Compression Module

The CompressionModule enables automatic response compression. The implementation is selected at runtime based on the detected JavaScript engine — no configuration required.

Runtime Backends

Runtime	gzip	deflate	brotli (br)
Bun	Bun.gzipSync	Bun.deflateSync	falls back to gzip
Node.js ≥ 20	node:zlib.gzipSync	node:zlib.deflateSync	node:zlib.brotliCompressSync

Compression only applies when the client sends an Accept-Encoding header that includes the configured encoding, and the response body exceeds the configured threshold.

Setup

import { Module, CompressionModule } from 'next-js-backend';

@Module({
  imports: [
    CompressionModule.register({
      encoding: 'gzip',   // 'gzip' | 'deflate' | 'br'
      threshold: 1024,    // minimum response size in bytes (default: 1024)
      level: 6,           // compression level 0–9 (default: 6)
    }),
  ],
})
export class AppModule {}

Configuration Options

Option	Type	Default	Description
encoding	'gzip' | 'deflate' | 'br'	'gzip'	Compression algorithm
threshold	number	1024	Minimum response body size in bytes to trigger compression
level	number	6	Compression level 0 (fastest) – 9 (best compression)

Brotli on Bun

Bun does not expose a native brotliSync API. When encoding: 'br' is configured and the app runs on Bun, compression falls back to gzip and the Content-Encoding: gzip header is set accordingly.

On Node.js ≥ 20, brotliCompressSync is used natively and the Content-Encoding: br header is sent correctly.

How It Works

The module hooks into Elysia's onAfterHandle lifecycle event. After the route handler produces a response:

1. Check if the client's Accept-Encoding header includes the configured encoding.
2. Read the response body as an ArrayBuffer.
3. Skip compression if the body is smaller than threshold.
4. Compress using the runtime-appropriate backend.
5. Return a new Response with the compressed body and updated Content-Encoding header. The Content-Length header is removed to let the transport layer recalculate it.

Handler Response → onAfterHandle hook → Accept-Encoding check →
threshold check → runtime compress → Response(compressed)