estimate of download speed

src/core/PsychoJS.js

@@ -176,7 +176,7 @@ export class PsychoJS
 		}
 
 		this.logger.info("[PsychoJS] Initialised.");
-		this.logger.info("[PsychoJS] @version 2021.3.0");
+		this.logger.info("[PsychoJS] @version 2022.1.0");
 
 		// hide the initialisation message:
 		jQuery("#root").addClass("is-ready");

src/core/ServerManager.js

@@ -404,7 +404,7 @@ export class ServerManager extends PsychObject
 	 * </ul>
 	 *
 	 * @name module:core.ServerManager#prepareResources
-	 * @param {Array.<{name: string, path: string, download: boolean} | Symbol>} [resources=[]] - the list of resources
+	 * @param {Array.<{name: string, path: string, download: boolean} | String | Symbol>} [resources=[]] - the list of resources
 	 * @function
 	 * @public
 	 */
@@ -471,6 +471,20 @@ export class ServerManager extends PsychObject
 						throw "resources must be manually specified when the experiment is running locally: ALL_RESOURCES cannot be used";
 					}
 
+					// convert those resources that are only a string to an object with name and path:
+					for (let r = 0; r < resources.length; ++r)
+					{
+						const resource = resources[r];
+						if (typeof resource === "string")
+						{
+							resources[r] = {
+								name: resource,
+								path: resource,
+								download: true
+							}
+						}
+					}
+
 					for (let { name, path, download } of resources)
 					{
 						if (!this._resources.has(name))
@@ -1179,6 +1193,11 @@ export class ServerManager extends PsychObject
 	 */
 	_setupPreloadQueue(resources)
 	{
+		const response = {
+			origin: "ServerManager._downloadResources",
+			context: "when downloading resources for experiment: " + this._psychoJS.config.experiment.name,
+		};
+
 		this._preloadQueue = new createjs.LoadQueue(true, "", true);
 
 		const self = this;

src/util/Util.js

@@ -1413,3 +1413,58 @@ export function extensionFromMimeType(mimeType)
 
 	return '.dat';
 }
+
+/**
+ * Get an estimate of the download speed, by repeatedly downloading an image file from a distant
+ * server.
+ *
+ * @name module:util.getDownloadSpeed
+ * @function
+ * @public
+ * @param {PsychoJS} psychoJS the instance of PsychoJS
+ * @param {number} [nbDownloads = 1] the number of image downloads over which to average
+ * 	the download speed
+ * @return {number} the download speed, in megabits per second
+ */
+export async function getDownloadSpeed(psychoJS, nbDownloads = 1)
+{
+	// url of the image to download and size of the image in bits:
+	// TODO use a variety of files, with different sizes
+	const imageUrl = "https://upload.wikimedia.org/wikipedia/commons/a/a6/Brandenburger_Tor_abends.jpg";
+	const imageSize_b = 2707459 * 8;
+
+	return new Promise( (resolve, reject) =>
+	{
+		let downloadTimeAccumulator = 0;
+		let downloadCounter = 0;
+
+		const download = new Image();
+		download.onload = () =>
+		{
+			const toc = performance.now();
+			downloadTimeAccumulator += (toc-tic);
+			++ downloadCounter;
+
+			if (downloadCounter === nbDownloads)
+			{
+				const speed_bps = (imageSize_b  * nbDownloads) / (downloadTimeAccumulator / 1000);
+				resolve(speed_bps / 1024 / 1024);
+			}
+			else
+			{
+				tic = performance.now();
+				download.src = `${imageUrl}?salt=${tic}`;
+			}
+		}
+
+		download.onerror = (event) =>
+		{
+			const errorMsg = `unable to estimate the download speed: ${JSON.stringify(event)}`;
+			psychoJS.logger.error(errorMsg);
+			reject(errorMsg);
+		}
+
+		let tic = performance.now();
+		download.src = `${imageUrl}?salt=${tic}`;
+	});
+}