Introduce LocalRestConnectionClosed exception

This allows tests to gracefully handle
peer nodes shutting down.

source/geod24/LocalRest.d

@@ -110,6 +110,15 @@ import std.traits : fullyQualifiedName, Parameters, ReturnType;
 import core.thread;
 import core.time;
 
+/// Thrown when the connection to a peer closed (peer node shut down)
+public final class LocalRestConnectionClosed : Exception
+{
+    this () @safe pure nothrow @nogc
+    {
+        super("Connection with peer closed");
+    }
+}
+
 /// Data sent by the caller
 private struct Command
 {
@@ -1130,7 +1139,7 @@ public final class RemoteAPI (API, alias S = VibeJSONSerializer!()) : API
                         auto command = Command(this.conn.getNextCommandId(), ovrld.mangleof, SerializedData(serialized));
 
                         if(!this.conn.sendCommand(command))
-                            throw new Exception("Connection with peer closed");
+                            throw new LocalRestConnectionClosed();
                         return this.conn.waitResponse(command.id, this.timeout);
                     }();
 
@@ -2075,9 +2084,8 @@ unittest
         node.myping(69);
         assert(0);
     }
-    catch (Exception ex)
+    catch (LocalRestConnectionClosed ex)
     {
-        assert(ex.msg == "Connection with peer closed");
     }
 }
 
@@ -2503,3 +2511,83 @@ unittest
     assert(extnode.required() == 42);
     assertThrown!ClientException(extnode.optional());
 }
+
+/// Graceful handling of shut down nodes
+unittest
+{
+    static import geod24.concurrency;
+    import core.atomic : atomicLoad, atomicStore;
+
+    static interface API
+    {
+        void test () @safe;
+        void shutdown () @safe;
+    }
+
+    static shared bool connection_closed;
+    __gshared Listener!API api_1;
+    __gshared Listener!API api_2;
+
+    static class Node1 : API
+    {
+        Timer timer;
+        RemoteAPI!API api;
+
+        @trusted:
+        public override void test ()
+        {
+            this.api = new RemoteAPI!API(api_2);
+            this.timer = setTimer(10.msecs, &infinite, true);
+        }
+
+        public override void shutdown ()
+        {
+            if (this.timer !is null)
+                this.timer.stop();
+        }
+
+        public void infinite () @trusted
+        {
+            try
+            {
+                this.api.test();
+            }
+            catch (LocalRestConnectionClosed)
+            {
+                atomicStore(connection_closed, true);
+            }
+        }
+    }
+
+    static class Node2 : API
+    {
+        @safe:
+        public override void test ()
+        {
+        }
+
+        public override void shutdown ()
+        {
+        }
+    }
+
+    scope (exit) thread_joinAll();
+
+    auto node_1 = RemoteAPI!API.spawn!Node1();
+    auto node_2 = RemoteAPI!API.spawn!Node2();
+    api_1 = node_1.ctrl.listener();
+    api_2 = node_2.ctrl.listener();
+
+    node_1.test();
+    node_2.ctrl.shutdown();
+    Thread.sleep(1.seconds);  // trigger calling shut down node
+    node_1.ctrl.shutdown();
+
+    size_t count;
+    while (!atomicLoad(connection_closed))
+    {
+        assert(count < 300);  // up to 3 seconds wait
+        count++;
+        Thread.sleep(10.msecs);
+    }
+}