fix PDU Sesion Release response: add missing PDUSessionResourceReleaseResponseTransfer IE

The PDUSessionResourceReleaseResponse message was missing the mandatory
pDUSessionResourceReleaseResponseTransfer IE in each released PDU session item. This caused Open5GS to send an error indication.

Changes:
- Add encode_ngap_pdusession_release_response_transfer() function to
  properly encode the transfer structure (empty since Secondary RAT Usage
  Information is optional and not used, per 9.3.4.21)
- Always include the mandatory PDUSessionResourceReleasedListRelRes IE
- Always encode the pDUSessionResourceReleaseResponseTransfer for each
  PDU session item
- Fix Release Command handler to decode and log Cause from command transfer:
  instead of incorrectly copying command data to response: the 2 transfer
  IEs in the Command and the Response messages are different and should
  not be mixed
- Split Command/Response struct type definitions
- Add missing includes

openair3/NGAP/ngap_gNB_handlers.c

@@ -1390,9 +1390,20 @@ static int ngap_gNB_handle_pdusession_release_command(sctp_assoc_t assoc_id, uin
   for (i = 0; i < ie->value.choice.PDUSessionResourceToReleaseListRelCmd.list.count; i++) {
     NGAP_PDUSessionResourceToReleaseItemRelCmd_t *item_p;
     item_p = ie->value.choice.PDUSessionResourceToReleaseListRelCmd.list.array[i];
-    pdusession_release_t *r = &msg->pdusession_release_params[i];
-    r->pdusession_id = item_p->pDUSessionID;
-    r->data = create_byte_array(item_p->pDUSessionResourceReleaseCommandTransfer.size, item_p->pDUSessionResourceReleaseCommandTransfer.buf);
+    msg->pdusession_ids[i] = item_p->pDUSessionID;
+
+    /* PDUSessionResourceReleaseCommandTransfer (Mandatory) */
+    void *decoded = decode_pdusession_transfer(&asn_DEF_NGAP_PDUSessionResourceReleaseCommandTransfer,
+                                               item_p->pDUSessionResourceReleaseCommandTransfer);
+    if (!decoded) {
+      NGAP_ERROR("Failed to decode PDUSessionResourceReleaseCommandTransfer for PDU Session %d\n", msg->pdusession_ids[i]);
+      return -1;
+    }
+    NGAP_PDUSessionResourceReleaseCommandTransfer_t *transfer = decoded;
+    ngap_cause_t cause = decode_ngap_cause(&transfer->cause);
+    NGAP_INFO("PDU Session %d release command: Cause type=%d value=%d\n", msg->pdusession_ids[i], cause.type, cause.value);
+    ASN_STRUCT_FREE_CONTENTS_ONLY(asn_DEF_NGAP_PDUSessionResourceReleaseCommandTransfer, transfer);
+    free(transfer);
   }
 
   itti_send_msg_to_task(TASK_RRC_GNB, ue_desc_p->gNB_instance->instance, message_p);

openair3/NGAP/ngap_gNB_nas_procedures.c

@@ -594,6 +594,24 @@ static byte_array_t encode_ngap_pdusession_setup_response_transfer(const pdusess
   return out;
 }
 
+/** @brief PDU Session Resource Release Response Transfer encoding (9.3.4.21 3GPP TS 38.413)
+ *  The transfer structure contains only an optional Secondary RAT Usage Information IE.
+ *  Since we don't use secondary RAT (MR-DC), we encode an empty structure. */
+static byte_array_t encode_ngap_pdusession_release_response_transfer(void)
+{
+  NGAP_PDUSessionResourceReleaseResponseTransfer_t pdusessionTransfer = {0};
+
+  // Encode
+  asn_encode_to_new_buffer_result_t res = asn_encode_to_new_buffer(NULL,
+                                                                   ATS_ALIGNED_CANONICAL_PER,
+                                                                   &asn_DEF_NGAP_PDUSessionResourceReleaseResponseTransfer,
+                                                                   &pdusessionTransfer);
+  AssertFatal(res.buffer, "ASN1 message encoding failed (%s, %lu)!\n", res.result.failed_type->name, res.result.encoded);
+  ASN_STRUCT_FREE_CONTENTS_ONLY(asn_DEF_NGAP_PDUSessionResourceReleaseResponseTransfer, &pdusessionTransfer);
+  byte_array_t out = {.buf = res.buffer, .len = res.result.encoded};
+  return out;
+}
+
 //------------------------------------------------------------------------------
 int ngap_gNB_initial_ctxt_resp(instance_t instance, ngap_initial_context_setup_resp_t *initial_ctxt_resp_p)
 //------------------------------------------------------------------------------
@@ -1200,22 +1218,28 @@ int ngap_gNB_pdusession_release_resp(instance_t instance, ngap_pdusession_releas
     ie->value.choice.RAN_UE_NGAP_ID = pdusession_release_resp_p->gNB_ue_ngap_id;
   }
 
-  /* optional */
-  if (pdusession_release_resp_p->nb_of_pdusessions_released > 0) {
+  /* PDU Session Resource Released List (mandatory) */
+  {
     asn1cSequenceAdd(out->protocolIEs.list, NGAP_PDUSessionResourceReleaseResponseIEs_t, ie);
     ie->id = NGAP_ProtocolIE_ID_id_PDUSessionResourceReleasedListRelRes;
     ie->criticality = NGAP_Criticality_ignore;
     ie->value.present = NGAP_PDUSessionResourceReleaseResponseIEs__value_PR_PDUSessionResourceReleasedListRelRes;
-    
+
     for (i = 0; i < pdusession_release_resp_p->nb_of_pdusessions_released; i++) {
-      asn1cSequenceAdd(ie->value.choice.PDUSessionResourceReleasedListRelRes.list, NGAP_PDUSessionResourceReleasedItemRelRes_t, item);
+      NGAP_PDUSessionResourceReleasedListRelRes_t *list = &ie->value.choice.PDUSessionResourceReleasedListRelRes;
+      asn1cSequenceAdd(list->list, NGAP_PDUSessionResourceReleasedItemRelRes_t, item);
       pdusession_release_t *r = &pdusession_release_resp_p->pdusession_release[i];
+      /* PDU Session ID (mandatory) */
       item->pDUSessionID = r->pdusession_id;
-      OCTET_STRING_fromBuf(&item->pDUSessionResourceReleaseResponseTransfer, (const char *)r->data.buf, r->data.len);
-      NGAP_DEBUG("pdusession_release_resp: pdusession ID %ld\n", item->pDUSessionID);
+      /* PDU Session Resource Release Response Transfer (mandatory) */
+      // Empty transfer is valid since Secondary RAT Usage Information is optional and not used
+      byte_array_t transfer = encode_ngap_pdusession_release_response_transfer();
+      OCTET_STRING_fromBuf(&item->pDUSessionResourceReleaseResponseTransfer, (const char *)transfer.buf, transfer.len);
+      free_byte_array(transfer);
+      NGAP_DEBUG("PDU Session Resource Release Response: pdusession ID %ld\n", item->pDUSessionID);
     }
   }
-  
+
   if (ngap_gNB_encode_pdu(&pdu, &buffer, &length) < 0) {
     NGAP_ERROR("Failed to encode release response\n");
     /* Encode procedure has failed... */

openair3/NGAP/ngap_msg_includes.h

@@ -58,6 +58,8 @@
 #include "NGAP_PDUSessionResourceSetupResponseTransfer.h"
 #include "NGAP_PDUSessionResourceSetupUnsuccessfulTransfer.h"
 #include "NGAP_PDUSessionResourceToReleaseItemRelCmd.h"
+#include "NGAP_PDUSessionResourceReleaseCommandTransfer.h"
+#include "NGAP_PDUSessionResourceReleaseResponseTransfer.h"
 #include "NGAP_PLMNSupportItem.h"
 #include "NGAP_ProtocolIE-Field.h"
 #include "NGAP_QosFlowAddOrModifyResponseItem.h"