perf: reduce String#toLowerCase call

lib/client.js

@@ -765,11 +765,14 @@ class Parser {
     }
 
     const key = this.headers[len - 2]
-    if (key.length === 10 && key.toString().toLowerCase() === 'keep-alive') {
-      this.keepAlive += buf.toString()
-    } else if (key.length === 10 && key.toString().toLowerCase() === 'connection') {
-      this.connection += buf.toString()
-    } else if (key.length === 14 && key.toString().toLowerCase() === 'content-length') {
+    if (key.length === 10) {
+      const headerName = util.bufferToLowerCasedHeaderName(key)
+      if (headerName === 'keep-alive') {
+        this.keepAlive += buf.toString()
+      } else if (headerName === 'connection') {
+        this.connection += buf.toString()
+      }
+    } else if (key.length === 14 && util.bufferToLowerCasedHeaderName(key) === 'content-length') {
       this.contentLength += buf.toString()
     }
 

lib/core/util.js

@@ -226,7 +226,14 @@ function parseKeepAliveTimeout (val) {
 function headerNameToString (value) {
   return typeof value === 'string'
     ? headerNameLowerCasedRecord[value] ?? value.toLowerCase()
-    : tree.lookup(value) ?? value.toString().toLowerCase()
+    : tree.lookup(value) ?? value.toString('latin1').toLowerCase()
+}
+
+/**
+ * @param {Buffer} value
+ */
+function bufferToLowerCasedHeaderName (value) {
+  return tree.lookup(value) ?? value.toString('latin1').toLowerCase()
 }
 
 /**
@@ -523,6 +530,7 @@ module.exports = {
   isAsyncIterable,
   isDestroyed,
   headerNameToString,
+  bufferToLowerCasedHeaderName,
   parseRawHeaders,
   parseHeaders,
   parseKeepAliveTimeout,

lib/fetch/body.js

@@ -374,7 +374,7 @@ function bodyMixinMethods (instance) {
       // If mimeType’s essence is "multipart/form-data", then:
       if (/multipart\/form-data/.test(contentType)) {
         const headers = {}
-        for (const [key, value] of this.headers) headers[key.toLowerCase()] = value
+        for (const [key, value] of this.headers) headers[key] = value
 
         const responseFormData = new FormData()
 

lib/fetch/headers.js

@@ -135,13 +135,22 @@ class HeadersList {
     }
   }
 
-  // https://fetch.spec.whatwg.org/#header-list-contains
+  /**
+   * @see https://fetch.spec.whatwg.org/#header-list-contains
+   * @param {string} name
+   */
   contains (name) {
     // A header list list contains a header name name if list
     // contains a header whose name is a byte-case-insensitive
     // match for name.
-    name = name.toLowerCase()
 
+    return this[kHeadersMap].has(name.toLowerCase())
+  }
+
+  /**
+   * @param {string} name
+   */
+  lowerCaseContains (name) {
     return this[kHeadersMap].has(name)
   }
 
@@ -151,7 +160,11 @@ class HeadersList {
     this.cookies = null
   }
 
-  // https://fetch.spec.whatwg.org/#concept-header-list-append
+  /**
+   * @see https://fetch.spec.whatwg.org/#concept-header-list-append
+   * @param {string} name
+   * @param {string} value
+   */
   append (name, value) {
     this[kHeadersSortedMap] = null
 
@@ -172,12 +185,42 @@ class HeadersList {
     }
 
     if (lowercaseName === 'set-cookie') {
-      this.cookies ??= []
-      this.cookies.push(value)
+      (this.cookies ??= []).push(value)
+    }
+  }
+
+  /**
+   * @param {string} name
+   * @param {string} value
+   */
+  lowerCaseAppend (name, value) {
+    this[kHeadersSortedMap] = null
+
+    // 1. If list contains name, then set name to the first such
+    //    header’s name.
+    const exists = this[kHeadersMap].get(name)
+
+    // 2. Append (name, value) to list.
+    if (exists) {
+      const delimiter = name === 'cookie' ? '; ' : ', '
+      this[kHeadersMap].set(name, {
+        name: exists.name,
+        value: `${exists.value}${delimiter}${value}`
+      })
+    } else {
+      this[kHeadersMap].set(name, { name, value })
+    }
+
+    if (name === 'set-cookie') {
+      (this.cookies ??= []).push(value)
     }
   }
 
-  // https://fetch.spec.whatwg.org/#concept-header-list-set
+  /**
+   * @see https://fetch.spec.whatwg.org/#concept-header-list-set
+   * @param {string} name
+   * @param {string} value
+   */
   set (name, value) {
     this[kHeadersSortedMap] = null
     const lowercaseName = name.toLowerCase()
@@ -193,11 +236,35 @@ class HeadersList {
     this[kHeadersMap].set(lowercaseName, { name, value })
   }
 
-  // https://fetch.spec.whatwg.org/#concept-header-list-delete
+  /**
+   * @param {string} name
+   * @param {string} value
+   */
+  lowerCaseSet (name, value) {
+    if (name === 'set-cookie') {
+      this.cookies = [value]
+    }
+
+    // 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.
+    this[kHeadersMap].set(name, { name, value })
+  }
+
+  /**
+   * @see https://fetch.spec.whatwg.org/#concept-header-list-delete
+   * @param {string} name
+   */
   delete (name) {
-    this[kHeadersSortedMap] = null
+    return this.lowerCaseDelete(name.toLowerCase())
+  }
 
-    name = name.toLowerCase()
+  /**
+   * @param {string} name
+   */
+  lowerCaseDelete (name) {
+    this[kHeadersSortedMap] = null
 
     if (name === 'set-cookie') {
       this.cookies = null
@@ -206,7 +273,11 @@ class HeadersList {
     this[kHeadersMap].delete(name)
   }
 
-  // https://fetch.spec.whatwg.org/#concept-header-list-get
+  /**
+   * @see https://fetch.spec.whatwg.org/#concept-header-list-get
+   * @param {string} name
+   * @returns {string | null}
+   */
   get (name) {
     const value = this[kHeadersMap].get(name.toLowerCase())
 
@@ -217,6 +288,14 @@ class HeadersList {
     return value === undefined ? null : value.value
   }
 
+  /**
+   * @param {string} name
+   * @returns {string | null}
+   */
+  lowerCaseGet (name) {
+    return this[kHeadersMap].get(name)?.value ?? null
+  }
+
   * [Symbol.iterator] () {
     // use the lowercased name
     for (const [name, { value }] of this[kHeadersMap]) {