How to compress responses

Problem

You want responses gzip/deflate-compressed when the client supports it, without touching every handler.

Solution

Add livery_compress to the stack. gzip and deflate are built in:

Stack = [
    {livery_compress, #{}}
    %% ... handler
].

It reads the request Accept-Encoding, picks a codec the client accepts, compresses the response body, and sets Content-Encoding plus Vary: Accept-Encoding. A client that sends no Accept-Encoding (or none the server has) gets the response uncompressed, so any HTTP client works: those that advertise gzip decode it transparently, the rest get identity.

What gets compressed

Eligible responses are {full, _} bodies at least min_size bytes and {chunked, _} streams, with a compressible Content-Type and no existing Content-Encoding. SSE, file, empty, and upgrade responses pass through untouched.

{livery_compress, #{
    min_size => 1024,                       %% default; full bodies only
    types => [<<"text/">>, <<"application/json">>]  %% compressible prefixes
}}

Content-Type matching is case-insensitive and ignores parameters, so Application/JSON; charset=utf-8 is compressed.

Negotiation and server preference

A coding is acceptable when its Accept-Encoding q-value is greater than zero (q=0 rejects). Among acceptable codings the SERVER decides which to use, in the order of the codec list; client q-weights are only an accept/reject filter. Control the order with codecs:

{livery_compress, #{codecs => [livery_codec_gzip]}}   %% gzip only

Adding more codecs

livery_compress negotiates over livery_codec:registered(), which is [livery_codec_gzip, livery_codec_deflate] plus any codec a separate app registered. A codec app implements the livery_codec behaviour and calls livery_codec:register(Module) at its own start; it is then negotiated automatically (e.g. a future livery_brotli advertising br). The built-ins are always present and cannot be displaced by registration.