Merge pull request #91 from Financial-Times/FTDCS-213-throw-errors-in…

…-getdata

Listen to error event and throw errors from getData

README.md

@@ -38,7 +38,7 @@ parseData: function (data) {
 
 * `stop()` - Stops polling
 
-* `getData()` - Returns the last set of data retrieved from the server (post-processed if `parseData` function exists)
+* `getData()` - Returns the last set of data retrieved from the server (post-processed if `parseData` function exists). This will throw an `HttpError` if the most recent fetch received an error.
 
 #### Events
 

src/poller.js

@@ -35,6 +35,12 @@ module.exports = EventEmitter => {
 			if (config.autostart) {
 				this.start ({initialRequest: true});
 			}
+
+			// We must listen to the error event to prevent throwing when we receive an HTTP error
+			// https://nodejs.org/docs/latest-v16.x/api/events.html#error-events
+			this.on('error', (error) => {
+				this.error = error;
+			});
 		}
 
 		isRunning () {
@@ -83,6 +89,7 @@ module.exports = EventEmitter => {
 				.then ((response) => {
 					const latency = new Date () - time;
 					if (response.ok) {
+						this.error = undefined;
 						this.emit ('ok', response, latency);
 					} else {
 						throw new errors.HttpError({url:this.url, method:this.options.method || 'GET', response});
@@ -103,6 +110,10 @@ module.exports = EventEmitter => {
 		}
 
 		getData () {
+			if (this.error) {
+				throw this.error;
+			}
+
 			return this.data;
 		}
 	};

tests/poller.spec.js

@@ -168,6 +168,59 @@ describe ('Poller', function () {
 
 	});
 
+	it ('Should throw from getData when fetch has received an HTTP error', function (done) {
+
+		const ft = nock ('http://example.com')
+			.get ('/')
+			.reply (503, {});
+
+		const p = new Poller({
+			url: 'http://example.com'
+		});
+
+		p.fetch ();
+
+		setTimeout (function () {
+			expect (ft.isDone ()).to.be.true; // ensure Nock has been used
+			expect (function () {
+				p.getData ();
+			}).to.throw ('HTTP Error 503 Service Unavailable');
+			done ();
+		}, 10);
+
+	});
+
+	it ('Should return data from getData when fetch has received an HTTP error followed by a success', function (done) {
+
+		const ft = nock ('http://example.com');
+
+		const p = new Poller({
+			url: 'http://example.com'
+		});
+
+		ft.get ('/').reply (503, '<h1>error</h1>');
+
+		p.fetch ();
+
+		setTimeout (function () {
+			expect (ft.isDone ()).to.be.true; // ensure Nock has been used
+			expect (function () {
+				p.getData ();
+			}).to.throw ('HTTP Error 503 Service Unavailable');
+
+			ft.get ('/').reply (200, '<h1>website</h1>')
+
+			p.fetch()
+
+			setTimeout (function () {
+				expect (p.getData ()).to.equal ('<h1>website</h1>');
+				done ();
+			}, 10);
+
+		}, 10);
+
+	});
+
 	it ('Should annotate the polling response with latency information', function (done) {
 
 		const ft = nock ('http://example.com')