Simple aiohttp retry client

Python 3.7 or higher.

Install: pip install aiohttp-retry.

Breaking API changes

• Everything between [2.7.0 - 2.8.3) is yanked.
  There is a bug with evaluate_response_callback, it led to infinite retries

• 2.8.0 is incorrect and yanked. #79

• Since 2.5.6 this is a new parameter in get_timeout func called "response".
  If you have defined your own RetryOptions, you should add this param into it. Issue about this: #59

Examples of usage:

from aiohttp_retry import RetryClient, ExponentialRetry

async def main():
    retry_options = ExponentialRetry(attempts=1)
    retry_client = RetryClient(raise_for_status=False, retry_options=retry_options)
    async with retry_client.get('https://ya.ru') as response:
        print(response.status)
        
    await retry_client.close()

from aiohttp import ClientSession
from aiohttp_retry import RetryClient 

async def main():
    client_session = ClientSession()
    retry_client = RetryClient(client_session=client_session)
    async with retry_client.get('https://ya.ru') as response:
        print(response.status)

    await client_session.close()

from aiohttp_retry import RetryClient, RandomRetry

async def main():
    retry_options = RandomRetry(attempts=1)
    retry_client = RetryClient(raise_for_status=False, retry_options=retry_options)

    response = await retry_client.get('/ping')
    print(response.status)
        
    await retry_client.close()

from aiohttp_retry import RetryClient

async def main():
    async with RetryClient() as client:
        async with client.get('https://ya.ru') as response:
            print(response.status)

You can change parameters between attempts by passing multiple requests params:

from aiohttp_retry import RetryClient, RequestParams, ExponentialRetry

async def main():
    retry_client = RetryClient(raise_for_status=False)

    async with retry_client.requests(
        params_list=[
            RequestParams(
                method='GET',
                url='https://ya.ru',
            ),
            RequestParams(
                method='GET',
                url='https://ya.ru',
                headers={'some_header': 'some_value'},
            ),
        ]
    ) as response:
        print(response.status)
        
    await retry_client.close()

You can also add some logic, F.E. logging, on failures by using trace mechanic.

import logging
import sys
from types import SimpleNamespace

from aiohttp import ClientSession, TraceConfig, TraceRequestStartParams

from aiohttp_retry import RetryClient, ExponentialRetry


handler = logging.StreamHandler(sys.stdout)
logging.basicConfig(handlers=[handler])
logger = logging.getLogger(__name__)
retry_options = ExponentialRetry(attempts=2)


async def on_request_start(
    session: ClientSession,
    trace_config_ctx: SimpleNamespace,
    params: TraceRequestStartParams,
) -> None:
    current_attempt = trace_config_ctx.trace_request_ctx['current_attempt']
    if retry_options.attempts <= current_attempt:
        logger.warning('Wow! We are in last attempt')


async def main():
    trace_config = TraceConfig()
    trace_config.on_request_start.append(on_request_start)
    retry_client = RetryClient(retry_options=retry_options, trace_configs=[trace_config])

    response = await retry_client.get('https://httpstat.us/503', ssl=False)
    print(response.status)

    await retry_client.close()

Look tests for more examples.
Be aware: last request returns as it is.
If the last request ended with exception, that this exception will be raised from RetryClient request

Documentation

RetryClient takes the same arguments as ClientSession[docs]
RetryClient has methods:

• request
• get
• options
• head
• post
• put
• patch
• put
• delete

They are same as for ClientSession, but take one possible additional argument:

class RetryOptionsBase:
    def __init__(
        self,
        attempts: int = 3,  # How many times we should retry
        statuses: Iterable[int] | None = None,  # On which statuses we should retry
        exceptions: Iterable[type[Exception]] | None = None,  # On which exceptions we should retry, by default on all
        retry_all_server_errors: bool = True,  # If should retry all 500 errors or not
        # a callback that will run on response to decide if retry
        evaluate_response_callback: EvaluateResponseCallbackType | None = None,
    ):
        ...

    @abc.abstractmethod
    def get_timeout(self, attempt: int, response: Optional[Response] = None) -> float:
        raise NotImplementedError

You can specify RetryOptions both for RetryClient and it's methods. RetryOptions in methods override RetryOptions defined in RetryClient constructor.

Important: by default all 5xx responses are retried + statuses you specified as statuses param If you will pass retry_all_server_errors=False than you can manually set what 5xx errors to retry.

You can define your own timeouts logic or use:

• ExponentialRetry with exponential backoff
• RandomRetry for random backoff
• ListRetry with backoff you predefine by list
• FibonacciRetry with backoff that looks like fibonacci sequence
• JitterRetry exponential retry with a bit of randomness

Important: you can proceed server response as an parameter for calculating next timeout.
However this response can be None, server didn't make a response or you have set up raise_for_status=True Look here for an example: #59

Additionally, you can specify evaluate_response_callback. It receive a ClientResponse and decide to retry or not by returning a bool. It can be useful, if server API sometimes response with malformed data.

Request Trace Context

RetryClient add current attempt number to request_trace_ctx (see examples, for more info see aiohttp doc).

Change parameters between retries

RetryClient also has a method called requests. This method should be used if you want to make requests with different params.

@dataclass
class RequestParams:
    method: str
    url: _RAW_URL_TYPE
    headers: dict[str, Any] | None = None
    trace_request_ctx: dict[str, Any] | None = None
    kwargs: dict[str, Any] | None = None

def requests(
    self,
    params_list: list[RequestParams],
    retry_options: RetryOptionsBase | None = None,
    raise_for_status: bool | None = None,
) -> _RequestContext:

You can find an example of usage above or in tests.
But basically RequestParams is a structure to define params for ClientSession.request func.
method, url, headers trace_request_ctx defined outside kwargs, because they are popular.

There is also an old way to change URL between retries by specifying url as list of urls. Example:

from aiohttp_retry import RetryClient

retry_client = RetryClient()
async with retry_client.get(url=['/internal_error', '/ping']) as response:
    text = await response.text()
    assert response.status == 200
    assert text == 'Ok!'

await retry_client.close()

In this example we request /interval_error, fail and then successfully request /ping. If you specify less urls than attempts number in RetryOptions, RetryClient will request last url at last attempts. This means that in example above we would request /ping once again in case of failure.

Types

aiohttp_retry is a typed project. It should be fully compatible with mypy.

It also introduce one special type:

ClientType = Union[ClientSession, RetryClient]

This type can be imported by from aiohttp_retry.types import ClientType