[minor] Remove async-limiter dependency

lib/limiter.js

@@ -0,0 +1,54 @@
+'use strict';
+
+const kDone = Symbol('kDone');
+const kRun = Symbol('kRun');
+
+/**
+ * A very simple job queue with adjustable concurrency. Adapted from
+ * https://github.com/STRML/async-limiter
+ */
+class Limiter {
+  /**
+   * Creates a new `Limiter`.
+   *
+   * @param {Number} concurrency The maximum number of jobs allowed to run
+   *     concurrently
+   */
+  constructor(concurrency) {
+    this[kDone] = () => {
+      this.pending--;
+      this[kRun]();
+    };
+    this.concurrency = concurrency;
+    this.jobs = [];
+    this.pending = 0;
+  }
+
+  /**
+   * Adds a job to the queue.
+   *
+   * @public
+   */
+  add(job) {
+    this.jobs.push(job);
+    this[kRun]();
+  }
+
+  /**
+   * Removes a job from the queue and runs it if possible.
+   *
+   * @private
+   */
+  [kRun]() {
+    if (this.pending === this.concurrency) return;
+
+    if (this.jobs.length) {
+      const job = this.jobs.shift();
+
+      this.pending++;
+      job(this[kDone]);
+    }
+  }
+}
+
+module.exports = Limiter;

lib/permessage-deflate.js

@@ -1,9 +1,9 @@
 'use strict';
 
-const Limiter = require('async-limiter');
 const zlib = require('zlib');
 
 const bufferUtil = require('./buffer-util');
+const Limiter = require('./limiter');
 const { kStatusCode, NOOP } = require('./constants');
 
 const TRAILER = Buffer.from([0x00, 0x00, 0xff, 0xff]);
@@ -64,7 +64,7 @@ class PerMessageDeflate {
         this._options.concurrencyLimit !== undefined
           ? this._options.concurrencyLimit
           : 10;
-      zlibLimiter = new Limiter({ concurrency });
+      zlibLimiter = new Limiter(concurrency);
     }
   }
 
@@ -286,15 +286,15 @@ class PerMessageDeflate {
   }
 
   /**
-   * Decompress data. Concurrency limited by async-limiter.
+   * Decompress data. Concurrency limited.
    *
    * @param {Buffer} data Compressed data
    * @param {Boolean} fin Specifies whether or not this is the last fragment
    * @param {Function} callback Callback
    * @public
    */
   decompress(data, fin, callback) {
-    zlibLimiter.push((done) => {
+    zlibLimiter.add((done) => {
       this._decompress(data, fin, (err, result) => {
         done();
         callback(err, result);
@@ -303,15 +303,15 @@ class PerMessageDeflate {
   }
 
   /**
-   * Compress data. Concurrency limited by async-limiter.
+   * Compress data. Concurrency limited.
    *
    * @param {Buffer} data Data to compress
    * @param {Boolean} fin Specifies whether or not this is the last fragment
    * @param {Function} callback Callback
    * @public
    */
   compress(data, fin, callback) {
-    zlibLimiter.push((done) => {
+    zlibLimiter.add((done) => {
       this._compress(data, fin, (err, result) => {
         done();
         if (err || result) {

package.json

@@ -30,9 +30,6 @@
     "integration": "npm run lint && mocha --throw-deprecation test/*.integration.js",
     "lint": "eslint --ignore-path .gitignore . && prettier --check --ignore-path .gitignore \"**/*.{json,md,yaml,yml}\""
   },
-  "dependencies": {
-    "async-limiter": "^1.0.0"
-  },
   "peerDependencies": {
     "bufferutil": "^4.0.1",
     "utf-8-validate": "^5.0.2"

test/limiter.test.js

@@ -0,0 +1,31 @@
+'use strict';
+
+const assert = require('assert');
+
+const Limiter = require('../lib/limiter');
+
+describe('Limiter', () => {
+  it('limits the number of jobs allowed to run concurrently', (done) => {
+    const limiter = new Limiter(1);
+
+    limiter.add((callback) => {
+      setImmediate(() => {
+        callback();
+
+        assert.strictEqual(limiter.jobs.length, 0);
+        assert.strictEqual(limiter.pending, 1);
+      });
+    });
+
+    limiter.add((callback) => {
+      setImmediate(() => {
+        callback();
+
+        assert.strictEqual(limiter.pending, 0);
+        done();
+      });
+    });
+
+    assert.strictEqual(limiter.jobs.length, 1);
+  });
+});