Added bacfile_read_offset() API to read offsets into a file during a restore after a backup.

src/bacnet/basic/object/bacfile.c

@@ -550,6 +550,32 @@ bacfile_read(uint32_t object_instance, uint8_t *buffer, uint32_t buffer_size)
     return (uint32_t)file_size;
 }
 
+/**
+ * @brief Read the entire file into a buffer
+ * @param  object_instance - object-instance number of the object
+ * @param  offset - offset in bytes from the beginning of the file
+ * @param  buffer - data store from the file
+ * @param  buffer_size - in bytes
+ * @return  number of bytes read, or 0 if not successful
+ */
+uint32_t bacfile_read_offset(
+    uint32_t object_instance,
+    int32_t offset,
+    uint8_t *buffer,
+    uint32_t buffer_size)
+{
+    const char *pathname = NULL;
+    long file_size = 0;
+
+    pathname = bacfile_pathname(object_instance);
+    if (pathname) {
+        file_size = bacfile_read_stream_data_callback(
+            pathname, offset, buffer, buffer_size);
+    }
+
+    return (uint32_t)file_size;
+}
+
 /**
  * @brief Write the entire file from a buffer
  * @param  object_instance - object-instance number of the object

src/bacnet/basic/object/bacfile.h

@@ -119,6 +119,12 @@ BACNET_STACK_EXPORT
 uint32_t
 bacfile_read(uint32_t object_instance, uint8_t *buffer, uint32_t buffer_size);
 BACNET_STACK_EXPORT
+uint32_t bacfile_read_offset(
+    uint32_t object_instance,
+    int32_t offset,
+    uint8_t *buffer,
+    uint32_t buffer_size);
+BACNET_STACK_EXPORT
 uint32_t bacfile_write(
     uint32_t object_instance, const uint8_t *buffer, uint32_t buffer_size);
 BACNET_STACK_EXPORT