DRY isReadableStream typeguard

Author: kuhe

.changeset/metal-snakes-remember.md

@@ -2,4 +2,4 @@
 "@smithy/util-stream": minor
 ---
 
-add stream splitting to sdkStreamMixin
+add splitStream and headStream utilities

packages/util-stream/src/headStream.ts

@@ -1,6 +1,7 @@
 import { Readable, Writable } from "stream";
 
 import { headStream as headWebStream } from "./headStream.browser";
+import { isReadableStreamInstance } from "./isReadableStream";
 
 /**
  * @internal
@@ -11,7 +12,6 @@ import { headStream as headWebStream } from "./headStream.browser";
  */
 export const headStream = (stream: Readable | ReadableStream, bytes: number): Promise<Uint8Array> => {
   if (isReadableStreamInstance(stream)) {
-    // Web stream API in Node.js
     return headWebStream(stream, bytes);
   }
   return new Promise((resolve, reject) => {
@@ -47,6 +47,3 @@ class Collector extends Writable {
     callback();
   }
 }
-
-const isReadableStreamInstance = (stream: unknown): stream is ReadableStream =>
-  typeof ReadableStream === "function" && stream instanceof ReadableStream;

packages/util-stream/src/isReadableStream.ts

@@ -0,0 +1,5 @@
+/**
+ * @internal
+ */
+export const isReadableStreamInstance = (stream: unknown): stream is ReadableStream =>
+  typeof ReadableStream === "function" && stream?.constructor?.name === ReadableStream.name;

packages/util-stream/src/sdk-stream-mixin.browser.ts

@@ -4,6 +4,8 @@ import { toBase64 } from "@smithy/util-base64";
 import { toHex } from "@smithy/util-hex-encoding";
 import { toUtf8 } from "@smithy/util-utf8";
 
+import { isReadableStreamInstance } from "./isReadableStream";
+
 const ERR_MSG_STREAM_HAS_BEEN_TRANSFORMED = "The stream has already been transformed.";
 
 /**
@@ -74,6 +76,3 @@ export const sdkStreamMixin = (stream: unknown): SdkStream<ReadableStream | Blob
 };
 
 const isBlobInstance = (stream: unknown): stream is Blob => typeof Blob === "function" && stream instanceof Blob;
-
-const isReadableStreamInstance = (stream: unknown): stream is ReadableStream =>
-  typeof ReadableStream === "function" && stream instanceof ReadableStream;

packages/util-stream/src/splitStream.ts

@@ -1,11 +1,21 @@
-import type { Readable as IReadable } from "stream";
+import type { Readable } from "stream";
 import { PassThrough } from "stream";
 
+import { isReadableStreamInstance } from "./isReadableStream";
+import { splitStream as splitWebStream } from "./splitStream.browser";
+
 /**
  * @param stream
  * @returns stream split into two identical streams.
  */
-export async function splitStream(stream: IReadable): Promise<[IReadable, IReadable]> {
+export async function splitStream(stream: Readable): Promise<[Readable, Readable]>;
+export async function splitStream(stream: ReadableStream): Promise<[ReadableStream, ReadableStream]>;
+export async function splitStream(
+  stream: Readable | ReadableStream
+): Promise<[Readable | ReadableStream, Readable | ReadableStream]> {
+  if (isReadableStreamInstance(stream)) {
+    return splitWebStream(stream);
+  }
   const stream1 = new PassThrough();
   const stream2 = new PassThrough();
   stream.pipe(stream1);