Add batching timeout

src/functions/functions.spec.ts

@@ -141,30 +141,35 @@ test.cb("map() emits errors during synchronous mapping", t => {
     source.push(null);
 });
 
-test.cb("map() emits errors during asynchronous mapping", t => {
-    t.plan(2);
-    const source = new Readable({ objectMode: true });
-    source
-        .pipe(
-            map(async (element: string) => {
-                await Promise.resolve();
-                if (element !== "a") {
-                    throw new Error("Failed mapping");
-                }
-                return element.toUpperCase();
-            }),
-        )
-        .resume()
-        .on("error", err => {
-            expect(err.message).to.equal("Failed mapping");
-            t.pass();
-        })
-        .on("end", t.end);
+test("map() emits errors during asynchronous mapping", t => {
+    t.plan(1);
+    return new Promise((resolve, reject) => {
+        const source = new Readable({ objectMode: true });
+        source
+            .pipe(
+                map(async (element: string) => {
+                    await Promise.resolve();
+                    if (element !== "a") {
+                        throw new Error("Failed mapping");
+                    }
+                    return element.toUpperCase();
+                }),
+            )
+            .resume()
+            .on("error", err => {
+                expect(err.message).to.equal("Failed mapping");
+                t.pass();
+                resolve();
+            })
+            .on("end", () => {
+                t.fail();
+            });
 
-    source.push("a");
-    source.push("b");
-    source.push("c");
-    source.push(null);
+        source.push("a");
+        source.push("b");
+        source.push("c");
+        source.push(null);
+    });
 });
 
 test.cb("flatMap() maps elements synchronously", t => {
@@ -1212,6 +1217,36 @@ test.cb("batch() batches chunks together", t => {
     source.push(null);
 });
 
+test.cb("batch() yields a batch after the timeout", t => {
+    t.plan(3);
+    const source = new Readable({
+        objectMode: true,
+        read(size: number) {},
+    });
+    const expectedElements = [["a", "b"], ["c"], ["d"]];
+    let i = 0;
+    source
+        .pipe(batch(3))
+        .on("data", (element: string[]) => {
+            console.error("DATA", element);
+            expect(element).to.deep.equal(expectedElements[i]);
+            t.pass();
+            i++;
+        })
+        .on("error", t.fail)
+        .on("end", t.end);
+
+    source.push("a");
+    source.push("b");
+    setTimeout(() => {
+        source.push("c");
+    }, 600);
+    setTimeout(() => {
+        source.push("d");
+        source.push(null);
+    }, 600 * 2);
+});
+
 test.cb("unbatch() unbatches", t => {
     t.plan(3);
     const source = new Readable({ objectMode: true });
@@ -1344,16 +1379,16 @@ test.cb("parallel() parallel mapping", t => {
                 orderedResults[5].start,
             );
             expect(orderedResults[0].start).to.be.lessThan(
-                orderedResults[2].start + offset
+                orderedResults[2].start + offset,
             );
             expect(orderedResults[1].start).to.be.lessThan(
-                orderedResults[3].start + offset
+                orderedResults[3].start + offset,
             );
             expect(orderedResults[2].start).to.be.lessThan(
-                orderedResults[4].start + offset
+                orderedResults[4].start + offset,
             );
             expect(orderedResults[3].start).to.be.lessThan(
-                orderedResults[5].start + offset
+                orderedResults[5].start + offset,
             );
             t.end();
         });

src/functions/functions.ts

@@ -49,19 +49,12 @@ export function map<T, R>(
     return new Transform({
         ...options,
         async transform(chunk: T, encoding, callback) {
-            let isPromise = false;
             try {
-                const mapped = mapper(chunk, encoding);
-                isPromise = mapped instanceof Promise;
-                callback(undefined, await mapped);
+                const mapped = await mapper(chunk, encoding);
+                this.push(mapped);
+                callback();
             } catch (err) {
-                if (isPromise) {
-                    // Calling the callback asynchronously with an error wouldn't emit the error, so emit directly
-                    this.emit("error", err);
-                    callback();
-                } else {
-                    callback(err);
-                }
+                callback(err);
             }
         },
     });
@@ -504,28 +497,33 @@ export function last<T>(readable: Readable): Promise<T | null> {
  * @param maxBatchAge Max lifetime of a batch
  */
 export function batch(batchSize: number = 1000, maxBatchAge: number = 500) {
-    const buffer: any[] = [];
-    let startTime: number | null = null;
+    let buffer: any[] = [];
+    let timer: NodeJS.Timer | null = null;
+    let sendChunk = (self: Transform) => {
+        timer && clearTimeout(timer);
+        timer = null;
+        self.push(buffer);
+        buffer = [];
+    };
     return new Transform({
         objectMode: true,
         transform(chunk, encoding, callback) {
-            if (
-                buffer.length === batchSize - 1 ||
-                (startTime !== null &&
-                    startTime - performance.now() >= maxBatchAge)
-            ) {
-                buffer.push(chunk);
-                callback(undefined, buffer.splice(0));
+            buffer.push(chunk);
+            if (buffer.length === batchSize) {
+                sendChunk(this);
             } else {
-                if (startTime === null) {
-                    startTime = performance.now();
+                if (timer === null) {
+                    timer = setInterval(() => {
+                        sendChunk(this);
+                    }, maxBatchAge);
                 }
-                buffer.push(chunk);
-                callback();
             }
+            callback();
         },
         flush(callback) {
-            callback(undefined, buffer.splice(0));
+            console.error("flushing");
+            sendChunk(this);
+            callback();
         },
     });
 }