Add initialization and unpacking functions for BACnet Character String buffer decoder. (#1242)

src/bacnet/bacdcode.c

@@ -3456,6 +3456,65 @@ int bacnet_character_string_buffer_context_decode(
     return apdu_len;
 }
 
+/**
+ * @brief Initializes a BACnet Character String buffer value
+ *
+ * @param value - the BACnet Character String buffer value to be initialized
+ * @param encoding - pointer to the BACnet Character String encoding value
+ * @param buffer - pointer to the buffer to hold the string value
+ * @param buffer_length - pointer to hold the buffer length
+ * @param buffer_size - size of the buffer in bytes
+ */
+void bacnet_character_string_buffer_init(
+    BACNET_CHARACTER_STRING_BUFFER *value,
+    uint8_t encoding,
+    char *buffer,
+    size_t buffer_size)
+{
+    if (value) {
+        value->encoding = encoding;
+        value->buffer = buffer;
+        value->buffer_size = buffer_size;
+        value->buffer_length = 0;
+    }
+}
+
+/**
+ * @brief Unpacks a BACnet Character String buffer value from bytes
+ *
+ * @param value - the BACnet Character String buffer value to be unpacked
+ * @param encoding - pointer to the BACnet Character String encoding value
+ * @param buffer - pointer to the buffer to hold the string value
+ * @param buffer_length - pointer to hold the buffer length
+ *
+ * @return true if unpacked successfully, false if errors occur
+ */
+bool bacnet_character_string_buffer_unpack(
+    const BACNET_CHARACTER_STRING_BUFFER *value,
+    uint8_t *encoding,
+    char *buffer,
+    uint32_t *buffer_length)
+{
+    if (value) {
+        if (value->buffer_length > value->buffer_size) {
+            /* fail if buffer length is greater than buffer size */
+            return false;
+        }
+        if (encoding) {
+            *encoding = value->encoding;
+        }
+        if (buffer_length) {
+            *buffer_length = value->buffer_length;
+        }
+        if (buffer && value->buffer && value->buffer_length) {
+            memcpy(buffer, value->buffer, value->buffer_length);
+        }
+        return true;
+    }
+
+    return false;
+}
+
 /**
  * @brief Decodes from bytes into a BACnet Unsigned value
  * from clause 20.2.4 Encoding of an Unsigned Integer Value

src/bacnet/bacdcode.h

@@ -524,6 +524,18 @@ int bacnet_character_string_buffer_context_decode(
     uint32_t apdu_size,
     uint8_t tag_value,
     BACNET_CHARACTER_STRING_BUFFER *value);
+BACNET_STACK_EXPORT
+void bacnet_character_string_buffer_init(
+    BACNET_CHARACTER_STRING_BUFFER *value,
+    uint8_t encoding,
+    char *buffer,
+    size_t buffer_size);
+BACNET_STACK_EXPORT
+bool bacnet_character_string_buffer_unpack(
+    const BACNET_CHARACTER_STRING_BUFFER *value,
+    uint8_t *encoding,
+    char *buffer,
+    uint32_t *buffer_length);
 
 BACNET_STACK_EXPORT
 int encode_bacnet_character_string(

src/bacnet/hostnport.c

@@ -457,9 +457,11 @@ int host_n_port_minimal_address_decode(
 {
     int apdu_len = 0, len = 0;
     uint8_t *buffer = NULL;
+    uint32_t buffer_length = 0;
     size_t buffer_size = 0;
     BACNET_TAG tag = { 0 };
     BACNET_CHARACTER_STRING_BUFFER char_string = { 0 };
+    bool status = false;
 
     /* default reject code */
     if (error_code) {
@@ -507,10 +509,9 @@ int host_n_port_minimal_address_decode(
     } else if (tag.context && (tag.number == 2)) {
         if (address) {
             address->tag = BACNET_HOST_ADDRESS_TAG_NAME;
-            char_string.buffer = address->host.name.fqdn;
-            char_string.buffer_size = sizeof(address->host.name.fqdn);
-            char_string.encoding = CHARACTER_ANSI_X34;
-            char_string.buffer_length = 0;
+            bacnet_character_string_buffer_init(
+                &char_string, CHARACTER_ANSI_X34, address->host.name.fqdn,
+                sizeof(address->host.name.fqdn));
         }
         len = bacnet_character_string_buffer_decode(
             &apdu[apdu_len], apdu_size - apdu_len, tag.len_value_type,
@@ -522,13 +523,16 @@ int host_n_port_minimal_address_decode(
             return BACNET_STATUS_REJECT;
         }
         if (address) {
-            if (char_string.buffer_length > char_string.buffer_size) {
+            status = bacnet_character_string_buffer_unpack(
+                &char_string, NULL, NULL, &buffer_length);
+            if (status) {
+                address->host.name.length = buffer_length;
+            } else {
                 if (error_code) {
                     *error_code = ERROR_CODE_REJECT_BUFFER_OVERFLOW;
                 }
                 return BACNET_STATUS_REJECT;
             }
-            address->host.name.length = char_string.buffer_length;
         }
         apdu_len += len;
     } else {