Merge pull request #6 from AKST/removes-end-listeners

Removes end event listens

Author: basicdays

lib/stream-to-async-iterator.js

@@ -11,6 +11,15 @@ export const states = {
     errored: Symbol('errored'),
 };
 
+/*
+ * A contract for a promise that requires a clean up
+ * function be called after the promise finishes.
+ */
+type PromiseWithCleanUp<T> = {
+    promise: Promise<T>,
+    cleanup: () => void,
+}
+
 /**
  * @typedef {Object} StreamAsyncToIterator~Options
  * @property {number} [size] - the size of each read from the stream for each iteration
@@ -106,9 +115,22 @@ export default class StreamAsyncToIterator {
      */
     async next(): Promise<Iteration> {
         if (this._state === states.notReadable) {
+            const read = this._untilReadable();
+            const end = this._untilEnd();
+
             //need to wait until the stream is readable or ended
-            await Promise.race([this._untilReadable(), this._untilEnd()]);
-            return this.next();
+            try {
+              await Promise.race([read.promise, end.promise]);
+              return this.next();
+            }
+            catch (e) {
+              throw e
+            }
+            finally {
+              //need to clean up any hanging event listeners
+              read.cleanup()
+              end.cleanup()
+            }
         } else if (this._state === states.ended) {
             return {done: true, value: null};
         } else if (this._state === states.errored) {
@@ -133,34 +155,63 @@ export default class StreamAsyncToIterator {
      * @private
      * @returns {Promise}
      */
-    _untilReadable(): Promise<void> {
-        return new Promise((resolve, reject) => {
-            const handleReadable = () => {
+    _untilReadable(): PromiseWithCleanUp<void> {
+        //let is used here instead of const because the exact reference is
+        //required to remove it, this is why it is not a curried function that
+        //accepts resolve & reject as parameters.
+        let eventListener = null;
+
+        const promise = new Promise((resolve, reject) => {
+            eventListener = () => {
                 this._state = states.readable;
                 this._rejections.delete(reject);
+
+                // we set this to null to info the clean up not to do anything
+                eventListener = null;
                 resolve();
             };
 
-            this._stream.once('readable', handleReadable);
+            //on is used here instead of once, because
+            //the listener is remove afterwards anyways.
+            this._stream.once('readable', eventListener);
             this._rejections.add(reject);
         });
+
+        const cleanup = () => {
+            if (eventListener == null) return;
+            this._stream.removeListener('readable', eventListener);
+        };
+
+        return { cleanup, promise }
     }
 
     /**
      * Waits until the stream is ended. Rejects if the stream errored out.
      * @private
      * @returns {Promise}
      */
-    _untilEnd(): Promise<void> {
-        return new Promise((resolve, reject) => {
-            const handleEnd = () => {
+    _untilEnd(): PromiseWithCleanUp<void> {
+        let eventListener = null;
+
+        const promise = new Promise((resolve, reject) => {
+            eventListener = () => {
                 this._state = states.ended;
                 this._rejections.delete(reject);
+
+                eventListener = null
                 resolve();
             };
-            this._stream.once('end', handleEnd);
+
+            this._stream.once('end', eventListener);
             this._rejections.add(reject);
-        })
+        });
+
+        const cleanup = () => {
+            if (eventListener == null) return;
+            this._stream.removeListener('end', eventListener);
+        };
+
+        return { cleanup, promise }
     }
 }