[Cronet] Enforce Cronet API never modified, only grown

components/cronet/tools/update_api.py

Index: components/cronet/tools/update_api.py
diff --git a/components/cronet/tools/update_api.py b/components/cronet/tools/update_api.py
new file mode 100755
index 0000000000000000000000000000000000000000..fe5efb3f90d03f4934a4636475d6a52e60360958
--- /dev/null
+++ b/components/cronet/tools/update_api.py
@@ -0,0 +1,141 @@
+#!/usr/bin/python
+# Copyright 2016 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.
+
+"""update_api.py - Update committed Cronet API."""
+
+import argparse
+import filecmp
+import fileinput
+import os
+import re
+import shutil
+import sys
+import tempfile
+
+# Filename of dump of current API.
+API_FILENAME = os.path.abspath(os.path.join(
+    os.path.dirname(__file__), '..', 'android', 'api.txt'))
+# Filename of file containing API version number.
+API_VERSION_FILENAME = os.path.abspath(os.path.join(
+    os.path.dirname(__file__), '..', 'android', 'api_version.txt'))
+
+# Regular expression that catches the beginning of lines that declare classes.
+# The first group returned by a match is the class name.
+CLASS_RE = re.compile(r'.*class ([^ ]*) .*\{')
+
+# Regular expression that matches a string containing an unnamed class name,
+# for example 'Foo$1'.
+UNNAMED_CLASS_RE = re.compile(r'.*\$[0-9]')
+
+
+def generate_api(api_jar, output_filename):
+  # Dumps the API in |api_jar| into |outpuf_filename|.
+
+  with open(output_filename, 'w') as output_file:
+    output_file.write(
+        'DO NOT EDIT THIS FILE, USE update_api.py TO UPDATE IT\n\n')
+
+  # Extract API class files from api_jar.
+  temp_dir = tempfile.mkdtemp()
+  old_cwd = os.getcwd()
+  api_jar_path = os.path.abspath(api_jar)
+  os.chdir(temp_dir)
+  if os.system('jar xf %s' % api_jar_path):
+    print 'ERROR: jar failed on ' + api_jar
+    return False
+  os.chdir(old_cwd)
+  shutil.rmtree(os.path.join(temp_dir, 'META-INF'))
+
+  # Collect names of all API class files
+  api_class_files = []
+  for root, _, filenames in os.walk(temp_dir):
+    api_class_files += [os.path.join(root, f) for f in filenames]
+  api_class_files.sort()
+
+  # Dump API class files into |output_filename|
+  javap_cmd = ('javap -protected %s >> %s' % (' '.join(api_class_files),
+      output_filename)).replace('$', '\\$')
+  if os.system(javap_cmd):
+    print 'ERROR: javap command failed: ' + javap_cmd
+    return False
+  shutil.rmtree(temp_dir)
+
+  # Strip out pieces we don't need to compare.
+  output_file = fileinput.FileInput(output_filename, inplace=True)
+  skip_to_next_class = False
+  for line in output_file:
+    # Skip 'Compiled from ' lines as they're not part of the API.
+    if line.startswith('Compiled from "'):
+      continue
+    if CLASS_RE.match(line):
+      skip_to_next_class = (
+          # Skip internal classes, they aren't exposed.
+          UNNAMED_CLASS_RE.match(line) or
+          # Skip experimental classes, they can be modified.
+          'Experimental' in line
+      )
+    if skip_to_next_class:
+      skip_to_next_class = line != '}'
+      continue
+    sys.stdout.write(line)
+  output_file.close()
+  return True
+
+
+def check_up_to_date(api_jar):
+  # Returns True if API_FILENAME matches the API exposed by |api_jar|.
+
+  [_, temp_filename] = tempfile.mkstemp()
+  if not generate_api(api_jar, temp_filename):
+    return False
+  ret = filecmp.cmp(API_FILENAME, temp_filename)
+  os.remove(temp_filename)
+  return ret
+
+
+def check_api_update(old_api, new_api):
+  # Enforce that lines are only added when updating API.
+  with open(old_api, 'r') as old_api_file, open(new_api, 'r') as new_api_file:
+    for old_line in old_api_file:
+      while True:
+        new_line = new_api_file.readline()
+        if new_line == old_line:
+          break
+        if not new_line:
+          print 'ERROR: This API was modified or removed:'
+          print '           ' + old_line
+          print '       Cronet API methods and classes cannot be modified.'
+          return False
+  return True
+
+
+def main(args):
+  parser = argparse.ArgumentParser(description='Update Cronet api.txt.')
+  parser.add_argument('--api_jar',
+                      help='Path to API jar (i.e. cronet_api.jar)',
+                      required=True,
+                      metavar='path/to/cronet_api.jar')
+  opts = parser.parse_args(args)
+
+  if check_up_to_date(opts.api_jar):
+    return True
+
+  [_, temp_filename] = tempfile.mkstemp()
+  if (generate_api(opts.api_jar, temp_filename) and
+      check_api_update(API_FILENAME, temp_filename)):
+    # Update API version number to new version number
+    with open(API_VERSION_FILENAME,'r+') as f:
+      version = int(f.read())
+      f.seek(0)
+      f.write(str(version + 1))
+    # Update API file to new API
+    shutil.move(temp_filename, API_FILENAME)
+    return True
+  os.remove(temp_filename)
+  return False
+
+
+if __name__ == '__main__':
+  sys.exit(0 if main(sys.argv[1:]) else -1)