From 399788edaea23ee1070f9c0620ea855c4c29e85a Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Wed, 30 Sep 2015 01:16:15 -0400
Subject: [PATCH] Propagate exceptions over RPC reply channels

---
 src/rpc.rkt | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/src/rpc.rkt b/src/rpc.rkt
index 4a717c0..8ff8adb 100644
--- a/src/rpc.rkt
+++ b/src/rpc.rkt
@@ -1,11 +1,15 @@
 #lang racket/base
 
-(provide rpc-request-evt
+(provide (struct-out exn:fail:rpc)
+         rpc-request-evt
          rpc-handler
          rpc-call
          rpc-cast!)
 
 (require racket/match)
+(require racket/exn)
+
+(struct exn:fail:rpc exn:fail (inner-exn) #:transparent)
 
 (define (rpc-request-evt)
   (handle-evt (thread-receive-evt)
@@ -15,16 +19,30 @@
   (match ch-and-req
     [(cons ch request)
      (define-values (reply-value new-state)
-       (match request
-         [(list argpat ...) body ...]
-         ...))
+       (with-handlers [(exn:fail? (lambda (e)
+                                    (channel-put ch e)
+                                    (raise e)))]
+         (match request
+           [(list argpat ...) body ...]
+           ...)))
      (when ch (channel-put ch reply-value))
      new-state]))
 
 (define (rpc-call thread . request)
   (define ch (make-channel))
   (thread-send thread (cons ch request))
-  (channel-get ch))
+  (define result
+    (sync (handle-evt thread
+                      (lambda (_)
+                        (raise (exn:fail:rpc "Server thread terminated unexpectedly"
+                                             (current-continuation-marks)
+                                             #f))))
+          ch))
+  (when (exn? result)
+    (raise (exn:fail:rpc (format "RPC exception:\n~a" (exn->string result))
+                         (current-continuation-marks)
+                         result)))
+  result)
 
 (define (rpc-cast! thread . request)
   (thread-send thread (cons #f request)))