Endpoints live in groups, and groups nest. A group is a path prefix plus middleware: an endpoint "/users" in a group "/api" under a group "/v1" answers at "/v1/api/users", wrapped by the middleware of every group above it, outermost first, then its own. NULL as the group is the root: no prefix, and the middleware given to ioxd_use. A prefix and what follows it are joined by a '/' when neither side brings one ("/api" and "users" is "/api/users"), and a repeated slash counts once.

Register everything before ioxd_run, from the main thread; methods, paths and prefixes are copied, so temporaries are fine, and anything registered once ioxd_run has started is ignored with a line on stderr. ioxd_run resolves it once: every endpoint's full path into a segment tree and its middleware into one flat chain, which the workers then share read-only. A request costs one walk down the tree - no scan, no regex - and one call through its chain.

An endpoint: method matched exactly, except that HEAD is answered by the GET of a path that has no HEAD of its own; path matched by segment below the group's prefix, with :name captures ("/users/:id") landing in req.route_params. A static segment beats a capture at any depth, and a static path that lacks the method falls through to a capture route that has it. A trailing slash is tolerated. Segments are matched as they arrive on the wire, so an escape in a static segment does not match it, but a captured value is handed over percent-decoded ("/users/a%2Fb" captures "a/b") - raw in the rare case that it does not fit IOXD_ROUTE_ARENA.

The verbs, for short: ioxd_get(api, "/users/:id", user).

Root middleware: every request, the fallbacks included.

The fallback when no path matches (a built-in 404 by default). A path that matches without the method gets a built-in 405 whose allow header lists every method that path has, on a capture route too. Both run behind the root's middleware only, so that allow header names methods a group's own middleware would otherwise have gated.

Registration as a block-structured script: a current group, which the block after IOXD_GROUP sets (the root outside any block), endpoints registered into it, with their own middleware listed after the handler, and IOXD_USE adding middleware to it - so a group's middleware is either listed after its prefix or added with IOXD_USE inside its block. Plain functions underneath, so everything is type-checked; a group's block runs exactly once, and leaving it early - break, return, goto - still closes the group.

IOXD_USE(log);
IOXD_GET("/", home);
IOXD_GROUP("/api", api_header) {
    IOXD_GET("/ping", ping);
    IOXD_GROUP("/admin", require_token) {
        IOXD_GET("/stats", stats, timing);
    }
}

A break, a return or a goto out of the block skips the loop's increment, so where the compiler has __attribute__((cleanup)) the pop is hung on the block's variable and runs on every way out; a block that ended on its own has already popped and nulled it. Elsewhere the plain form stands, and a group still open at ioxd_run is reported.