mc-server-manager/agent/source/app.d

import std.stdio;
import std.json;
import std.algorithm;
import std.string;
import std.array;
import std.process;
import std.file;
import std.path;
import std.datetime;
import std.conv;

import requests;
import mcrcd;

import shared_utils.server_status;
import shared_utils.discord;

/**
 * The set of information about each server that we can obtain by reading the
 * server's directory and files in it (service file, properties, etc.).
 */
struct ServerInfo {
	/// The name of the server, as declared in servers.json.
	string name;
	/// The directory to find the server's files in.
	string directory;
	/// The name of the server's SystemD service, as determined by searching the server's directory.
	string serviceName;
	ushort port;
	string rconPassword;
	ushort rconPort;
	int maxPlayers;
}

struct AgentConfig {
	string webUrl = "http://localhost:8080";
	string agentKey = "abc";
	int serverInactivityTimeoutMinutes = 30;
}

/**
 * This program will run frequently (maybe every minute or more), and does the following:
 * - Fetches a list of requested servers from the mc-server-manager API, and starts them.
 * - Checks for any servers without any players online, and writes a blank file to track.
 * - For servers with nobody online, and a timestamp file older than N minutes, the server is shut down.
 */
void main() {
	AgentConfig config = readConfig();
	ServerInfo[] servers = getServers();
	ServerStatus[] statuses = servers.map!(getStatus).array;
	try {
		sendServerStatusToWeb(statuses, config);
	} catch (Exception e) {
		stderr.writeln(e.msg);
	}
	checkForEmptyServers(servers, statuses, config);
	try {
		startRequestedServers(servers, config);
	} catch (Exception e) {
		stderr.writeln(e.msg);
	}
}

void sendServerStatusToWeb(ServerStatus[] statuses, AgentConfig config) {
	import std.json;
	import requests;
	JSONValue jsonPayload = serializeServerStatuses(statuses);
	string payload = jsonPayload.toJSON();
	Request rq = Request();
	rq.addHeaders(["X-Agent-Key": config.agentKey]);
	Response resp = rq.post(config.webUrl ~ "/api/servers", payload, "application/json");
	if (resp.code >= 300) {
		import std.format;
		throw new Exception(
			format!"Failed to post server statuses: Error code %d, Response body: %s"(
				resp.code,
				resp.responseBody
			)
		);
	}
}

void startRequestedServers(ServerInfo[] servers, AgentConfig config) {
	auto content = getContent(config.webUrl ~ "/api/server-requests");
	JSONValue jsonContent = parseJSON(cast(string) content.data);
	string[] serverNames;
	foreach (item; jsonContent.array) {
		serverNames ~= item.str;
	}

	foreach (server; servers) {
		foreach (serverName; serverNames) {
			if (serverName == server.name) {
				writeln("Starting server " ~ serverName);
				Pid pid = spawnProcess(["sudo", "systemctl", "start", server.serviceName]);
				int result = wait(pid);
				if (result != 0) {
					writefln!"Starting server %s failed with code %d"(serverName, result);
					throw new Exception("Failed to start server.");
				}
				import std.format;
				sendDiscordMessage(format!"Started server %s as a result of a user request."(serverName));
			}
		}
	}
}

void checkForEmptyServers(ServerInfo[] servers, ServerStatus[] statuses, AgentConfig config) {
	foreach (i, server; servers) {
		ServerStatus status = statuses[i];
		const string idleTrackerFile = "agent-idle-tracker__" ~ server.name ~ ".txt";
		if (std.file.exists(idleTrackerFile)) {
			// Tracker file already exists.
			if (status.online && status.playersOnline > 0) {
				// Players are active, remove the tracker file.
				std.file.remove(idleTrackerFile);
				writeln("Removed idle tracker for server " ~ server.name);
			} else if (status.online && status.playersOnline == 0) {
				// No players are active, check if trackerfile is older than N minutes.
				SysTime timestamp = std.file.timeLastModified(idleTrackerFile);
				Duration dur = Clock.currTime - timestamp;
				writefln!"Server %s has been idle for at least %d minutes"(server.name, dur.total!"minutes");
				if (dur.total!"minutes" > config.serverInactivityTimeoutMinutes) {
					// Inactivity for too long, so shut down the server.
					writeln("Shutting down server " ~ server.name ~ " after a period of inactivity.");
					import std.process;
					Pid pid = spawnProcess(["sudo", "systemctl", "stop", server.serviceName]);
					int result = wait(pid);
					if (result == 0) {
						std.file.remove(idleTrackerFile);
						import std.format;
						sendDiscordMessage(format!"Shut down server %s after inactivity for more than %d minutes."(
							server.name,
							config.serverInactivityTimeoutMinutes
						));
					} else {
						stderr.writefln!"Failed to stop server %s. systemctl stop exited with code %d."(server.name, result);
					}
				}
			}
		} else if (status.online && status.playersOnline == 0) {
			// Create new tracker file.
			File f = File(idleTrackerFile, "w");
			f.close();
			writeln("Created idle tracker for server " ~ server.name ~ " because nobody is online.");
		}
	}
}

ServerInfo[] getServers() {
	import std.json;
	import properd;

	JSONValue arr = parseJSON(readText("servers.json"));
	return arr.array.map!((s) {
		ServerInfo info;
		info.name = s.object["name"].str;
		info.directory = s.object["directory"].str;
		string propsFile = buildPath(info.directory, "server.properties");
		if (!exists(propsFile)) throw new Exception("Missing server properties file: " ~ propsFile);
		try {
			auto props = readProperties(propsFile);
			info.port = props.as!(ushort)("server-port");
			info.rconPassword = props["rcon.password"];
			info.rconPort = props.as!(ushort)("rcon.port");
			info.maxPlayers = props.as!(int)("max-players");
		} catch (PropertyException e) {
			stderr.writefln!"Error parsing properties from %s: %s"(propsFile, e.msg);
			throw e;
		}

		info.serviceName = null;
		foreach (DirEntry entry; dirEntries(info.directory, SpanMode.shallow, false)) {
			if (entry.name.endsWith(".service")) {
				info.serviceName = baseName(stripExtension(entry.name));
				break;
			}
		}
		if (info.serviceName is null) throw new Exception("No SystemD service file found in " ~ info.directory);

		return info;
	}).array;
}

ServerStatus getStatus(ServerInfo server) {
	ServerStatus status;
	status.identifier = server.name;
	status.name = server.name; // TODO: Add display name to servers.json.
	status.online = isServiceActive(server.serviceName);
	status.maxPlayers = server.maxPlayers;
	if (status.online) {
		MCRconResponse response = executeRconCommand(server, "list");
		string playersList;
		int tmp;
		import std.format;
		response.text.formattedRead!"There are %d of a max of %d players online: %s"(
			status.playersOnline,
			tmp,
			playersList
		);
		status.playerNames = playersList.strip.split(",")
			.filter!(s => s !is null && s.strip.length > 0)
			.map!(s => s.strip)
			.array;
	}
	return status;
}

bool isServiceActive(string serviceName) {
	import std.process;
	Pid pid = spawnProcess(["systemctl", "is-active", "--quiet", serviceName]);
	int result = wait(pid);
	return result == 0;
}

MCRconResponse executeRconCommand(ServerInfo server, string command) {
	MCRcon rcon = new MCRcon();
	rcon.connect("127.0.0.1", server.rconPort);
	scope(exit) {
		rcon.disconnect();
	}
	rcon.login(server.rconPassword);
	return rcon.command(command);
}

AgentConfig readConfig() {
	import properd;
	AgentConfig config;
	if (std.file.exists("agent-config.properties")) {
		auto props = readProperties("agent-config.properties");
		config.webUrl = props["webUrl"];
		config.agentKey = props["agentKey"];
		config.serverInactivityTimeoutMinutes = props.as!(int)("serverInactivityTimeoutMinutes");
	}
	return config;
}