Bugfix/service request refactor size check (#553)

* refactor service requests from service header

* add APDU size checking and length feature

* add unit tests to check for length when passing NULL buffer

---------

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

src/bacnet/awf.c

@@ -129,6 +129,28 @@ int awf_service_encode_apdu(uint8_t *apdu, BACNET_ATOMIC_WRITE_FILE_DATA *data)
     return apdu_len;
 }
 
+/**
+ * @brief Encode the AtomicWriteFile service request
+ * @param apdu Pointer to the buffer for encoded values
+ * @param apdu_size number of bytes available in the buffer
+ * @param data  Pointer to the service data used for encoding values
+ * @return number of bytes encoded, or zero if unable to encode or too large
+ */
+int atomicwritefile_service_request_encode(
+    uint8_t *apdu, size_t apdu_size, BACNET_ATOMIC_WRITE_FILE_DATA *data)
+{
+    size_t apdu_len = 0; /* total length of the apdu, return value */
+
+    apdu_len = awf_service_encode_apdu(NULL, data);
+    if (apdu_len > apdu_size) {
+        apdu_len = 0;
+    } else {
+        apdu_len = awf_service_encode_apdu(apdu, data);
+    }
+
+    return apdu_len;
+}
+
 /**
  * @brief Encode the AtomicWriteFile service request
  * @param apdu  Pointer to the buffer for decoding.