middleware.md

Router-level Middleware

There are two types of router-level middleware procs in twebserver: enter and leave. The enter proc is called before the matched route handler is called and the leave proc is called after the matched route handler has executed.

The enter proc has access to the context and request dictionaries. The leave proc has access to the context, request, and response dictionaries.

An enter middleware function can end the request-response cycle by returning "error" e.g. return -code error -options [::twebserver::build_response 429 text/plain "too many requests"]. Otherwise, it should return to continue processing the request.

Router-level middleware is bound to an instance of a router:

set router [::twebserver::create_router]

proc example_enter {ctx req} {
    puts "entering example"
    return $req
}

proc example_leave {ctx req res} {
    puts "leaving example"
    return $res
}

::twebserver::add_middleware \
  -enter_proc example_enter \
  -leave_proc example_leave \
  $router

See tsession for an example of router-level middleware.