Compression Middleware

compression() compresses res.json(), res.text(), and res.html() responses based on the client's Accept-Encoding header. Brotli is preferred when supported, falling back to gzip, then deflate.

Coming from Express?

Works like the compression npm package. Same threshold, same filter, same level option.

Basic usage

import { compression } from "bunway";

app.use(compression());

Clients that send Accept-Encoding: br, gzip receive Brotli-compressed responses. Clients that only send gzip receive gzip. Responses below the threshold (default 1 KB) are sent uncompressed.

Encoding priority

1. Brotli (br) — best ratio, used when the client supports it
2. gzip — wide compatibility fallback
3. deflate — last resort

Threshold

Responses smaller than the threshold are never compressed:

app.use(compression({ threshold: 2048 })); // 2 KB minimum

Default: 1024 bytes.

Compression level

Controls the gzip/deflate compression level (1–9). Brotli uses its own default:

app.use(compression({ level: 9 })); // maximum compression

Default: 6.

Custom filter

Skip compression for specific content types:

app.use(compression({
  filter: (contentType) => contentType.includes("text/"),
}));

The default filter compresses: text/*, application/json, application/javascript, application/xml, application/xhtml+xml, image/svg+xml.

Options reference

Option	Type	Default	Description
level	number	6	gzip/deflate compression level (1–9).
threshold	number	1024	Minimum response size in bytes to compress.
filter	(contentType: string) => boolean	compressible types	Return true to compress this content type.

For type details see CompressionOptions in the API Reference.