event_filter: add <log> node

genodelabs/genode#4069

repos/os/src/server/event_filter/README

@@ -35,6 +35,13 @@ one of the following filters:
   content into the '<remap>' node. The included ROM must have a '<remap>'
   top-level node.
 
+:<log>:
+
+  Logs debug information about key presses and releases to the component's 'Log'
+  session. An optional 'prefix' attribute can be provided in order to
+  distinguish multiple '<log>' filters. The given prefix is placed at the
+  beginning of each log message.
+
 :<merge>:
 
   Merges the results of any number of filters that appear as child nodes.

repos/os/src/server/event_filter/log_source.h

@@ -0,0 +1,84 @@
+/*
+ * \brief  Input-event source that logs key events from another source
+ * \author Johannes Schlatow
+ * \date   2021-04-26
+ */
+
+/*
+ * Copyright (C) 2021 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _EVENT_FILTER__LOG_SOURCE_H_
+#define _EVENT_FILTER__LOG_SOURCE_H_
+
+/* Genode includes */
+#include <input/keycodes.h>
+
+/* local includes */
+#include <include_accessor.h>
+#include <source.h>
+#include <key_code_by_name.h>
+
+namespace Event_filter { class Log_source; }
+
+
+class Event_filter::Log_source : public Source, Source::Filter
+{
+	private:
+
+		typedef String<32> Prefix;
+
+		Prefix _prefix = "";
+
+		Owner _owner;
+
+		Source &_source;
+
+		unsigned _event_cnt = 0;
+		int      _key_cnt   = 0;
+
+		/**
+		 * Filter interface
+		 */
+		void filter_event(Source::Sink &destination, Input::Event const &event) override
+		{
+			/* only log presses and releases */
+			if (event.press() || event.release()) {
+				if (event.press())   ++_key_cnt;
+				if (event.release()) --_key_cnt;
+
+				log(_prefix, "event #", _event_cnt++, "\t", event, "\tkey count: ", _key_cnt);
+			}
+
+			/* forward event */
+			destination.submit(event);
+		}
+
+		void _apply_config(Xml_node const config)
+		{
+			_prefix = config.attribute_value("prefix", _prefix);
+		}
+
+	public:
+
+		static char const *name() { return "log"; }
+
+		Log_source(Owner &owner, Xml_node config, Source::Factory &factory)
+		:
+			Source(owner),
+			_owner(factory),
+			_source(factory.create_source(_owner, input_sub_node(config)))
+		{
+			_apply_config(config);
+		}
+
+		void generate(Source::Sink &destination) override
+		{
+			Source::Filter::apply(destination, *this, _source);
+		}
+};
+
+#endif /* _EVENT_FILTER__LOG_SOURCE_H_ */

repos/os/src/server/event_filter/main.cc

@@ -24,6 +24,7 @@
 #include <chargen_source.h>
 #include <button_scroll_source.h>
 #include <accelerate_source.h>
+#include <log_source.h>
 #include <event_session.h>
 
 namespace Event_filter { struct Main; }
@@ -246,6 +247,9 @@ struct Event_filter::Main : Source::Factory, Source::Trigger
 		if (node.type() == Accelerate_source::name())
 			return *new (_heap) Accelerate_source(owner, node, *this);
 
+		if (node.type() == Log_source::name())
+			return *new (_heap) Log_source(owner, node, *this);
+
 		warning("unknown <", node.type(), "> input-source node type");
 		throw Source::Invalid_config();
 	}

repos/os/src/server/event_filter/source.h

@@ -46,7 +46,8 @@ class Event_filter::Source
 			    || node.type() == "chargen"
 			    || node.type() == "merge"
 			    || node.type() == "button-scroll"
-			    || node.type() == "accelerate";
+			    || node.type() == "accelerate"
+			    || node.type() == "log";
 
 			return false;
 		}