LibIPC: Don't handle incoming messages right away when draining

When draining the socket in IServerConnection, we would previously
handle each incoming (local endpoint) message as it came in.

This would cause unexpected things to happen while blocked waiting
for a synchronous response. That's definitely not what we want,
so this patch puts all of the incoming messages in a queue and does
a separate pass over the queue to handle everything in order.

Libraries/LibIPC/IServerConnection.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <AK/NonnullOwnPtrVector.h>
 #include <LibCore/CEvent.h>
 #include <LibCore/CEventLoop.h>
 #include <LibCore/CLocalSocket.h>
@@ -25,6 +26,7 @@ public:
         m_connection->set_blocking(true);
         m_notifier->on_ready_to_read = [this] {
             drain_messages_from_server();
+            handle_messages();
         };
 
         int retries = 100000;
@@ -131,7 +133,7 @@ private:
         for (size_t index = 0; index < (size_t)bytes.size(); index += decoded_bytes) {
             auto remaining_bytes = ByteBuffer::wrap(bytes.data() + index, bytes.size() - index);
             if (auto message = LocalEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
-                m_local_endpoint.handle(*message);
+                m_unprocessed_messages.append(move(message));
             } else if (auto message = PeerEndpoint::decode_message(remaining_bytes, decoded_bytes)) {
                 m_unprocessed_messages.append(move(message));
             } else {
@@ -142,6 +144,15 @@ private:
         return true;
     }
 
+    void handle_messages()
+    {
+        auto messages = move(m_unprocessed_messages);
+        for (auto& message : messages) {
+            if (message->endpoint_magic() == LocalEndpoint::static_magic())
+                m_local_endpoint.handle(*message);
+        }
+    }
+
     LocalEndpoint& m_local_endpoint;
     RefPtr<CLocalSocket> m_connection;
     RefPtr<CNotifier> m_notifier;