From 1265e94d9275357c77276b1ddba6c07a3e2e529e Mon Sep 17 00:00:00 2001
From: David Florness <david@florness.com>
Date: Tue, 10 Mar 2020 16:00:41 -0600
Subject: [PATCH] When a client quits, let the bulletin know

---
 bulletin.rkt | 12 +++++++++++-
 client.rkt   | 27 +++++++++++++++++++--------
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/bulletin.rkt b/bulletin.rkt
index 1b65e45..7bc42b0 100644
--- a/bulletin.rkt
+++ b/bulletin.rkt
@@ -185,6 +185,15 @@
              "Too early to request sums"
              #:code 403))))
 
+  (define (quit request)
+    (let* ([token (string->symbol
+                   (hash-ref
+                    (bytes->jsexpr (request-post-data/raw request))
+                    'token))]
+           [username (hash-ref (hash-ref _peers token) 'username)])
+      (displayln (format "~a quit!" username))
+      (hash-remove! _peers token)))
+
   (define-values (dispatch-route url-generator)
     (dispatch-rules
      [("register")   #:method "post" register  ]
@@ -195,7 +204,8 @@
      [("outputs")    #:method "post" outputs   ]
      [("values")     #:method "post" _values   ]
      [("sum")        #:method "post" sum       ]
-     [("sums")       #:method "get"  sums      ]))
+     [("sums")       #:method "get"  sums      ]
+     [("quit")       #:method "post" quit      ]))
 
   (define/contract (internal-server-error url ex)
     (url? any/c . -> . can-be-response?)
diff --git a/client.rkt b/client.rkt
index 391bd00..a4f1652 100644
--- a/client.rkt
+++ b/client.rkt
@@ -72,13 +72,6 @@
          [point    : Integer]
          [bulletin : requester]
          [token    : JSExpr])
-  (display "retrieving candidates...")
-  (define candidates (cast (json-response-body
-                            (retry-request (get bulletin "/candidates")))
-                           (Listof String)))
-  (define cand-count (cast (length candidates) Positive-Integer))
-  (newline)
-
   (display "waiting for voting to commence...")
   (define peer-count (cast
                       (json-response-body
@@ -86,6 +79,15 @@
                       Positive-Integer))
   (newline)
 
+  (break-enabled #f) ; voting has begun!
+
+  (display "retrieving candidates...")
+  (define candidates (cast (json-response-body
+                            (retry-request (get bulletin "/candidates")))
+                           (Listof String)))
+  (define cand-count (cast (length candidates) Positive-Integer))
+  (newline)
+
   (define vote
     (let* ([vote (get-vote candidates)]
            [m    cand-count]
@@ -170,6 +172,8 @@
                          (Listof String))))))))
   (newline)
 
+  (break-enabled #t) ; it's ok if the client quits at this point
+
   (display "finding constant...")
   (define constant
     (let ([k (length peer-inputs)]
@@ -331,7 +335,14 @@
   ; the bulletin can have multiple elections, so loop
   (let loop ()
     (with-handlers
-      ([exn:fail:network:http:error?
+      ([exn:break?
+        (λ ([ex : exn:break])
+          (post bulletin "/quit"
+                #:data
+                (jsexpr->string
+                 (hasheq
+                  'token token))))]
+       [exn:fail:network:http:error?
         (λ ([ex : exn:fail:network:http:error])
           (break-enabled #t)
           (if (eqv? 410 (exn:fail:network:http:error-code ex))
-- 
2.38.4