websocket: add fast-path for string input

lib/web/websocket/frame.js

@@ -89,6 +89,49 @@ class WebsocketFrameSend {
 
     return buffer
   }
+
+  /**
+   * @param {string | Uint8Array} body
+   */
+  static createFastTextFrame (body) {
+    const maskKey = generateMask()
+
+    const buffer = typeof body === 'string' ? Buffer.from(body) : body
+    const bodyLength = buffer.length
+
+    // mask body
+    for (let i = 0; i < bodyLength; ++i) {
+      buffer[i] ^= maskKey[i & 3]
+    }
+
+    let payloadLength = bodyLength
+    let offset = 6
+
+    if (bodyLength > maxUnsigned16Bit) {
+      offset += 8 // payload length is next 8 bytes
+      payloadLength = 127
+    } else if (bodyLength > 125) {
+      offset += 2 // payload length is next 2 bytes
+      payloadLength = 126
+    }
+    const head = Buffer.allocUnsafeSlow(offset)
+
+    head[0] = 0x80 /* FIN */ | 0x1 /* opcode TEXT */
+    head[1] = payloadLength | 0x80 /* MASK */
+    head[offset - 4] = maskKey[0]
+    head[offset - 3] = maskKey[1]
+    head[offset - 2] = maskKey[2]
+    head[offset - 1] = maskKey[3]
+
+    if (payloadLength === 126) {
+      head.writeUInt16BE(bodyLength, 2)
+    } else if (payloadLength === 127) {
+      head[2] = head[3] = 0
+      head.writeUIntBE(bodyLength, 4, 6)
+    }
+
+    return [head, buffer]
+  }
 }
 
 module.exports = {

lib/web/websocket/sender.js

@@ -34,16 +34,25 @@ class SendQueue {
 
   add (item, cb, hint) {
     if (hint !== sendHints.blob) {
-      const frame = createFrame(item, hint)
       if (!this.#running) {
-        // fast-path
-        this.#socket.write(frame, cb)
+        // TODO(@tsctx): support fast-path for string on running
+        if (hint === sendHints.string) {
+          // special fast-path for string
+          const { 0: head, 1: body } = WebsocketFrameSend.createFastTextFrame(item)
+          this.#socket.cork()
+          this.#socket.write(head)
+          this.#socket.write(body, cb)
+          this.#socket.uncork()
+        } else {
+          // direct writing
+          this.#socket.write(createFrame(item, hint), cb)
+        }
       } else {
         /** @type {SendQueueNode} */
         const node = {
           promise: null,
           callback: cb,
-          frame
+          frame: createFrame(item, hint)
         }
         this.#queue.push(node)
       }