Add error event hander for the body stream even if the body isn't accessed (#379)

Fixes #378

src/body.js

@@ -12,6 +12,7 @@ const Stream = require('stream');
 const { PassThrough } = require('stream');
 
 const DISTURBED = Symbol('disturbed');
+const ERROR = Symbol('error');
 
 let convert;
 try { convert = require('encoding').convert; } catch(e) {}
@@ -49,8 +50,15 @@ export default function Body(body, {
 	}
 	this.body = body;
 	this[DISTURBED] = false;
+	this[ERROR] = null;
 	this.size = size;
 	this.timeout = timeout;
+
+	if (this.body instanceof Stream) {
+		this.body.on('error', err => {
+			this[ERROR] = new FetchError(`Invalid response body while trying to fetch ${this.url}: ${err.message}`, 'system', err);
+		});
+	}
 }
 
 Body.prototype = {
@@ -153,6 +161,10 @@ function consumeBody(body) {
 
 	this[DISTURBED] = true;
 
+	if (this[ERROR]) {
+		return Body.Promise.reject(this[ERROR]);
+	}
+
 	// body is null
 	if (this.body === null) {
 		return Body.Promise.resolve(Buffer.alloc(0));

test/test.js

@@ -587,6 +587,40 @@ describe('node-fetch', () => {
 		});
 	});
 
+	it('should handle errors on the body stream even if it is not used', function(done) {
+		url = `${base}invalid-content-encoding`;
+		fetch(url)
+			.then(res => {
+				expect(res.status).to.equal(200);
+			})
+			.catch(() => {})
+			.then(() => {
+				// Wait a few ms to see if a uncaught error occurs
+				setTimeout(() => {
+					done();
+				}, 50);
+			});
+	});
+
+	it('should collect handled errors on the body stream to reject if the body is used later', function() {
+
+		function delay(value) {
+			return new Promise((resolve) => {
+				setTimeout(() => {
+					resolve(value)
+				}, 100);
+			});
+		}
+
+		url = `${base}invalid-content-encoding`;
+		return fetch(url).then(delay).then(res => {
+			expect(res.headers.get('content-type')).to.equal('text/plain');
+			return expect(res.text()).to.eventually.be.rejected
+				.and.be.an.instanceOf(FetchError)
+				.and.have.property('code', 'Z_DATA_ERROR');
+		});
+	});
+
 	it('should allow disabling auto decompression', function() {
 		url = `${base}gzip`;
 		opts = {