}," ~
                    "\"players\": {" ~
                        "\"max\": " ~ to!string(maxPlayers) ~ "," ~
                        "\"online\": " ~ to!string(onlinePlayers) ~
                    "}," ~
                    "\"description\": \"" ~ motd ~ "\"" ~
                "}".dup;
                auto jsonLength = toVarint(json.length);
                auto toSend = toVarint(0) ~ jsonLength ~ cast(ubyte[]) json;
                toSend = toVarint(toSend.length) ~ toSend;
                c.send(toSend);
                writeln("Sent response.");
                c.close();
            }
            if (c.isAlive()) c.close();
        }
    }

    private void shutdown() {
        if (c !is null) c.close();
        if (s !is null) s.close();
    }

    private int fromVarint(Socket s) {
        if (!s.isAlive()) throw new Exception("Socket is closed");
        int d = 0;
        int i = 0;
        while (true) {
            auto bs = new byte[1];
            s.receive(bs);
            auto b = bs[0];
            d |= (b & 0x7F) << 7 * i;
            i++;
            if (!(b & 0x80)) return d;
        }
    }

    private ubyte[] toVarint(long input) {
        ubyte[]ret;
        int x;
        if (input < 0) ret.length = 10; // shortcut negative numbers, this is always the case
        else {
            long tmp = input;
            for (x = 1; tmp >= 128; x++) {
                // arithmetic shift is fine, because we've already checked for
                // negative numbers
                tmp >>= 7;
            }
            ret.length = x;
        }
        for (x = 0; x < ret.length; x++) {
            // set the top bit
            ret[x] = cast(ubyte) (1 << 7);
            ret[x] |= (cast(ubyte) input) & 0b1111111;
            input >>= 7;
        }
        // unset the top bit of the last data element
        ret[$-1] &= 0b1111111;
        return ret;
    }

}