Add module for parsing BIRD's OSPF dumps

birdvisu/ospffile.py

@@ -0,0 +1,90 @@
+"""
+A simple implementation of parsing and creating BIRD's OSPF state descriptions
+
+The code-facing data structure is list of directives, which are tuples of string
+(directive) and list of sub-directives. For example, the following input:
+
+	```
+	BIRD 2.0.9 ready.
+	
+	area 0.0.0.0
+
+		router 172.23.100.1
+			distance 30
+			network [172.23.100.4-3] metric 10
+			network [172.23.100.10-2] metric 10
+	
+	```
+
+would be parsed into:
+
+	```python3
+	[('BIRD 2.0.9 ready.', []),
+	 ('area 0.0.0.0', [
+		('router 172.23.100.1', [
+			('distance 30', []),
+			('network [172.23.100.4-3] metric 10', []),
+			('network [172.23.100.10-2] metric 10', []),
+			]),
+		]), # end of area directive
+	] # end of the whole representation
+	```
+
+We expect that users will read the representation sequentially, so we do not
+provide any means of accessing individual sub-directives directly.
+
+Here we only deal with syntax. What the directives mean and how to act on them
+is up to modules using this. Therefore, we only handle strings and do not try
+to understand them here. We only strip comments and whitespace. (We are
+guessing here that the '#' symbol will not appear in real BIRD output.)
+
+We use lists instead of tuples just for convenience. When encoding, we SHOULD
+support other sequences as well. Our users likewise SHOULD not depend on this
+being a list. Supplying a string instead of a tuple with an empty sequence is
+supported and equivalent to specifying the tuple, both representing a directive
+without children. Using empty list is currently considered canonical.
+
+We provide functions dump, dumps, load and loads, similar to the API of json,
+marshal, pickle and possibly others. Note however that unlike those, we cannot
+represent arbitrary data, just the tuple-list trees described above.
+"""
+
+import re
+
+def _tree_lines(tree: list, depth):
+	result = []
+	for child in tree:
+		if isinstance(child, str):
+			node = child
+			subtree = []
+		else:
+			node, subtree = child
+		result.append('\t'*depth + node)
+		result.extend(_tree_lines(subtree, depth+1))
+	return result
+
+def dumps(tree):
+	return '\n'.join(_tree_lines(tree, 0))
+
+def dump(tree, fp):
+	fp.write(dumps(tree))
+
+def loads(s):
+	line_regex = re.compile(r'(\t*)([^#]*)(#.*)?')
+	result = []
+	open_directives = [result]
+	for line in s.splitlines():
+		indent, directive, comment = line_regex.match(line).groups()
+		directive = directive.strip()
+		indent = len(indent)
+		if directive == '': continue
+		new_node = (directive, [])
+		open_directives = open_directives[:indent+1]
+		open_directives[indent].append(new_node)
+		open_directives.append(new_node[1])
+	return result
+
+def load(fp):
+	return loads(fp.read())
+
+