livery_etag (livery v0.2.0)

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ETag / conditional-GET middleware.

For cacheable GET/HEAD responses it ensures an ETag header and answers 304 Not Modified when the request's If-None-Match matches, skipping the body transfer.

Stack = [{livery_etag, #{}} | Rest].

By default a strong ETag is computed automatically from a {full, _} body that has no ETag; a handler may instead set its own (via livery_resp:with_etag/2), which is respected on ANY body variant. Config keys (all optional): auto (default true), weak (default false, auto ETags are strong), statuses (cacheable statuses, default [200]).

Placement: put livery_etag OUTSIDE livery_compress (earlier in the stack list) so the ETag covers the bytes actually sent; otherwise the ETag is of the uncompressed body and you rely on Vary: Accept-Encoding (which livery_compress already sets).

Summary

Functions

call(Req, Next, State)

Add an ETag and answer 304 on a matching conditional GET.

if_none_match(Req, ETag)

True if the request's If-None-Match matches ETag.

Functions

call(Req, Next, State)

-spec call(livery_req:req(), livery_middleware:next(), map() | undefined) -> livery_resp:resp().

Add an ETag and answer 304 on a matching conditional GET.

if_none_match(Req, ETag)

-spec if_none_match(livery_req:req(), binary()) -> boolean().

True if the request's If-None-Match matches ETag.

Honors * and uses RFC 9110 weak comparison. Exposed so other handlers (e.g. livery_static) share one conditional-request implementation.