From 31e14a0a069e85398a0cf0acc9d2b267c1413976 Mon Sep 17 00:00:00 2001
From: Julien Dessaux
Date: Sat, 10 Jun 2023 00:56:10 +0200
Subject: Reworked the network code to improve sending rate management

---
 lib/api.js | 125 +++++++++++++++++++++++++++++++++++++------------------------
 1 file changed, 76 insertions(+), 49 deletions(-)

diff --git a/lib/api.js b/lib/api.js
index d8010a9..7bbd156 100644
--- a/lib/api.js
+++ b/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,
 		};
+		queue.enqueue(data, request.priority ? request.priority : 10);
 		if (!busy) {
-			busy = true;
-			send_this(data);
-		} else {
-			queue.enqueue(data, request.priority ? request.priority : 10);
+			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) {
@@ -61,41 +84,45 @@ 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${data.request.endpoint}`, options)
-		.then(response => response.json())
-		.then(async response => {
-			switch(response.error?.code) {
-				//case 401: // 401 means a server reset happened
-				// close database file
-				// rm database file
-				// logrotate
-				// spawnSync
-				// break;
-			case 429:  // 429 means rate limited, let's hold back for 10 seconds
-				await sleep(10000);
-				queue.enqueue(data, 1);
-				break;
-			default:
-				fs.writeFileSync('log', JSON.stringify({event: 'response', date: new Date(), data: response}) + '\n', {flag: 'a+'});
-				return data.resolve(response);
-			}})
-		.catch(async err => {
-			fs.writeFileSync('log', JSON.stringify({event: 'error', date: new Date(), data: err}) + '\n', {flag: 'a+'});
-			switch(err.cause?.code) {
-			case 503:  // 503 means maintenance mode, let's hold back for 1 minute
-				await sleep(60000);
-				queue.enqueue(data, 1);
-				break;
-			case 'ECONNRESET':
-				queue.enqueue(data, 1);
-				break;
-			case 'UND_ERR_CONNECT_TIMEOUT':
-				queue.enqueue(data, 1);
-				break;
-			default:
-				data.reject(err);
-			}});
-	setTimeout(send_next, 400); // 333 should work, but 400 will still allow manual requests to go through during development
+	let response = await fetch(`https://api.spacetraders.io/v2${data.request.endpoint}`, options);
+	if (response.ok) {
+		response = await response.json();
+		switch(response.error?.code) {
+			//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 as instructed
+			backoffSeconds = response.error.data.retryAfter;
+			queue.enqueue(data, 1);
+			break;
+		default: // no error!
+			fs.writeFileSync('log', JSON.stringify({event: 'response', date: new Date(), data: response}) + '\n', {flag: 'a+'});
+			return data.resolve(response);
+		}
+	} else {
+		fs.writeFileSync('log', JSON.stringify({event: 'error', date: new Date(), data: response}) + '\n', {flag: 'a+'});
+		switch(response.cause?.code) {
+		case 503:  // 503 means maintenance mode, let's hold back for 1 minute
+			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':
+			queue.enqueue(data, 1);
+			break;
+		case 'UND_ERR_CONNECT_TIMEOUT':
+			queue.enqueue(data, 1);
+			break;
+		default:
+			data.reject(response);
+		}
+	}
 }
 
 export function debugLog(ctx) {
-- 
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