Add HTTP caching feature (RFC 7234)

Implement a new :caching feature that stores and reuses HTTP responses
according to RFC 7234 freshness and validation semantics. Only GET and
HEAD responses are cached. Supports Cache-Control (max-age, no-cache,
no-store), Expires, ETag / If-None-Match, and Last-Modified /
If-Modified-Since for freshness checks and conditional revalidation.
Ships with a default in-memory store. Custom stores can be passed via
the store option.

Closes #223.

Author: sferik

.mutant.yml

@@ -25,6 +25,7 @@ matcher:
     - HTTP::URI*
     - HTTP::Headers*
     - HTTP::Redirector*
+    - HTTP::Features::Caching*
     - HTTP::Features::RaiseError*
     - HTTP::Base64*
   ignore:

CHANGELOG.md

@@ -37,6 +37,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- HTTP caching feature (`HTTP.use(:caching)`) that stores and reuses responses
+  according to RFC 7234. Supports `Cache-Control` (`max-age`, `no-cache`,
+  `no-store`), `Expires`, `ETag` / `If-None-Match`, and
+  `Last-Modified` / `If-Modified-Since` for freshness checks and conditional
+  revalidation. Ships with a default in-memory store; custom stores can be
+  passed via `store:` option. Only GET and HEAD responses are cached. ([#223])
 - `HTTP.base_uri` for setting a base URI that resolves relative request paths
   per RFC 3986. Supports chaining (`HTTP.base_uri("https://api.example.com/v1")
   .get("users")`), and integrates with `persistent` connections by deriving the

Steepfile

@@ -12,6 +12,7 @@ target :lib do
   library "singleton"
   library "socket"
   library "tempfile"
+  library "time"
   library "timeout"
   library "uri"
   library "zlib"

lib/http/feature.rb

@@ -78,6 +78,7 @@ def on_error(_request, _error); end
 
 require "http/features/auto_inflate"
 require "http/features/auto_deflate"
+require "http/features/caching"
 require "http/features/instrumentation"
 require "http/features/logging"
 require "http/features/normalize_uri"