websocket: use FixedQueue instead of Set

lib/web/websocket/sender.js

@@ -3,14 +3,33 @@
 const { WebsocketFrameSend } = require('./frame')
 const { opcodes, sendHints } = require('./constants')
 
-/** @type {Uint8Array} */
+/** @type {typeof Uint8Array} */
 const FastBuffer = Buffer[Symbol.species]
 
-class SendQueue {
-  #queued = new Set()
-  #size = 0
+/**
+ * @typedef {object} SendQueueNode
+ * @property {SendQueueNode | null} next
+ * @property {Promise<void> | null} promise
+ * @property {((...args: any[]) => any)} callback
+ * @property {Buffer | null} frame
+ */
 
-  /** @type {import('net').Socket} */
+class SendQueue {
+  /**
+   * @type {SendQueueNode | null}
+   */
+  #head = null
+  /**
+   * @type {SendQueueNode | null}
+   */
+  #tail = null
+
+  /**
+   * @type {boolean}
+   */
+  #running = false
+
+  /** @type {import('node:net').Socket} */
   #socket
 
   constructor (socket) {
@@ -19,66 +38,85 @@ class SendQueue {
 
   add (item, cb, hint) {
     if (hint !== sendHints.blob) {
-      const data = clone(item, hint)
-
-      if (this.#size === 0) {
-        this.#dispatch(data, cb, hint)
+      const frame = createFrame(item, hint)
+      if (!this.#running) {
+        // fast-path
+        this.#socket.write(frame, cb)
       } else {
-        this.#queued.add([data, cb, true, hint])
-        this.#size++
-
-        this.#run()
+        /** @type {SendQueueNode} */
+        const node = {
+          next: null,
+          promise: null,
+          callback: cb,
+          frame
+        }
+        if (this.#tail !== null) {
+          this.#tail.next = node
+        }
+        this.#tail = node
       }
-
       return
     }
 
-    const promise = item.arrayBuffer()
-    const queue = [null, cb, false, hint]
-    promise.then((ab) => {
-      queue[0] = clone(ab, hint)
-      queue[2] = true
-
-      this.#run()
-    })
-
-    this.#queued.add(queue)
-    this.#size++
-  }
-
-  #run () {
-    for (const queued of this.#queued) {
-      const [data, cb, done, hint] = queued
+    /** @type {SendQueueNode} */
+    const node = {
+      next: null,
+      promise: item.arrayBuffer().then((ab) => {
+        node.promise = null
+        node.frame = createFrame(ab, hint)
+      }),
+      callback: cb,
+      frame: null
+    }
 
-      if (!done) return
+    if (this.#tail === null) {
+      this.#tail = node
+    }
 
-      this.#queued.delete(queued)
-      this.#size--
+    if (this.#head === null) {
+      this.#head = node
+    }
 
-      this.#dispatch(data, cb, hint)
+    if (!this.#running) {
+      this.#run()
     }
   }
 
-  #dispatch (data, cb, hint) {
-    const frame = new WebsocketFrameSend()
-    const opcode = hint === sendHints.string ? opcodes.TEXT : opcodes.BINARY
-
-    frame.frameData = data
-    const buffer = frame.createFrame(opcode)
-
-    this.#socket.write(buffer, cb)
+  async #run () {
+    this.#running = true
+    /** @type {SendQueueNode | null} */
+    let node = this.#head
+    while (node !== null) {
+      // wait pending promise
+      if (node.promise !== null) {
+        await node.promise
+      }
+      // write
+      this.#socket.write(node.frame, node.callback)
+      // cleanup
+      node.callback = node.frame = null
+      // set next
+      node = node.next
+    }
+    this.#head = null
+    this.#tail = null
+    this.#running = false
   }
 }
 
-function clone (data, hint) {
+function createFrame (data, hint) {
+  return new WebsocketFrameSend(toBuffer(data, hint)).createFrame(hint === sendHints.string ? opcodes.TEXT : opcodes.BINARY)
+}
+
+function toBuffer (data, hint) {
   switch (hint) {
     case sendHints.string:
       return Buffer.from(data)
     case sendHints.arrayBuffer:
     case sendHints.blob:
       return new FastBuffer(data)
     case sendHints.typedArray:
-      return Buffer.copyBytesFrom(data)
+      return new FastBuffer(data.buffer, data.byteOffset, data.byteLength)
   }
 }