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/list_element.c

@@ -18,7 +18,7 @@
 #include "bacnet/list_element.h"
 
 /**
- * @brief Encode the Add/Remove ListElement service request only
+ * @brief Encode the Add/Remove ListElement service request APDU
  *
  *  AddListElement-Request ::= SEQUENCE {
  *      object-identifier       [0] BACnetObjectIdentifier,
@@ -85,6 +85,28 @@ int list_element_encode_service_request(
     return apdu_len;
 }
 
+/**
+ * @brief Encode the Add/Remove ListElement service request only
+ * @param apdu  Pointer to the buffer for encoding into
+ * @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
+ */
+size_t list_element_service_request_encode(
+    uint8_t *apdu, size_t apdu_size, BACNET_LIST_ELEMENT_DATA *data)
+{
+    size_t apdu_len = 0; /* total length of the apdu, return value */
+
+    apdu_len = list_element_encode_service_request(NULL, data);
+    if (apdu_len > apdu_size) {
+        apdu_len = 0;
+    } else {
+        apdu_len = list_element_encode_service_request(apdu, data);
+    }
+
+    return apdu_len;
+}
+
 /**
  * @brief Decode the Add/Remove ListElement service request only
  * @param apdu  Pointer to the buffer for decoding.
@@ -273,7 +295,6 @@ int list_element_error_ack_encode(
     return apdu_len;
 }
 
-#if !BACNET_SVC_SERVER
 /**
  * @brief Decoding for AddListElement or RemoveListElement Error Ack
  *  AddListElement-Error ::= SEQUENCE {
@@ -362,4 +383,3 @@ int list_element_error_ack_decode(
 
     return apdu_len;
 }
-#endif