Reduce footprint of registry controlled domain table

net/tools/tld_cleanup/make_dafsa.py

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
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+#!/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())