Mbed TLS configuration file manipulation library and tool

This is meant to be a drop-in replacement for config.pl which can
additionally be used as a library in a Python script.

So far this script supports the commands 'get', 'set' and 'realfull'
but not the other built-in configurations.

scripts/config.py

@@ -0,0 +1,298 @@
+#!/usr/bin/env python3
+
+"""Mbed TLS configuration file manipulation library and tool
+
+Basic usage, to read the Mbed TLS or Mbed Crypto configuration:
+    config = ConfigFile()
+    if 'MBEDTLS_RSA_C' in config: print('RSA is enabled')
+"""
+
+## Copyright (C) 2019, ARM Limited, All Rights Reserved
+## SPDX-License-Identifier: Apache-2.0
+##
+## Licensed under the Apache License, Version 2.0 (the "License"); you may
+## not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+## http://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+## WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
+##
+## This file is part of Mbed TLS (https://tls.mbed.org)
+
+import re
+
+class Setting:
+    """Representation of one Mbed TLS config.h setting.
+
+    Fields:
+    * name: the symbol name ('MBEDTLS_xxx').
+    * value: the value of the macro. The empty string for a plain #define
+      with no value.
+    * active: True if name is defined, False if a #define for name is
+      present in config.h but commented out.
+    """
+    # pylint: disable=too-few-public-methods
+    def __init__(self, active, name, value=''):
+        self.active = active
+        self.name = name
+        self.value = value
+
+class Config:
+    """Representation of the Mbed TLS configuration.
+
+    In the documentation of this class, a symbol is said to be *active*
+    if there is a #define for it that is not commented out, and *known*
+    if there is a #define for it whether commented out or not.
+
+    This class supports the following protocols:
+    * `name in config` is True if the symbol `name` is set in the
+      configuration, False otherwise (whether `name` is known but commented
+      out or not known at all).
+    * `config[name]` is the value of the macro `name`. If `name` is not
+      set, raise `KeyError` (even if a definition for `name` is present
+      but commented out).
+    * `config[name] = value` sets the value associated to `name`. `name`
+      must be known, but does not need to be set. This does not cause
+      name to become set.
+    """
+
+    def __init__(self):
+        self.settings = {}
+
+    def __contains__(self, name):
+        """True if the given symbol is active (i.e. set).
+
+        False if the given symbol is not set, even if a definition
+        is present but commented out.
+        """
+        return name in self.settings and self.settings[name].active
+
+    def all(self, *names):
+        """True if all the elements of names are active (i.e. set)."""
+        return all(self.__contains__(name) for name in names)
+
+    def any(self, *names):
+        """True if at least one symbol in names are active (i.e. set)."""
+        return any(self.__contains__(name) for name in names)
+
+    def known(self, name):
+        """True if a #define for name is present, whether it's commented out or not."""
+        return name in self.settings
+
+    def __getitem__(self, name):
+        """Get the value of name, i.e. what the preprocessor symbol expands to.
+
+        If name is not known, raise KeyError. name does not need to be active.
+        """
+        return self.settings[name].value
+
+    def get(self, name, default=None):
+        """Get the value of name. If name is inactive (not set), return default.
+
+        If a #define for name is present and not commented out, return
+        its expansion, even if this is the empty string.
+
+        If a #define for name is present but commented out, return default.
+        """
+        if name in self.settings:
+            return self.settings[name].value
+        else:
+            return default
+
+    def __setitem__(self, name, value):
+        """If name is known, set its value.
+
+        If name is not known, raise KeyError.
+        """
+        self.settings[name].value = value
+
+    def set(self, name, value=None):
+        """Set name to the given value and make it active.
+
+        If value is None and name is already known, don't change its value.
+        If value is None and name is not known, set its value to the empty
+        string.
+        """
+        if name in self.settings:
+            if value is not None:
+                self.settings[name].value = value
+            self.settings[name].active = True
+        else:
+            self.settings[name] = Setting(True, name, value=value)
+
+    def unset(self, name):
+        """Make name unset (inactive).
+
+        name remains known.
+        """
+        self.set(name)
+        self.settings[name].active = False
+
+    def adapt(self, adapter):
+        """Run adapter on each known symbol and (de)activate it accordingly.
+
+        `adapter` must be a function that returns a boolean. It is called as
+        `adapter(name, active)` for each setting, where `active` is `True`
+        if `name` is set and `False` if `name` is known but unset. If
+        `adapter` returns `True`, then set `name` (i.e. make it active),
+        otherwise unset `name` (i.e. make it known but inactive).
+        """
+        for setting in self.settings.values():
+            setting.active = adapter(setting.name, setting.active)
+
+def realfull_adapter(_name, _set):
+    """Uncomment everything."""
+    return True
+
+class ConfigFile(Config):
+    """Representation of the Mbed TLS configuration read for a file.
+
+    See the documentation of the `Config` class for methods to query
+    and modify the configuration.
+    """
+
+    default_path = 'include/mbedtls/config.h'
+
+    def __init__(self, filename=None):
+        """Read the Mbed TLS configuration file."""
+        if filename is None:
+            filename = self.default_path
+        super().__init__()
+        self.filename = filename
+        with open(filename) as file:
+            self.templates = [self._parse_line(line) for line in file]
+
+    def set(self, name, value=None):
+        if name not in self.settings:
+            self.templates.append((name, '', '#define ' + name + ' '))
+        super().set(name, value)
+
+    _define_line_regexp = (r'(?P<indentation>\s*)' +
+                           r'(?P<commented_out>(//\s*)?)' +
+                           r'(?P<define>#\s*define\s+)' +
+                           r'(?P<name>\w+)' +
+                           r'(?P<arguments>(?:\((?:\w|\s|,)*\))?)' +
+                           r'(?P<separator>\s*)' +
+                           r'(?P<value>.*)')
+    def _parse_line(self, line):
+        """Parse a line in config.h and return the corresponding template."""
+        line = line.rstrip('\r\n')
+        m = re.match(self._define_line_regexp, line)
+        if m:
+            active = not m.group('commented_out')
+            name = m.group('name')
+            value = m.group('value')
+            template = (name,
+                        m.group('indentation'),
+                        m.group('define') + name +
+                        m.group('arguments') + m.group('separator'))
+            self.settings[name] = Setting(active, name, value)
+            return template
+        else:
+            return line
+
+    def _format_template(self, name, indent, middle):
+        """Build a line for config.h for the given setting.
+
+        The line has the form "<indent>#define <name><middle> <value>".
+        """
+        setting = self.settings[name]
+        return ''.join([indent,
+                        '' if setting.active else '//',
+                        middle,
+                        setting.value]).rstrip()
+
+    def write_to_stream(self, output):
+        """Write the whole configuration to output."""
+        for template in self.templates:
+            if isinstance(template, str):
+                line = template
+            else:
+                line = self._format_template(*template)
+            output.write(line + '\n')
+
+    def write(self, filename=None):
+        """Write the whole configuration to the file it was read from.
+
+        If filename is specified, write to this file instead.
+        """
+        if filename is None:
+            filename = self.filename
+        with open(filename, 'w') as output:
+            self.write_to_stream(output)
+
+if __name__ == '__main__':
+    def main():
+        """Command line config.h manipulation tool."""
+        parser = argparse.ArgumentParser(description="""
+        Mbed TLS and Mbed Crypto configuration file manipulation tool.
+        """)
+        parser.add_argument('--file', '-f',
+                            help="""File to read (and modify if requested).
+                            Default: {}.
+                            """.format(ConfigFile.default_path))
+        parser.add_argument('--force', '-o',
+                            help="""For the set command, if SYMBOL is not
+                            present, add a definition for it.""")
+        subparsers = parser.add_subparsers(dest='command',
+                                           title='Commands')
+        parser_get = subparsers.add_parser('get',
+                                           help="""Find the value of SYMBOL
+                                           and print it. Exit with
+                                           status 0 if a #define for SYMBOL is
+                                           found, 1 otherwise.
+                                           """)
+        parser_get.add_argument('symbol', metavar='SYMBOL')
+        parser_set = subparsers.add_parser('set',
+                                           help="""Set SYMBOL to VALUE.
+                                           If VALUE is omitted, just uncomment
+                                           the #define for SYMBOL.
+                                           Error out of a line defining
+                                           SYMBOL (commented or not) is not
+                                           found, unless --force is passed.
+                                           """)
+        parser_set.add_argument('symbol', metavar='SYMBOL')
+        parser_set.add_argument('value', metavar='VALUE', nargs='?')
+        parser_unset = subparsers.add_parser('unset',
+                                             help="""Comment out the #define
+                                             for SYMBOL. Do nothing if none
+                                             is present.""")
+        parser_unset.add_argument('symbol', metavar='SYMBOL')
+
+        def add_adapter(name, function, description):
+            subparser = subparsers.add_parser(name, help=description)
+            subparser.set_defaults(adapter=function)
+        add_adapter('realfull', realfull_adapter,
+                    """Uncomment all #defines. No exceptions.""")
+
+        args = parser.parse_args()
+        config = ConfigFile(args.file)
+        if args.command == 'get':
+            if args.symbol in config:
+                value = config[args.symbol]
+                if value:
+                    sys.stdout.write(value + '\n')
+            return args.symbol not in config
+        elif args.command == 'set':
+            if not args.force and args.symbol not in config:
+                sys.stderr.write("A #define for the symbol {} "
+                                 "was not found in {}"
+                                 .format(args.symbol, args.file))
+                return 1
+            config.set(args.symbol, value=args.value)
+        elif args.command == 'unset':
+            config.unset(args.symbol)
+        else:
+            config.adapt(args.adapter)
+        config.write()
+
+    # Import modules only used by main only if main is defined and called.
+    # pylint: disable=wrong-import-position
+    import argparse
+    import sys
+    sys.exit(main())