Index: net/tools/tld_cleanup/make_dafsa.py |
diff --git a/net/tools/tld_cleanup/make_dafsa.py b/net/tools/tld_cleanup/make_dafsa.py |
new file mode 100755 |
index 0000000000000000000000000000000000000000..78358effa840d7b072875f1198f502ad39fb96f9 |
--- /dev/null |
+++ b/net/tools/tld_cleanup/make_dafsa.py |
@@ -0,0 +1,469 @@ |
+#!/usr/bin/env python |
+# Copyright 2014 The Chromium Authors. All rights reserved. |
+# Use of this source code is governed by a BSD-style license that can be |
+# found in the LICENSE file. |
+ |
+""" |
+A Deterministic acyclic finite state automaton (DAFSA) is a compact |
+representation of an unordered word list (dictionary). |
+ |
+http://en.wikipedia.org/wiki/Deterministic_acyclic_finite_state_automaton |
+ |
+This python program converts a list of strings to a byte array in C++. |
+This python program fetches strings and return values from a gperf file |
+and generates a C++ file with a byte array representing graph that can be |
+used as a memory efficient replacement for the perfect hash table. |
+ |
+The input strings are assumed to consist of printable 7-bit ASCII characters |
+and the return values are assumed to be one digit integers. |
+ |
+In this program a DAFSA is a diamond shaped graph starting at a common |
+source node and ending at a common sink node. All internal nodes contain |
+a label and each word is represented by the labels in one path from |
+the source node to the sink node. |
+ |
+The following python represention is used for nodes: |
+ |
+ Source node: [ children ] |
+ Internal node: (label, [ children ]) |
+ Sink node: None |
+ |
+The graph is first compressed by prefixes like a trie. In the next step |
+suffixes are compressed so that the graph gets diamond shaped. Finally |
+one to one linked nodes are replaced by nodes with the labels joined. |
+ |
+The order of the operations is crucial since lookups will be performed |
+starting from the source with no backtracking. Thus a node must have at |
+most one child with a label starting by the same character. The output |
+is also arranged so that all jumps are to increasing addresses, thus forward |
+in memory. |
+ |
+The generated output has suffix free decoding so that the sign of leading |
+bits in a link (a reference to a child node) indicate if it has a size of one, |
+two or three bytes and if it is the last outgoing link from the actual node. |
+A node label is terminated by a byte with the leading bit set. |
+ |
+The generated byte array can described by the following BNF: |
+ |
+<byte> ::= < 8-bit value in range [0x00-0xFF] > |
+ |
+<char> ::= < printable 7-bit ASCII character, byte in range [0x20-0x7F] > |
+<end_char> ::= < char + 0x80, byte in range [0xA0-0xFF] > |
+<return value> ::= < value + 0x80, byte in range [0x80-0x8F] > |
+ |
+<offset1> ::= < byte in range [0x00-0x3F] > |
+<offset2> ::= < byte in range [0x40-0x5F] > |
+<offset3> ::= < byte in range [0x60-0x7F] > |
+ |
+<end_offset1> ::= < byte in range [0x80-0xBF] > |
+<end_offset2> ::= < byte in range [0xC0-0xDF] > |
+<end_offset3> ::= < byte in range [0xE0-0xFF] > |
+ |
+<prefix> ::= <char> |
+ |
+<label> ::= <end_char> |
+ | <char> <label> |
+ |
+<end_label> ::= <return_value> |
+ | <char> <end_label> |
+ |
+<offset> ::= <offset1> |
+ | <offset2> <byte> |
+ | <offset3> <byte> <byte> |
+ |
+<end_offset> ::= <end_offset1> |
+ | <end_offset2> <byte> |
+ | <end_offset3> <byte> <byte> |
+ |
+<offsets> ::= <end_offset> |
+ | <offset> <offsets> |
+ |
+<source> ::= <offsets> |
+ |
+<node> ::= <label> <offsets> |
+ | <prefix> <node> |
+ | <end_label> |
+ |
+<dafsa> ::= <source> |
+ | <dafsa> <node> |
+ |
+Decoding: |
+ |
+<char> -> printable 7-bit ASCII character |
+<end_char> & 0x7F -> printable 7-bit ASCII character |
+<return value> & 0x0F -> integer |
+<offset1 & 0x3F> -> integer |
+((<offset2> & 0x1F>) << 8) + <byte> -> integer |
+((<offset3> & 0x1F>) << 16) + (<byte> << 8) + <byte> -> integer |
+ |
+end_offset1, end_offset2 and and_offset3 are decoded same as offset1, |
+offset2 and offset3 respectively. |
+ |
+The first offset in a list of offsets is the distance in bytes between the |
+offset itself and the first child node. Subsequent offsets are the distance |
+between previous child node and next child node. Thus each offset links a node |
+to a child node. The distance is always counted between start addresses, i.e. |
+first byte in decoded offset or first byte in child node. |
+ |
+Example 1: |
+ |
+%% |
+aa, 1 |
+a, 2 |
+%% |
+ |
+The input is first parsed to a list of words: |
+["aa1", "a2"] |
+ |
+A fully expanded graph is created from the words: |
+source = [node1, node4] |
+node1 = ("a", [node2]) |
+node2 = ("a", [node3]) |
+node3 = ("\x01", [sink]) |
+node4 = ("a", [node5]) |
+node5 = ("\x02", [sink]) |
+sink = None |
+ |
+Compression results in the following graph: |
+source = [node1] |
+node1 = ("a", [node2, node3]) |
+node2 = ("\x02", [sink]) |
+node3 = ("a\x01", [sink]) |
+sink = None |
+ |
+A C++ representation of the compressed graph is generated: |
+ |
+const unsigned char dafsa[7] = { |
+ 0x81, 0xE1, 0x02, 0x81, 0x82, 0x61, 0x81, |
+}; |
+ |
+The bytes in the generated array has the following meaning: |
+ |
+ 0: 0x81 <end_offset1> child at position 0 + (0x81 & 0x3F) -> jump to 1 |
+ |
+ 1: 0xE1 <end_char> label character (0xE1 & 0x7F) -> match "a" |
+ 2: 0x02 <offset1> child at position 2 + (0x02 & 0x3F) -> jump to 4 |
+ |
+ 3: 0x81 <end_offset1> child at position 4 + (0x81 & 0x3F) -> jump to 5 |
+ 4: 0x82 <return_value> 0x82 & 0x0F -> return 2 |
+ |
+ 5: 0x61 <char> label character 0x61 -> match "a" |
+ 6: 0x81 <return_value> 0x81 & 0x0F -> return 1 |
+ |
+Example 2: |
+ |
+%% |
+aa, 1 |
+bbb, 2 |
+baa, 1 |
+%% |
+ |
+The input is first parsed to a list of words: |
+["aa1", "bbb2", "baa1"] |
+ |
+Compression results in the following graph: |
+source = [node1, node2] |
+node1 = ("b", [node2, node3]) |
+node2 = ("aa\x01", [sink]) |
+node3 = ("bb\x02", [sink]) |
+sink = None |
+ |
+A C++ representation of the compressed graph is generated: |
+ |
+const unsigned char dafsa[11] = { |
+ 0x02, 0x83, 0xE2, 0x02, 0x83, 0x61, 0x61, 0x81, 0x62, 0x62, 0x82, |
+}; |
+ |
+The bytes in the generated array has the following meaning: |
+ |
+ 0: 0x02 <offset1> child at position 0 + (0x02 & 0x3F) -> jump to 2 |
+ 1: 0x83 <end_offset1> child at position 2 + (0x83 & 0x3F) -> jump to 5 |
+ |
+ 2: 0xE2 <end_char> label character (0xE2 & 0x7F) -> match "b" |
+ 3: 0x02 <offset1> child at position 3 + (0x02 & 0x3F) -> jump to 5 |
+ 4: 0x83 <end_offset1> child at position 5 + (0x83 & 0x3F) -> jump to 8 |
+ |
+ 5: 0x61 <char> label character 0x61 -> match "a" |
+ 6: 0x61 <char> label character 0x61 -> match "a" |
+ 7: 0x81 <return_value> 0x81 & 0x0F -> return 1 |
+ |
+ 8: 0x62 <char> label character 0x62 -> match "b" |
+ 9: 0x62 <char> label character 0x62 -> match "b" |
+10: 0x82 <return_value> 0x82 & 0x0F -> return 2 |
+""" |
+ |
+import sys |
+ |
+class InputError(Exception): |
+ """Exception raised for errors in the input file.""" |
+ |
+ |
+def to_dafsa(words): |
+ """Generates a DAFSA from a word list and returns the source node. |
+ |
+ Each word is split into characters so that each character is represented by |
+ a unique node. It is assumed the word list is not empty. |
+ """ |
+ if not words: |
+ raise InputError('The domain list must not be empty') |
+ def ToNodes(word): |
+ """Split words into characters""" |
+ if not 0x1F < ord(word[0]) < 0x80: |
+ raise InputError('Domain names must be printable 7-bit ASCII') |
+ if len(word) == 1: |
+ return chr(ord(word[0]) & 0x0F), [None] |
+ return word[0], [ToNodes(word[1:])] |
+ return [ToNodes(word) for word in words] |
+ |
+ |
+def to_words(node): |
+ """Generates a word list from all paths starting from an internal node.""" |
+ if not node: |
+ return [''] |
+ return [(node[0] + word) for child in node[1] for word in to_words(child)] |
+ |
+ |
+def reverse(dafsa): |
+ """Generates a new DAFSA that is reversed, so that the old sink node becomes |
+ the new source node. |
+ """ |
+ sink = [] |
+ nodemap = {} |
+ |
+ def dfs(node, parent): |
+ """Creates reverse nodes. |
+ |
+ A new reverse node will be created for each old node. The new node will |
+ get a reversed label and the parents of the old node as children. |
+ """ |
+ if not node: |
+ sink.append(parent) |
+ elif id(node) not in nodemap: |
+ nodemap[id(node)] = (node[0][::-1], [parent]) |
+ for child in node[1]: |
+ dfs(child, nodemap[id(node)]) |
+ else: |
+ nodemap[id(node)][1].append(parent) |
+ |
+ for node in dafsa: |
+ dfs(node, None) |
+ return sink |
+ |
+ |
+def join_labels(dafsa): |
+ """Generates a new DAFSA where internal nodes are merged if there is a one to |
+ one connection. |
+ """ |
+ parentcount = { id(None): 2 } |
+ nodemap = { id(None): None } |
+ |
+ def count_parents(node): |
+ """Count incoming references""" |
+ if id(node) in parentcount: |
+ parentcount[id(node)] += 1 |
+ else: |
+ parentcount[id(node)] = 1 |
+ for child in node[1]: |
+ count_parents(child) |
+ |
+ def join(node): |
+ """Create new nodes""" |
+ if id(node) not in nodemap: |
+ children = [join(child) for child in node[1]] |
+ if len(children) == 1 and parentcount[id(node[1][0])] == 1: |
+ child = children[0] |
+ nodemap[id(node)] = (node[0] + child[0], child[1]) |
+ else: |
+ nodemap[id(node)] = (node[0], children) |
+ return nodemap[id(node)] |
+ |
+ for node in dafsa: |
+ count_parents(node) |
+ return [join(node) for node in dafsa] |
+ |
+ |
+def join_suffixes(dafsa): |
+ """Generates a new DAFSA where nodes that represent the same word lists |
+ towards the sink are merged. |
+ """ |
+ nodemap = { frozenset(('',)): None } |
+ |
+ def join(node): |
+ """Returns a macthing node. A new node is created if no matching node |
+ exists. The graph is accessed in dfs order. |
+ """ |
+ suffixes = frozenset(to_words(node)) |
+ if suffixes not in nodemap: |
+ nodemap[suffixes] = (node[0], [join(child) for child in node[1]]) |
+ return nodemap[suffixes] |
+ |
+ return [join(node) for node in dafsa] |
+ |
+ |
+def top_sort(dafsa): |
+ """Generates list of nodes in topological sort order.""" |
+ incoming = {} |
+ |
+ def count_incoming(node): |
+ """Counts incoming references.""" |
+ if node: |
+ if id(node) not in incoming: |
+ incoming[id(node)] = 1 |
+ for child in node[1]: |
+ count_incoming(child) |
+ else: |
+ incoming[id(node)] += 1 |
+ |
+ for node in dafsa: |
+ count_incoming(node) |
+ |
+ for node in dafsa: |
+ incoming[id(node)] -= 1 |
+ |
+ waiting = [node for node in dafsa if incoming[id(node)] == 0] |
+ nodes = [] |
+ |
+ while waiting: |
+ node = waiting.pop() |
+ assert incoming[id(node)] == 0 |
+ nodes.append(node) |
+ for child in node[1]: |
+ if child: |
+ incoming[id(child)] -= 1 |
+ if incoming[id(child)] == 0: |
+ waiting.append(child) |
+ return nodes |
+ |
+ |
+def encode_links(children, offsets, current): |
+ """Encodes a list of children as one, two or three byte offsets.""" |
+ if not children[0]: |
+ # This is an <end_label> node and no links follow such nodes |
+ assert len(children) == 1 |
+ return [] |
+ guess = 3 * len(children) |
+ assert children |
+ children = sorted(children, key = lambda x: -offsets[id(x)]) |
+ while True: |
+ offset = current + guess |
+ buf = [] |
+ for child in children: |
+ last = len(buf) |
+ distance = offset - offsets[id(child)] |
+ assert distance > 0 and distance < (1 << 21) |
+ |
+ if distance < (1 << 6): |
+ # A 6-bit offset: "s0xxxxxx" |
+ buf.append(distance) |
+ elif distance < (1 << 13): |
+ # A 13-bit offset: "s10xxxxxxxxxxxxx" |
+ buf.append(0x40 | (distance >> 8)) |
+ buf.append(distance & 0xFF) |
+ else: |
+ # A 21-bit offset: "s11xxxxxxxxxxxxxxxxxxxxx" |
+ buf.append(0x60 | (distance >> 16)) |
+ buf.append((distance >> 8) & 0xFF) |
+ buf.append(distance & 0xFF) |
+ # Distance in first link is relative to following record. |
+ # Distance in other links are relative to previous link. |
+ offset -= distance |
+ if len(buf) == guess: |
+ break |
+ guess = len(buf) |
+ # Set most significant bit to mark end of links in this node. |
+ buf[last] |= (1 << 7) |
+ buf.reverse() |
+ return buf |
+ |
+ |
+def encode_prefix(label): |
+ """Encodes a node label as a list of bytes without a trailing high byte. |
+ |
+ This method encodes a node if there is exactly one child and the |
+ child follows immidiately after so that no jump is needed. This label |
+ will then be a prefix to the label in the child node. |
+ """ |
+ assert label |
+ return [ord(c) for c in reversed(label)] |
+ |
+ |
+def encode_label(label): |
+ """Encodes a node label as a list of bytes with a trailing high byte >0x80. |
+ """ |
+ buf = encode_prefix(label) |
+ # Set most significant bit to mark end of label in this node. |
+ buf[0] |= (1 << 7) |
+ return buf |
+ |
+ |
+def encode(dafsa): |
+ """Encodes a DAFSA to a list of bytes""" |
+ output = [] |
+ offsets = {} |
+ |
+ for node in reversed(top_sort(dafsa)): |
+ if (len(node[1]) == 1 and node[1][0] and |
+ (offsets[id(node[1][0])] == len(output))): |
+ output.extend(encode_prefix(node[0])) |
+ else: |
+ output.extend(encode_links(node[1], offsets, len(output))) |
+ output.extend(encode_label(node[0])) |
+ offsets[id(node)] = len(output) |
+ |
+ output.extend(encode_links(dafsa, offsets, len(output))) |
+ output.reverse() |
+ return output |
+ |
+ |
+def to_cxx(data): |
+ """Generates C++ code from a list of encoded bytes.""" |
+ text = '/* This file is generated. DO NOT EDIT!\n\n' |
+ text += 'The byte array encodes effective tld names. See make_dafsa.py for' |
+ text += ' documentation.' |
+ text += '*/\n\n' |
+ text += 'const unsigned char kDafsa[%s] = {\n' % len(data) |
+ for i in range(0, len(data), 12): |
+ text += ' ' |
+ text += ', '.join('0x%02x' % byte for byte in data[i:i + 12]) |
+ text += ',\n' |
+ text += '};\n' |
+ return text |
+ |
+ |
+def words_to_cxx(words): |
+ """Generates C++ code from a word list""" |
+ dafsa = to_dafsa(words) |
+ for fun in (reverse, join_suffixes, reverse, join_suffixes, join_labels): |
+ dafsa = fun(dafsa) |
+ return to_cxx(encode(dafsa)) |
+ |
+ |
+def parse_gperf(infile): |
+ """Parses gperf file and extract strings and return code""" |
+ lines = [line.strip() for line in infile] |
+ # Extract strings after the first '%%' and before the second '%%'. |
+ begin = lines.index('%%') + 1 |
+ end = lines.index('%%', begin) |
+ lines = lines[begin:end] |
+ for line in lines: |
+ if line[-3:-1] != ', ': |
+ raise InputError('Expected "domainname, <digit>", found "%s"' % line) |
+ # Technically the DAFSA format could support return values in range [0-31], |
+ # but the values below are the only with a defined meaning. |
+ if line[-1] not in '0124': |
+ raise InputError('Expected value to be one of {0,1,2,4}, found "%s"' % |
+ line[-1]) |
+ return [line[:-3] + line[-1] for line in lines] |
+ |
+ |
+def main(): |
+ if len(sys.argv) != 3: |
+ print('usage: %s infile outfile' % sys.argv[0]) |
+ return 1 |
+ with open(sys.argv[1], 'r') as infile, open(sys.argv[2], 'w') as outfile: |
+ outfile.write(words_to_cxx(parse_gperf(infile))) |
+ return 0 |
+ |
+ |
+if __name__ == '__main__': |
+ sys.exit(main()) |