improve uniformity of node/web checksumstream api

Author: kuhe

packages/util-stream/src/checksum/createChecksumStream.browser.ts

@@ -1,6 +1,8 @@
 import { Checksum, Encoder } from "@smithy/types";
 import { toBase64 } from "@smithy/util-base64";
 
+import { isReadableStream } from "../stream-type-check";
+
 /**
  * @internal
  */
@@ -59,7 +61,7 @@ export const createChecksumStream = ({
   checksumSourceLocation,
   base64Encoder,
 }: ChecksumStreamInit): ReadableStreamType => {
-  if (!(source instanceof ReadableStream)) {
+  if (!isReadableStream(source)) {
     throw new Error(
       `@smithy/util-stream: unsupported source type ${(source as any)?.constructor?.name ?? source} in ChecksumStream.`
     );
@@ -100,5 +102,21 @@ export const createChecksumStream = ({
   });
 
   source.pipeThrough(transform);
-  return transform.readable;
+  const readable = transform.readable;
+  Object.setPrototypeOf(readable, ChecksumStream.prototype);
+  return readable;
 };
+
+/**
+ * This stub exists so that the readable returned by createChecksumStream
+ * identifies as "ChecksumStream" in alignment with the Node.js
+ * implementation.
+ *
+ * @extends ReadableStream
+ */
+export class ChecksumStream {}
+
+if (typeof ReadableStream === "function") {
+  ChecksumStream.prototype = Object.create(ReadableStream.prototype);
+  ChecksumStream.prototype.constructor = ChecksumStream;
+}

packages/util-stream/src/checksum/createChecksumStream.spec.ts

@@ -4,7 +4,8 @@ import { toUtf8 } from "@smithy/util-utf8";
 import { Readable } from "stream";
 
 import { headStream } from "../headStream";
-import { createChecksumStream } from "./createChecksumStream";
+import { ChecksumStream, createChecksumStream } from "./createChecksumStream";
+import { ChecksumStream as ChecksumStreamWeb } from "./createChecksumStream.browser";
 
 describe("Checksum streams", () => {
   /**
@@ -44,6 +45,7 @@ describe("Checksum streams", () => {
 
       expect(checksumStream.constructor.name).toEqual("ChecksumStream");
       expect(checksumStream).toBeInstanceOf(Readable);
+      expect(checksumStream).toBeInstanceOf(ChecksumStream);
 
       const collected = toUtf8(await headStream(checksumStream, Infinity));
       expect(collected).toEqual(canonicalUtf8);
@@ -99,7 +101,9 @@ describe("Checksum streams", () => {
         source: stream,
       });
 
+      expect(checksumStream.constructor.name).toEqual("ChecksumStream");
       expect(checksumStream).toBeInstanceOf(ReadableStream);
+      expect(checksumStream).toBeInstanceOf(ChecksumStreamWeb);
 
       const collected = toUtf8(await headStream(checksumStream, Infinity));
       expect(collected).toEqual(canonicalUtf8);

packages/util-stream/src/checksum/createChecksumStream.ts

@@ -56,7 +56,7 @@ export function createChecksumStream(
  * buffering the stream.
  *
  */
-class ChecksumStream extends Duplex {
+export class ChecksumStream extends Duplex {
   private expectedChecksum: string;
   private checksumSourceLocation: string;
   private checksum: Checksum;

packages/util-stream/src/index.ts

@@ -4,3 +4,4 @@ export * from "./sdk-stream-mixin";
 export * from "./splitStream";
 export * from "./headStream";
 export * from "./stream-type-check";
+export * from "./checksum/createChecksumStream";