From 6eae4ded849b959f0bee57cede47ae990b7fbb30 Mon Sep 17 00:00:00 2001
From: Ken Bannister <kb2ma@runbox.com>
Date: Fri, 17 Apr 2020 06:10:16 -0400
Subject: [PATCH] net/gcoap: create CoAP ping request

---
 sys/include/net/gcoap.h                   |  6 ++++-
 sys/net/application_layer/gcoap/gcoap.c   | 32 ++++++++++++++---------
 tests/unittests/tests-gcoap/tests-gcoap.c | 23 ++++++++++++++++
 3 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/sys/include/net/gcoap.h b/sys/include/net/gcoap.h
index a0cdb03c32..d2c104a65e 100644
--- a/sys/include/net/gcoap.h
+++ b/sys/include/net/gcoap.h
@@ -734,10 +734,14 @@ void gcoap_register_listener(gcoap_listener_t *listener);
 /**
  * @brief   Initializes a CoAP request PDU on a buffer.
  *
+ * If @p code is COAP_CODE_EMPTY, prepares a complete "CoAP ping" 4 byte empty
+ * message request, ready to send.
+ *
  * @param[out] pdu      Request metadata
  * @param[out] buf      Buffer containing the PDU
  * @param[in] len       Length of the buffer
- * @param[in] code      Request code, one of COAP_METHOD_XXX
+ * @param[in] code      Request code, one of COAP_METHOD_XXX or COAP_CODE_EMPTY
+ *                      to ping
  * @param[in] path      Resource path, may be NULL
  *
  * @pre @p path must start with `/` if not NULL
diff --git a/sys/net/application_layer/gcoap/gcoap.c b/sys/net/application_layer/gcoap/gcoap.c
index 8121502b7c..5c3bd4ba9b 100644
--- a/sys/net/application_layer/gcoap/gcoap.c
+++ b/sys/net/application_layer/gcoap/gcoap.c
@@ -657,22 +657,28 @@ int gcoap_req_init(coap_pkt_t *pdu, uint8_t *buf, size_t len,
     pdu->hdr = (coap_hdr_t *)buf;
 
     /* generate token */
+    uint16_t msgid = (uint16_t)atomic_fetch_add(&_coap_state.next_message_id, 1);
+    ssize_t res;
+    if (code) {
 #if CONFIG_GCOAP_TOKENLEN
-    uint8_t token[CONFIG_GCOAP_TOKENLEN];
-    for (size_t i = 0; i < CONFIG_GCOAP_TOKENLEN; i += 4) {
-        uint32_t rand = random_uint32();
-        memcpy(&token[i],
-               &rand,
-               (CONFIG_GCOAP_TOKENLEN - i >= 4) ? 4 : CONFIG_GCOAP_TOKENLEN - i);
-    }
-    uint16_t msgid = (uint16_t)atomic_fetch_add(&_coap_state.next_message_id, 1);
-    ssize_t res = coap_build_hdr(pdu->hdr, COAP_TYPE_NON, &token[0],
-                                 CONFIG_GCOAP_TOKENLEN, code, msgid);
+        uint8_t token[CONFIG_GCOAP_TOKENLEN];
+        for (size_t i = 0; i < CONFIG_GCOAP_TOKENLEN; i += 4) {
+            uint32_t rand = random_uint32();
+            memcpy(&token[i],
+                   &rand,
+                   (CONFIG_GCOAP_TOKENLEN - i >= 4) ? 4 : CONFIG_GCOAP_TOKENLEN - i);
+        }
+        res = coap_build_hdr(pdu->hdr, COAP_TYPE_NON, &token[0],
+                             CONFIG_GCOAP_TOKENLEN, code, msgid);
 #else
-    uint16_t msgid = (uint16_t)atomic_fetch_add(&_coap_state.next_message_id, 1);
-    ssize_t res = coap_build_hdr(pdu->hdr, COAP_TYPE_NON, NULL,
-                                 CONFIG_GCOAP_TOKENLEN, code, msgid);
+        res = coap_build_hdr(pdu->hdr, COAP_TYPE_NON, NULL,
+                             CONFIG_GCOAP_TOKENLEN, code, msgid);
 #endif
+    }
+    else {
+        /* ping request */
+        res = coap_build_hdr(pdu->hdr, COAP_TYPE_CON, NULL, 0, code, msgid);
+    }
 
     coap_pkt_init(pdu, buf, len - CONFIG_GCOAP_REQ_OPTIONS_BUF, res);
     if (path != NULL) {
diff --git a/tests/unittests/tests-gcoap/tests-gcoap.c b/tests/unittests/tests-gcoap/tests-gcoap.c
index c458046ac8..10047629dc 100644
--- a/tests/unittests/tests-gcoap/tests-gcoap.c
+++ b/tests/unittests/tests-gcoap/tests-gcoap.c
@@ -203,6 +203,28 @@ static void test_gcoap__client_get_path_defer(void)
     TEST_ASSERT_EQUAL_STRING(&path[0], &uri[0]);
 }
 
+/*
+ * Validate client CoAP ping empty message request.
+ */
+static void test_gcoap__client_ping(void)
+{
+    uint8_t buf[CONFIG_GCOAP_PDU_BUF_SIZE];
+    coap_pkt_t pdu;
+    int res;
+
+    res = gcoap_req_init(&pdu, buf, CONFIG_GCOAP_PDU_BUF_SIZE, COAP_CODE_EMPTY,
+                         NULL);
+
+    TEST_ASSERT_EQUAL_INT(0, res);
+    TEST_ASSERT_EQUAL_INT(COAP_CODE_EMPTY, coap_get_code(&pdu));
+    TEST_ASSERT_EQUAL_INT(COAP_TYPE_CON, coap_get_type(&pdu));
+    TEST_ASSERT_EQUAL_INT(0, coap_get_token_len(&pdu));
+
+    /* confirm length */
+    res = coap_opt_finish(&pdu, COAP_OPT_FINISH_NONE);
+    TEST_ASSERT_EQUAL_INT(4, res);
+}
+
 /*
  * Helper for server_get tests below.
  * Request from libcoap example for gcoap_cli /cli/stats resource
@@ -371,6 +393,7 @@ Test *tests_gcoap_tests(void)
         new_TestFixture(test_gcoap__client_put_req),
         new_TestFixture(test_gcoap__client_put_req_overfill),
         new_TestFixture(test_gcoap__client_get_path_defer),
+        new_TestFixture(test_gcoap__client_ping),
         new_TestFixture(test_gcoap__server_get_req),
         new_TestFixture(test_gcoap__server_get_resp),
         new_TestFixture(test_gcoap__server_con_req),