4 files changed, 111 insertions, 0 deletions
diff --git a/modules/edns_keepalive/.packaging/test.config b/modules/edns_keepalive/.packaging/test.config
new file mode 100644
index 0000000..5c71c79
--- /dev/null
+++ b/modules/edns_keepalive/.packaging/test.config
@@ -0,0 +1,10 @@
+-- SPDX-License-Identifier: GPL-3.0-or-later
+modules.load('edns_keepalive')
+
+for _,item in ipairs(modules.list()) do
+	if item == "edns_keepalive" then
+		os.exit(0)
+	end
+end
+
+os.exit(1)
diff --git a/modules/edns_keepalive/README.rst b/modules/edns_keepalive/README.rst
new file mode 100644
index 0000000..d8034d2
--- /dev/null
+++ b/modules/edns_keepalive/README.rst
@@ -0,0 +1,22 @@
+.. SPDX-License-Identifier: GPL-3.0-or-later
+
+.. _mod-edns_keepalive:
+
+EDNS keepalive
+==============
+
+The ``edns_keepalive`` module implements :rfc:`7828` for *clients*
+connecting to Knot Resolver via TCP and TLS.
+The module just allows clients to discover the connection timeout,
+client connections are always timed-out the same way *regardless*
+of clients sending the EDNS option.
+
+When connecting to servers, Knot Resolver does not send this EDNS option.
+It still attempts to reuse established connections intelligently.
+
+This module is loaded by default. For debugging purposes it can be
+unloaded using standard means:
+
+.. code-block:: lua
+
+        modules.unload('edns_keepalive')
diff --git a/modules/edns_keepalive/edns_keepalive.c b/modules/edns_keepalive/edns_keepalive.c
new file mode 100644
index 0000000..30d5df3
--- /dev/null
+++ b/modules/edns_keepalive/edns_keepalive.c
@@ -0,0 +1,61 @@
+/*  Copyright (C) CZ.NIC, z.s.p.o. <knot-resolver@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+/**
+ * @file edns_keepalive.c
+ * @brief Minimalistic EDNS keepalive implementation on server side.
+ *        If keepalive option is present in query,
+ *        always reply with constant timeout value.
+ *
+ */
+#include <libknot/packet/pkt.h>
+#include "daemon/worker.h"
+#include "lib/module.h"
+#include "lib/layer.h"
+
+static int edns_keepalive_finalize(kr_layer_t *ctx)
+{
+	struct kr_request *req = ctx->req;
+	knot_pkt_t *answer = req->answer;
+	const knot_rrset_t *src_opt = req->qsource.packet->opt_rr;
+	knot_rrset_t *answ_opt = answer->opt_rr;
+
+	const bool ka_want =
+		req->qsource.flags.tcp &&
+		src_opt != NULL &&
+		knot_edns_get_option(src_opt, KNOT_EDNS_OPTION_TCP_KEEPALIVE, NULL) &&
+		answ_opt != NULL;
+	if (!ka_want) {
+		return ctx->state;
+	}
+	const struct network *net = &the_worker->engine->net;
+	uint64_t timeout = net->tcp.in_idle_timeout / 100;
+	if (timeout > UINT16_MAX) {
+		timeout = UINT16_MAX;
+	}
+	knot_mm_t *pool = &answer->mm;
+	uint16_t ka_size = knot_edns_keepalive_size(timeout);
+	uint8_t ka_buf[ka_size];
+	int ret = knot_edns_keepalive_write(ka_buf, ka_size, timeout);
+	if (ret == KNOT_EOK) {
+		ret = knot_edns_add_option(answ_opt, KNOT_EDNS_OPTION_TCP_KEEPALIVE,
+					   ka_size, ka_buf, pool);
+	}
+	if (ret != KNOT_EOK) {
+		ctx->state = KR_STATE_FAIL;
+	}
+	return ctx->state;
+}
+
+KR_EXPORT int edns_keepalive_init(struct kr_module *self)
+{
+	static const kr_layer_api_t layer = {
+		.answer_finalize = &edns_keepalive_finalize,
+	};
+	self->layer = &layer;
+	return kr_ok();
+}
+
+KR_MODULE_EXPORT(edns_keepalive)
+
diff --git a/modules/edns_keepalive/meson.build b/modules/edns_keepalive/meson.build
new file mode 100644
index 0000000..d125ec4
--- /dev/null
+++ b/modules/edns_keepalive/meson.build
@@ -0,0 +1,18 @@
+# C module: edns_keepalive
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+edns_keepalive_src = files([
+  'edns_keepalive.c',
+])
+c_src_lint += edns_keepalive_src
+
+edns_keepalive_mod = shared_module(
+  'edns_keepalive',
+  edns_keepalive_src,
+  dependencies: libknot,
+  include_directories: mod_inc_dir,
+  name_prefix: '',
+  install: true,
+  install_dir: modules_dir,
+  link_with: kresd,
+)