Remove stream reuse check

Fixes #1803

source/core/index.ts

@@ -151,7 +151,6 @@ export default class Request extends Duplex implements RequestEvents<Request> {
 	private _downloadedSize: number;
 	private _uploadedSize: number;
 	private _stopReading: boolean;
-	private _startedReading: boolean;
 	private readonly _pipedServerResponses: Set<ServerResponse>;
 	private _request?: ClientRequest;
 	private _responseSize?: number;
@@ -180,7 +179,6 @@ export default class Request extends Duplex implements RequestEvents<Request> {
 		this._downloadedSize = 0;
 		this._uploadedSize = 0;
 		this._stopReading = false;
-		this._startedReading = false;
 		this._pipedServerResponses = new Set<ServerResponse>();
 		this._cannotHaveBody = false;
 		this._unproxyEvents = noop;
@@ -435,7 +433,6 @@ export default class Request extends Duplex implements RequestEvents<Request> {
 			let data;
 			while ((data = response.read()) !== null) {
 				this._downloadedSize += data.length;
-				this._startedReading = true;
 
 				const progress = this.downloadProgress;
 
@@ -522,10 +519,6 @@ export default class Request extends Duplex implements RequestEvents<Request> {
 	}
 
 	pipe<T extends NodeJS.WritableStream>(destination: T, options?: {end?: boolean}): T {
-		if (this._startedReading) {
-			throw new Error('Failed to pipe. The response has been emitted already.');
-		}
-
 		if (destination instanceof ServerResponse) {
 			this._pipedServerResponses.add(destination);
 		}

test/stream.ts

@@ -1,7 +1,7 @@
 import {promisify} from 'util';
 import fs from 'fs';
 import {Agent as HttpAgent} from 'http';
-import stream, {PassThrough as PassThroughStream, Readable as ReadableStream, Writable} from 'stream';
+import stream, {Readable as ReadableStream, Writable} from 'stream';
 import {Readable as Readable2} from 'readable-stream';
 import test from 'ava';
 import {Handler} from 'express';
@@ -274,23 +274,6 @@ test('skips proxying headers after server has sent them already', withServer, as
 	t.is(headers.unicorn, undefined);
 });
 
-test('throws when trying to proxy through a closed stream', withServer, async (t, server, got) => {
-	server.get('/', defaultHandler);
-
-	const stream = got.stream('');
-	const promise = getStream(stream);
-
-	stream.once('data', () => {
-		t.throws(() => {
-			stream.pipe(new PassThroughStream());
-		}, {
-			message: 'Failed to pipe. The response has been emitted already.',
-		});
-	});
-
-	await promise;
-});
-
 test('proxies `content-encoding` header when `options.decompress` is false', withServer, async (t, server, got) => {
 	server.get('/', defaultHandler);
 	server.get('/proxy', async (_request, response) => {