fix: handle all types of BodyInit correctly

.circleci/config.yml

@@ -8,7 +8,7 @@ references:
 
   node18: &node18
     docker:
-      - image: cimg/node:18.0
+      - image: cimg/node:18.11
   nodelts: &nodelts
     docker:
       - image: cimg/node:lts

docs/docs/@fetch-mock/core/configuration.md

@@ -15,17 +15,11 @@ fetchMock.config.sendAsJson = false;
 
 Options marked with a `†` can also be overridden for individual calls to `.mock(matcher, response, options)` by setting as properties on the `options` parameter
 
-### sendAsJson<sup>†</sup>
-
-`{Boolean}` default: `true`
-
-Always convert objects passed to `.mock()` to JSON strings before building reponses. Can be useful to set to `false` globally if e.g. dealing with a lot of `ArrayBuffer`s. When `true` the `Content-Type: application/json` header will also be set on each response.
-
 ### includeContentLength<sup>†</sup>
 
 `{Boolean}` default: `true`
 
-Sets a `Content-Length` header on each response.
+Sets a `Content-Length` header on each response, with the exception of responses whose body is a `FormData` or `ReadableStream` instance as these are hard/impossible to calculate up front.
 
 ### matchPartialBody
 

docs/docs/@fetch-mock/core/route/response.md

@@ -32,9 +32,13 @@ If the object _only_ contains properties from among those listed below it is use
 
 ### body
 
-`{String|Object}`
+`{String|Object|BodyInit}`
 
-Set the `Response` body, e.g. `"Server responded ok"`, `{ token: 'abcdef' }`. See the `Object` section of the docs below for behaviour when passed an `Object`.
+Set the `Response` body. This could be
+
+- a string e.g. `"Server responded ok"`, `{ token: 'abcdef' }`.
+- an object literal (see the `Object` section of the docs below).
+- Anything else that satisfies the specification for the [body parameter of new Response()](https://developer.mozilla.org/en-US/docs/Web/API/Response/Response#body). This currently allows instances of Blob, ArrayBuffer, TypedArray, DataView, FormData, ReadableStream, URLSearchParams, and String.
 
 ### status
 
@@ -62,9 +66,15 @@ Forces `fetch` to return a `Promise` rejected with the value of `throws` e.g. `n
 
 ## Object
 
-`{Object|ArrayBuffer|...`
+`{Object}`
+
+Any object literal that does not match the schema for a response config will be converted to a `JSON` string and set as the response `body`.
+
+The `Content-Type: application/json` header will also be set on each response. To send JSON responses that do not set this header (e.g. to mock a poorly configured server) manually convert the object to a string first e.g.
 
-If the `sendAsJson` option is set to `true`, any object that does not match the schema for a response config will be converted to a `JSON` string and set as the response `body`. Otherwise, the object will be set as the response `body` (useful for `ArrayBuffer`s etc.)
+```js
+fetchMock.route('http://a.com', JSON.stringify({ prop: 'value' }));
+```
 
 ## Promise
 

packages/core/package.json

@@ -18,7 +18,7 @@
 	"types": "./dist/esm/index.d.ts",
 	"type": "module",
 	"engines": {
-		"node": ">=18.0.0"
+		"node": ">=18.11.0"
 	},
 	"dependencies": {
 		"@types/glob-to-regexp": "^0.4.4",

packages/core/src/FetchMock.ts

@@ -5,7 +5,6 @@ import CallHistory from './CallHistory.js';
 import * as requestUtils from './RequestUtils.js';
 
 export type FetchMockGlobalConfig = {
-	sendAsJson?: boolean;
 	includeContentLength?: boolean;
 	matchPartialBody?: boolean;
 	allowRelativeUrls?: boolean;
@@ -20,7 +19,6 @@ export type FetchMockConfig = FetchMockGlobalConfig & FetchImplementations;
 
 export const defaultFetchMockConfig: FetchMockConfig = {
 	includeContentLength: true,
-	sendAsJson: true,
 	matchPartialBody: false,
 	Request: globalThis.Request,
 	Response: globalThis.Response,

packages/core/src/Route.ts

@@ -42,7 +42,7 @@ export type RouteConfig = UserRouteConfig &
 	FetchImplementations &
 	InternalRouteConfig;
 export type RouteResponseConfig = {
-	body?: string | object;
+	body?: BodyInit | object;
 	status?: number;
 	headers?: {
 		[key: string]: string;
@@ -72,6 +72,22 @@ export type RouteResponse =
 	| RouteResponseFunction;
 export type RouteName = string;
 
+function isBodyInit(body: BodyInit | object): body is BodyInit {
+	return (
+		body instanceof Blob ||
+		body instanceof ArrayBuffer ||
+		// checks for TypedArray
+		ArrayBuffer.isView(body) ||
+		body instanceof DataView ||
+		body instanceof FormData ||
+		body instanceof ReadableStream ||
+		body instanceof URLSearchParams ||
+		body instanceof String ||
+		typeof body === 'string' ||
+		body === null
+	);
+}
+
 function sanitizeStatus(status?: number): number {
 	if (!status) {
 		return 200;
@@ -194,31 +210,48 @@ class Route {
 	constructResponseBody(
 		responseInput: RouteResponseConfig,
 		responseOptions: ResponseInitUsingHeaders,
-	): string | null {
-		// start to construct the body
+	): BodyInit {
 		let body = responseInput.body;
-		// convert to json if we need to
-		if (typeof body === 'object') {
-			if (this.config.sendAsJson && responseInput.body != null) {
+		const bodyIsBodyInit = isBodyInit(body);
+
+		if (!bodyIsBodyInit) {
+			if (typeof body === 'undefined') {
+				body = null;
+			} else if (typeof body === 'object') {
+				// convert to json if we need to
 				body = JSON.stringify(body);
 				if (!responseOptions.headers.has('Content-Type')) {
 					responseOptions.headers.set('Content-Type', 'application/json');
 				}
+			} else {
+				throw new TypeError('Invalid body provided to construct response');
 			}
 		}
 
-		if (typeof body === 'string') {
-			// add a Content-Length header if we need to
-			if (
-				this.config.includeContentLength &&
-				!responseOptions.headers.has('Content-Length')
+		// add a Content-Length header if we need to
+		if (
+			this.config.includeContentLength &&
+			!responseOptions.headers.has('Content-Length') &&
+			!(body instanceof ReadableStream) &&
+			!(body instanceof FormData)
+		) {
+			let length = 0;
+			if (body instanceof Blob) {
+				length = body.size;
+			} else if (
+				body instanceof ArrayBuffer ||
+				ArrayBuffer.isView(body) ||
+				body instanceof DataView
 			) {
-				responseOptions.headers.set('Content-Length', body.length.toString());
+				length = body.byteLength;
+			} else if (body instanceof URLSearchParams) {
+				length = body.toString().length;
+			} else if (typeof body === 'string' || body instanceof String) {
+				length = body.length;
 			}
-			return body;
+			responseOptions.headers.set('Content-Length', length.toString());
 		}
-		// @ts-expect-error TODO need to implement handling of non-string bodies properlyy
-		return body || null;
+		return body as BodyInit;
 	}
 
 	static defineMatcher(matcher: MatcherDefinition) {

packages/core/src/Router.ts

@@ -273,8 +273,8 @@ export default class Router {
 				if (typeof response[name] === 'function') {
 					//@ts-expect-error TODO probably make use of generics here
 					return new Proxy(response[name], {
-						apply: (matcherFunction, thisArg, args) => {
-							const result = matcherFunction.apply(response, args);
+						apply: (func, thisArg, args) => {
+							const result = func.apply(response, args);
 							if (result.then) {
 								pendingPromises.push(
 									//@ts-expect-error TODO probably make use of generics here