fix(ClientRequest): ensure "options._defaultAgent" is always set base…

…d on the protocol (#221)

* chore(http.request): improve the log

* fix(ClientRequest): ensure "options._defaultAgent" is always set based on the protocol

src/interceptors/ClientRequest/http.request.ts

@@ -15,7 +15,7 @@ export function request(
   observer: Observer
 ) {
   return (...args: ClientRequestArgs): ClientRequest => {
-    log('intercepted request:', args)
+    log('request call (protocol "%s"):', protocol, args)
 
     const clientRequestArgs = normalizeClientRequestArgs(
       `${protocol}:`,

src/interceptors/ClientRequest/utils/normalizeClientRequestArgs.test.ts

@@ -1,5 +1,6 @@
 import { parse } from 'url'
-import { Agent as HttpsAgent } from 'https'
+import { globalAgent as httpGlobalAgent, RequestOptions } from 'http'
+import { Agent as HttpsAgent, globalAgent as httpsGlobalAgent } from 'https'
 import { getUrlByRequestOptions } from '../../../utils/getUrlByRequestOptions'
 import { normalizeClientRequestArgs } from './normalizeClientRequestArgs'
 
@@ -192,8 +193,9 @@ test('handles [URL, RequestOptions, callback] input', () => {
   expect(url.href).toEqual('https://mswjs.io/resource')
 
   // Options must be preserved.
-  expect(options).toEqual({
+  expect(options).toEqual<RequestOptions>({
     agent: false,
+    _defaultAgent: httpsGlobalAgent,
     protocol: url.protocol,
     method: 'GET',
     headers: {
@@ -294,12 +296,11 @@ test('sets fallback Agent based on the URL protocol', () => {
     'https:',
     'https://github.com'
   )
+  const agent = options.agent as HttpsAgent
 
-  expect(options.agent).toBeInstanceOf(HttpsAgent)
-  expect(
-    // @ts-expect-error Protocol is an internal property.
-    options.agent.protocol
-  ).toEqual(url.protocol)
+  expect(agent).toBeInstanceOf(HttpsAgent)
+  expect(agent).toHaveProperty('defaultPort', 443)
+  expect(agent).toHaveProperty('protocol', url.protocol)
 })
 
 test('does not set any fallback Agent given "agent: false" option', () => {
@@ -312,6 +313,41 @@ test('does not set any fallback Agent given "agent: false" option', () => {
   expect(options.agent).toEqual(false)
 })
 
+test('sets the default Agent for HTTP request', () => {
+  const [, options] = normalizeClientRequestArgs(
+    'http:',
+    'http://github.com',
+    {}
+  )
+
+  expect(options._defaultAgent).toEqual(httpGlobalAgent)
+})
+
+test('sets the default Agent for HTTPS request', () => {
+  const [, options] = normalizeClientRequestArgs(
+    'https:',
+    'https://github.com',
+    {}
+  )
+
+  expect(options._defaultAgent).toEqual(httpsGlobalAgent)
+})
+
+test('preserves a custom default Agent when set', () => {
+  const [, options] = normalizeClientRequestArgs(
+    'https:',
+    'https://github.com',
+    {
+      /**
+       * @note Intentionally incorrect Agent for HTTPS request.
+       */
+      _defaultAgent: httpGlobalAgent,
+    }
+  )
+
+  expect(options._defaultAgent).toEqual(httpGlobalAgent)
+})
+
 test('merges URL-based RequestOptions with the custom RequestOptions', () => {
   const [url, options] = normalizeClientRequestArgs(
     'https:',

src/interceptors/ClientRequest/utils/normalizeClientRequestArgs.ts

@@ -1,6 +1,14 @@
 import { debug } from 'debug'
-import { Agent as HttpAgent, IncomingMessage } from 'http'
-import { RequestOptions, Agent as HttpsAgent } from 'https'
+import {
+  Agent as HttpAgent,
+  globalAgent as httpGlobalAgent,
+  IncomingMessage,
+} from 'http'
+import {
+  RequestOptions,
+  Agent as HttpsAgent,
+  globalAgent as httpsGlobalAgent,
+} from 'https'
 import { Url as LegacyURL } from 'url'
 import { getRequestOptionsByUrl } from '../../../utils/getRequestOptionsByUrl'
 import {
@@ -198,8 +206,27 @@ export function normalizeClientRequestArgs(
     log('resolved fallback agent:', agent)
   }
 
+  /**
+   * Ensure that the default Agent is always set.
+   * This prevents the protocol mismatch for requests with { agent: false },
+   * where the global Agent is inferred.
+   * @see https://github.com/mswjs/msw/issues/1150
+   * @see https://github.com/nodejs/node/blob/418ff70b810f0e7112d48baaa72932a56cfa213b/lib/_http_client.js#L130
+   * @see https://github.com/nodejs/node/blob/418ff70b810f0e7112d48baaa72932a56cfa213b/lib/_http_client.js#L157-L159
+   */
+  if (!options._defaultAgent) {
+    log(
+      'has no default agent, setting the default agent for "%s"',
+      options.protocol
+    )
+
+    options._defaultAgent =
+      options.protocol === 'https:' ? httpsGlobalAgent : httpGlobalAgent
+  }
+
   log('successfully resolved url:', url.href)
   log('successfully resolved options:', options)
+  log('successfully resolved callback:', callback)
 
   return [url, options, callback]
 }