Add based query response system, info broker

The new InfoBroker class' job is to fetch system information and return 
it in a standardised format.

src/lib/SystemQuery.mjs

@@ -3,10 +3,12 @@
 import sysinfo from 'systeminformation';
 
 import Agent from './agent/Agent.mjs';
+import InfoBroker from './core/InfoBroker.mjs';
 
 class SystemQuery {
 	constructor(config) {
 		this.config = config;
+		this.info = new InfoBroker();
 	}
 	
 	async init() {
@@ -24,7 +26,16 @@ class SystemQuery {
 	}
 	
 	async handle_query(peer, msg) {
+		// 1: Validate input
+		if(typeof msg.table !== "string"
+			|| !this.info.is_valid_table(msg.table)) return;
 		
+		// 2: Fetch system info
+		let table = await this.info.fetch_table(msg.table);
+		if(table === null) return;
+		
+		// 3: Return to requester
+		await peer.send("query-response", { result: table });
 	}
 	async handle_query_response(peer, msg) {
 		

src/lib/core/InfoBroker.mjs

@@ -0,0 +1,32 @@
+"use strict";
+
+import sysinfo from 'systeminformation';
+
+import log from '../../lib/io/NamespacedLog.mjs'; const l = log("infobroker");
+
+class InfoBroker {
+	constructor() {
+		this.allowed_tables = {
+			// name → sysinfo name
+			cpu: "cpu",
+		};
+	}
+	
+	is_valid_table(name) {
+		return Object.keys(this.allowed_tables).includes(name);
+	}
+	
+	async fetch_table(name) {
+		if(!(typeof name === "string"))
+			throw new Exception(`Error: Expected name to be of type string, but received value of type ${typeof name} instead.`);
+		
+		if(!this.is_valid_table(name)) {
+			l.warn(`Unrecognised table '${name}' requested, returning null`);
+			return null;
+		}
+		
+		return await sysinfo[this.allowed_tables[name]]();
+	}
+}
+
+export default InfoBroker;