Clone URLSearchParams to avoid mutation (#547)

* And make sure Request/Response set Content-Type per Fetch Spec
* And make sure users can read the body as string via text()

src/body.js

@@ -37,6 +37,7 @@ export default function Body(body, {
 	} else if (typeof body === 'string') {
 		// body is string
 	} else if (isURLSearchParams(body)) {
+		body = Buffer.from(body.toString());
 		// body is a URLSearchParams
 	} else if (body instanceof Blob) {
 		// body is blob
@@ -415,9 +416,7 @@ export function clone(instance) {
  *
  * @param   Mixed  instance  Response or Request instance
  */
-export function extractContentType(instance) {
-	const {body} = instance;
-
+export function extractContentType(body) {
 	// istanbul ignore if: Currently, because of a guard in Request, body
 	// can never be null. Included here for completeness.
 	if (body === null) {
@@ -444,10 +443,13 @@ export function extractContentType(instance) {
 	} else if (typeof body.getBoundary === 'function') {
 		// detect form data input from form-data module
 		return `multipart/form-data;boundary=${body.getBoundary()}`;
-	} else {
+	} else if (body instanceof Stream) {
 		// body is stream
 		// can't really do much about this
 		return null;
+	} else {
+		// Body constructor defaults other things to string
+		return 'text/plain;charset=UTF-8';
 	}
 }
 

src/request.js

@@ -90,9 +90,9 @@ export default class Request {
 
 		const headers = new Headers(init.headers || input.headers || {});
 
-		if (init.body != null) {
-			const contentType = extractContentType(this);
-			if (contentType !== null && !headers.has('Content-Type')) {
+		if (inputBody != null && !headers.has('Content-Type')) {
+			const contentType = extractContentType(inputBody);
+			if (contentType) {
 				headers.append('Content-Type', contentType);
 			}
 		}

src/response.js

@@ -8,7 +8,7 @@
 import http from 'http';
 
 import Headers from './headers.js';
-import Body, { clone } from './body';
+import Body, { clone, extractContentType } from './body';
 
 const INTERNALS = Symbol('Response internals');
 
@@ -27,12 +27,20 @@ export default class Response {
 		Body.call(this, body, opts);
 
 		const status = opts.status || 200;
+		const headers = new Headers(opts.headers)
+
+		if (body != null && !headers.has('Content-Type')) {
+			const contentType = extractContentType(body);
+			if (contentType) {
+				headers.append('Content-Type', contentType);
+			}
+		}
 
 		this[INTERNALS] = {
 			url: opts.url,
 			status,
 			statusText: opts.statusText || STATUS_CODES[status],
-			headers: new Headers(opts.headers)
+			headers
 		};
 	}
 

test/test.js

@@ -1365,6 +1365,38 @@ describe('node-fetch', () => {
 	});
 
 	const itUSP = typeof URLSearchParams === 'function' ? it : it.skip;
+
+	itUSP('constructing a Response with URLSearchParams as body should have a Content-Type', function() {
+		const params = new URLSearchParams();
+		const res = new Response(params);
+		res.headers.get('Content-Type');
+		expect(res.headers.get('Content-Type')).to.equal('application/x-www-form-urlencoded;charset=UTF-8');
+	});
+
+	itUSP('constructing a Request with URLSearchParams as body should have a Content-Type', function() {
+		const params = new URLSearchParams();
+		const req = new Request(base, { method: 'POST', body: params });
+		expect(req.headers.get('Content-Type')).to.equal('application/x-www-form-urlencoded;charset=UTF-8');
+	});
+
+	itUSP('Reading a body with URLSearchParams should echo back the result', function() {
+		const params = new URLSearchParams();
+		params.append('a','1');
+		return new Response(params).text().then(text => {
+			expect(text).to.equal('a=1');
+		});
+	});
+
+	// Body should been cloned...
+	itUSP('constructing a Request/Response with URLSearchParams and mutating it should not affected body', function() {
+		const params = new URLSearchParams();
+		const req = new Request(`${base}inspect`, { method: 'POST', body: params })
+		params.append('a','1')
+		return req.text().then(text => {
+			expect(text).to.equal('');
+		});
+	});
+
 	itUSP('should allow POST request with URLSearchParams as body', function() {
 		const params = new URLSearchParams();
 		params.append('a','1');