Reworked the network code to improve sending rate management

lib/api.js

@@ -1,12 +1,45 @@
 import * as fs from 'fs';
+import * as events from 'events';
 
 import { getToken } from '../database/config.js';
 import { PriorityQueue } from './priority_queue.js';
 
-let busy = false; // lets us know if we are already sending api requests or not.
+// queue processor module variables
+const bus = new events.EventEmitter(); // a bus to notify the queue processor to start processing messages
+let busy = false; // true if we are already sending api requests.
+let backoffSeconds = 0;
+let running = false;
+// other module variables
 let headers = undefined; // a file scope variable so that we only evaluate these once.
 let queue = new PriorityQueue(); // a priority queue to hold api calls we want to send, allows for throttling.
 
+// a single queue processor should be running at any time, otherwise there will be trouble!
+async function queue_processor() {
+	if (running) {
+		throw 'refusing to start a second queue processor';
+	}
+	running = true;
+	while(true) {
+		try {
+			if (backoffSeconds > 0) {
+				await sleep(backoffSeconds * 1000);
+				backoffSeconds = 0;
+			}
+			if (queue.isEmpty()) {
+				busy = false;
+				await new Promise(resolve => bus.once('send', resolve));
+				busy = true;
+			}
+			await send_this(queue.dequeue().element);
+			await sleep(400); // 333 should work, but 400 should still allow some manual requests to go through during development
+		} catch (e) {
+			running = false;
+			throw e;
+		}
+	}
+}
+queue_processor();
+
 // send takes a request object as argument and an optional context ctx
 // example request: {
 //    endpoint: the path part of the url to call,
@@ -22,25 +55,15 @@ export function send(request, ctx) {
 			request: request,
 			resolve: resolve,
 		};
-		if (!busy) {
-			busy = true;
-			send_this(data);
-		} else {
 		queue.enqueue(data, request.priority ? request.priority : 10);
+		if (!busy) {
+			bus.emit('send'); // the queue was previously empty, let's wake up the queue_processor
 		}
 	});
 }
 
-function send_next() {
-	if (queue.isEmpty()) {
-		busy = false;
-	} else {
-		send_this(queue.dequeue().element);
-	}
-}
-
 // send_this take a data object as argument built in the send function above
-function send_this(data) {
+async function send_this(data) {
 	if (headers === undefined) {
 		const token = getToken();
 		if (token === null) {
@@ -61,29 +84,33 @@ function send_this(data) {
 		options['body'] = JSON.stringify(data.request.payload);
 	}
 	fs.writeFileSync('log', JSON.stringify({event: 'send', date: new Date(), data: data}) + '\n', {flag: 'a+'});
-	fetch(`https://api.spacetraders.io/v2${data.request.endpoint}`, options)
+	let response = await fetch(`https://api.spacetraders.io/v2${data.request.endpoint}`, options);
-		.then(response => response.json())
+	if (response.ok) {
-		.then(async response => {
+		response = await response.json();
 		switch(response.error?.code) {
-				//case 401: // 401 means a server reset happened
+			//case 401: // TODO 401 means a server reset happened
 			// close database file
 			// rm database file
 			// logrotate
 			// spawnSync
 			// break;
-			case 429:  // 429 means rate limited, let's hold back for 10 seconds
+		case 429:  // 429 means rate limited, let's hold back as instructed
-				await sleep(10000);
+			backoffSeconds = response.error.data.retryAfter;
 			queue.enqueue(data, 1);
 			break;
-			default:
+		default: // no error!
 			fs.writeFileSync('log', JSON.stringify({event: 'response', date: new Date(), data: response}) + '\n', {flag: 'a+'});
 			return data.resolve(response);
-			}})
+		}
-		.catch(async err => {
+	} else {
-			fs.writeFileSync('log', JSON.stringify({event: 'error', date: new Date(), data: err}) + '\n', {flag: 'a+'});
+		fs.writeFileSync('log', JSON.stringify({event: 'error', date: new Date(), data: response}) + '\n', {flag: 'a+'});
-			switch(err.cause?.code) {
+		switch(response.cause?.code) {
 		case 503:  // 503 means maintenance mode, let's hold back for 1 minute
-				await sleep(60000);
+			backoffSeconds = 60;
+			queue.enqueue(data, 1);
+			break;
+		case 'EAI_AGAIN': // DNS lookup timed out error, let's hold back for 5 seconds
+			backoffSeconds = 5;
 			queue.enqueue(data, 1);
 			break;
 		case 'ECONNRESET':
@@ -93,9 +120,9 @@ function send_this(data) {
 			queue.enqueue(data, 1);
 			break;
 		default:
-				data.reject(err);
+			data.reject(response);
-			}});
+		}
-	setTimeout(send_next, 400); // 333 should work, but 400 will still allow manual requests to go through during development
+	}
 }
 
 export function debugLog(ctx) {