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# 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
from collections import deque
import copy
import functools
import re
# 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 positional 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 str(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 str(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)))
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)
def get_field(request, field):
"""Get the value of a field from a given dictionary.
Args:
request (dict | Message): A dictionary or a Message object.
field (str): The key to the request in dot notation.
Returns:
The value of the field.
"""
parts = field.split(".")
value = request
for part in parts:
if not isinstance(value, dict):
value = getattr(value, part, None)
else:
value = value.get(part)
if isinstance(value, dict):
return
return value
def delete_field(request, field):
"""Delete the value of a field from a given dictionary.
Args:
request (dict | Message): A dictionary object or a Message.
field (str): The key to the request in dot notation.
"""
parts = deque(field.split("."))
while len(parts) > 1:
part = parts.popleft()
if not isinstance(request, dict):
if hasattr(request, part):
request = getattr(request, part, None)
else:
return
else:
request = request.get(part)
part = parts.popleft()
if not isinstance(request, dict):
if hasattr(request, part):
request.ClearField(part)
else:
return
else:
request.pop(part, None)
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
def transcode(http_options, message=None, **request_kwargs):
"""Transcodes a grpc request pattern into a proper HTTP request following the rules outlined here,
https://github.com/googleapis/googleapis/blob/master/google/api/http.proto#L44-L312
Args:
http_options (list(dict)): A list of dicts which consist of these keys,
'method' (str): The http method
'uri' (str): The path template
'body' (str): The body field name (optional)
(This is a simplified representation of the proto option `google.api.http`)
message (Message) : A request object (optional)
request_kwargs (dict) : A dict representing the request object
Returns:
dict: The transcoded request with these keys,
'method' (str) : The http method
'uri' (str) : The expanded uri
'body' (dict | Message) : A dict or a Message representing the body (optional)
'query_params' (dict | Message) : A dict or Message mapping query parameter variables and values
Raises:
ValueError: If the request does not match the given template.
"""
transcoded_value = message or request_kwargs
bindings = []
for http_option in http_options:
request = {}
# Assign path
uri_template = http_option["uri"]
fields = [
(m.group("name"), m.group("template"))
for m in _VARIABLE_RE.finditer(uri_template)
]
bindings.append((uri_template, fields))
path_args = {field: get_field(transcoded_value, field) for field, _ in fields}
request["uri"] = expand(uri_template, **path_args)
if not validate(uri_template, request["uri"]) or not all(path_args.values()):
continue
# Remove fields used in uri path from request
leftovers = copy.deepcopy(transcoded_value)
for path_field, _ in fields:
delete_field(leftovers, path_field)
# Assign body and query params
body = http_option.get("body")
if body:
if body == "*":
request["body"] = leftovers
if message:
request["query_params"] = message.__class__()
else:
request["query_params"] = {}
else:
try:
if message:
request["body"] = getattr(leftovers, body)
delete_field(leftovers, body)
else:
request["body"] = leftovers.pop(body)
except (KeyError, AttributeError):
continue
request["query_params"] = leftovers
else:
request["query_params"] = leftovers
request["method"] = http_option["method"]
return request
bindings_description = [
'\n\tURI: "{}"'
"\n\tRequired request fields:\n\t\t{}".format(
uri,
"\n\t\t".join(
[
'field: "{}", pattern: "{}"'.format(n, p if p else "*")
for n, p in fields
]
),
)
for uri, fields in bindings
]
raise ValueError(
"Invalid request."
"\nSome of the fields of the request message are either not initialized or "
"initialized with an invalid value."
"\nPlease make sure your request matches at least one accepted HTTP binding."
"\nTo match a binding the request message must have all the required fields "
"initialized with values matching their patterns as listed below:{}".format(
"\n".join(bindings_description)
)
)