perf(fetch): avoid redundant conversion

lib/web/fetch/body.js

@@ -121,17 +121,21 @@ function extractBody (object, keepalive = false) {
 
     for (const [name, value] of object) {
       if (typeof value === 'string') {
-        const chunk = textEncoder.encode(prefix +
-          `; name="${escape(normalizeLinefeeds(name))}"` +
-          `\r\n\r\n${normalizeLinefeeds(value)}\r\n`)
+        const chunk = textEncoder.encode(
+          `${prefix}; name="${escape(
+            normalizeLinefeeds(name)
+          )}"\r\n\r\n${normalizeLinefeeds(value)}\r\n`
+        )
         blobParts.push(chunk)
         length += chunk.byteLength
       } else {
-        const chunk = textEncoder.encode(`${prefix}; name="${escape(normalizeLinefeeds(name))}"` +
-          (value.name ? `; filename="${escape(value.name)}"` : '') + '\r\n' +
-          `Content-Type: ${
+        const chunk = textEncoder.encode(
+          `${prefix}; name="${escape(normalizeLinefeeds(name))}"${
+            value.name ? `; filename="${escape(value.name)}"` : ''
+          }\r\nContent-Type: ${
             value.type || 'application/octet-stream'
-          }\r\n\r\n`)
+          }\r\n\r\n`
+        )
         blobParts.push(chunk, value, rn)
         if (typeof value.size === 'number') {
           length += chunk.byteLength + value.size + rn.byteLength

lib/web/fetch/index.js

@@ -1475,7 +1475,7 @@ async function httpNetworkOrCacheFetch (
   //    user agents should append `User-Agent`/default `User-Agent` value to
   //    httpRequest’s header list.
   if (!httpRequest.headersList.contains('user-agent', true)) {
-    httpRequest.headersList.append('user-agent', defaultUserAgent)
+    httpRequest.headersList.append('user-agent', defaultUserAgent, true)
   }
 
   //    15. If httpRequest’s cache mode is "default" and httpRequest’s header

lib/web/fetch/request.js

@@ -467,7 +467,8 @@ class Request {
       // list, append header’s name/header’s value to this’s headers.
       if (headers instanceof HeadersList) {
         for (const [key, val] of headers) {
-          headersList.append(key, val)
+          // Note: The header names are already in lowercase.
+          headersList.append(key, val, true)
         }
         // Note: Copy the `set-cookie` meta-data.
         headersList.cookies = headers.cookies
@@ -892,16 +893,18 @@ webidl.converters.Request = webidl.interfaceConverter(
 )
 
 // https://fetch.spec.whatwg.org/#requestinfo
+
+// DOMString is used because the value is converted to a USVString in `new URL()`.
 webidl.converters.RequestInfo = function (V) {
   if (typeof V === 'string') {
-    return webidl.converters.USVString(V)
+    return webidl.converters.DOMString(V)
   }
 
   if (V instanceof Request) {
     return webidl.converters.Request(V)
   }
 
-  return webidl.converters.USVString(V)
+  return webidl.converters.DOMString(V)
 }
 
 webidl.converters.AbortSignal = webidl.interfaceConverter(
@@ -921,7 +924,7 @@ webidl.converters.RequestInit = webidl.dictionaryConverter([
   {
     key: 'body',
     converter: webidl.nullableConverter(
-      webidl.converters.BodyInit
+      webidl.converters.BodyInit_DOMString
     )
   },
   {

lib/web/fetch/response.js

@@ -77,7 +77,8 @@ class Response {
 
     webidl.argumentLengthCheck(arguments, 1, { header: 'Response.redirect' })
 
-    url = webidl.converters.USVString(url)
+    // DOMString is used because the value is converted to a USVString in `new URL()`.
+    url = webidl.converters.DOMString(url)
     status = webidl.converters['unsigned short'](status)
 
     // 1. Let parsedURL be the result of parsing url with current settings
@@ -120,7 +121,7 @@ class Response {
     }
 
     if (body !== null) {
-      body = webidl.converters.BodyInit(body)
+      body = webidl.converters.BodyInit_DOMString(body)
     }
 
     init = webidl.converters.ResponseInit(init)
@@ -516,9 +517,10 @@ webidl.converters.URLSearchParams = webidl.interfaceConverter(
 )
 
 // https://fetch.spec.whatwg.org/#typedefdef-xmlhttprequestbodyinit
-webidl.converters.XMLHttpRequestBodyInit = function (V) {
+
+webidl.converters.XMLHttpRequestBodyInit_DOMString = function (V) {
   if (typeof V === 'string') {
-    return webidl.converters.USVString(V)
+    return webidl.converters.DOMString(V)
   }
 
   if (isBlobLike(V)) {
@@ -541,7 +543,7 @@ webidl.converters.XMLHttpRequestBodyInit = function (V) {
 }
 
 // https://fetch.spec.whatwg.org/#bodyinit
-webidl.converters.BodyInit = function (V) {
+webidl.converters.BodyInit_DOMString = function (V) {
   if (V instanceof ReadableStream) {
     return webidl.converters.ReadableStream(V)
   }
@@ -552,7 +554,7 @@ webidl.converters.BodyInit = function (V) {
     return V
   }
 
-  return webidl.converters.XMLHttpRequestBodyInit(V)
+  return webidl.converters.XMLHttpRequestBodyInit_DOMString(V)
 }
 
 webidl.converters.ResponseInit = webidl.dictionaryConverter([

test/fetch/request.js

@@ -504,3 +504,8 @@ test('fromInnerRequest', () => {
   assert.strictEqual(request[kHeaders][kGuard], 'immutable')
   assert.strictEqual(request[kHeaders][kRealm], realm)
 })
+
+test('surrogate pair url', async () => {
+  const request = new Request('https://asd/\ud801')
+  assert.deepStrictEqual(request.url, 'https://asd/%EF%BF%BD')
+})

test/fetch/response.js

@@ -288,3 +288,8 @@ test('fromInnerResponse', () => {
   assert.strictEqual(response[kHeaders][kGuard], 'immutable')
   assert.strictEqual(response[kHeaders][kRealm], realm)
 })
+
+test('surrogate pair', async () => {
+  const response = new Response('\ud801')
+  assert.deepStrictEqual(await response.text(), '\ufffd')
+})