fix(NODE-3559): incorrect GridFS stream type (#2981)

src/gridfs/download.ts

@@ -73,7 +73,7 @@ export interface GridFSBucketReadStreamPrivate {
  * Do not instantiate this class directly. Use `openDownloadStream()` instead.
  * @public
  */
-export class GridFSBucketReadStream extends Readable {
+export class GridFSBucketReadStream extends Readable implements NodeJS.ReadableStream {
   /** @internal */
   s: GridFSBucketReadStreamPrivate;
 

src/gridfs/upload.ts

@@ -37,7 +37,7 @@ export interface GridFSBucketWriteStreamOptions extends WriteConcernOptions {
  * Do not instantiate this class directly. Use `openUploadStream()` instead.
  * @public
  */
-export class GridFSBucketWriteStream extends Writable {
+export class GridFSBucketWriteStream extends Writable implements NodeJS.WritableStream {
   bucket: GridFSBucket;
   chunks: Collection<GridFSChunk>;
   filename: string;
@@ -118,12 +118,16 @@ export class GridFSBucketWriteStream extends Writable {
    * @param callback - Function to call when the chunk was added to the buffer, or if the entire chunk was persisted to MongoDB if this chunk caused a flush.
    * @returns False if this write required flushing a chunk to MongoDB. True otherwise.
    */
-  write(chunk: Buffer): boolean;
-  write(chunk: Buffer, callback: Callback<void>): boolean;
-  write(chunk: Buffer, encoding: BufferEncoding | undefined): boolean;
-  write(chunk: Buffer, encoding: BufferEncoding | undefined, callback: Callback<void>): boolean;
+  write(chunk: Buffer | string): boolean;
+  write(chunk: Buffer | string, callback: Callback<void>): boolean;
+  write(chunk: Buffer | string, encoding: BufferEncoding | undefined): boolean;
   write(
-    chunk: Buffer,
+    chunk: Buffer | string,
+    encoding: BufferEncoding | undefined,
+    callback: Callback<void>
+  ): boolean;
+  write(
+    chunk: Buffer | string,
     encodingOrCallback?: Callback<void> | BufferEncoding,
     callback?: Callback<void>
   ): boolean {
@@ -417,7 +421,7 @@ function createFilesDoc(
 
 function doWrite(
   stream: GridFSBucketWriteStream,
-  chunk: Buffer,
+  chunk: Buffer | string,
   encoding?: BufferEncoding,
   callback?: Callback<void>
 ): boolean {

test/types/gridfs_types.test-d.ts

@@ -0,0 +1,13 @@
+import { Readable } from 'stream';
+import { expectType } from 'tsd';
+import type { GridFSBucket, GridFSBucketWriteStream } from '../../src';
+
+(function test(bucket: GridFSBucket) {
+  const readable = new Readable();
+
+  const uploadStream = bucket.openUploadStream('test');
+  expectType<GridFSBucketWriteStream>(uploadStream);
+
+  // should be pipeable as a WriteStream
+  readable.pipe(uploadStream);
+})({} as GridFSBucket);