From 677d941cb320aecf4f127e77f041f348d80f6d62 Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Sun, 22 Mar 2026 15:16:17 +0000
Subject: [PATCH] Simplify web server exception handling

This used to be more complicated as the exception handler was
configurable, but now it's not so this can be simplified.
---
 knots/web-server.scm | 87 ++++++++++++++++++++------------------------
 1 file changed, 39 insertions(+), 48 deletions(-)

diff --git a/knots/web-server.scm b/knots/web-server.scm
index a99b971..99abfdc 100644
--- a/knots/web-server.scm
+++ b/knots/web-server.scm
@@ -317,26 +317,6 @@ on the procedure being called at any particular time."
   ;; Close the client port
   #f)
 
-(define (exception-handler exn request)
-  (let* ((error-string
-          (call-with-output-string
-            (lambda (port)
-              (simple-format
-               port
-               "exception when processing: ~A ~A\n"
-               (request-method request)
-               (uri-path (request-uri request)))
-              (print-backtrace-and-exception/knots
-               exn
-               #:port port)))))
-    (display/knots error-string
-                   (current-error-port)))
-
-  (values (build-response #:code 500)
-          ;; TODO Make this configurable
-          (string->utf8
-           "internal server error")))
-
 (define* (handle-request handler client
                          read-request-exception-handler
                          write-response-exception-handler
@@ -362,36 +342,47 @@ on the procedure being called at any particular time."
                                   (connection . (close))))
                      #vu8()))
             (else
-             (call-with-escape-continuation
-              (lambda (return)
-                (with-exception-handler
-                    (lambda (exn)
+             (with-exception-handler
+                 (lambda (exn)
+                   (sanitize-response
+                    request
+                    (build-response #:code 500)
+                    (string->utf8
+                     "internal server error")))
+               (lambda ()
+                 (with-exception-handler
+                     (lambda (exn)
+                       (let* ((error-string
+                               (call-with-output-string
+                                 (lambda (port)
+                                   (simple-format
+                                    port
+                                    "exception when processing: ~A ~A\n"
+                                    (request-method request)
+                                    (uri-path (request-uri request)))
+                                   (print-backtrace-and-exception/knots
+                                    exn
+                                    #:port port)))))
+                         (display/knots error-string
+                                        (current-error-port))))
+                   (lambda ()
+                     (start-stack
+                      #t
                       (call-with-values
                           (lambda ()
-                            (exception-handler exn request))
-                        (lambda (response body)
-                          (call-with-values
-                              (lambda ()
-                                (sanitize-response request response body))
-                            return))))
-                  (lambda ()
-                    (start-stack
-                     #t
-                     (call-with-values
-                         (lambda ()
-                           (handler request))
-                       (match-lambda*
-                         ((response body)
-                          (sanitize-response request response body))
-                         (other
-                          (raise-exception
-                           (make-exception-with-irritants
-                            (list (make-exception-with-message
-                                   (simple-format
-                                    #f
-                                    "wrong number of values returned from handler, expecting 2, got ~A"
-                                    (length other)))
-                                  handler)))))))))))))))
+                            (handler request))
+                        (match-lambda*
+                          ((response body)
+                           (sanitize-response request response body))
+                          (other
+                           (raise-exception
+                            (make-exception-with-irritants
+                             (list (make-exception-with-message
+                                    (simple-format
+                                     #f
+                                     "wrong number of values returned from handler, expecting 2, got ~A"
+                                     (length other)))
+                                   handler)))))))))))))))
       (with-exception-handler
           (lambda (exn)
             (write-response-exception-handler exn request))