From 7664f3d20e1704d4d53cb3a10f293366bfb857c7 Mon Sep 17 00:00:00 2001
From: David Florness <david@florness.com>
Date: Sun, 8 Mar 2020 15:37:26 -0600
Subject: [PATCH] Client checks if it can register before trying

---
 bulletin.rkt | 14 ++++++++------
 client.rkt   | 16 ++++++++++++++--
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/bulletin.rkt b/bulletin.rkt
index 3fdcb83..6cecfcc 100644
--- a/bulletin.rkt
+++ b/bulletin.rkt
@@ -186,8 +186,8 @@
 
   (define-values (dispatch-route url-generator)
     (dispatch-rules
-     [("candidates") #:method "get"  candidates]
      [("register")   #:method "post" register  ]
+     [("candidates") #:method "get"  candidates]
      [("peer-count") #:method "get"  peer-count]
      [("commit")     #:method "post" commit    ]
      [("peers")      #:method "get"  peers     ]
@@ -198,7 +198,9 @@
 
   (define/contract (internal-server-error url ex)
     (url? any/c . -> . can-be-response?)
-    (response/full 400 #"Bad Request" (current-seconds) #f empty empty))
+    (response/jsexpr
+     empty
+     #:code 400))
 
   (define/contract (dispatcher req)
     (request? . -> . any)
@@ -213,8 +215,8 @@
    #:port 1984
    #:servlet-regexp #rx""
    #:command-line? #t
-   ;; #:servlet-responder internal-server-error
-   ))
+   ; comment out the following to get client-side tracebacks
+   #:servlet-responder internal-server-error))
 
 (module+ main
   (void (thread server))
@@ -259,8 +261,8 @@
                                                       (string->symbol election)
                                                       election)])
                                    (election-set! election))]
-                       [(? eof-object?)
-                        (displayln "set what? options are `election'")]
+                      [(? eof-object?)
+                       (displayln "set what? options are `election'")]
                       [else (displayln "cannot set that")])]
               ['open
                (if (memq state '(closed registering))
diff --git a/client.rkt b/client.rkt
index 0578a9f..9ad7cbc 100644
--- a/client.rkt
+++ b/client.rkt
@@ -286,6 +286,15 @@
          (get bulletin "/candidates")
          (void))))
 
+(define (can-we-register? [bulletin : requester]) : (Values Boolean (Option String))
+  (with-handlers ([exn:fail:network:http:error?
+                   (λ ([ex : exn:fail:network:http:error])
+                     (if (eqv? (exn:fail:network:http:error-code ex) 400)
+                         (values #t #f)
+                         (values #f (exn-message ex))))])
+    (post bulletin "/register" #:data (jsexpr->string empty))
+    (values #t #f)))
+
 (module+ main
   (define point (gen))
 
@@ -294,8 +303,11 @@
                               (readline "Bulletin host: "))
                  1984))
 
-  (displayln "waiting for the election to open...")
-  (wait-for-open-election bulletin)
+  ; check if we're allowed to register
+  (let-values ([(answer why) (can-we-register? bulletin)])
+    (when (not answer)
+      (displayln (format "Cannot register: ~a" why))
+      (exit)))
 
   (define token
     (let ([username (readline "Username: ")]
-- 
2.38.4