tests: net: openthread: rpc: initial server unit tests

1. Extend mock nRF RPC transport to support simulated
   reception of an nRF RPC packet.
2. Add initial unit tests for the OpenThread RPC server.
   This includes mocking Zephyr OpenThread L2 functions
   and certain nRF RPC APIs to support single-threaded
   mode of operation.

Signed-off-by: Damian Krolik <[email protected]>

Author: Damian-Nordic

subsys/net/openthread/rpc/Kconfig

@@ -31,7 +31,7 @@ config OPENTHREAD_RPC_CLIENT
 
 config OPENTHREAD_RPC_SERVER
 	bool "OpenThread over RPC server"
-	depends on NET_L2_OPENTHREAD
+	depends on NET_L2_OPENTHREAD || ZTEST
 	help
 	  Enables OpenThread over RPC server role that runs the full OpenThread
 	  stack and exposes OpenThread functions using nRF RPC library to a client

subsys/net/openthread/rpc/client/CMakeLists.txt

@@ -17,5 +17,4 @@ zephyr_library_include_directories(
   ${CMAKE_CURRENT_SOURCE_DIR}/../common
 )
 
-# TODO: add dependency on NET_L2_OPENTHREAD and remove the code below
 zephyr_include_directories(${ZEPHYR_OPENTHREAD_MODULE_DIR}/include)

subsys/net/openthread/rpc/server/CMakeLists.txt

@@ -9,13 +9,13 @@ zephyr_library()
 zephyr_library_sources(
   ot_rpc_cli_server.c
   ot_rpc_ctrl_server.c
+)
+
+zephyr_library_sources_ifdef(CONFIG_NET_L2_OPENTHREAD
   ot_rpc_if_server.c
   ot_rpc_commissioning_server.c
 )
 
 zephyr_library_include_directories(
   ${CMAKE_CURRENT_SOURCE_DIR}/../common
 )
-
-# TODO: add dependency on NET_L2_OPENTHREAD and remove the code below
-zephyr_include_directories(${ZEPHYR_OPENTHREAD_MODULE_DIR}/include)

tests/include/mock_nrf_rpc_transport.h

@@ -57,6 +57,12 @@ void mock_nrf_rpc_tr_expect_done(void);
  * @brief Clears the list of expected nRF RPC packets.
  */
 void mock_nrf_rpc_tr_expect_reset(void);
+
+/**
+ * @brief Simulates an nRF RPC packet reception from the remote node.
+ */
+void mock_nrf_rpc_tr_receive(mock_nrf_rpc_pkt_t packet);
+
 /**
  * @}
  */

tests/mocks/nrf_rpc/mock_nrf_rpc_transport.c

@@ -28,12 +28,33 @@ typedef struct mock_nrf_rpc_tr_ctx {
 	struct k_work response_work;
 } mock_nrf_rpc_tr_ctx_t;
 
+static void log_payload(const char *caption, const uint8_t *payload, size_t length)
+{
+	char payload_str[32];
+
+	if (!bin2hex(payload, length, payload_str, sizeof(payload_str))) {
+		/*
+		 * If bin2hex() returns 0, this means that the payload converted to HEX is too
+		 * large to fit within 'payload_str'. In such a case, log as long prefix of the
+		 * payload as possible, followed by "...". The code below calculates the prefix
+		 * length.
+		 */
+		length = (sizeof(payload_str) - sizeof("...")) / 2;
+		bin2hex(payload, length, payload_str, sizeof(payload_str));
+		strcat(payload_str, "...");
+	}
+
+	printk("%s: %s of length %zu\n", caption, payload_str, length);
+}
+
 /* Asynchronous task to simulate reception of a response packet. */
 static void response_send(struct k_work *work)
 {
 	mock_nrf_rpc_tr_ctx_t *ctx = CONTAINER_OF(work, mock_nrf_rpc_tr_ctx_t, response_work);
 	mock_nrf_rpc_pkt_t *response = ctx->cur_response;
 
+	log_payload("Responding with nRF RPC packet", response->data, response->len);
+
 	ctx->receive_cb(ctx->transport, response->data, response->len, ctx->receive_ctx);
 }
 
@@ -51,25 +72,6 @@ static int init(const struct nrf_rpc_tr *transport, nrf_rpc_tr_receive_handler_t
 	return 0;
 }
 
-static void log_payload(const char *caption, const uint8_t *payload, size_t length)
-{
-	char payload_str[32];
-
-	if (!bin2hex(payload, length, payload_str, sizeof(payload_str))) {
-		/*
-		 * If bin2hex() returns 0, this means that the payload converted to HEX is too
-		 * large to fit within 'payload_str'. In such a case, log as long prefix of the
-		 * payload as possible, followed by "...". The code below calculates the prefix
-		 * length.
-		 */
-		length = (sizeof(payload_str) - sizeof("...")) / 2;
-		bin2hex(payload, length, payload_str, sizeof(payload_str));
-		strcat(payload_str, "...");
-	}
-
-	printk("%s: %s of length %zu\n", caption, payload_str, length);
-}
-
 static int send(const struct nrf_rpc_tr *transport, const uint8_t *data, size_t length)
 {
 	mock_nrf_rpc_tr_ctx_t *ctx = transport->ctx;
@@ -158,3 +160,14 @@ void mock_nrf_rpc_tr_expect_reset(void)
 	ctx->num_expected = 0;
 	ctx->cur_expected = 0;
 }
+
+void mock_nrf_rpc_tr_receive(mock_nrf_rpc_pkt_t packet)
+{
+	mock_nrf_rpc_tr_ctx_t *ctx = mock_nrf_rpc_tr.ctx;
+
+	zassert_not_null(ctx->receive_cb);
+
+	log_payload("Received nRF RPC packet", packet.data, packet.len);
+
+	ctx->receive_cb(ctx->transport, packet.data, packet.len, ctx->receive_ctx);
+}

tests/subsys/net/openthread/rpc/server/CMakeLists.txt

@@ -0,0 +1,34 @@
+#
+# Copyright (c) 2024 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(ot_rpc_server_test)
+
+FILE(GLOB app_sources src/*.c)
+
+target_include_directories(app PRIVATE
+  # Needed to access OpenThread RPC command IDs.
+  ${ZEPHYR_NRF_MODULE_DIR}/subsys/net/openthread/rpc/common
+)
+
+target_sources(app PRIVATE
+  ${app_sources}
+)
+
+# Fill the gaps due to not setting NET_L2_OPENTHREAD.
+zephyr_include_directories(
+  ${ZEPHYR_OPENTHREAD_MODULE_DIR}/include
+)
+
+zephyr_compile_definitions(
+  CONFIG_OPENTHREAD_PKT_LIST_SIZE=1
+)
+
+# Enforce single-threaded nRF RPC command processing.
+target_link_options(app PUBLIC
+  -Wl,--wrap=nrf_rpc_os_init,--wrap=nrf_rpc_os_thread_pool_send
+)

tests/subsys/net/openthread/rpc/server/prj.conf

@@ -0,0 +1,19 @@
+#
+# Copyright (c) 2024 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+
+# Ztest configuration
+CONFIG_ZTEST=y
+CONFIG_TEST_RANDOM_GENERATOR=y
+
+CONFIG_OPENTHREAD_RPC=y
+CONFIG_OPENTHREAD_RPC_SERVER=y
+CONFIG_NRF_RPC_CBKPROXY_OUT_SLOTS=0
+
+CONFIG_MOCK_NRF_RPC=y
+CONFIG_MOCK_NRF_RPC_TRANSPORT=y
+
+CONFIG_KERNEL_MEM_POOL=y
+CONFIG_HEAP_MEM_POOL_SIZE=4096