Brotli vs Gzip in Node: CPU Tradeoffs at the CDN Edge

// src/compress.ts
import { gzipSync, brotliCompressSync, constants } from "node:zlib";

export function encodeBody(buf: Buffer, accept: string | undefined, kind: "static" | "dynamic") {
 if (buf.length < 1024) return { body: buf, encoding: undefined as string | undefined };
 const wantsBr = /\bbr\b/.test(accept ?? "");
 const wantsGz = /\bgzip\b/.test(accept ?? "");

 if (kind === "static" && wantsBr) {
 // ✅ Higher quality OK offline
 return {
 body: brotliCompressSync(buf, {
 params: { [constants.BROTLI_PARAM_QUALITY]: 11 },
 }),
 encoding: "br",
 };
 }
 if (wantsBr && kind === "dynamic" && buf.length > 16_384) {
 // ✅ Lower quality on request path
 return {
 body: brotliCompressSync(buf, {
 params: { [constants.BROTLI_PARAM_QUALITY]: 4 },
 }),
 encoding: "br",
 };
 }
 if (wantsGz) {
 return { body: gzipSync(buf, { level: 5 }), encoding: "gzip" };
 }
 return { body: buf, encoding: undefined };
}

// ❌ Brotli quality 11 inside the request handler for every JSON response
app.use(compress({ brotli: { params: { [zlib.constants.BROTLI_PARAM_QUALITY]: 11 } } }));

import { performance } from "node:perf_hooks";

export function timedEncode(fn: () => Buffer) {
 const t0 = performance.now();
 const body = fn();
 metrics.timing("compress.encode_ms", performance.now() - t0);
 metrics.histogram("compress.bytes", body.length);
 return body;
}

# ✅ Build-time assets
brotli -q 11 -k dist/assets/*.js
gzip -9 -k dist/assets/*.js
# Upload .br/.gz alongside originals; set Content-Encoding + Vary

import { createGzip } from "node:zlib";
import { pipeline } from "node:stream/promises";
import { Readable } from "node:stream";

export async function streamGzip(res: NodeJS.WritableStream, src: Readable) {
 res.setHeader?.("Content-Encoding", "gzip");
 await pipeline(src, createGzip({ level: 5 }), res as any);
}