fix(fetch): send headers in the case that they were sent

lib/fetch/headers.js

@@ -3,7 +3,7 @@
 'use strict'
 
 const { kHeadersList } = require('../core/symbols')
-const { kGuard } = require('./symbols')
+const { kGuard, kHeadersCaseInsensitive } = require('./symbols')
 const { kEnumerableProperty } = require('../core/util')
 const {
   makeIterator,
@@ -96,27 +96,27 @@ class HeadersList {
 
     // 1. If list contains name, then set name to the first such
     //    header’s name.
-    name = name.toLowerCase()
-    const exists = this[kHeadersMap].get(name)
+    const lowercaseName = name.toLowerCase()
+    const exists = this[kHeadersMap].get(lowercaseName)
 
     // 2. Append (name, value) to list.
     if (exists) {
-      this[kHeadersMap].set(name, `${exists}, ${value}`)
+      this[kHeadersMap].set(lowercaseName, { name: exists.name, value: `${exists.value}, ${value}` })
     } else {
-      this[kHeadersMap].set(name, `${value}`)
+      this[kHeadersMap].set(lowercaseName, { name, value })
     }
   }
 
   // https://fetch.spec.whatwg.org/#concept-header-list-set
   set (name, value) {
     this[kHeadersSortedMap] = null
-    name = name.toLowerCase()
+    const lowercaseName = name.toLowerCase()
 
     // 1. If list contains name, then set the value of
     //    the first such header to value and remove the
     //    others.
     // 2. Otherwise, append header (name, value) to list.
-    return this[kHeadersMap].set(name, value)
+    return this[kHeadersMap].set(lowercaseName, { name, value })
   }
 
   // https://fetch.spec.whatwg.org/#concept-header-list-delete
@@ -137,14 +137,26 @@ class HeadersList {
     // 2. Return the values of all headers in list whose name
     //    is a byte-case-insensitive match for name,
     //    separated from each other by 0x2C 0x20, in order.
-    return this[kHeadersMap].get(name.toLowerCase()) ?? null
+    return this[kHeadersMap].get(name.toLowerCase())?.value ?? null
   }
 
   * [Symbol.iterator] () {
-    for (const pair of this[kHeadersMap]) {
-      yield pair
+    // use the lowercased name
+    for (const [name, { value }] of this[kHeadersMap]) {
+      yield [name, value]
     }
   }
+
+  get [kHeadersCaseInsensitive] () {
+    /** @type {string[]} */
+    const flatList = []
+
+    for (const { name, value } of this[kHeadersMap].values()) {
+      flatList.push(name, value)
+    }
+
+    return flatList
+  }
 }
 
 // https://fetch.spec.whatwg.org/#headers-class

lib/fetch/index.js

@@ -39,7 +39,7 @@ const {
   readableStreamClose,
   isomorphicEncode
 } = require('./util')
-const { kState, kHeaders, kGuard, kRealm } = require('./symbols')
+const { kState, kHeaders, kGuard, kRealm, kHeadersCaseInsensitive } = require('./symbols')
 const assert = require('assert')
 const { safelyExtractBody } = require('./body')
 const {
@@ -840,8 +840,8 @@ async function schemeFetch (fetchParams) {
       const response = makeResponse({
         statusText: 'OK',
         headersList: [
-          ['content-length', length],
-          ['content-type', type]
+          ['content-length', { name: 'Content-Length', value: length }],
+          ['content-type', { name: 'Content-Type', value: type }]
         ]
       })
 
@@ -870,7 +870,7 @@ async function schemeFetch (fetchParams) {
       return makeResponse({
         statusText: 'OK',
         headersList: [
-          ['content-type', mimeType]
+          ['content-type', { name: 'Content-Type', value: mimeType }]
         ],
         body: safelyExtractBody(dataURLStruct.body)[0]
       })
@@ -1938,7 +1938,7 @@ async function httpNetworkFetch (
         origin: url.origin,
         method: request.method,
         body: fetchParams.controller.dispatcher.isMockActive ? request.body && request.body.source : body,
-        headers: [...request.headersList].flat(),
+        headers: request.headersList[kHeadersCaseInsensitive],
         maxRedirections: 0,
         bodyTimeout: 300_000,
         headersTimeout: 300_000

lib/fetch/symbols.js

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

test/wpt/server/server.mjs

@@ -316,6 +316,23 @@ const server = createServer(async (req, res) => {
       res.end('none')
       break
     }
+    case '/xhr/resources/echo-headers.py': {
+      res.statusCode = 200
+      res.setHeader('Content-Type', 'text/plain')
+
+      // wpt runner sends this as 1 chunk
+      let body = ''
+
+      for (let i = 0; i < req.rawHeaders.length; i += 2) {
+        const key = req.rawHeaders[i]
+        const value = req.rawHeaders[i + 1]
+
+        body += `${key}: ${value}`
+      }
+
+      res.end(body)
+      break
+    }
     default: {
       res.statusCode = 200
       res.end('body')

test/wpt/status/fetch.status.json

@@ -49,12 +49,12 @@
 	"header-value-combining.any.js": {
 		"fail": [
 			"response.headers.get('content-length') expects 0, 0",
-			"response.headers.get('double-trouble') expects , ",
 			"response.headers.get('foo-test') expects 1, 2, 3",
 			"response.headers.get('heya') expects , \\x0B\f, 1, , , 2"
 		],
 		"flaky": [
 			"response.headers.get('content-length') expects 0",
+      "response.headers.get('double-trouble') expects , ",
 			"response.headers.get('www-authenticate') expects 1, 2, 3, 4"
 		]
 	},
@@ -207,4 +207,4 @@
 			"fetch() with value %1F"
 		]
 	}
-}
+}

test/wpt/tests/fetch/api/basic/request-headers-case.any.js

@@ -0,0 +1,13 @@
+// META: global=window,worker
+
+promise_test(() => {
+  return fetch("/xhr/resources/echo-headers.py", {headers: [["THIS-is-A-test", 1], ["THIS-IS-A-TEST", 2]] }).then(res => res.text()).then(body => {
+    assert_regexp_match(body, /THIS-is-A-test: 1, 2/)
+  })
+}, "Multiple headers with the same name, different case (THIS-is-A-test first)")
+
+promise_test(() => {
+  return fetch("/xhr/resources/echo-headers.py", {headers: [["THIS-IS-A-TEST", 1], ["THIS-is-A-test", 2]] }).then(res => res.text()).then(body => {
+    assert_regexp_match(body, /THIS-IS-A-TEST: 1, 2/)
+  })
+}, "Multiple headers with the same name, different case (THIS-IS-A-TEST first)")