From 6f9a866e9c8f7e1ead8eda4fa1781ca4a9f74298 Mon Sep 17 00:00:00 2001
From: Robin Mueller <muellerr@irs.uni-stuttgart.de>
Date: Fri, 9 Sep 2022 10:43:18 +0200
Subject: [PATCH] implement basic CFDP handler

---
 bsp_hosted/core/CfdpHandler.cpp |  7 +++---
 tmtc/tmtcc.py                   | 40 ++++++++++++++++++++++++++++++++-
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/bsp_hosted/core/CfdpHandler.cpp b/bsp_hosted/core/CfdpHandler.cpp
index c2975a4..d5e49f4 100644
--- a/bsp_hosted/core/CfdpHandler.cpp
+++ b/bsp_hosted/core/CfdpHandler.cpp
@@ -92,9 +92,10 @@ ReturnValue_t CfdpHandler::handleCfdpPacket(TmTcMessage& msg) {
     PacketInfo info(type, msg.getStorageId());
     result = destHandler.passPacket(info);
   } else {
-    // Route depending on directive type. Retrieve directive type from raw stream for better
-    // performance (with sanity and directive code check). The routing is based on section 4.5 of
-    // the CFDP standard which specifies the PDU forwarding procedure.
+    // Route depending on PDU type and directive type if applicable. It retrieves directive type
+    // from the raw stream for better performance (with sanity and directive code check).
+    // The routing is based on section 4.5 of the CFDP standard which specifies the PDU forwarding
+    // procedure.
 
     // PDU header only. Invalid supplied data. A directive packet should have a valid data field
     // with at least one byte being the directive code
diff --git a/tmtc/tmtcc.py b/tmtc/tmtcc.py
index 5117dc6..3ede6c3 100755
--- a/tmtc/tmtcc.py
+++ b/tmtc/tmtcc.py
@@ -5,7 +5,8 @@ import time
 from pathlib import Path
 from typing import Sequence
 
-from spacepackets.cfdp import ConditionCode, TransmissionModes
+from spacepackets.cfdp import ConditionCode, TransmissionModes, PduType, DirectiveType
+from spacepackets.cfdp.pdu import AbstractFileDirectiveBase, PduHolder
 from spacepackets.ecss import PusVerificator
 
 import tmtccmd
@@ -80,6 +81,43 @@ class CfdpHandler(CfdpUserBase):
             put_request, self.remote_cfg_table.get_remote_entity(self.dest_id)
         )
 
+    def pass_packet(self, packet: AbstractFileDirectiveBase):
+        """This function routes the packets based on PDU type and directive type if applicable.
+
+        The routing is based on section 4.5 of the CFDP standard whcih specifies the PDU forwarding
+        procedure.
+        """
+        if packet.pdu_type == PduType.FILE_DATA:
+            self.dest_handler.pass_packet(packet)
+        else:
+            if packet.directive_type in [
+                DirectiveType.METADATA_PDU,
+                DirectiveType.EOF_PDU,
+                DirectiveType.PROMPT_PDU,
+            ]:
+                # Section b) of 4.5.3: These PDUs should always be targeted towards the file
+                # receiver a.k.a. the destination handler
+                self.dest_handler.pass_packet(packet)
+            elif packet.directive_type in [
+                DirectiveType.FINISHED_PDU,
+                DirectiveType.NAK_PDU,
+                DirectiveType.KEEP_ALIVE_PDU,
+            ]:
+                # Section c) of 4.5.3: These PDUs should always be targeted towards the file sender
+                # a.k.a. the source handler
+                self.source_handler.pass_packet(packet)
+            elif packet.directive_type == DirectiveType.ACK_PDU:
+                # Section a): Recipient depends on the type of PDU that is being acknowledged.
+                # We can simply extract the PDU type from the raw stream. If it is an EOF PDU,
+                # this packet is passed to the source handler. For a finished PDU, it is
+                # passed to the destination handler
+                pdu_holder = PduHolder(packet)
+                ack_pdu = pdu_holder.to_ack_pdu()
+                if ack_pdu.directive_code_of_acked_pdu == DirectiveType.EOF_PDU:
+                    self.source_handler.pass_packet(packet)
+                elif ack_pdu.directive_code_of_acked_pdu == DirectiveType.FINISHED_PDU:
+                    self.dest_handler.pass_packet(packet)
+
     def transaction_indication(self, transaction_id: TransactionId):
         pass