path: root/python/google/protobuf/text_format.py

# Protocol Buffers - Google's data interchange format
# Copyright 2008 Google Inc.  All rights reserved.
# https://developers.google.com/protocol-buffers/
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
#     * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following disclaimer
# in the documentation and/or other materials provided with the
# distribution.
#     * Neither the name of Google Inc. nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

"""Contains routines for printing protocol messages in text format.

Simple usage example:

  # Create a proto object and serialize it to a text proto string.
  message = my_proto_pb2.MyMessage(foo='bar')
  text_proto = text_format.MessageToString(message)

  # Parse a text proto string.
  message = text_format.Parse(text_proto, my_proto_pb2.MyMessage())
"""

__author__ = 'kenton@google.com (Kenton Varda)'

import io
import re

import six

if six.PY3:
  long = int  # pylint: disable=redefined-builtin,invalid-name

# pylint: disable=g-import-not-at-top
from google.protobuf.internal import type_checkers
from google.protobuf import descriptor
from google.protobuf import text_encoding

__all__ = ['MessageToString', 'Parse', 'PrintMessage', 'PrintField',
           'PrintFieldValue', 'Merge', 'MessageToBytes']

_INTEGER_CHECKERS = (type_checkers.Uint32ValueChecker(),
                     type_checkers.Int32ValueChecker(),
                     type_checkers.Uint64ValueChecker(),
                     type_checkers.Int64ValueChecker())
_FLOAT_INFINITY = re.compile('-?inf(?:inity)?f?$', re.IGNORECASE)
_FLOAT_NAN = re.compile('nanf?$', re.IGNORECASE)
_FLOAT_TYPES = frozenset([descriptor.FieldDescriptor.CPPTYPE_FLOAT,
                          descriptor.FieldDescriptor.CPPTYPE_DOUBLE])
_QUOTES = frozenset(("'", '"'))
_ANY_FULL_TYPE_NAME = 'google.protobuf.Any'


class Error(Exception):
  """Top-level module error for text_format."""


class ParseError(Error):
  """Thrown in case of text parsing or tokenizing error."""

  def __init__(self, message=None, line=None, column=None):
    if message is not None and line is not None:
      loc = str(line)
      if column is not None:
        loc += ':{0}'.format(column)
      message = '{0} : {1}'.format(loc, message)
    if message is not None:
      super(ParseError, self).__init__(message)
    else:
      super(ParseError, self).__init__()
    self._line = line
    self._column = column

  def GetLine(self):
    return self._line

  def GetColumn(self):
    return self._column


class TextWriter(object):

  def __init__(self, as_utf8):
    if six.PY2:
      self._writer = io.BytesIO()
    else:
      self._writer = io.StringIO()

  def write(self, val):
    if six.PY2:
      if isinstance(val, six.text_type):
        val = val.encode('utf-8')
    return self._writer.write(val)

  def close(self):
    return self._writer.close()

  def getvalue(self):
    return self._writer.getvalue()


def MessageToString(message,
                    as_utf8=False,
                    as_one_line=False,
                    use_short_repeated_primitives=False,
                    pointy_brackets=False,
                    use_index_order=False,
                    float_format=None,
                    use_field_number=False,
                    descriptor_pool=None,
                    indent=0,
                    message_formatter=None):
  # type: (...) -> str
  """Convert protobuf message to text format.

  Floating point values can be formatted compactly with 15 digits of
  precision (which is the most that IEEE 754 "double" can guarantee)
  using float_format='.15g'. To ensure that converting to text and back to a
  proto will result in an identical value, float_format='.17g' should be used.

  Args:
    message: The protocol buffers message.
    as_utf8: Return unescaped Unicode for non-ASCII characters.
        In Python 3 actual Unicode characters may appear as is in strings.
        In Python 2 the return value will be valid UTF-8 rather than only ASCII.
    as_one_line: Don't introduce newlines between fields.
    use_short_repeated_primitives: Use short repeated format for primitives.
    pointy_brackets: If True, use angle brackets instead of curly braces for
      nesting.
    use_index_order: If True, fields of a proto message will be printed using
      the order defined in source code instead of the field number, extensions
      will be printed at the end of the message and their relative order is
      determined by the extension number. By default, use the field number
      order.
    float_format: If set, use this to specify floating point number formatting
      (per the "Format Specification Mini-Language"); otherwise, str() is used.
    use_field_number: If True, print field numbers instead of names.
    descriptor_pool: A DescriptorPool used to resolve Any types.
    indent: The indent level, in terms of spaces, for pretty print.
    message_formatter: A function(message, indent, as_one_line): unicode|None
      to custom format selected sub-messages (usually based on message type).
      Use to pretty print parts of the protobuf for easier diffing.

  Returns:
    A string of the text formatted protocol buffer message.
  """
  out = TextWriter(as_utf8)
  printer = _Printer(out, indent, as_utf8, as_one_line,
                     use_short_repeated_primitives, pointy_brackets,
                     use_index_order, float_format, use_field_number,
                     descriptor_pool, message_formatter)
  printer.PrintMessage(message)
  result = out.getvalue()
  out.close()
  if as_one_line:
    return result.rstrip()
  return result


def MessageToBytes(message, **kwargs):
  # type: (...) -> bytes
  """Convert protobuf message to encoded text format.  See MessageToString."""
  text = MessageToString(message, **kwargs)
  if isinstance(text, bytes):
    return text
  codec = 'utf-8' if kwargs.get('as_utf8') else 'ascii'
  return text.encode(codec)


def _IsMapEntry(field):
  return (field.type == descriptor.FieldDescriptor.TYPE_MESSAGE and
          field.message_type.has_options and
          field.message_type.GetOptions().map_entry)


def PrintMessage(message,
                 out,
                 indent=0,
                 as_utf8=False,
                 as_one_line=False,
                 use_short_repeated_primitives=False,
                 pointy_brackets=False,
                 use_index_order=False,
                 float_format=None,
                 use_field_number=False,
                 descriptor_pool=None,
                 message_formatter=None):
  printer = _Printer(out, indent, as_utf8, as_one_line,
                     use_short_repeated_primitives, pointy_brackets,
                     use_index_order, float_format, use_field_number,
                     descriptor_pool, message_formatter)
  printer.PrintMessage(message)


def PrintField(field,
               value,
               out,
               indent=0,
               as_utf8=False,
               as_one_line=False,
               use_short_repeated_primitives=False,
               pointy_brackets=False,
               use_index_order=False,
               float_format=None,
               message_formatter=None):
  """Print a single field name/value pair."""
  printer = _Printer(out, indent, as_utf8, as_one_line,
                     use_short_repeated_primitives, pointy_brackets,
                     use_index_order, float_format, message_formatter)
  printer.PrintField(field, value)


def PrintFieldValue(field,
                    value,
                    out,
                    indent=0,
                    as_utf8=False,
                    as_one_line=False,
                    use_short_repeated_primitives=False,
                    pointy_brackets=False,
                    use_index_order=False,
                    float_format=None,
                    message_formatter=None):
  """Print a single field value (not including name)."""
  printer = _Printer(out, indent, as_utf8, as_one_line,
                     use_short_repeated_primitives, pointy_brackets,
                     use_index_order, float_format, message_formatter)
  printer.PrintFieldValue(field, value)


def _BuildMessageFromTypeName(type_name, descriptor_pool):
  """Returns a protobuf message instance.

  Args:
    type_name: Fully-qualified protobuf  message type name string.
    descriptor_pool: DescriptorPool instance.

  Returns:
    A Message instance of type matching type_name, or None if the a Descriptor
    wasn't found matching type_name.
  """
  # pylint: disable=g-import-not-at-top
  if descriptor_pool is None:
    from google.protobuf import descriptor_pool as pool_mod
    descriptor_pool = pool_mod.Default()
  from google.protobuf import symbol_database
  database = symbol_database.Default()
  try:
    message_descriptor = descriptor_pool.FindMessageTypeByName(type_name)
  except KeyError:
    return None
  message_type = database.GetPrototype(message_descriptor)
  return message_type()


class _Printer(object):
  """Text format printer for protocol message."""

  def __init__(self,
               out,
               indent=0,
               as_utf8=False,
               as_one_line=False,
               use_short_repeated_primitives=False,
               pointy_brackets=False,
               use_index_order=False,
               float_format=None,
               use_field_number=False,
               descriptor_pool=None,
               message_formatter=None):
    """Initialize the Printer.

    Floating point values can be formatted compactly with 15 digits of
    precision (which is the most that IEEE 754 "double" can guarantee)
    using float_format='.15g'. To ensure that converting to text and back to a
    proto will result in an identical value, float_format='.17g' should be used.

    Args:
      out: To record the text format result.
      indent: The indent level for pretty print.
      as_utf8: Return unescaped Unicode for non-ASCII characters.
          In Python 3 actual Unicode characters may appear as is in strings.
          In Python 2 the return value will be valid UTF-8 rather than ASCII.
      as_one_line: Don't introduce newlines between fields.
      use_short_repeated_primitives: Use short repeated format for primitives.
      pointy_brackets: If True, use angle brackets instead of curly braces for
        nesting.
      use_index_order: If True, print fields of a proto message using the order
        defined in source code instead of the field number. By default, use the
        field number order.
      float_format: If set, use this to specify floating point number formatting
        (per the "Format Specification Mini-Language"); otherwise, str() is
        used.
      use_field_number: If True, print field numbers instead of names.
      descriptor_pool: A DescriptorPool used to resolve Any types.
      message_formatter: A function(message, indent, as_one_line): unicode|None
        to custom format selected sub-messages (usually based on message type).
        Use to pretty print parts of the protobuf for easier diffing.
    """
    self.out = out
    self.indent = indent
    self.as_utf8 = as_utf8
    self.as_one_line = as_one_line
    self.use_short_repeated_primitives = use_short_repeated_primitives
    self.pointy_brackets = pointy_brackets
    self.use_index_order = use_index_order
    self.float_format = float_format
    self.use_field_number = use_field_number
    self.descriptor_pool = descriptor_pool
    self.message_formatter = message_formatter

  def _TryPrintAsAnyMessage(self, message):
    """Serializes if message is a google.protobuf.Any field."""
    packed_message = _BuildMessageFromTypeName(message.TypeName(),
                                               self.descriptor_pool)
    if packed_message:
      packed_message.MergeFromString(message.value)
      self.out.write('%s[%s]' % (self.indent * ' ', message.type_url))
      self._PrintMessageFieldValue(packed_message)
      self.out.write(' ' if self.as_one_line else '\n')
      return True
    else:
      return False

  def _TryCustomFormatMessage(self, message):
    formatted = self.message_formatter(message, self.indent, self.as_one_line)
    if formatted is None:
      return False

    out = self.out
    out.write(' ' * self.indent)
    out.write(formatted)
    out.write(' ' if self.as_one_line else '\n')
    return True

  def PrintMessage(self, message):
    """Convert protobuf message to text format.

    Args:
      message: The protocol buffers message.
    """
    if self.message_formatter and self._TryCustomFormatMessage(message):
      return
    if (message.DESCRIPTOR.full_name == _ANY_FULL_TYPE_NAME and
        self._TryPrintAsAnyMessage(message)):
      return
    fields = message.ListFields()
    if self.use_index_order:
      fields.sort(
          key=lambda x: x[0].number if x[0].is_extension else x[0].index)
    for field, value in fields:
      if _IsMapEntry(field):
        for key in sorted(value):
          # This is slow for maps with submessage entries because it copies the
          # entire tree.  Unfortunately this would take significant refactoring
          # of this file to work around.
          #
          # TODO(haberman): refactor and optimize if this becomes an issue.
          entry_submsg = value.GetEntryClass()(key=key, value=value[key])
          self.PrintField(field, entry_submsg)
      elif field.label == descriptor.FieldDescriptor.LABEL_REPEATED:
        if (self.use_short_repeated_primitives
            and field.cpp_type != descriptor.FieldDescriptor.CPPTYPE_MESSAGE
            and field.cpp_type != descriptor.FieldDescriptor.CPPTYPE_STRING):
          self._PrintShortRepeatedPrimitivesValue(field, value)
        else:
          for element in value:
            self.PrintField(field, element)
      else:
        self.PrintField(field, value)

  def _PrintFieldName(self, field):
    """Print field name."""
    out = self.out
    out.write(' ' * self.indent)
    if self.use_field_number:
      out.write(str(field.number))
    else:
      if field.is_extension:
        out.write('[')
        if (field.containing_type.GetOptions().message_set_wire_format and
            field.type == descriptor.FieldDescriptor.TYPE_MESSAGE and
            field.label == descriptor.FieldDescriptor.LABEL_OPTIONAL):
          out.write(field.message_type.full_name)
        else:
          out.write(field.full_name)
        out.write(']')
      elif field.type == descriptor.FieldDescriptor.TYPE_GROUP:
        # For groups, use the capitalized name.
        out.write(field.message_type.name)
      else:
        out.write(field.name)

    if field.cpp_type != descriptor.FieldDescriptor.CPPTYPE_MESSAGE:
      # The colon is optional in this case, but our cross-language golden files
      # don't include it.
      out.write(': ')

  def PrintField(self, field, value):
    """Print a single field name/value pair."""
    self._PrintFieldName(field)
    self.PrintFieldValue(field, value)
    self.out.write(' ' if self.as_one_line else '\n')

  def _PrintShortRepeatedPrimitivesValue(self, field, value):
    # Note: this is called only when value has at least one element.
    self._PrintFieldName(field)
    self.out.write('[')
    for i in xrange(len(value) - 1):
      self.PrintFieldValue(field, value[i])
      self.out.write(', ')
    self.PrintFieldValue(field, value[-1])
    self.out.write(']')
    self.out.write(' ' if self.as_one_line else '\n')

  def _PrintMessageFieldValue(self, value):
    if self.pointy_brackets:
      openb = '<'
      closeb = '>'
    else:
      openb = '{'
      closeb = '}'

    if self.as_one_line:
      self.out.write(' %s ' % openb)
      self.PrintMessage(value)
      self.out.write(closeb)
    else:
      self.out.write(' %s\n' % openb)
      self.indent += 2
      self.PrintMessage(value)
      self.indent -= 2
      self.out.write(' ' * self.indent + closeb)

  def PrintFieldValue(self, field, value):
    """Print a single field value (not including name).

    For repeated fields, the value should be a single element.

    Args:
      field: The descriptor of the field to be printed.
      value: The value of the field.
    """
    out = self.out
    if field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_MESSAGE:
      self._PrintMessageFieldValue(value)
    elif field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_ENUM:
      enum_value = field.enum_type.values_by_number.get(value, None)
      if enum_value is not None:
        out.write(enum_value.name)
      else:
        out.write(str(value))
    elif field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_STRING:
      out.write('\"')
      if isinstance(value, six.text_type) and (six.PY2 or not self.as_utf8):
        out_value = value.encode('utf-8')
      else:
        out_value = value
      if field.type == descriptor.FieldDescriptor.TYPE_BYTES:
        # We always need to escape all binary data in TYPE_BYTES fields.
        out_as_utf8 = False
      else:
        out_as_utf8 = self.as_utf8
      out.write(text_encoding.CEscape(out_value, out_as_utf8))
      out.write('\"')
    elif field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_BOOL:
      if value:
        out.write('true')
      else:
        out.write('false')
    elif field.cpp_type in _FLOAT_TYPES and self.float_format is not None:
      out.write('{1:{0}}'.format(self.float_format, value))
    else:
      out.write(str(value))


def Parse(text,
          message,
          allow_unknown_extension=False,
          allow_field_number=False,
          descriptor_pool=None):
  """Parses a text representation of a protocol message into a message.

  NOTE: for historical reasons this function does not clear the input
  message. This is different from what the binary msg.ParseFrom(...) does.

  Example
    a = MyProto()
    a.repeated_field.append('test')
    b = MyProto()

    text_format.Parse(repr(a), b)
    text_format.Parse(repr(a), b) # repeated_field contains ["test", "test"]

    # Binary version:
    b.ParseFromString(a.SerializeToString()) # repeated_field is now "test"

  Caller is responsible for clearing the message as needed.

  Args:
    text: Message text representation.
    message: A protocol buffer message to merge into.
    allow_unknown_extension: if True, skip over missing extensions and keep
      parsing
    allow_field_number: if True, both field number and field name are allowed.
    descriptor_pool: A DescriptorPool used to resolve Any types.

  Returns:
    The same message passed as argument.

  Raises:
    ParseError: On text parsing problems.
  """
  return ParseLines(text.split(b'\n' if isinstance(text, bytes) else u'\n'),
                    message,
                    allow_unknown_extension,
                    allow_field_number,
                    descriptor_pool=descriptor_pool)


def Merge(text,
          message,
          allow_unknown_extension=False,
          allow_field_number=False,
          descriptor_pool=None):
  """Parses a text representation of a protocol message into a message.

  Like Parse(), but allows repeated values for a non-repeated field, and uses
  the last one.

  Args:
    text: Message text representation.
    message: A protocol buffer message to merge into.
    allow_unknown_extension: if True, skip over missing extensions and keep
      parsing
    allow_field_number: if True, both field number and field name are allowed.
    descriptor_pool: A DescriptorPool used to resolve Any types.

  Returns:
    The same message passed as argument.

  Raises:
    ParseError: On text parsing problems.
  """
  return MergeLines(
      text.split(b'\n' if isinstance(text, bytes) else u'\n'),
      message,
      allow_unknown_extension,
      allow_field_number,
      descriptor_pool=descriptor_pool)


def ParseLines(lines,
               message,
               allow_unknown_extension=False,
               allow_field_number=False,
               descriptor_pool=None):
  """Parses a text representation of a protocol message into a message.

  Args:
    lines: An iterable of lines of a message's text representation.
    message: A protocol buffer message to merge into.
    allow_unknown_extension: if True, skip over missing extensions and keep
      parsing
    allow_field_number: if True, both field number and field name are allowed.
    descriptor_pool: A DescriptorPool used to resolve Any types.

  Returns:
    The same message passed as argument.

  Raises:
    ParseError: On text parsing problems.
  """
  parser = _Parser(allow_unknown_extension,
                   allow_field_number,
                   descriptor_pool=descriptor_pool)
  return parser.ParseLines(lines, message)


def MergeLines(lines,
               message,
               allow_unknown_extension=False,
               allow_field_number=False,
               descriptor_pool=None):
  """Parses a text representation of a protocol message into a message.

  Like ParseLines(), but allows repeated values for a non-repeated field, and
  uses the last one.

  Args:
    lines: An iterable of lines of a message's text representation.
    message: A protocol buffer message to merge into.
    allow_unknown_extension: if True, skip over missing extensions and keep
      parsing
    allow_field_number: if True, both field number and field name are allowed.
    descriptor_pool: A DescriptorPool used to resolve Any types.

  Returns:
    The same message passed as argument.

  Raises:
    ParseError: On text parsing problems.
  """
  parser = _Parser(allow_unknown_extension,
                   allow_field_number,
                   descriptor_pool=descriptor_pool)
  return parser.MergeLines(lines, message)


class _Parser(object):
  """Text format parser for protocol message."""

  def __init__(self,
               allow_unknown_extension=False,
               allow_field_number=False,
               descriptor_pool=None):
    self.allow_unknown_extension = allow_unknown_extension
    self.allow_field_number = allow_field_number
    self.descriptor_pool = descriptor_pool

  def ParseLines(self, lines, message):
    """Parses a text representation of a protocol message into a message."""
    self._allow_multiple_scalars = False
    self._ParseOrMerge(lines, message)
    return message

  def MergeLines(self, lines, message):
    """Merges a text representation of a protocol message into a message."""
    self._allow_multiple_scalars = True
    self._ParseOrMerge(lines, message)
    return message

  def _ParseOrMerge(self, lines, message):
    """Converts a text representation of a protocol message into a message.

    Args:
      lines: Lines of a message's text representation.
      message: A protocol buffer message to merge into.

    Raises:
      ParseError: On text parsing problems.
    """
    # Tokenize expects native str lines.
    if six.PY2:
      str_lines = (line if isinstance(line, str) else line.encode('utf-8')
                   for line in lines)
    else:
      str_lines = (line if isinstance(line, str) else line.decode('utf-8')
                   for line in lines)
    tokenizer = Tokenizer(str_lines)
    while not tokenizer.AtEnd():
      self._MergeField(tokenizer, message)

  def _MergeField(self, tokenizer, message):
    """Merges a single protocol message field into a message.

    Args:
      tokenizer: A tokenizer to parse the field name and values.
      message: A protocol message to record the data.

    Raises:
      ParseError: In case of text parsing problems.
    """
    message_descriptor = message.DESCRIPTOR
    if (message_descriptor.full_name == _ANY_FULL_TYPE_NAME and
        tokenizer.TryConsume('[')):
      type_url_prefix, packed_type_name = self._ConsumeAnyTypeUrl(tokenizer)
      tokenizer.Consume(']')
      tokenizer.TryConsume(':')
      if tokenizer.TryConsume('<'):
        expanded_any_end_token = '>'
      else:
        tokenizer.Consume('{')
        expanded_any_end_token = '}'
      expanded_any_sub_message = _BuildMessageFromTypeName(packed_type_name,
                                                           self.descriptor_pool)
      if not expanded_any_sub_message:
        raise ParseError('Type %s not found in descriptor pool' %
                         packed_type_name)
      while not tokenizer.TryConsume(expanded_any_end_token):
        if tokenizer.AtEnd():
          raise tokenizer.ParseErrorPreviousToken('Expected "%s".' %
                                                  (expanded_any_end_token,))
        self._MergeField(tokenizer, expanded_any_sub_message)
      message.Pack(expanded_any_sub_message,
                   type_url_prefix=type_url_prefix)
      return

    if tokenizer.TryConsume('['):
      name = [tokenizer.ConsumeIdentifier()]
      while tokenizer.TryConsume('.'):
        name.append(tokenizer.ConsumeIdentifier())
      name = '.'.join(name)

      if not message_descriptor.is_extendable:
        raise tokenizer.ParseErrorPreviousToken(
            'Message type "%s" does not have extensions.' %
            message_descriptor.full_name)
      # pylint: disable=protected-access
      field = message.Extensions._FindExtensionByName(name)
      # pylint: enable=protected-access
      if not field:
        if self.allow_unknown_extension:
          field = None
        else:
          raise tokenizer.ParseErrorPreviousToken(
              'Extension "%s" not registered. '
              'Did you import the _pb2 module which defines it? '
              'If you are trying to place the extension in the MessageSet '
              'field of another message that is in an Any or MessageSet field, '
              'that message\'s _pb2 module must be imported as well' % name)
      elif message_descriptor != field.containing_type:
        raise tokenizer.ParseErrorPreviousToken(
            'Extension "%s" does not extend message type "%s".' %
            (name, message_descriptor.full_name))

      tokenizer.Consume(']')

    else:
      name = tokenizer.ConsumeIdentifierOrNumber()
      if self.allow_field_number and name.isdigit():
        number = ParseInteger(name, True, True)
        field = message_descriptor.fields_by_number.get(number, None)
        if not field and message_descriptor.is_extendable:
          field = message.Extensions._FindExtensionByNumber(number)
      else:
        field = message_descriptor.fields_by_name.get(name, None)

        # Group names are expected to be capitalized as they appear in the
        # .proto file, which actually matches their type names, not their field
        # names.
        if not field:
          field = message_descriptor.fields_by_name.get(name.lower(), None)
          if field and field.type != descriptor.FieldDescriptor.TYPE_GROUP:
            field = None

        if (field and field.type == descriptor.FieldDescriptor.TYPE_GROUP and
            field.message_type.name != name):
          field = None

      if not field:
        raise tokenizer.ParseErrorPreviousToken(
            'Message type "%s" has no field named "%s".' %
            (message_descriptor.full_name, name))

    if field:
      if not self._allow_multiple_scalars and field.containing_oneof:
        # Check if there's a different field set in this oneof.
        # Note that we ignore the case if the same field was set before, and we
        # apply _allow_multiple_scalars to non-scalar fields as well.
        which_oneof = message.WhichOneof(field.containing_oneof.name)
        if which_oneof is not None and which_oneof != field.name:
          raise tokenizer.ParseErrorPreviousToken(
              'Field "%s" is specified along with field "%s", another member '
              'of oneof "%s" for message type "%s".' %
              (field.name, which_oneof, field.containing_oneof.name,
               message_descriptor.full_name))

      if field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_MESSAGE:
        tokenizer.TryConsume(':')
        merger = self._MergeMessageField
      else:
        tokenizer.Consume(':')
        merger = self._MergeScalarField

      if (field.label == descriptor.FieldDescriptor.LABEL_REPEATED and
          tokenizer.TryConsume('[')):
        # Short repeated format, e.g. "foo: [1, 2, 3]"
        if not tokenizer.TryConsume(']'):
          while True:
            merger(tokenizer, message, field)
            if tokenizer.TryConsume(']'):
              break
            tokenizer.Consume(',')

      else:
        merger(tokenizer, message, field)

    else:  # Proto field is unknown.
      assert self.allow_unknown_extension
      _SkipFieldContents(tokenizer)

    # For historical reasons, fields may optionally be separated by commas or
    # semicolons.
    if not tokenizer.TryConsume(','):
      tokenizer.TryConsume(';')

  def _ConsumeAnyTypeUrl(self, tokenizer):
    """Consumes a google.protobuf.Any type URL and returns the type name."""
    # Consume "type.googleapis.com/".
    prefix = [tokenizer.ConsumeIdentifier()]
    tokenizer.Consume('.')
    prefix.append(tokenizer.ConsumeIdentifier())
    tokenizer.Consume('.')
    prefix.append(tokenizer.ConsumeIdentifier())
    tokenizer.Consume('/')
    # Consume the fully-qualified type name.
    name = [tokenizer.ConsumeIdentifier()]
    while tokenizer.TryConsume('.'):
      name.append(tokenizer.ConsumeIdentifier())
    return '.'.join(prefix), '.'.join(name)

  def _MergeMessageField(self, tokenizer, message, field):
    """Merges a single scalar field into a message.

    Args:
      tokenizer: A tokenizer to parse the field value.
      message: The message of which field is a member.
      field: The descriptor of the field to be merged.

    Raises:
      ParseError: In case of text parsing problems.
    """
    is_map_entry = _IsMapEntry(field)

    if tokenizer.TryConsume('<'):
      end_token = '>'
    else:
      tokenizer.Consume('{')
      end_token = '}'

    if field.label == descriptor.FieldDescriptor.LABEL_REPEATED:
      if field.is_extension:
        sub_message = message.Extensions[field].add()
      elif is_map_entry:
        sub_message = getattr(message, field.name).GetEntryClass()()
      else:
        sub_message = getattr(message, field.name).add()
    else:
      if field.is_extension:
        if (not self._allow_multiple_scalars and
            message.HasExtension(field)):
          raise tokenizer.ParseErrorPreviousToken(
              'Message type "%s" should not have multiple "%s" extensions.' %
              (message.DESCRIPTOR.full_name, field.full_name))
        sub_message = message.Extensions[field]
      else:
        # Also apply _allow_multiple_scalars to message field.
        # TODO(jieluo): Change to _allow_singular_overwrites.
        if (not self._allow_multiple_scalars and
            message.HasField(field.name)):
          raise tokenizer.ParseErrorPreviousToken(
              'Message type "%s" should not have multiple "%s" fields.' %
              (message.DESCRIPTOR.full_name, field.name))
        sub_message = getattr(message, field.name)
      sub_message.SetInParent()

    while not tokenizer.TryConsume(end_token):
      if tokenizer.AtEnd():
        raise tokenizer.ParseErrorPreviousToken('Expected "%s".' % (end_token,))
      self._MergeField(tokenizer, sub_message)

    if is_map_entry:
      value_cpptype = field.message_type.fields_by_name['value'].cpp_type
      if value_cpptype == descriptor.FieldDescriptor.CPPTYPE_MESSAGE:
        value = getattr(message, field.name)[sub_message.key]
        value.MergeFrom(sub_message.value)
      else:
        getattr(message, field.name)[sub_message.key] = sub_message.value

  @staticmethod
  def _IsProto3Syntax(message):
    message_descriptor = message.DESCRIPTOR
    return (hasattr(message_descriptor, 'syntax') and
            message_descriptor.syntax == 'proto3')

  def _MergeScalarField(self, tokenizer, message, field):
    """Merges a single scalar field into a message.

    Args:
      tokenizer: A tokenizer to parse the field value.
      message: A protocol message to record the data.
      field: The descriptor of the field to be merged.

    Raises:
      ParseError: In case of text parsing problems.
      RuntimeError: On runtime errors.
    """
    _ = self.allow_unknown_extension
    value = None

    if field.type in (descriptor.FieldDescriptor.TYPE_INT32,
                      descriptor.FieldDescriptor.TYPE_SINT32,
                      descriptor.FieldDescriptor.TYPE_SFIXED32):
      value = _ConsumeInt32(tokenizer)
    elif field.type in (descriptor.FieldDescriptor.TYPE_INT64,
                        descriptor.FieldDescriptor.TYPE_SINT64,
                        descriptor.FieldDescriptor.TYPE_SFIXED64):
      value = _ConsumeInt64(tokenizer)
    elif field.type in (descriptor.FieldDescriptor.TYPE_UINT32,
                        descriptor.FieldDescriptor.TYPE_FIXED32):
      value = _ConsumeUint32(tokenizer)
    elif field.type in (descriptor.FieldDescriptor.TYPE_UINT64,
                        descriptor.FieldDescriptor.TYPE_FIXED64):
      value = _ConsumeUint64(tokenizer)
    elif field.type in (descriptor.FieldDescriptor.TYPE_FLOAT,
                        descriptor.FieldDescriptor.TYPE_DOUBLE):
      value = tokenizer.ConsumeFloat()
    elif field.type == descriptor.FieldDescriptor.TYPE_BOOL:
      value = tokenizer.ConsumeBool()
    elif field.type == descriptor.FieldDescriptor.TYPE_STRING:
      value = tokenizer.ConsumeString()
    elif field.type == descriptor.FieldDescriptor.TYPE_BYTES:
      value = tokenizer.ConsumeByteString()
    elif field.type == descriptor.FieldDescriptor.TYPE_ENUM:
      value = tokenizer.ConsumeEnum(field)
    else:
      raise RuntimeError('Unknown field type %d' % field.type)

    if field.label == descriptor.FieldDescriptor.LABEL_REPEATED:
      if field.is_extension:
        message.Extensions[field].append(value)
      else:
        getattr(message, field.name).append(value)
    else:
      # Proto3 doesn't represent presence so we can't test if multiple scalars
      # have occurred. We have to allow them.
      can_check_presence = not self._IsProto3Syntax(message)
      if field.is_extension:
        if (not self._allow_multiple_scalars and can_check_presence and
            message.HasExtension(field)):
          raise tokenizer.ParseErrorPreviousToken(
              'Message type "%s" should not have multiple "%s" extensions.' %
              (message.DESCRIPTOR.full_name, field.full_name))
        else:
          message.Extensions[field] = value
      else:
        if (not self._allow_multiple_scalars and can_check_presence and
            message.HasField(field.name)):
          raise tokenizer.ParseErrorPreviousToken(
              'Message type "%s" should not have multiple "%s" fields.' %
              (message.DESCRIPTOR.full_name, field.name))
        else:
          setattr(message, field.name, value)


def _SkipFieldContents(tokenizer):
  """Skips over contents (value or message) of a field.

  Args:
    tokenizer: A tokenizer to parse the field name and values.
  """
  # Try to guess the type of this field.
  # If this field is not a message, there should be a ":" between the
  # field name and the field value and also the field value should not
  # start with "{" or "<" which indicates the beginning of a message body.
  # If there is no ":" or there is a "{" or "<" after ":", this field has
  # to be a message or the input is ill-formed.
  if tokenizer.TryConsume(':') and not tokenizer.LookingAt(
      '{') and not tokenizer.LookingAt('<'):
    _SkipFieldValue(tokenizer)
  else:
    _SkipFieldMessage(tokenizer)


def _SkipField(tokenizer):
  """Skips over a complete field (name and value/message).

  Args:
    tokenizer: A tokenizer to parse the field name and values.
  """
  if tokenizer.TryConsume('['):
    # Consume extension name.
    tokenizer.ConsumeIdentifier()
    while tokenizer.TryConsume('.'):
      tokenizer.ConsumeIdentifier()
    tokenizer.Consume(']')
  else:
    tokenizer.ConsumeIdentifierOrNumber()

  _SkipFieldContents(tokenizer)

  # For historical reasons, fields may optionally be separated by commas or
  # semicolons.
  if not tokenizer.TryConsume(','):
    tokenizer.TryConsume(';')


def _SkipFieldMessage(tokenizer):
  """Skips over a field message.

  Args:
    tokenizer: A tokenizer to parse the field name and values.
  """

  if tokenizer.TryConsume('<'):
    delimiter = '>'
  else:
    tokenizer.Consume('{')
    delimiter = '}'

  while not tokenizer.LookingAt('>') and not tokenizer.LookingAt('}'):
    _SkipField(tokenizer)

  tokenizer.Consume(delimiter)


def _SkipFieldValue(tokenizer):
  """Skips over a field value.

  Args:
    tokenizer: A tokenizer to parse the field name and values.

  Raises:
    ParseError: In case an invalid field value is found.
  """
  # String/bytes tokens can come in multiple adjacent string literals.
  # If we can consume one, consume as many as we can.
  if tokenizer.TryConsumeByteString():
    while tokenizer.TryConsumeByteString():
      pass
    return

  if (not tokenizer.TryConsumeIdentifier() and
      not _TryConsumeInt64(tokenizer) and not _TryConsumeUint64(tokenizer) and
      not tokenizer.TryConsumeFloat()):
    raise ParseError('Invalid field value: ' + tokenizer.token)


class Tokenizer(object):
  """Protocol buffer text representation tokenizer.

  This class handles the lower level string parsing by splitting it into
  meaningful tokens.

  It was directly ported from the Java protocol buffer API.
  """

  _WHITESPACE = re.compile(r'\s+')
  _COMMENT = re.compile(r'(\s*#.*$)', re.MULTILINE)
  _WHITESPACE_OR_COMMENT = re.compile(r'(\s|(#.*$))+', re.MULTILINE)
  _TOKEN = re.compile('|'.join([
      r'[a-zA-Z_][0-9a-zA-Z_+-]*',  # an identifier
      r'([0-9+-]|(\.[0-9]))[0-9a-zA-Z_.+-]*',  # a number
  ] + [  # quoted str for each quote mark
      # Avoid backtracking! https://stackoverflow.com/a/844267
      r'{qt}[^{qt}\n\\]*((\\.)+[^{qt}\n\\]*)*({qt}|\\?$)'.format(qt=mark)
      for mark in _QUOTES
  ]))

  _IDENTIFIER = re.compile(r'[^\d\W]\w*')
  _IDENTIFIER_OR_NUMBER = re.compile(r'\w+')

  def __init__(self, lines, skip_comments=True):
    self._position = 0
    self._line = -1
    self._column = 0
    self._token_start = None
    self.token = ''
    self._lines = iter(lines)
    self._current_line = ''
    self._previous_line = 0
    self._previous_column = 0
    self._more_lines = True
    self._skip_comments = skip_comments
    self._whitespace_pattern = (skip_comments and self._WHITESPACE_OR_COMMENT
                                or self._WHITESPACE)
    self._SkipWhitespace()
    self.NextToken()

  def LookingAt(self, token):
    return self.token == token

  def AtEnd(self):
    """Checks the end of the text was reached.

    Returns:
      True iff the end was reached.
    """
    return not self.token

  def _PopLine(self):
    while len(self._current_line) <= self._column:
      try:
        self._current_line = next(self._lines)
      except StopIteration:
        self._current_line = ''
        self._more_lines = False
        return
      else:
        self._line += 1
        self._column = 0

  def _SkipWhitespace(self):
    while True:
      self._PopLine()
      match = self._whitespace_pattern.match(self._current_line, self._column)
      if not match:
        break
      length = len(match.group(0))
      self._column += length

  def TryConsume(self, token):
    """Tries to consume a given piece of text.

    Args:
      token: Text to consume.

    Returns:
      True iff the text was consumed.
    """
    if self.token == token:
      self.NextToken()
      return True
    return False

  def Consume(self, token):
    """Consumes a piece of text.

    Args:
      token: Text to consume.

    Raises:
      ParseError: If the text couldn't be consumed.
    """
    if not self.TryConsume(token):
      raise self.ParseError('Expected "%s".' % token)

  def ConsumeComment(self):
    result = self.token
    if not self._COMMENT.match(result):
      raise self.ParseError('Expected comment.')
    self.NextToken()
    return result

  def ConsumeCommentOrTrailingComment(self):
    """Consumes a comment, returns a 2-tuple (trailing bool, comment str)."""

    # Tokenizer initializes _previous_line and _previous_column to 0. As the
    # tokenizer starts, it looks like there is a previous token on the line.
    just_started = self._line == 0 and self._column == 0

    before_parsing = self._previous_line
    comment = self.ConsumeComment()

    # A trailing comment is a comment on the same line than the previous token.
    trailing = (self._previous_line == before_parsing
                and not just_started)

    return trailing, comment

  def TryConsumeIdentifier(self):
    try:
      self.ConsumeIdentifier()
      return True
    except ParseError:
      return False

  def ConsumeIdentifier(self):
    """Consumes protocol message field identifier.

    Returns:
      Identifier string.

    Raises:
      ParseError: If an identifier couldn't be consumed.
    """
    result = self.token
    if not self._IDENTIFIER.match(result):
      raise self.ParseError('Expected identifier.')
    self.NextToken()
    return result

  def TryConsumeIdentifierOrNumber(self):
    try:
      self.ConsumeIdentifierOrNumber()
      return True
    except ParseError:
      return False

  def ConsumeIdentifierOrNumber(self):
    """Consumes protocol message field identifier.

    Returns:
      Identifier string.

    Raises:
      ParseError: If an identifier couldn't be consumed.
    """
    result = self.token
    if not self._IDENTIFIER_OR_NUMBER.match(result):
      raise self.ParseError('Expected identifier or number, got %s.' % result)
    self.NextToken()
    return result

  def TryConsumeInteger(self):
    try:
      # Note: is_long only affects value type, not whether an error is raised.
      self.ConsumeInteger()
      return True
    except ParseError:
      return False

  def ConsumeInteger(self, is_long=False):
    """Consumes an integer number.

    Args:
      is_long: True if the value should be returned as a long integer.
    Returns:
      The integer parsed.

    Raises:
      ParseError: If an integer couldn't be consumed.
    """
    try:
      result = _ParseAbstractInteger(self.token, is_long=is_long)
    except ValueError as e:
      raise self.ParseError(str(e))
    self.NextToken()
    return result

  def TryConsumeFloat(self):
    try:
      self.ConsumeFloat()
      return True
    except ParseError:
      return False

  def ConsumeFloat(self):
    """Consumes an floating point number.

    Returns:
      The number parsed.

    Raises:
      ParseError: If a floating point number couldn't be consumed.
    """
    try:
      result = ParseFloat(self.token)
    except ValueError as e:
      raise self.ParseError(str(e))
    self.NextToken()
    return result

  def ConsumeBool(self):
    """Consumes a boolean value.

    Returns:
      The bool parsed.

    Raises:
      ParseError: If a boolean value couldn't be consumed.
    """
    try:
      result = ParseBool(self.token)
    except ValueError as e:
      raise self.ParseError(str(e))
    self.NextToken()
    return result

  def TryConsumeByteString(self):
    try:
      self.ConsumeByteString()
      return True
    except ParseError:
      return False

  def ConsumeString(self):
    """Consumes a string value.

    Returns:
      The string parsed.

    Raises:
      ParseError: If a string value couldn't be consumed.
    """
    the_bytes = self.ConsumeByteString()
    try:
      return six.text_type(the_bytes, 'utf-8')
    except UnicodeDecodeError as e:
      raise self._StringParseError(e)

  def ConsumeByteString(self):
    """Consumes a byte array value.

    Returns:
      The array parsed (as a string).

    Raises:
      ParseError: If a byte array value couldn't be consumed.
    """
    the_list = [self._ConsumeSingleByteString()]
    while self.token and self.token[0] in _QUOTES:
      the_list.append(self._ConsumeSingleByteString())
    return b''.join(the_list)

  def _ConsumeSingleByteString(self):
    """Consume one token of a string literal.

    String literals (whether bytes or text) can come in multiple adjacent
    tokens which are automatically concatenated, like in C or Python.  This
    method only consumes one token.

    Returns:
      The token parsed.
    Raises:
      ParseError: When the wrong format data is found.
    """
    text = self.token
    if len(text) < 1 or text[0] not in _QUOTES:
      raise self.ParseError('Expected string but found: %r' % (text,))

    if len(text) < 2 or text[-1] != text[0]:
      raise self.ParseError('String missing ending quote: %r' % (text,))

    try:
      result = text_encoding.CUnescape(text[1:-1])
    except ValueError as e:
      raise self.ParseError(str(e))
    self.NextToken()
    return result

  def ConsumeEnum(self, field):
    try:
      result = ParseEnum(field, self.token)
    except ValueError as e:
      raise self.ParseError(str(e))
    self.NextToken()
    return result

  def ParseErrorPreviousToken(self, message):
    """Creates and *returns* a ParseError for the previously read token.

    Args:
      message: A message to set for the exception.

    Returns:
      A ParseError instance.
    """
    return ParseError(message, self._previous_line + 1,
                      self._previous_column + 1)

  def ParseError(self, message):
    """Creates and *returns* a ParseError for the current token."""
    return ParseError('\'' + self._current_line + '\': ' + message,
                      self._line + 1, self._column + 1)

  def _StringParseError(self, e):
    return self.ParseError('Couldn\'t parse string: ' + str(e))

  def NextToken(self):
    """Reads the next meaningful token."""
    self._previous_line = self._line
    self._previous_column = self._column

    self._column += len(self.token)
    self._SkipWhitespace()

    if not self._more_lines:
      self.token = ''
      return

    match = self._TOKEN.match(self._current_line, self._column)
    if not match and not self._skip_comments:
      match = self._COMMENT.match(self._current_line, self._column)
    if match:
      token = match.group(0)
      self.token = token
    else:
      self.token = self._current_line[self._column]

# Aliased so it can still be accessed by current visibility violators.
# TODO(dbarnett): Migrate violators to textformat_tokenizer.
_Tokenizer = Tokenizer  # pylint: disable=invalid-name


def _ConsumeInt32(tokenizer):
  """Consumes a signed 32bit integer number from tokenizer.

  Args:
    tokenizer: A tokenizer used to parse the number.

  Returns:
    The integer parsed.

  Raises:
    ParseError: If a signed 32bit integer couldn't be consumed.
  """
  return _ConsumeInteger(tokenizer, is_signed=True, is_long=False)


def _ConsumeUint32(tokenizer):
  """Consumes an unsigned 32bit integer number from tokenizer.

  Args:
    tokenizer: A tokenizer used to parse the number.

  Returns:
    The integer parsed.

  Raises:
    ParseError: If an unsigned 32bit integer couldn't be consumed.
  """
  return _ConsumeInteger(tokenizer, is_signed=False, is_long=False)


def _TryConsumeInt64(tokenizer):
  try:
    _ConsumeInt64(tokenizer)
    return True
  except ParseError:
    return False


def _ConsumeInt64(tokenizer):
  """Consumes a signed 32bit integer number from tokenizer.

  Args:
    tokenizer: A tokenizer used to parse the number.

  Returns:
    The integer parsed.

  Raises:
    ParseError: If a signed 32bit integer couldn't be consumed.
  """
  return _ConsumeInteger(tokenizer, is_signed=True, is_long=True)


def _TryConsumeUint64(tokenizer):
  try:
    _ConsumeUint64(tokenizer)
    return True
  except ParseError:
    return False


def _ConsumeUint64(tokenizer):
  """Consumes an unsigned 64bit integer number from tokenizer.

  Args:
    tokenizer: A tokenizer used to parse the number.

  Returns:
    The integer parsed.

  Raises:
    ParseError: If an unsigned 64bit integer couldn't be consumed.
  """
  return _ConsumeInteger(tokenizer, is_signed=False, is_long=True)


def _TryConsumeInteger(tokenizer, is_signed=False, is_long=False):
  try:
    _ConsumeInteger(tokenizer, is_signed=is_signed, is_long=is_long)
    return True
  except ParseError:
    return False


def _ConsumeInteger(tokenizer, is_signed=False, is_long=False):
  """Consumes an integer number from tokenizer.

  Args:
    tokenizer: A tokenizer used to parse the number.
    is_signed: True if a signed integer must be parsed.
    is_long: True if a long integer must be parsed.

  Returns:
    The integer parsed.

  Raises:
    ParseError: If an integer with given characteristics couldn't be consumed.
  """
  try:
    result = ParseInteger(tokenizer.token, is_signed=is_signed, is_long=is_long)
  except ValueError as e:
    raise tokenizer.ParseError(str(e))
  tokenizer.NextToken()
  return result


def ParseInteger(text, is_signed=False, is_long=False):
  """Parses an integer.

  Args:
    text: The text to parse.
    is_signed: True if a signed integer must be parsed.
    is_long: True if a long integer must be parsed.

  Returns:
    The integer value.

  Raises:
    ValueError: Thrown Iff the text is not a valid integer.
  """
  # Do the actual parsing. Exception handling is propagated to caller.
  result = _ParseAbstractInteger(text, is_long=is_long)

  # Check if the integer is sane. Exceptions handled by callers.
  checker = _INTEGER_CHECKERS[2 * int(is_long) + int(is_signed)]
  checker.CheckValue(result)
  return result


def _ParseAbstractInteger(text, is_long=False):
  """Parses an integer without checking size/signedness.

  Args:
    text: The text to parse.
    is_long: True if the value should be returned as a long integer.

  Returns:
    The integer value.

  Raises:
    ValueError: Thrown Iff the text is not a valid integer.
  """
  # Do the actual parsing. Exception handling is propagated to caller.
  orig_text = text
  c_octal_match = re.match(r'(-?)0(\d+)$', text)
  if c_octal_match:
    # Python 3 no longer supports 0755 octal syntax without the 'o', so
    # we always use the '0o' prefix for multi-digit numbers starting with 0.
    text = c_octal_match.group(1) + '0o' + c_octal_match.group(2)
  try:
    # We force 32-bit values to int and 64-bit values to long to make
    # alternate implementations where the distinction is more significant
    # (e.g. the C++ implementation) simpler.
    if is_long:
      return long(text, 0)
    else:
      return int(text, 0)
  except ValueError:
    raise ValueError('Couldn\'t parse integer: %s' % orig_text)


def ParseFloat(text):
  """Parse a floating point number.

  Args:
    text: Text to parse.

  Returns:
    The number parsed.

  Raises:
    ValueError: If a floating point number couldn't be parsed.
  """
  try:
    # Assume Python compatible syntax.
    return float(text)
  except ValueError:
    # Check alternative spellings.
    if _FLOAT_INFINITY.match(text):
      if text[0] == '-':
        return float('-inf')
      else:
        return float('inf')
    elif _FLOAT_NAN.match(text):
      return float('nan')
    else:
      # assume '1.0f' format
      try:
        return float(text.rstrip('f'))
      except ValueError:
        raise ValueError('Couldn\'t parse float: %s' % text)


def ParseBool(text):
  """Parse a boolean value.

  Args:
    text: Text to parse.

  Returns:
    Boolean values parsed

  Raises:
    ValueError: If text is not a valid boolean.
  """
  if text in ('true', 't', '1', 'True'):
    return True
  elif text in ('false', 'f', '0', 'False'):
    return False
  else:
    raise ValueError('Expected "true" or "false".')


def ParseEnum(field, value):
  """Parse an enum value.

  The value can be specified by a number (the enum value), or by
  a string literal (the enum name).

  Args:
    field: Enum field descriptor.
    value: String value.

  Returns:
    Enum value number.

  Raises:
    ValueError: If the enum value could not be parsed.
  """
  enum_descriptor = field.enum_type
  try:
    number = int(value, 0)
  except ValueError:
    # Identifier.
    enum_value = enum_descriptor.values_by_name.get(value, None)
    if enum_value is None:
      raise ValueError('Enum type "%s" has no value named %s.' %
                       (enum_descriptor.full_name, value))
  else:
    # Numeric value.
    if hasattr(field.file, 'syntax'):
      # Attribute is checked for compatibility.
      if field.file.syntax == 'proto3':
        # Proto3 accept numeric unknown enums.
        return number
    enum_value = enum_descriptor.values_by_number.get(number, None)
    if enum_value is None:
      raise ValueError('Enum type "%s" has no value with number %d.' %
                       (enum_descriptor.full_name, number))
  return enum_value.number