Fix #361, add option for trailer bytes in CFDP PDUs

Adds an option to insert platform-specific padding at the end of CFDP
PDU encapsulation.  The padding area may be utilized by the deployment
to add arbitrary verification information to the PDU.

fsw/inc/cf_platform_cfg.h

@@ -348,6 +348,28 @@ typedef uint32 CF_TransactionSeq_t;
  */
 #define CF_STARTUP_SEM_TASK_DELAY 100
 
+/**
+ * @brief Number of trailing bytes to add to CFDP PDU
+ *
+ * @par Description
+ *      Additional padding bytes to be appended to the tail of CFDP PDUs
+ *      This reserves extra space to the software bus encapsulation buffer for every
+ *      CFDP PDU such that platform-specific trailer information may be added.  This
+ *      includes, but is not limited to a separate CRC or error control field in addition
+ *      to the error control field(s) within the the nominal CFDP protocol.
+ *
+ *      These extra bytes are added at the software bus encapsulation layer, they are not
+ *      part of the CFDP PDU itself.
+ *
+ *      Set to 0 to disable this feature, such that the software bus buffer
+ *      encapsulates only the CFDP PDU and no extra bytes are added.
+ *
+ *  @par Limits:
+ *       Maximum value is the difference between the maximum size of a CFDP PDU and the
+ *       maximum size of an SB message.
+ */
+#define CF_PDU_ENCAPSULATION_EXTRA_TRAILING_BYTES 0
+
 /**
  * \brief Mission specific version number
  *

fsw/src/cf_cfdp_sbintf.c

@@ -100,7 +100,8 @@ CF_Logical_PduBuffer_t *CF_CFDP_MsgOutGet(const CF_Transaction_t *t, bool silent
         /* Allocate message buffer on success */
         if (os_status == OS_SUCCESS)
         {
-            CF_AppData.engine.out.msg = CFE_SB_AllocateMessageBuffer(offsetof(CF_PduTlmMsg_t, ph) + CF_MAX_PDU_SIZE);
+            CF_AppData.engine.out.msg = CFE_SB_AllocateMessageBuffer(offsetof(CF_PduTlmMsg_t, ph) + CF_MAX_PDU_SIZE +
+                                                                     CF_PDU_ENCAPSULATION_EXTRA_TRAILING_BYTES);
         }
 
         if (!CF_AppData.engine.out.msg)
@@ -153,6 +154,7 @@ void CF_CFDP_Send(uint8 chan_num, const CF_Logical_PduBuffer_t *ph)
     sb_msgsize = offsetof(CF_PduTlmMsg_t, ph);
     sb_msgsize += ph->pdu_header.header_encoded_length;
     sb_msgsize += ph->pdu_header.data_encoded_length;
+    sb_msgsize += CF_PDU_ENCAPSULATION_EXTRA_TRAILING_BYTES;
 
     CFE_MSG_SetSize(&CF_AppData.engine.out.msg->Msg, sb_msgsize);
     CFE_MSG_SetMsgTime(&CF_AppData.engine.out.msg->Msg, CFE_TIME_GetTime());
@@ -198,6 +200,16 @@ void CF_CFDP_ReceiveMessage(CF_Channel_t *c)
         CFE_ES_PerfLogEntry(CF_PERF_ID_PDURCVD(chan_num));
         CFE_MSG_GetSize(&bufptr->Msg, &msg_size);
         CFE_MSG_GetType(&bufptr->Msg, &msg_type);
+        if (msg_size > CF_PDU_ENCAPSULATION_EXTRA_TRAILING_BYTES)
+        {
+            /* Ignore/subtract any fixed trailing bytes */
+            msg_size -= CF_PDU_ENCAPSULATION_EXTRA_TRAILING_BYTES;
+        }
+        else
+        {
+            /* bad message size - not supposed to happen */
+            msg_size = 0;
+        }
         if (msg_type == CFE_MSG_Type_Tlm)
         {
             CF_CFDP_DecodeStart(&CF_AppData.engine.in.decode, bufptr, ph, offsetof(CF_PduTlmMsg_t, ph), msg_size);

unit-test/cf_cfdp_sbintf_tests.c

@@ -67,7 +67,7 @@ static void UT_CFDP_SetupBasicRxState(CF_Logical_PduBuffer_t *pdu_buffer)
     UT_SetDataBuffer(UT_KEY(CFE_SB_ReceiveBuffer), &bufptr, sizeof(bufptr), true);
 
     /* setup for a potential call to CFE_MSG_GetSize() */
-    sz = sizeof(UT_r_msg);
+    sz = sizeof(UT_r_msg) + CF_PDU_ENCAPSULATION_EXTRA_TRAILING_BYTES;
     UT_SetDataBuffer(UT_KEY(CFE_MSG_GetSize), &sz, sizeof(sz), true);
 
     /* setup for a potential call to CFE_MSG_GetType() */
@@ -218,6 +218,7 @@ void Test_CF_CFDP_ReceiveMessage(void)
     CF_Transaction_t *      t;
     CF_Logical_PduBuffer_t *ph;
     CFE_MSG_Type_t          msg_type = CFE_MSG_Type_Tlm;
+    size_t *                msg_size_buf;
 
     /* no-config - the max per wakeup will be 0, and this is a noop */
     UT_CFDP_SetupBasicTestState(UT_CF_Setup_NONE, NULL, &c, NULL, NULL, NULL);
@@ -229,6 +230,16 @@ void Test_CF_CFDP_ReceiveMessage(void)
     UT_SetDeferredRetcode(UT_KEY(CFE_SB_ReceiveBuffer), 1, CFE_SB_NO_MESSAGE);
     UtAssert_VOIDCALL(CF_CFDP_ReceiveMessage(c));
 
+    /* Set up with a zero size input message, this should fail decoding */
+    msg_size_buf = 0;
+    UT_SetDeferredRetcode(UT_KEY(CF_CFDP_RecvPh), 1, -1);
+    UT_SetDataBuffer(UT_KEY(CFE_MSG_GetSize), &msg_size_buf, sizeof(msg_size_buf), false);
+    UT_SetDataBuffer(UT_KEY(CFE_MSG_GetType), &msg_type, sizeof(msg_type), false);
+    UtAssert_VOIDCALL(CF_CFDP_ReceiveMessage(c));
+    UT_ResetState(UT_KEY(CF_CFDP_RecvPh));
+    UT_ResetState(UT_KEY(CFE_MSG_GetSize));
+    UT_ResetState(UT_KEY(CFE_MSG_GetType));
+
     /*
      *  - CF_CFDP_RecvPh() succeeds
      *  - CF_FindTransactionBySequenceNumber() returns NULL