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mrgnhnt96/revali ★9999⑂99

Compression

Gzip responses for clients that ask for them

Revali gzips responses by default. It is negotiated, so only a client that sent Accept-Encoding: gzip ever receives a compressed body — turning this on cannot break a client that did not ask.

There is nothing to enable.

What gets compressed#

A response is compressed only when all of these hold:

  • The client sent Accept-Encoding: gzip.
  • The Content-Type is text-shaped — JSON, HTML, CSS, JavaScript, XML, SVG, plain text, CSV, Markdown.
  • The body is at least minBytes (1 KB by default).
  • The response is not already encoded, and is not partial content (206).

Compressed responses also carry Vary: Accept-Encoding, so a cache in front of the server keeps the compressed and uncompressed variants apart instead of serving one to a client that cannot read it.

What deliberately does not#

Bodies of unknown length, which in practice means streaming responses and SSE. Gzip buffers, so compressing a stream would hold back chunks the handler meant to flush immediately — the compression would come at the cost of the thing streaming exists for.

Already-compressed media. Images, video and archives come out marginally larger after gzip, having spent CPU to get there.

Small bodies. Below roughly a packet there is nothing to save, and gzip's own header can make a tiny response bigger.

Tuning it#

@App()
final class MyApp extends AppConfig {
  const MyApp() : super(host: 'localhost', port: 8080);

  @override
  CompressionSettings get compression => const CompressionSettings(
    minBytes: 4096,
    mimeTypes: {...CompressionSettings.defaultMimeTypes, 'application/hal+json'},
  );
}

Turning it off#

Worth doing when something in front of the server already compresses — a CDN, or a reverse proxy like nginx — so you are not paying for it twice: 

@override
CompressionSettings get compression => const CompressionSettings.disabled();

What's next?#