Perl PAGI Middleware

Middleware in PAGI A port of the sample app from What Is Middleware? — which builds the same three-layer stack in Plack/PSGI (Perl) and Starlette/ASGI (Python) — to PAGI , an async, ASGI-style application interface for Perl. The app is deliberately tiny but exercises the three things middleware exists to do: Logger — wrap the request, time it, log method/path in and status/duration out. Authenticator — inspect a header, inject context for downstream layers on success, or short-circuit with a 401 on failure. ProfileRouter — answer one specific route from inside the stack, reading the context the Authenticator injected. All code below was run under perl-5.40.0 with PAGI::Test::Client ; the log lines and responses shown in Running it are the actual captured output, not hand-written. The PAGI middleware contract A PAGI application is, in the spec's words, "a single coderef returning a Future": an async sub over the ($scope, $receive, $send) triple — the same shape as ASGI. $scope is the per-connection metadata hash ( type , method , path , headers , …), $receive pulls inbound events, $send pushes outbound ones ( http.response.start , then http.response.body ), and the Future it returns resolving is what tells the server the response is complete. Middleware is just as plain: a subroutine that takes an application and returns a new application, wrapping the inner one. That is the whole spec-level contract — app in, app out: sub middleware { my ( $app ) = @_ ; return async sub ($scope, $receive, $send) { # ... before ... await $app -> ( $scope , $receive , $send ); # call the inner app # ... after ... }; } A middleware propagates the inner app's Future — its completion and any exception flow straight through — and never reads its return value, which the spec defines as inert; to observe or rewrite the response it wraps $send instead, and to add per-request context it clones $scope (top-level edits stay visible downward only). PAGI::Middleware , from PAGI-Tools rather than