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# Copyright 2021 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.
"""Helpers for server-side streaming in REST."""
from collections import deque
import string
from typing import Deque, Union
import proto
import requests
import google.protobuf.message
from google.protobuf.json_format import Parse
class ResponseIterator:
"""Iterator over REST API responses.
Args:
response (requests.Response): An API response object.
response_message_cls (Union[proto.Message, google.protobuf.message.Message]): A response
class expected to be returned from an API.
Raises:
ValueError: If `response_message_cls` is not a subclass of `proto.Message` or `google.protobuf.message.Message`.
"""
def __init__(
self,
response: requests.Response,
response_message_cls: Union[proto.Message, google.protobuf.message.Message],
):
self._response = response
self._response_message_cls = response_message_cls
# Inner iterator over HTTP response's content.
self._response_itr = self._response.iter_content(decode_unicode=True)
# Contains a list of JSON responses ready to be sent to user.
self._ready_objs: Deque[str] = deque()
# Current JSON response being built.
self._obj = ""
# Keeps track of the nesting level within a JSON object.
self._level = 0
# Keeps track whether HTTP response is currently sending values
# inside of a string value.
self._in_string = False
# Whether an escape symbol "\" was encountered.
self._escape_next = False
def cancel(self):
"""Cancel existing streaming operation."""
self._response.close()
def _process_chunk(self, chunk: str):
if self._level == 0:
if chunk[0] != "[":
raise ValueError(
"Can only parse array of JSON objects, instead got %s" % chunk
)
for char in chunk:
if char == "{":
if self._level == 1:
# Level 1 corresponds to the outermost JSON object
# (i.e. the one we care about).
self._obj = ""
if not self._in_string:
self._level += 1
self._obj += char
elif char == "}":
self._obj += char
if not self._in_string:
self._level -= 1
if not self._in_string and self._level == 1:
self._ready_objs.append(self._obj)
elif char == '"':
# Helps to deal with an escaped quotes inside of a string.
if not self._escape_next:
self._in_string = not self._in_string
self._obj += char
elif char in string.whitespace:
if self._in_string:
self._obj += char
elif char == "[":
if self._level == 0:
self._level += 1
else:
self._obj += char
elif char == "]":
if self._level == 1:
self._level -= 1
else:
self._obj += char
else:
self._obj += char
self._escape_next = not self._escape_next if char == "\\" else False
def __next__(self):
while not self._ready_objs:
try:
chunk = next(self._response_itr)
self._process_chunk(chunk)
except StopIteration as e:
if self._level > 0:
raise ValueError("Unfinished stream: %s" % self._obj)
raise e
return self._grab()
def _grab(self):
# Add extra quotes to make json.loads happy.
if issubclass(self._response_message_cls, proto.Message):
return self._response_message_cls.from_json(self._ready_objs.popleft())
elif issubclass(self._response_message_cls, google.protobuf.message.Message):
return Parse(self._ready_objs.popleft(), self._response_message_cls())
else:
raise ValueError(
"Response message class must be a subclass of proto.Message or google.protobuf.message.Message."
)
def __iter__(self):
return self