feat: remove headers filtering

lib/fetch/request.js

@@ -383,10 +383,10 @@ class Request {
     // 30. Set this’s headers to a new Headers object with this’s relevant
     // Realm, whose header list is request’s header list and guard is
     // "request".
-    this[kHeaders] = new Headers()
+    this[kHeaders] = new Headers(request.headersList)
     this[kHeaders][kGuard] = 'request'
-    this[kHeaders][kHeadersList] = request.headersList
     this[kHeaders][kRealm] = this[kRealm]
+    this[kState].headersList = this[kHeaders][kHeadersList]
 
     // 31. If this’s request’s mode is "no-cors", then:
     if (mode === 'no-cors') {
@@ -406,26 +406,26 @@ class Request {
     if (Object.keys(init).length !== 0) {
       // 1. Let headers be a copy of this’s headers and its associated header
       // list.
-      let headers = new Headers(this.headers)
+      let headers = new Headers(this[kHeaders])
 
       // 2. If init["headers"] exists, then set headers to init["headers"].
       if (init.headers !== undefined) {
         headers = init.headers
       }
 
       // 3. Empty this’s headers’s header list.
-      this[kState].headersList = new HeadersList()
-      this[kHeaders][kHeadersList] = this[kState].headersList
+      this[kHeaders] = new Headers()
+      this[kState].headersList = this[kHeaders][kHeadersList]
 
       // 4. If headers is a Headers object, then for each header in its header
       // list, append header’s name/header’s value to this’s headers.
       if (headers.constructor.name === 'Headers') {
-        for (const [key, val] of headers[kHeadersList] || headers) {
-          this[kState].headersList.append(key, val)
+        for (const [key, val] of headers) {
+          this[kHeaders].append(key, val)
         }
       } else {
         // 5. Otherwise, fill this’s headers with headers.
-        fillHeaders(this[kState].headersList, headers)
+        fillHeaders(this[kHeaders], headers)
       }
     }
 
@@ -461,7 +461,7 @@ class Request {
       // not contain `Content-Type`, then append `Content-Type`/Content-Type to
       // this’s headers.
       if (contentType && !this[kHeaders].has('content-type')) {
-        this[kState].headersList.append('content-type', contentType)
+        this[kHeaders].append('content-type', contentType)
       }
     }