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Source code for google.api_core.path_template
# Copyright 2017 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Expand and validate URL path templates.
This module provides the :func:`expand` and :func:`validate` functions for
interacting with Google-style URL `path templates`_ which are commonly used
in Google APIs for `resource names`_.
.. _path templates: https://github.com/googleapis/googleapis/blob
/57e2d376ac7ef48681554204a3ba78a414f2c533/google/api/http.proto#L212
.. _resource names: https://cloud.google.com/apis/design/resource_names
"""
from __future__ import unicode_literals
import functools
import re
import six
# Regular expression for extracting variable parts from a path template.
# The variables can be expressed as:
#
# - "*": a single-segment positional variable, for example: "books/*"
# - "**": a multi-segment positional variable, for example: "shelf/**/book/*"
# - "{name}": a single-segment wildcard named variable, for example
# "books/{name}"
# - "{name=*}: same as above.
# - "{name=**}": a multi-segment wildcard named variable, for example
# "shelf/{name=**}"
# - "{name=/path/*/**}": a multi-segment named variable with a sub-template.
_VARIABLE_RE = re.compile(
r"""
( # Capture the entire variable expression
(?P<positional>\*\*?) # Match & capture * and ** positional variables.
|
# Match & capture named variables {name}
{
(?P<name>[^/]+?)
# Optionally match and capture the named variable's template.
(?:=(?P<template>.+?))?
}
)
""",
re.VERBOSE,
)
# Segment expressions used for validating paths against a template.
_SINGLE_SEGMENT_PATTERN = r"([^/]+)"
_MULTI_SEGMENT_PATTERN = r"(.+)"
def _expand_variable_match(positional_vars, named_vars, match):
"""Expand a matched variable with its value.
Args:
positional_vars (list): A list of positonal variables. This list will
be modified.
named_vars (dict): A dictionary of named variables.
match (re.Match): A regular expression match.
Returns:
str: The expanded variable to replace the match.
Raises:
ValueError: If a positional or named variable is required by the
template but not specified or if an unexpected template expression
is encountered.
"""
positional = match.group("positional")
name = match.group("name")
if name is not None:
try:
return six.text_type(named_vars[name])
except KeyError:
raise ValueError(
"Named variable '{}' not specified and needed by template "
"`{}` at position {}".format(name, match.string, match.start())
)
elif positional is not None:
try:
return six.text_type(positional_vars.pop(0))
except IndexError:
raise ValueError(
"Positional variable not specified and needed by template "
"`{}` at position {}".format(match.string, match.start())
)
else:
raise ValueError("Unknown template expression {}".format(match.group(0)))
[docs]def expand(tmpl, *args, **kwargs):
"""Expand a path template with the given variables.
..code-block:: python
>>> expand('users/*/messages/*', 'me', '123')
users/me/messages/123
>>> expand('/v1/{name=shelves/*/books/*}', name='shelves/1/books/3')
/v1/shelves/1/books/3
Args:
tmpl (str): The path template.
args: The positional variables for the path.
kwargs: The named variables for the path.
Returns:
str: The expanded path
Raises:
ValueError: If a positional or named variable is required by the
template but not specified or if an unexpected template expression
is encountered.
"""
replacer = functools.partial(_expand_variable_match, list(args), kwargs)
return _VARIABLE_RE.sub(replacer, tmpl)
def _replace_variable_with_pattern(match):
"""Replace a variable match with a pattern that can be used to validate it.
Args:
match (re.Match): A regular expression match
Returns:
str: A regular expression pattern that can be used to validate the
variable in an expanded path.
Raises:
ValueError: If an unexpected template expression is encountered.
"""
positional = match.group("positional")
name = match.group("name")
template = match.group("template")
if name is not None:
if not template:
return _SINGLE_SEGMENT_PATTERN.format(name)
elif template == "**":
return _MULTI_SEGMENT_PATTERN.format(name)
else:
return _generate_pattern_for_template(template)
elif positional == "*":
return _SINGLE_SEGMENT_PATTERN
elif positional == "**":
return _MULTI_SEGMENT_PATTERN
else:
raise ValueError("Unknown template expression {}".format(match.group(0)))
def _generate_pattern_for_template(tmpl):
"""Generate a pattern that can validate a path template.
Args:
tmpl (str): The path template
Returns:
str: A regular expression pattern that can be used to validate an
expanded path template.
"""
return _VARIABLE_RE.sub(_replace_variable_with_pattern, tmpl)
[docs]def validate(tmpl, path):
"""Validate a path against the path template.
.. code-block:: python
>>> validate('users/*/messages/*', 'users/me/messages/123')
True
>>> validate('users/*/messages/*', 'users/me/drafts/123')
False
>>> validate('/v1/{name=shelves/*/books/*}', /v1/shelves/1/books/3)
True
>>> validate('/v1/{name=shelves/*/books/*}', /v1/shelves/1/tapes/3)
False
Args:
tmpl (str): The path template.
path (str): The expanded path.
Returns:
bool: True if the path matches.
"""
pattern = _generate_pattern_for_template(tmpl) + "$"
return True if re.match(pattern, path) is not None else False
