+def GetBytes(node, propname, size, default=None):
+ """Get a set of bytes from a property
+
+ Args:
+ node (Node): Node object to read from
+ propname (str): property name to read
+ size (int): Number of bytes to expect
+ default (bytes): Default value or None
+
+ Returns:
+ bytes: Bytes value read, or default if none
+ """
+ prop = node.props.get(propname)
+ if not prop:
+ return default
+ if len(prop.bytes) != size:
+ raise ValueError("Node '%s' property '%s' has length %d, expecting %d" %
+ (node.name, propname, len(prop.bytes), size))
+ return prop.bytes
+