sunet/scheme/httpd/error.scm

;;; Error stuff for the http server. -*- Scheme -*-

;;; This file is part of the Scheme Untergrund Networking package.

;;; For copyright information, see the file COPYING which comes with
;;; the distribution.

;;; An http error condition is a data structure with the following pieces:
;;;     (error-code request message . irritants)
;;; You recognise one with HTTP-ERROR?, and retrieve the pieces with
;;; CONDITION-STUFF.
;;;

;;; HTTP error condition
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Define a sub-type of the S48 error condition, the HTTP error condition.
;;; An HTTP error is one that corresponds to one of the HTTP error response
;;; codes, so you can reliably use an HTTP error condition to construct an
;;; error response message to send back to the HTTP client.

(define-condition-type 'http-error '(error))

(define http-error? (condition-predicate 'http-error))

;; See make-error-response for what you have to stuff into args for
;; each status-code. (All http-errors will be caught by the top-level
;; error-handler of process-toplevel-request, and will be turned into
;; calls of make-error-response).
(define (http-error status-code req . args)
  (apply signal 'http-error status-code req args))


;;; Syntax error condition
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Scheme 48 has a "syntax error" error condition, but it isn't an error
;;; condition! It's a warning condition. I don't understand this. 
;;; We define a *fatal* syntax error here for the parsers to use.


;; fatal-syntax-error isn't really a different type of error - it's
;; just an abbreviated notation:
;; (fatal-syntax-error msg irritants) 
;; is equivalent to
;; (http-error (status-code bad-request) #f msg irritants)
;; -> use fatal-syntax-error where the client request cannot be parsed
;; because of bad syntax

(define-condition-type 'fatal-syntax-error '(error))

(define fatal-syntax-error? (condition-predicate 'fatal-syntax-error))

;; as with http-errors fatal-syntax-errors will be caught by the
;; top-level error-handler of process-toplevel-request and turned into
;; calls of make-error-response
(define (fatal-syntax-error msg . irritants)
  (apply signal 'fatal-syntax-error msg irritants))