1 files changed, 260 insertions, 0 deletions
diff --git a/std/node/_stream/async_iterator.ts b/std/node/_stream/async_iterator.ts
new file mode 100644
index 000000000..cd1b6db3c
--- /dev/null
+++ b/std/node/_stream/async_iterator.ts
@@ -0,0 +1,260 @@
+// Copyright Node.js contributors. All rights reserved. MIT License.
+import type { Buffer } from "../buffer.ts";
+import finished from "./end-of-stream.ts";
+import Readable from "./readable.ts";
+import type Stream from "./stream.ts";
+
+const kLastResolve = Symbol("lastResolve");
+const kLastReject = Symbol("lastReject");
+const kError = Symbol("error");
+const kEnded = Symbol("ended");
+const kLastPromise = Symbol("lastPromise");
+const kHandlePromise = Symbol("handlePromise");
+const kStream = Symbol("stream");
+
+// TODO(Soremwar)
+// Add Duplex streams
+type IterableStreams = Stream | Readable;
+
+type IterableItem = Buffer | string | Uint8Array | undefined;
+type ReadableIteratorResult = IteratorResult<IterableItem>;
+
+function initIteratorSymbols(
+  o: ReadableStreamAsyncIterator,
+  symbols: symbol[],
+) {
+  const properties: PropertyDescriptorMap = {};
+  for (const sym in symbols) {
+    properties[sym] = {
+      configurable: false,
+      enumerable: false,
+      writable: true,
+    };
+  }
+  Object.defineProperties(o, properties);
+}
+
+// TODO(Soremwar)
+// Bring back once requests are implemented
+// function isRequest(stream: any) {
+//   return stream && stream.setHeader && typeof stream.abort === "function";
+// }
+
+//TODO(Soremwar)
+//Should be any implementation of stream
+// deno-lint-ignore no-explicit-any
+function destroyer(stream: any, err?: Error | null) {
+  // TODO(Soremwar)
+  // Bring back once requests are implemented
+  // if (isRequest(stream)) return stream.abort();
+  // if (isRequest(stream.req)) return stream.req.abort();
+  if (typeof stream.destroy === "function") return stream.destroy(err);
+  if (typeof stream.close === "function") return stream.close();
+}
+
+function createIterResult(
+  value: IterableItem,
+  done: boolean,
+): ReadableIteratorResult {
+  return { value, done };
+}
+
+function readAndResolve(iter: ReadableStreamAsyncIterator) {
+  const resolve = iter[kLastResolve];
+  if (resolve !== null) {
+    const data = iter[kStream].read();
+    if (data !== null) {
+      iter[kLastPromise] = null;
+      iter[kLastResolve] = null;
+      iter[kLastReject] = null;
+      resolve(createIterResult(data, false));
+    }
+  }
+}
+
+function onReadable(iter: ReadableStreamAsyncIterator) {
+  queueMicrotask(() => readAndResolve(iter));
+}
+
+function wrapForNext(
+  lastPromise: Promise<ReadableIteratorResult>,
+  iter: ReadableStreamAsyncIterator,
+) {
+  return (
+    resolve: (value: ReadableIteratorResult) => void,
+    reject: (error: Error) => void,
+  ) => {
+    lastPromise.then(() => {
+      if (iter[kEnded]) {
+        resolve(createIterResult(undefined, true));
+        return;
+      }
+
+      iter[kHandlePromise](resolve, reject);
+    }, reject);
+  };
+}
+
+function finish(self: ReadableStreamAsyncIterator, err?: Error) {
+  return new Promise(
+    (
+      resolve: (result: ReadableIteratorResult) => void,
+      reject: (error: Error) => void,
+    ) => {
+      const stream = self[kStream];
+
+      finished(stream, (err) => {
+        if (err && err.code !== "ERR_STREAM_PREMATURE_CLOSE") {
+          reject(err);
+        } else {
+          resolve(createIterResult(undefined, true));
+        }
+      });
+      destroyer(stream, err);
+    },
+  );
+}
+
+const AsyncIteratorPrototype = Object.getPrototypeOf(
+  Object.getPrototypeOf(async function* () {}).prototype,
+);
+
+class ReadableStreamAsyncIterator
+  implements AsyncIterableIterator<IterableItem> {
+  [kEnded]: boolean;
+  [kError]: Error | null = null;
+  [kHandlePromise] = (
+    resolve: (value: ReadableIteratorResult) => void,
+    reject: (value: Error) => void,
+  ) => {
+    const data = this[kStream].read();
+    if (data) {
+      this[kLastPromise] = null;
+      this[kLastResolve] = null;
+      this[kLastReject] = null;
+      resolve(createIterResult(data, false));
+    } else {
+      this[kLastResolve] = resolve;
+      this[kLastReject] = reject;
+    }
+  };
+  [kLastPromise]: null | Promise<ReadableIteratorResult>;
+  [kLastReject]: null | ((value: Error) => void) = null;
+  [kLastResolve]: null | ((value: ReadableIteratorResult) => void) = null;
+  [kStream]: Readable;
+  [Symbol.asyncIterator] = AsyncIteratorPrototype[Symbol.asyncIterator];
+
+  constructor(stream: Readable) {
+    this[kEnded] = stream.readableEnded || stream._readableState.endEmitted;
+    this[kStream] = stream;
+    initIteratorSymbols(this, [
+      kEnded,
+      kError,
+      kHandlePromise,
+      kLastPromise,
+      kLastReject,
+      kLastResolve,
+      kStream,
+    ]);
+  }
+
+  get stream() {
+    return this[kStream];
+  }
+
+  next(): Promise<ReadableIteratorResult> {
+    const error = this[kError];
+    if (error !== null) {
+      return Promise.reject(error);
+    }
+
+    if (this[kEnded]) {
+      return Promise.resolve(createIterResult(undefined, true));
+    }
+
+    if (this[kStream].destroyed) {
+      return new Promise((resolve, reject) => {
+        if (this[kError]) {
+          reject(this[kError]);
+        } else if (this[kEnded]) {
+          resolve(createIterResult(undefined, true));
+        } else {
+          finished(this[kStream], (err) => {
+            if (err && err.code !== "ERR_STREAM_PREMATURE_CLOSE") {
+              reject(err);
+            } else {
+              resolve(createIterResult(undefined, true));
+            }
+          });
+        }
+      });
+    }
+
+    const lastPromise = this[kLastPromise];
+    let promise;
+
+    if (lastPromise) {
+      promise = new Promise(wrapForNext(lastPromise, this));
+    } else {
+      const data = this[kStream].read();
+      if (data !== null) {
+        return Promise.resolve(createIterResult(data, false));
+      }
+
+      promise = new Promise(this[kHandlePromise]);
+    }
+
+    this[kLastPromise] = promise;
+
+    return promise;
+  }
+
+  return(): Promise<ReadableIteratorResult> {
+    return finish(this);
+  }
+
+  throw(err: Error): Promise<ReadableIteratorResult> {
+    return finish(this, err);
+  }
+}
+
+const createReadableStreamAsyncIterator = (stream: IterableStreams) => {
+  // deno-lint-ignore no-explicit-any
+  if (typeof (stream as any).read !== "function") {
+    const src = stream;
+    stream = new Readable({ objectMode: true }).wrap(src);
+    finished(stream, (err) => destroyer(src, err));
+  }
+
+  const iterator = new ReadableStreamAsyncIterator(stream as Readable);
+  iterator[kLastPromise] = null;
+
+  finished(stream, { writable: false }, (err) => {
+    if (err && err.code !== "ERR_STREAM_PREMATURE_CLOSE") {
+      const reject = iterator[kLastReject];
+      if (reject !== null) {
+        iterator[kLastPromise] = null;
+        iterator[kLastResolve] = null;
+        iterator[kLastReject] = null;
+        reject(err);
+      }
+      iterator[kError] = err;
+      return;
+    }
+
+    const resolve = iterator[kLastResolve];
+    if (resolve !== null) {
+      iterator[kLastPromise] = null;
+      iterator[kLastResolve] = null;
+      iterator[kLastReject] = null;
+      resolve(createIterResult(undefined, true));
+    }
+    iterator[kEnded] = true;
+  });
+
+  stream.on("readable", onReadable.bind(null, iterator));
+
+  return iterator;
+};
+
+export default createReadableStreamAsyncIterator;