[gnunet-scheme] branch master updated (a5e9d35 -> fd4321e)

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maxime-devos pushed a change to branch master
in repository gnunet-scheme.

    from a5e9d35  dht/client: Verify that 'start-get!' can be called from 
callbacks.
     new 113fc69  dht: Allow cancelling get operations.
     new fd4321e  examples/web: Cancel the search when done.

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Summary of changes:
 doc/distributed-hash-table.tm |  7 +++++++
 examples/web.scm              | 12 ++++++++----
 gnu/gnunet/dht/client.scm     | 25 ++++++++++++++++++++++++-
 3 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/doc/distributed-hash-table.tm b/doc/distributed-hash-table.tm
index 46eb5db..784c804 100644
--- a/doc/distributed-hash-table.tm
+++ b/doc/distributed-hash-table.tm
@@ -156,6 +156,13 @@
     to make a copy of the search result, using <scm|copy-search-result>.
   </explain>
 
+  <\explain>
+    <scm|(stop-get! <var|search>)><index|stop-get!>
+  </explain|Cancel the get operation described by the search object
+  <var|search>. This is an asynchronuous operation; it does not have an
+  immediate effect. This is an idempotent operation: cancelling a search does
+  not have any additional effect.>
+
   <\explain>
     <scm|(put! <var|server> <var|insertion> <var|#:confirmed>)><index|put!>
   <|explain>
diff --git a/examples/web.scm b/examples/web.scm
index 8f105b6..c73094b 100644
--- a/examples/web.scm
+++ b/examples/web.scm
@@ -1,5 +1,5 @@
 ;; This file is part of scheme-GNUnet.
-;; Copyright (C) 2021 GNUnet e.V.
+;; Copyright © 2021, 2022 GNUnet e.V.
 ;;
 ;; scheme-GNUnet is free software: you can redistribute it and/or modify it
 ;; under the terms of the GNU Affero General Public License as published
@@ -163,12 +163,16 @@ If incorrect, return @code{#false}. TODO more validation."
   (define (found %search-result)
     ;; TODO: document necessity of copies and this procedure
     (set! search-result (dht:copy-search-result %search-result))
-    (signal-condition! found?))
+    (unless (signal-condition! found?)
+      (pk "already signalled, is cancelling working correctly, or was this \
+merely a race?")))
   (define query (parameters->query parameters))
   (if query
-      (begin
-       (dht:start-get! dht-server query found)
+      (let ((search-handle (dht:start-get! dht-server query found)))
        (wait found?)
+       ;; For this example application, a single response is sufficient.
+       ;; TODO: cancel from within 'found' (probably buggy)
+       (dht:stop-get! search-handle)
        ;; TODO: properly format the result, streaming, stop searching
        ;; after something has been found or if the client closes the 
connection ...
        (respond/html `(div (p "Found! ")
diff --git a/gnu/gnunet/dht/client.scm b/gnu/gnunet/dht/client.scm
index 2520bf6..8b74f43 100644
--- a/gnu/gnunet/dht/client.scm
+++ b/gnu/gnunet/dht/client.scm
@@ -581,7 +581,7 @@ currently unsupported."
              ;; Atomic box holding an unsigned 64-bit integer.
              (immutable next-unique-id/box server-next-unique-id/box)
              ;; Hash table from operation ids to their corresponding
-             ;; <get> object.
+             ;; <get> object.  TODO: hash maps are thread-unsafe
              (immutable id->operation-map server-id->operation-map)))
 
     (define (maybe-send-control-message!* terminal-condition control-channel
@@ -619,6 +619,13 @@ do anything if @var{server} has been permanently 
disconnected."
                                              (get:unique-id get)
                                              (get:options get))))
 
+    (define (send-stop-get! mq get)
+      "Send a message for stopping the get operation @var{get}."
+      (send-message!
+       mq
+       (construct-client-get-stop (query-key (get:query get))
+                                 (get:unique-id get))))
+
     (define (fresh-id server)
       "Generate a fresh numeric ID to use for communication with @var{server}."
       ;; Atomically increment the ‘next unique id’, but avoid
@@ -673,6 +680,13 @@ search result, using @lisp{copy-search-result}."
       (maybe-send-control-message! server 'start-get! handle)
       handle)
 
+    (define (stop-get! search)
+      "Cancel the get operation @var{search}.  This is an asynchronuous 
operation;
+it does not have an immediate effect.  This is an idempotent operation; 
cancelling
+a search twice does not have any additional effect."
+      (maybe-send-control-message! (get:server search) 'stop-get! get)
+      (values))
+
     (define* (put! server insertion #:key (confirmed values))
       "Perform the insertion @var{insertion}. When the datum has been inserted,
 the thunk @var{confirmed} is called. A @emph{put object} is returned which can
@@ -862,6 +876,15 @@ code automatically tries to reconnect, so @var{connected} 
can be called after
           (send-get! mq get)
           ;; Continue!
           (control))
+         (('stop-get! get)
+          ;; TODO: tests!
+          ;; TODO: racy!
+          ;; TODO: cancel outstanding messages to the DHT services for this
+          ;; get operation (including the request to start searching), if
+          ;; any.
+          (when (hashv-ref id->operation-map (get:unique-id get))
+            (hashv-set! id->operation-map (get:unique-id get) #false)
+            (send-stop-get! mq get)))
          (('put! put)
           ;; Send the put operation to the DHT service.
           (send-message! mq (put:message put))

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