Roadmap

go-ruby-rack/rack is grown test-first, each capability differential-tested against the rack gem rather than built in isolation. The deterministic, interpreter-independent slice of Rack 3.x's pure-compute surface extracted from rbgo's internals is complete.

Stage	What	Status
Query & parameters	ParseQuery / ParseNestedQuery bracket nesting (foo[bar], foo[], x[][a]), the array-of-hash vs nested-array subtleties, ParameterTypeError / ParamsTooDeepError, and BuildQuery / BuildNestedQuery inverses.	Done
Escaping	Escape / Unescape, EscapePath / UnescapePath (RFC 2396), EscapeHTML / UnescapeHTML — byte-identical to MRI.	Done
Status codes & headers	The full HTTPStatusCodes table, symbol → code reverse map (deprecated aliases), StatusWithNoEntityBody, and the insertion-ordered, key-down-casing Headers.	Done
Content negotiation & cookies	QValues, BestQMatch, GetByteRanges; ParseCookiesHeader, MakeCookieHeader / MakeDeleteCookieHeader and the …Into mutators.	Done
Request over an Env	Method predicates, PathInfo / QueryString / GET / POST / Params / Cookies, ContentType / MediaType, Host / Port / Scheme / SSL / BaseURL / URL, XHR, IP with trusted-proxy filter.	Done
Response & SPEC tuple	NewResponse / NewResponseString / ResponseTuple, Write, Finish / ToA, SetStatus, SetCookie / DeleteCookie, Redirect, status-class predicates.	Done
Body/Input seam	The single Input interface through which the host supplies the request body, memoised into the env like the gem.	Done
Differential oracle & coverage	Escape, query, status, cookie, media-type, byte-range and Response#finish checked byte-for-byte against ruby + the rack gem; 100% coverage, green across 6 arches and 3 OSes.	Done

Documented out-of-scope boundaries

These are deliberate, recorded so the module's surface is unambiguous:

• No HTTP server. Rack::Handler, the socket accept loop and TLS are the host's job. This library never touches the network; the request body comes in through the one explicit Input seam.
• No interpreter. The library implements the deterministic compute; it never runs arbitrary Ruby (Rack::Builder DSL, middleware call chains). Anything that needs a live binding is the consumer's job — that is why rbgo binds this module rather than the reverse.
• Reference is the rack gem (Rack 3.x, MRI). Byte-for-byte conformance targets the reference gem's behaviour, pinned by the differential oracle.
• Standalone & reusable. The module has no dependency on the Ruby runtime; the dependency runs the other way.

See Usage & API for the surface and Why pure Go for the deterministic/interpreter split.