2.16 Wrapping Requests & Responses

(require web-server/dispatchers/dispatch-wrap)
	package: web-server-lib

The web-server/dispatchers/dispatch-wrap module provides a general-purpose wrapping dispatcher that allows one to intercept an incoming request as well as the response returned by other servlets

procedure
(make servlet req-trans res-trans) → dispatcher/c
  servlet : (-> request? response?)
  req-trans : (-> request? request?)
  res-trans : (-> response? response?)

Returns a dispatcher that wraps res-trans around servlet, which itself receives requests transformed by req-trans. Put differently, the servlet underlying the dispatcher returned by make is equivalent to (λ (r) (res-trans (servlet (req-trans r)))).

If you’re not interested in transforming requests, pass in identity (the identity function) for req-trans. Similarly, using identity for res-trans will cause responses to pass through unchanged. (Using identity for both req-trans and res-trans is equivalent to just using servlet as-is.)

A typical use case for this dispatcher would be to inject headers into requests or responses. Similarly, functionally updating existing headers also fits into this pattern. Since the entire request – not just its headers – is available to req-trans (and similarly for the response and res-trans), arbitrary rewriting of request/response bodies is possible. Side effects in req-trans and res-trans are permitted as long as make’s contracts are adhered to.

Changed in version 1.9 of package web-server-lib: First version of this dispatcher

1	Dispatching Server
2	Dispatchers
3	Launching Servers
4	Web Servers
5	Internal APIs
6	Troubleshooting and Tips
	Index

2.1	General
2.2	Mapping URLs to Paths
2.3	Sequencing
2.4	Timeouts
2.5	Lifting Procedures
2.6	Filtering Requests by URL
2.7	Filtering Requests by Method
2.8	Procedure Invocation upon Request
2.9	Logging
2.10	Password Protection
2.11	Virtual Hosts
2.12	Serving Files
2.13	Serving Servlets
2.14	Statistics
2.15	Limiting Requests
2.16	Wrapping Requests & Responses