xref: /external/protobuf/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 (at] google.com (Kenton Varda)'

import io
import re

import six

if six.PY3:
  long = int

from google.protobuf.internal import type_checkers
from google.protobuf import descriptor
from google.protobuf import text_encoding

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


_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(("'", '"'))


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


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


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,
                    pointy_brackets=False, use_index_order=False,
                    float_format=None, use_field_number=False):
  """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: Produce text output in UTF8 format.
    as_one_line: Don't introduce newlines between fields.
    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.

  Returns:
    A string of the text formatted protocol buffer message.
  """
  out = TextWriter(as_utf8)
  printer = _Printer(out, 0, as_utf8, as_one_line,
                     pointy_brackets, use_index_order, float_format,
                     use_field_number)
  printer.PrintMessage(message)
  result = out.getvalue()
  out.close()
  if as_one_line:
    return result.rstrip()
  return result


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


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


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


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

  def __init__(self, out, indent=0, as_utf8=False, as_one_line=False,
               pointy_brackets=False, use_index_order=False, float_format=None,
               use_field_number=False):
    """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: Produce text output in UTF8 format.
      as_one_line: Don't introduce newlines between fields.
      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.
    """
    self.out = out
    self.indent = indent
    self.as_utf8 = as_utf8
    self.as_one_line = as_one_line
    self.pointy_brackets = pointy_brackets
    self.use_index_order = use_index_order
    self.float_format = float_format
    self.use_field_number = use_field_number

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

    Args:
      message: The protocol buffers message.
    """
    fields = message.ListFields()
    if self.use_index_order:
      fields.sort(key=lambda x: x[0].index)
    for field, value in fields:
      if _IsMapEntry(field):
        for key in sorted(value):
          # This is slow for maps with submessage entires 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 = field.message_type._concrete_class(
              key=key, value=value[key])
          self.PrintField(field, entry_submsg)
      elif field.label == descriptor.FieldDescriptor.LABEL_REPEATED:
        for element in value:
          self.PrintField(field, element)
      else:
        self.PrintField(field, value)

  def PrintField(self, field, value):
    """Print a single field name/value pair."""
    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(': ')

    self.PrintFieldValue(field, value)
    if self.as_one_line:
      out.write(' ')
    else:
      out.write('\n')

  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 self.pointy_brackets:
      openb = '<'
      closeb = '>'
    else:
      openb = '{'
      closeb = '}'

    if field.cpp_type == descriptor.FieldDescriptor.CPPTYPE_MESSAGE:
      if self.as_one_line:
        out.write(' %s ' % openb)
        self.PrintMessage(value)
        out.write(closeb)
      else:
        out.write(' %s\n' % openb)
        self.indent += 2
        self.PrintMessage(value)
        self.indent -= 2
        out.write(' ' * self.indent + closeb)
    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):
        out_value = value.encode('utf-8')
      else:
        out_value = value
      if field.type == descriptor.FieldDescriptor.TYPE_BYTES:
        # We need to escape non-UTF8 chars in TYPE_BYTES field.
        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):
  """Parses an text representation of a protocol message into a message.

  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.

  Returns:
    The same message passed as argument.

  Raises:
    ParseError: On text parsing problems.
  """
  if not isinstance(text, str):
    text = text.decode('utf-8')
  return ParseLines(text.split('\n'), message, allow_unknown_extension,
                    allow_field_number)


def Merge(text, message, allow_unknown_extension=False,
          allow_field_number=False):
  """Parses an 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.

  Returns:
    The same message passed as argument.

  Raises:
    ParseError: On text parsing problems.
  """
  return MergeLines(text.split('\n'), message, allow_unknown_extension,
                    allow_field_number)


def ParseLines(lines, message, allow_unknown_extension=False,
               allow_field_number=False):
  """Parses an 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.

  Returns:
    The same message passed as argument.

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


def MergeLines(lines, message, allow_unknown_extension=False,
               allow_field_number=False):
  """Parses an 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.

  Returns:
    The same message passed as argument.

  Raises:
    ParseError: On text parsing problems.
  """
  parser = _Parser(allow_unknown_extension, allow_field_number)
  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):
    self.allow_unknown_extension = allow_unknown_extension
    self.allow_field_number = allow_field_number

  def ParseFromString(self, text, message):
    """Parses an text representation of a protocol message into a message."""
    if not isinstance(text, str):
      text = text.decode('utf-8')
    return self.ParseLines(text.split('\n'), message)

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

  def MergeFromString(self, text, message):
    """Merges an text representation of a protocol message into a message."""
    return self._MergeLines(text.split('\n'), message)

  def MergeLines(self, lines, message):
    """Merges an 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 an 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.
    """
    tokenizer = _Tokenizer(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 (hasattr(message_descriptor, 'syntax') and
        message_descriptor.syntax == 'proto3'):
      # Proto3 doesn't represent presence so we can't test if multiple
      # scalars have occurred.  We have to allow them.
      self._allow_multiple_scalars = True
    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.' % 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.ConsumeIdentifier()
      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]"
        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 _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:
        # pylint: disable=protected-access
        sub_message = field.message_type._concrete_class()
      else:
        sub_message = getattr(message, field.name).add()
    else:
      if field.is_extension:
        sub_message = message.Extensions[field]
      else:
        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

  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 = tokenizer.ConsumeInt32()
    elif field.type in (descriptor.FieldDescriptor.TYPE_INT64,
                        descriptor.FieldDescriptor.TYPE_SINT64,
                        descriptor.FieldDescriptor.TYPE_SFIXED64):
      value = tokenizer.ConsumeInt64()
    elif field.type in (descriptor.FieldDescriptor.TYPE_UINT32,
                        descriptor.FieldDescriptor.TYPE_FIXED32):
      value = tokenizer.ConsumeUint32()
    elif field.type in (descriptor.FieldDescriptor.TYPE_UINT64,
                        descriptor.FieldDescriptor.TYPE_FIXED64):
      value = tokenizer.ConsumeUint64()
    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:
      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))
        else:
          message.Extensions[field] = value
      else:
        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))
        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.ConsumeIdentifier()

  _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 tokenizer.TryConsumeInt64() and
      not tokenizer.TryConsumeUint64() 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('(\\s|(#.*$))+', re.MULTILINE)
  _TOKEN = re.compile('|'.join([
      r'[a-zA-Z_][0-9a-zA-Z_+-]*',             # an identifier
      r'([0-9+-]|(\.[0-9]))[0-9a-zA-Z_.+-]*',  # a number
  ] + [                                        # quoted str for each quote mark
      r'{qt}([^{qt}\n\\]|\\.)*({qt}|\\?$)'.format(qt=mark) for mark in _QUOTES
  ]))

  _IDENTIFIER = re.compile(r'\w+')

  def __init__(self, lines):
    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._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.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 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 ConsumeInt32(self):
    """Consumes a signed 32bit integer number.

    Returns:
      The integer parsed.

    Raises:
      ParseError: If a signed 32bit integer couldn't be consumed.
    """
    try:
      result = ParseInteger(self.token, is_signed=True, is_long=False)
    except ValueError as e:
      raise self._ParseError(str(e))
    self.NextToken()
    return result

  def ConsumeUint32(self):
    """Consumes an unsigned 32bit integer number.

    Returns:
      The integer parsed.

    Raises:
      ParseError: If an unsigned 32bit integer couldn't be consumed.
    """
    try:
      result = ParseInteger(self.token, is_signed=False, is_long=False)
    except ValueError as e:
      raise self._ParseError(str(e))
    self.NextToken()
    return result

  def TryConsumeInt64(self):
    try:
      self.ConsumeInt64()
      return True
    except ParseError:
      return False

  def ConsumeInt64(self):
    """Consumes a signed 64bit integer number.

    Returns:
      The integer parsed.

    Raises:
      ParseError: If a signed 64bit integer couldn't be consumed.
    """
    try:
      result = ParseInteger(self.token, is_signed=True, is_long=True)
    except ValueError as e:
      raise self._ParseError(str(e))
    self.NextToken()
    return result

  def TryConsumeUint64(self):
    try:
      self.ConsumeUint64()
      return True
    except ParseError:
      return False

  def ConsumeUint64(self):
    """Consumes an unsigned 64bit integer number.

    Returns:
      The integer parsed.

    Raises:
      ParseError: If an unsigned 64bit integer couldn't be consumed.
    """
    try:
      result = ParseInteger(self.token, is_signed=False, is_long=True)
    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('%d:%d : %s' % (
        self._previous_line + 1, self._previous_column + 1, message))

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

  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 match:
      token = match.group(0)
      self.token = token
    else:
      self.token = self._current_line[self._column]


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.
  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:
      result = long(text, 0)
    else:
      result = int(text, 0)
  except ValueError:
    raise ValueError('Couldn\'t parse integer: %s' % text)

  # 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 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'):
    return True
  elif text in ('false', 'f', '0'):
    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.
    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