fix: mock fetch headers shouldn't be an array (#2080)

lib/fetch/headers.js

@@ -3,7 +3,7 @@
 'use strict'
 
 const { kHeadersList } = require('../core/symbols')
-const { kGuard, kHeadersCaseInsensitive } = require('./symbols')
+const { kGuard } = require('./symbols')
 const { kEnumerableProperty } = require('../core/util')
 const {
   makeIterator,
@@ -173,15 +173,16 @@ class HeadersList {
     }
   }
 
-  get [kHeadersCaseInsensitive] () {
-    /** @type {string[]} */
-    const flatList = []
+  get entries () {
+    const headers = {}
 
-    for (const { name, value } of this[kHeadersMap].values()) {
-      flatList.push(name, value)
+    if (this[kHeadersMap].size) {
+      for (const { name, value } of this[kHeadersMap].values()) {
+        headers[name] = value
+      }
     }
 
-    return flatList
+    return headers
   }
 }
 

lib/fetch/index.js

@@ -42,7 +42,7 @@ const {
   urlIsHttpHttpsScheme,
   urlHasHttpsScheme
 } = require('./util')
-const { kState, kHeaders, kGuard, kRealm, kHeadersCaseInsensitive } = require('./symbols')
+const { kState, kHeaders, kGuard, kRealm } = require('./symbols')
 const assert = require('assert')
 const { safelyExtractBody } = require('./body')
 const {
@@ -1950,7 +1950,7 @@ async function httpNetworkFetch (
         origin: url.origin,
         method: request.method,
         body: fetchParams.controller.dispatcher.isMockActive ? request.body && request.body.source : body,
-        headers: request.headersList[kHeadersCaseInsensitive],
+        headers: request.headersList.entries,
         maxRedirections: 0,
         upgrade: request.mode === 'websocket' ? 'websocket' : undefined
       },

lib/fetch/symbols.js

@@ -6,6 +6,5 @@ module.exports = {
   kSignal: Symbol('signal'),
   kState: Symbol('state'),
   kGuard: Symbol('guard'),
-  kRealm: Symbol('realm'),
-  kHeadersCaseInsensitive: Symbol('headers case insensitive')
+  kRealm: Symbol('realm')
 }

test/issue-2078.js

@@ -0,0 +1,30 @@
+'use strict'
+
+const { test, skip } = require('tap')
+const { nodeMajor, nodeMinor } = require('../lib/core/util')
+const { MockAgent, getGlobalDispatcher, setGlobalDispatcher, fetch } = require('..')
+
+if (nodeMajor < 16 || (nodeMajor === 16 && nodeMinor < 8)) {
+  skip('fetch is not supported in node < v16.8.0')
+  process.exit()
+}
+
+test('MockPool.reply headers are an object, not an array - issue #2078', async (t) => {
+  const global = getGlobalDispatcher()
+  const mockAgent = new MockAgent()
+  const mockPool = mockAgent.get('http://localhost')
+
+  t.teardown(() => setGlobalDispatcher(global))
+  setGlobalDispatcher(mockAgent)
+
+  mockPool.intercept({
+    path: '/foo',
+    method: 'GET'
+  }).reply((options) => {
+    t.ok(!Array.isArray(options.headers))
+
+    return { statusCode: 200 }
+  })
+
+  await t.resolves(fetch('http://localhost/foo'))
+})