config endpoint must handle functions in module configs

js/main.js

@@ -475,7 +475,20 @@ const MM = (function () {
 	const loadConfig = async function () {
 		try {
 			const res = await fetch(new URL("config/", `${location.origin}${config.basePath}`));
-			config = JSON.parse(await res.text());
+
+			// The server tags functions as { __mmFunction: "<source>" } because
+			// JSON.stringify can't serialise live functions. This reviver turns
+			// those tagged objects back into callable functions.
+			config = JSON.parse(await res.text(), (key, value) => {
+				if (value && typeof value === "object" && typeof value.__mmFunction === "string") {
+					try {
+						return new Function(`return (${value.__mmFunction})`)();
+					} catch {
+						Log.warn(`Failed to revive function for config key "${key}".`);
+					}
+				}
+				return value;
+			});
 		} catch (error) {
 			Log.error("Unable to retrieve config", error);
 		}

js/server.js

@@ -111,12 +111,21 @@ function Server (configObj) {
 			const getStartup = (req, res) => res.send(startUp);
 
 			const getConfig = (req, res) => {
-				if (config.hideConfigSecrets) {
-					res.send(configObj.redactedConf);
-				} else {
-					res.send(configObj.fullConf);
-				}
+				const obj = config.hideConfigSecrets ? configObj.redactedConf : configObj.fullConf;
+				// Functions can't survive JSON.stringify, so we wrap them in a
+				// tagged object { __mmFunction: "<source>" }. The client-side
+				// JSON reviver in main.js recognises this tag and reconstructs
+				// the live function from the source string.
+				const jsonString = JSON.stringify(obj, (key, value) => {
+					if (typeof value === "function") {
+						return { __mmFunction: value.toString() };
+					}
+					return value;
+				});
+				res.set("Content-Type", "application/json");
+				res.send(jsonString);
 			};
+
 			app.get("/config", (req, res) => getConfig(req, res));
 
 			app.get("/cors", async (req, res) => await cors(req, res));

tests/configs/config_functions.js

@@ -0,0 +1,35 @@
+/*eslint object-shorthand: ["error", "always", { "methodsIgnorePattern": "^roundToInt2$" }]*/
+
+let config = require(`${process.cwd()}/tests/configs/default.js`).configFactory({
+	modules: [
+		{
+			module: "clock",
+			position: "middle_center",
+			config: {
+				moduleFunctions: {
+					roundToInt1: (value) => {
+						try {
+							return Math.round(parseFloat(value));
+						} catch {
+							return value;
+						}
+					},
+					roundToInt2: function (value) {
+						try {
+							return Math.round(parseFloat(value));
+						} catch {
+							return value;
+						}
+					}
+				},
+				stringWithArrow: "a => b is not a function",
+				stringWithFunction: "this function keyword is just text"
+			}
+		}
+	]
+});
+
+/*************** DO NOT EDIT THE LINE BELOW ***************/
+if (typeof module !== "undefined") {
+	module.exports = config;
+}

tests/e2e/config_functions_spec.js

@@ -0,0 +1,21 @@
+const helpers = require("./helpers/global-setup");
+
+describe("config with module function", () => {
+	beforeAll(async () => {
+		await helpers.startApplication("tests/configs/config_functions.js");
+	});
+
+	afterAll(async () => {
+		await helpers.stopApplication();
+	});
+
+	it("config should resolve module functions", () => {
+		expect(config.modules[0].config.moduleFunctions.roundToInt1(13.3)).toBe(13);
+		expect(config.modules[0].config.moduleFunctions.roundToInt2(13.3)).toBe(13);
+	});
+
+	it("config should not revive plain strings containing arrow or function keywords", () => {
+		expect(config.modules[0].config.stringWithArrow).toBe("a => b is not a function");
+		expect(config.modules[0].config.stringWithFunction).toBe("this function keyword is just text");
+	});
+});