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# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
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# http://www.apache.org/licenses/LICENSE-2.0
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"""``PTransform`` for reading from and writing to Web APIs."""
import abc
import concurrent.futures
import contextlib
import logging
import sys
from typing import Generic
from typing import Optional
from typing import TypeVar
import apache_beam as beam
from apache_beam.pvalue import PCollection
RequestT = TypeVar('RequestT')
ResponseT = TypeVar('ResponseT')
DEFAULT_TIMEOUT_SECS = 30 # seconds
_LOGGER = logging.getLogger(__name__)
[docs]class UserCodeExecutionException(Exception):
"""Base class for errors related to calling Web APIs."""
[docs]class UserCodeQuotaException(UserCodeExecutionException):
"""Extends ``UserCodeExecutionException`` to signal specifically that
the Web API client encountered a Quota or API overuse related error.
"""
[docs]class UserCodeTimeoutException(UserCodeExecutionException):
"""Extends ``UserCodeExecutionException`` to signal a user code timeout."""
[docs]class Caller(contextlib.AbstractContextManager, abc.ABC):
"""Interface for user custom code intended for API calls.
For setup and teardown of clients when applicable, implement the
``__enter__`` and ``__exit__`` methods respectively."""
@abc.abstractmethod
def __call__(self, request: RequestT, *args, **kwargs) -> ResponseT:
"""Calls a Web API with the ``RequestT`` and returns a
``ResponseT``. ``RequestResponseIO`` expects implementations of the
``__call__`` method to throw either a ``UserCodeExecutionException``,
``UserCodeQuotaException``, or ``UserCodeTimeoutException``.
"""
pass
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
return None
[docs]class ShouldBackOff(abc.ABC):
"""
ShouldBackOff provides mechanism to apply adaptive throttling.
"""
pass
[docs]class Repeater(abc.ABC):
"""Repeater provides mechanism to repeat requests for a
configurable condition."""
pass
[docs]class CacheReader(abc.ABC):
"""CacheReader provides mechanism to read from the cache."""
pass
[docs]class CacheWriter(abc.ABC):
"""CacheWriter provides mechanism to write to the cache."""
pass
[docs]class PreCallThrottler(abc.ABC):
"""PreCallThrottler provides a throttle mechanism before sending request."""
pass
[docs]class RequestResponseIO(beam.PTransform[beam.PCollection[RequestT],
beam.PCollection[ResponseT]]):
"""A :class:`RequestResponseIO` transform to read and write to APIs.
Processes an input :class:`~apache_beam.pvalue.PCollection` of requests
by making a call to the API as defined in :class:`Caller`'s `__call__`
and returns a :class:`~apache_beam.pvalue.PCollection` of responses.
"""
def __init__(
self,
caller: [Caller],
timeout: Optional[float] = DEFAULT_TIMEOUT_SECS,
should_backoff: Optional[ShouldBackOff] = None,
repeater: Optional[Repeater] = None,
cache_reader: Optional[CacheReader] = None,
cache_writer: Optional[CacheWriter] = None,
throttler: Optional[PreCallThrottler] = None,
):
"""
Instantiates a RequestResponseIO transform.
Args:
caller (~apache_beam.io.requestresponseio.Caller): an implementation of
`Caller` object that makes call to the API.
timeout (float): timeout value in seconds to wait for response from API.
should_backoff (~apache_beam.io.requestresponseio.ShouldBackOff):
(Optional) provides methods for backoff.
repeater (~apache_beam.io.requestresponseio.Repeater): (Optional)
provides methods to repeat requests to API.
cache_reader (~apache_beam.io.requestresponseio.CacheReader): (Optional)
provides methods to read external cache.
cache_writer (~apache_beam.io.requestresponseio.CacheWriter): (Optional)
provides methods to write to external cache.
throttler (~apache_beam.io.requestresponseio.PreCallThrottler):
(Optional) provides methods to pre-throttle a request.
"""
self._caller = caller
self._timeout = timeout
self._should_backoff = should_backoff
self._repeater = repeater
self._cache_reader = cache_reader
self._cache_writer = cache_writer
self._throttler = throttler
[docs] def expand(self, requests: PCollection[RequestT]) -> PCollection[ResponseT]:
# TODO(riteshghorse): add Cache and Throttle PTransforms.
return requests | _Call(
caller=self._caller,
timeout=self._timeout,
should_backoff=self._should_backoff,
repeater=self._repeater)
class _Call(beam.PTransform[beam.PCollection[RequestT],
beam.PCollection[ResponseT]]):
"""(Internal-only) PTransform that invokes a remote function on each element
of the input PCollection.
This PTransform uses a `Caller` object to invoke the actual API calls,
and uses ``__enter__`` and ``__exit__`` to manage setup and teardown of
clients when applicable. Additionally, a timeout value is specified to
regulate the duration of each call, defaults to 30 seconds.
Args:
caller (:class:`apache_beam.io.requestresponseio.Caller`): a callable
object that invokes API call.
timeout (float): timeout value in seconds to wait for response from API.
"""
def __init__(
self,
caller: Caller,
timeout: Optional[float] = DEFAULT_TIMEOUT_SECS,
should_backoff: Optional[ShouldBackOff] = None,
repeater: Optional[Repeater] = None,
):
"""Initialize the _Call transform.
Args:
caller (:class:`apache_beam.io.requestresponseio.Caller`): a callable
object that invokes API call.
timeout (float): timeout value in seconds to wait for response from API.
should_backoff (~apache_beam.io.requestresponseio.ShouldBackOff):
(Optional) provides methods for backoff.
repeater (~apache_beam.io.requestresponseio.Repeater): (Optional) provides
methods to repeat requests to API.
"""
self._caller = caller
self._timeout = timeout
self._should_backoff = should_backoff
self._repeater = repeater
def expand(
self,
requests: beam.PCollection[RequestT]) -> beam.PCollection[ResponseT]:
return requests | beam.ParDo(_CallDoFn(self._caller, self._timeout))
class _CallDoFn(beam.DoFn, Generic[RequestT, ResponseT]):
def setup(self):
self._caller.__enter__()
def __init__(self, caller: Caller, timeout: float):
self._caller = caller
self._timeout = timeout
def process(self, request, *args, **kwargs):
with concurrent.futures.ThreadPoolExecutor() as executor:
future = executor.submit(self._caller, request)
try:
yield future.result(timeout=self._timeout)
except concurrent.futures.TimeoutError:
raise UserCodeTimeoutException(
f'Timeout {self._timeout} exceeded '
f'while completing request: {request}')
except RuntimeError:
raise UserCodeExecutionException('could not complete request')
def teardown(self):
self._caller.__exit__(*sys.exc_info())