Add dds_get_guid to get the GUID of a local entity

This is merely a more convenient way of obtaining it: otherwise one has
subscribe to the correct built-in topic, read the sample corresponding
to the entity's instance handle and get the "key" field.  That's a bit
of a detour to get the network-wide unique identifier.

Signed-off-by: Erik Boasson <eb@ilities.com>

src/core/ddsc/include/dds/dds.h

@@ -418,6 +418,26 @@ dds_get_mask(dds_entity_t condition, uint32_t *mask);
 DDS_EXPORT dds_return_t
 dds_get_instance_handle(dds_entity_t entity, dds_instance_handle_t *ihdl);
 
+/**
+ * @brief Returns the GUID that represents the entity in the network,
+ * and therefore only supports participants, readers and writers.
+ *
+ * @param[in]   entity  Entity of which to get the instance handle.
+ * @param[out]  guid    Where to store the GUID.
+ *
+ * @returns A dds_return_t indicating success or failure.
+ *
+ * @retval DDS_RETCODE_OK
+ *             Success.
+ * @retval DDS_RETCODE_ILLEGAL_OPERATION
+ *             The operation is invoked on an inappropriate object.
+ * @retval DDS_RETCODE_ERROR
+ *             An internal error has occurred.
+ */
+/* TODO: Check list of return codes is complete. */
+DDS_EXPORT dds_return_t
+dds_get_guid (dds_entity_t entity, dds_guid_t *guid);
+
 /*
   All entities have a set of "status conditions" (following the DCPS
   spec), read peeks, take reads & resets (analogously to read & take

src/core/ddsc/src/dds_entity.c

@@ -25,6 +25,7 @@
 #include "dds/ddsi/ddsi_pmd.h"
 #include "dds/ddsi/ddsi_xqos.h"
 #include "dds/ddsi/q_transmit.h"
+#include "dds/ddsi/q_bswap.h"
 
 extern inline dds_entity *dds_entity_from_handle_link (struct dds_handle_link *hdllink);
 extern inline bool dds_entity_is_enabled (const dds_entity *e);
@@ -1285,6 +1286,36 @@ dds_return_t dds_get_instance_handle (dds_entity_t entity, dds_instance_handle_t
   return ret;
 }
 
+dds_return_t dds_get_guid (dds_entity_t entity, dds_guid_t *guid)
+{
+  dds_entity *e;
+  dds_return_t ret;
+
+  if (guid == NULL)
+    return DDS_RETCODE_BAD_PARAMETER;
+
+  if ((ret = dds_entity_pin (entity, &e)) != DDS_RETCODE_OK)
+    return ret;
+  switch (dds_entity_kind (e))
+  {
+    case DDS_KIND_PARTICIPANT:
+    case DDS_KIND_READER:
+    case DDS_KIND_WRITER: {
+      DDSRT_STATIC_ASSERT (sizeof (dds_guid_t) == sizeof (ddsi_guid_t));
+      ddsi_guid_t tmp = nn_ntoh_guid (e->m_guid);
+      memcpy (guid, &tmp, sizeof (*guid));
+      ret = DDS_RETCODE_OK;
+      break;
+    }
+    default: {
+      ret = DDS_RETCODE_ILLEGAL_OPERATION;
+      break;
+    }
+  }
+  dds_entity_unpin(e);
+  return ret;
+}
+
 dds_return_t dds_entity_pin (dds_entity_t hdl, dds_entity **eptr)
 {
   dds_return_t hres;

src/core/ddsc/tests/entity_api.c

@@ -255,6 +255,28 @@ CU_Test(ddsc_entity, status, .init = create_entity, .fini = delete_entity)
     CU_ASSERT_EQUAL_FATAL(status1, DDS_RETCODE_OK);
 }
 
+CU_Test(ddsc_entity, guid, .init = create_entity, .fini = delete_entity)
+{
+    dds_return_t status;
+    dds_guid_t guid, zero;
+    memset(&zero, 0, sizeof(zero));
+
+    /* Don't check actual handle contents. That's a job
+     * for the specific entity children, not for the generic part. */
+
+    /* Check getting Handle with bad parameters. */
+    status = dds_get_guid (0, NULL);
+    CU_ASSERT_EQUAL_FATAL(status, DDS_RETCODE_BAD_PARAMETER);
+    status = dds_get_guid (entity, NULL);
+    CU_ASSERT_EQUAL_FATAL(status, DDS_RETCODE_BAD_PARAMETER);
+    status = dds_get_guid (0, &guid);
+    CU_ASSERT_EQUAL_FATAL(status, DDS_RETCODE_BAD_PARAMETER);
+
+    /* Get Instance Handle, which should not be 0 for a participant. */
+    status = dds_get_guid (entity, &guid);
+    CU_ASSERT_EQUAL_FATAL(status, DDS_RETCODE_OK);
+    CU_ASSERT_FATAL(memcmp(&guid, &zero, sizeof(guid)) != 0);
+}
 
 CU_Test(ddsc_entity, instance_handle, .init = create_entity, .fini = delete_entity)
 {