Discard confirmed APDU from original broadcast in BIP and BIP6 datalink (#149)

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

src/bacnet/npdu.c

@@ -501,6 +501,38 @@ int bacnet_npdu_decode(uint8_t *npdu,
     return len;
 }
 
+/**
+ * @brief Helper for datalink detecting an application confirmed service
+ * @param pdu [in]  Buffer containing the NPDU and APDU of the received packet.
+ * @param pdu_len [in] The size of the received message in the pdu[] buffer.
+ * @return true if the PDU is a confirmed APDU
+ */
+bool npdu_confirmed_service(
+    uint8_t *pdu,
+    uint16_t pdu_len)
+{
+    bool status = false;
+    int apdu_offset = 0;
+    BACNET_NPDU_DATA npdu_data = { 0 };
+
+    if (pdu_len > 0) {
+        if (pdu[0] == BACNET_PROTOCOL_VERSION) {
+            /* only handle the version that we know how to handle */
+            apdu_offset =
+                bacnet_npdu_decode(&pdu[0], pdu_len, NULL, NULL, &npdu_data);
+            if ((!npdu_data.network_layer_message) && (apdu_offset > 0) &&
+                (apdu_offset < pdu_len)) {
+                if ((pdu[apdu_offset] & 0xF0) ==
+                    PDU_TYPE_CONFIRMED_SERVICE_REQUEST) {
+                    status = true;
+                }
+            }
+        }
+    }
+
+    return status;
+}
+
 #ifdef BAC_TEST
 #include <assert.h>
 #include <string.h>