Avoid depending on Node's 'util' module for promisify()

Historically this wasn't a problem as bundlers would automatically
include polyfills for Node modules, but that's no longer true (in
Webpack 5 it's mildly awkward, and with ESBuild even more so) so it's
useful to avoid these where possible.

Author: pimterry

package.json

@@ -46,13 +46,15 @@
   "homepage": "https://github.com/httptoolkit/http-encoding#readme",
   "dependencies": {
     "brotli-wasm": "^1.1.0",
+    "pify": "^5.0.0",
     "zstd-codec": "^0.1.4"
   },
   "devDependencies": {
     "@types/chai": "^4.2.18",
     "@types/chai-as-promised": "^7.1.4",
     "@types/mocha": "^8.2.2",
     "@types/node": "^15.3.0",
+    "@types/pify": "^5.0.1",
     "assert": "^2.0.0",
     "browserify-zlib": "^0.2.0",
     "buffer": "^6.0.3",

src/index.ts

@@ -1,7 +1,11 @@
 import * as zlib from 'zlib';
-import { promisify } from 'util';
 import type { ZstdStreaming } from 'zstd-codec';
 
+// We want promisify, but for easy browser usage downstream we want to avoid using Node's util
+// version. We replace it with pify, but we import util here purely to get the more accurate types.
+import { promisify as utilPromisify } from 'util';
+const promisify: typeof utilPromisify = require('pify');
+
 export type SUPPORTED_ENCODING =
     | 'identity'
     | 'gzip'