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Async http client/server framework (asyncio)

Project description

Async http client/server framework

aiohttp logo

GitHub Actions status for master branch status for master branch Latest PyPI package version Latest Read The Docs Discourse status Chat on Gitter

Key Features

  • Supports both client and server side of HTTP protocol.

  • Supports both client and server Web-Sockets out-of-the-box and avoids Callback Hell.

  • Provides Web-server with middlewares and plugable routing.

Getting started


To get something from the web:

import aiohttp
import asyncio

async def main():

    async with aiohttp.ClientSession() as session:
        async with session.get('') as response:

            print("Status:", response.status)
            print("Content-type:", response.headers['content-type'])

            html = await response.text()
            print("Body:", html[:15], "...")

loop = asyncio.get_event_loop()

This prints:

Status: 200
Content-type: text/html; charset=utf-8
Body: <!doctype html> ...

Coming from requests ? Read why we need so many lines.


An example using a simple server:

# examples/
from aiohttp import web

async def handle(request):
    name = request.match_info.get('name', "Anonymous")
    text = "Hello, " + name
    return web.Response(text=text)

async def wshandle(request):
    ws = web.WebSocketResponse()
    await ws.prepare(request)

    async for msg in ws:
        if msg.type == web.WSMsgType.text:
            await ws.send_str("Hello, {}".format(
        elif msg.type == web.WSMsgType.binary:
            await ws.send_bytes(
        elif msg.type == web.WSMsgType.close:

    return ws

app = web.Application()
app.add_routes([web.get('/', handle),
                web.get('/echo', wshandle),
                web.get('/{name}', handle)])

if __name__ == '__main__':



Communication channels

aio-libs discourse group:

gitter chat

We support Stack Overflow. Please add aiohttp tag to your question there.


Optionally you may install the cChardet and aiodns libraries (highly recommended for sake of speed).


aiohttp is offered under the Apache 2 license.


The aiohttp community would like to thank Keepsafe ( for its support in the early days of the project.

Source code

The latest developer version is available in a GitHub repository:


If you are interested in efficiency, the AsyncIO community maintains a list of benchmarks on the official wiki:


3.7.4.post0 (2021-03-06)


  • Bumped upper bound of the chardet runtime dependency to allow their v4.0 version stream. #5366

3.7.4 (2021-02-25)


  • (SECURITY BUG) Started preventing open redirects in the aiohttp.web.normalize_path_middleware middleware. For more details, see

    Thanks to Beast Glatisant for finding the first instance of this issue and Jelmer Vernooij for reporting and tracking it down in aiohttp. #5497

  • Fix interpretation difference of the pure-Python and the Cython-based HTTP parsers construct a yarl.URL object for HTTP request-target.

    Before this fix, the Python parser would turn the URI’s absolute-path for //some-path into / while the Cython code preserved it as //some-path. Now, both do the latter. #5498

3.7.3 (2020-11-18)


  • Use Brotli instead of brotlipy #3803

  • Made exceptions pickleable. Also changed the repr of some exceptions. #4077


  • Raise a ClientResponseError instead of an AssertionError for a blank HTTP Reason Phrase. #3532

  • Fix web_middlewares.normalize_path_middleware behavior for patch without slash. #3669

  • Fix overshadowing of overlapped sub-applications prefixes. #3701

  • Make BaseConnector.close() a coroutine and wait until the client closes all connections. Drop deprecated “with Connector():” syntax. #3736

  • Reset the sock_read timeout each time data is received for a aiohttp.client response. #3808

  • Fixed type annotation for add_view method of UrlDispatcher to accept any subclass of View #3880

  • Fixed querying the address families from DNS that the current host supports. #5156

  • Change return type of MultipartReader.__aiter__() and BodyPartReader.__aiter__() to AsyncIterator. #5163

  • Provide x86 Windows wheels. #5230

Improved Documentation

  • Add documentation for aiohttp.web.FileResponse. #3958

  • Removed deprecation warning in tracing example docs #3964

  • Fixed wrong “Usage” docstring of aiohttp.client.request. #4603

  • Add aiohttp-pydantic to third party libraries #5228


3.7.2 (2020-10-27)


  • Fixed static files handling for loops without .sendfile() support #5149

3.7.1 (2020-10-25)


  • Fixed a type error caused by the conditional import of Protocol. #5111

  • Server doesn’t send Content-Length for 1xx or 204 #4901

  • Fix run_app typing #4957

  • Always require typing_extensions library. #5107

  • Fix a variable-shadowing bug causing ThreadedResolver.resolve to return the resolved IP as the hostname in each record, which prevented validation of HTTPS connections. #5110

  • Added annotations to all public attributes. #5115

  • Fix flaky test_when_timeout_smaller_second #5116

  • Ensure sending a zero byte file does not throw an exception #5124

  • Fix a bug in web.run_app() about Python version checking on Windows #5127

3.7.0 (2020-10-24)


  • Response headers are now prepared prior to running on_response_prepare hooks, directly before headers are sent to the client. #1958

  • Add a quote_cookie option to CookieJar, a way to skip quotation wrapping of cookies containing special characters. #2571

  • Call AccessLogger.log with the current exception available from sys.exc_info(). #3557

  • web.UrlDispatcher.add_routes and web.Application.add_routes return a list of registered AbstractRoute instances. AbstractRouteDef.register (and all subclasses) return a list of registered resources registered resource. #3866

  • Added properties of default ClientSession params to ClientSession class so it is available for introspection #3882

  • Don’t cancel web handler on peer disconnection, raise OSError on reading/writing instead. #4080

  • Implement BaseRequest.get_extra_info() to access a protocol transports’ extra info. #4189

  • Added ClientSession.timeout property. #4191

  • allow use of SameSite in cookies. #4224

  • Use loop.sendfile() instead of custom implementation if available. #4269

  • Apply SO_REUSEADDR to test server’s socket. #4393

  • Use .raw_host instead of slower .host in client API #4402

  • Allow configuring the buffer size of input stream by passing read_bufsize argument. #4453

  • Pass tests on Python 3.8 for Windows. #4513

  • Add method and url attributes to TraceRequestChunkSentParams and TraceResponseChunkReceivedParams. #4674

  • Add ClientResponse.ok property for checking status code under 400. #4711

  • Don’t ceil timeouts that are smaller than 5 seconds. #4850

  • TCPSite now listens by default on all interfaces instead of just IPv4 when None is passed in as the host. #4894

  • Bump http_parser to 2.9.4 #5070


  • Fix keepalive connections not being closed in time #3296

  • Fix failed websocket handshake leaving connection hanging. #3380

  • Fix tasks cancellation order on exit. The run_app task needs to be cancelled first for cleanup hooks to run with all tasks intact. #3805

  • Don’t start heartbeat until _writer is set #4062

  • Fix handling of multipart file uploads without a content type. #4089

  • Preserve view handler function attributes across middlewares #4174

  • Fix the string representation of ServerDisconnectedError. #4175

  • Raising RuntimeError when trying to get encoding from not read body #4214

  • Remove warning messages from noop. #4282

  • Raise ClientPayloadError if FormData re-processed. #4345

  • Fix a warning about unfinished task in #4408

  • Fixed ‘deflate’ compression. According to RFC 2616 now. #4506

  • Fixed OverflowError on platforms with 32-bit time_t #4515

  • Fixed request.body_exists returns wrong value for methods without body. #4528

  • Fix connecting to link-local IPv6 addresses. #4554

  • Fix a problem with connection waiters that are never awaited. #4562

  • Always make sure transport is not closing before reuse a connection.

    Reuse a protocol based on keepalive in headers is unreliable. For example, uWSGI will not support keepalive even it serves a HTTP 1.1 request, except explicitly configure uWSGI with a --http-keepalive option.

    Servers designed like uWSGI could cause aiohttp intermittently raise a ConnectionResetException when the protocol poll runs out and some protocol is reused. #4587

  • Handle the last CRLF correctly even if it is received via separate TCP segment. #4630

  • Fix the register_resource function to validate route name before splitting it so that route name can include python keywords. #4691

  • Improve typing annotations for web.Request, aiohttp.ClientResponse and multipart module. #4736

  • Fix resolver task is not awaited when connector is cancelled #4795

  • Fix a bug “Aiohttp doesn’t return any error on invalid request methods” #4798

  • Fix HEAD requests for static content. #4809

  • Fix incorrect size calculation for memoryview #4890

  • Add HTTPMove to _all__. #4897

  • Fixed the type annotations in the tracing module. #4912

  • Fix typing for multipart __aiter__. #4931

  • Fix for race condition on connections in BaseConnector that leads to exceeding the connection limit. #4936

  • Add forced UTF-8 encoding for application/rdap+json responses. #4938

  • Fix inconsistency between Python and C http request parsers in parsing pct-encoded URL. #4972

  • Fix connection closing issue in HEAD request. #5012

  • Fix type hint on BaseRunner.addresses (from List[str] to List[Any]) #5086

  • Make web.run_app() more responsive to Ctrl+C on Windows for Python < 3.8. It slightly increases CPU load as a side effect. #5098

Improved Documentation

  • Fix example code in client quick-start #3376

  • Updated the docs so there is no contradiction in ttl_dns_cache default value #3512

  • Add ‘Deploy with SSL’ to docs. #4201

  • Change typing of the secure argument on StreamResponse.set_cookie from Optional[str] to Optional[bool] #4204

  • Changes ttl_dns_cache type from int to Optional[int]. #4270

  • Simplify README hello word example and add a documentation page for people coming from requests. #4272

  • Improve some code examples in the documentation involving websockets and starting a simple HTTP site with an AppRunner. #4285

  • Fix typo in code example in Multipart docs #4312

  • Fix code example in Multipart section. #4314

  • Update contributing guide so new contributors read the most recent version of that guide. Update command used to create test coverage reporting. #4810

  • Spelling: Change “canonize” to “canonicalize”. #4986

  • Add aiohttp-sse-client library to third party usage list. #5084


3.6.3 (2020-10-12)


  • Pin yarl to <1.6.0 to avoid buggy behavior that will be fixed by the next aiohttp release.

3.6.2 (2019-10-09)


  • Made exceptions pickleable. Also changed the repr of some exceptions. #4077

  • Use Iterable type hint instead of Sequence for Application middleware parameter. #4125


  • Reset the sock_read timeout each time data is received for a aiohttp.ClientResponse. #3808

  • Fix handling of expired cookies so they are not stored in CookieJar. #4063

  • Fix misleading message in the string representation of ClientConnectorError; self.ssl == None means default SSL context, not SSL disabled #4097

  • Don’t clobber HTTP status when using FileResponse. #4106

Improved Documentation

  • Added minimal required logging configuration to logging documentation. #2469

  • Update docs to reflect proxy support. #4100

  • Fix typo in code example in testing docs. #4108


3.6.1 (2019-09-19)


  • Compatibility with Python 3.8. #4056


  • correct some exception string format #4068

  • Emit a warning when ssl.OP_NO_COMPRESSION is unavailable because the runtime is built against an outdated OpenSSL. #4052

  • Update multidict requirement to >= 4.5 #4057

Improved Documentation

  • Provide pytest-aiohttp namespace for pytest fixtures in docs. #3723

3.6.0 (2019-09-06)


  • Add support for Named Pipes (Site and Connector) under Windows. This feature requires Proactor event loop to work. #3629

  • Removed Transfer-Encoding: chunked header from websocket responses to be compatible with more http proxy servers. #3798

  • Accept non-GET request for starting websocket handshake on server side. #3980


  • Raise a ClientResponseError instead of an AssertionError for a blank HTTP Reason Phrase. #3532

  • Fix an issue where cookies would sometimes not be set during a redirect. #3576

  • Change normalize_path_middleware to use 308 redirect instead of 301.

    This behavior should prevent clients from being unable to use PUT/POST methods on endpoints that are redirected because of a trailing slash. #3579

  • Drop the processed task from all_tasks() list early. It prevents logging about a task with unhandled exception when the server is used in conjunction with #3587

  • Signal type annotation changed from Signal[Callable[['TraceConfig'], Awaitable[None]]] to Signal[Callable[ClientSession, SimpleNamespace, ...]. #3595

  • Use sanitized URL as Location header in redirects #3614

  • Improve typing annotations for along with changes required by mypy in files that references #3621

  • Close session created inside aiohttp.request when unhandled exception occurs #3628

  • Cleanup per-chunk data in generic data read. Memory leak fixed. #3631

  • Use correct type for add_view and family #3633

  • Fix _keepalive field in __slots__ of RequestHandler. #3644

  • Properly handle ConnectionResetError, to silence the “Cannot write to closing transport” exception when clients disconnect uncleanly. #3648

  • Suppress pytest warnings due to test_utils classes #3660

  • Fix overshadowing of overlapped sub-application prefixes. #3701

  • Fixed return type annotation for WSMessage.json() #3720

  • Properly expose TooManyRedirects publicly as documented. #3818

  • Fix missing brackets for IPv6 in proxy CONNECT request #3841

  • Make the signature of aiohttp.test_utils.TestClient.request match asyncio.ClientSession.request according to the docs #3852

  • Use correct style for re-exported imports, makes mypy --strict mode happy. #3868

  • Fixed type annotation for add_view method of UrlDispatcher to accept any subclass of View #3880

  • Made cython HTTP parser set Reason-Phrase of the response to an empty string if it is missing. #3906

  • Add URL to the string representation of ClientResponseError. #3959

  • Accept istr keys in LooseHeaders type hints. #3976

  • Fixed race conditions in _resolve_host caching and throttling when tracing is enabled. #4013

  • For URLs like “unix://localhost/…” set Host HTTP header to “localhost” instead of “localhost:None”. #4039

Improved Documentation

  • Modify documentation for Background Tasks to remove deprecated usage of event loop. #3526

  • use if __name__ == '__main__': in server examples. #3775

  • Update documentation reference to the default access logger. #3783

  • Improve documentation for web.BaseRequest.path and web.BaseRequest.raw_path. #3791

  • Removed deprecation warning in tracing example docs #3964

3.5.4 (2019-01-12)


  • Fix stream .read() / .readany() / .iter_any() which used to return a partial content only in case of compressed content #3525

3.5.3 (2019-01-10)


  • Fix type stubs for aiohttp.web.run_app(access_log=True) and fix edge case of access_log=True and the event loop being in debug mode. #3504

  • Fix aiohttp.ClientTimeout type annotations to accept None for fields #3511

  • Send custom per-request cookies even if session jar is empty #3515

  • Restore Linux binary wheels publishing on PyPI

3.5.2 (2019-01-08)


  • FileResponse from uses a ThreadPoolExecutor to work with files asynchronously. I/O based payloads from uses a ThreadPoolExecutor to work with I/O objects asynchronously. #3313

  • Internal Server Errors in plain text if the browser does not support HTML. #3483


  • Preserve MultipartWriter parts headers on write. Refactor the way how Payload.headers are handled. Payload instances now always have headers and Content-Type defined. Fix Payload Content-Disposition header reset after initial creation. #3035

  • Log suppressed exceptions in GunicornWebWorker. #3464

  • Remove wildcard imports. #3468

  • Use the same task for app initialization and web server handling in gunicorn workers. It allows to use Python3.7 context vars smoothly. #3471

  • Fix handling of chunked+gzipped response when first chunk does not give uncompressed data #3477

  • Replace collections.MutableMapping with to avoid a deprecation warning. #3480

  • Payload.size type annotation changed from Optional[float] to Optional[int]. #3484

  • Ignore done tasks when cancels pending activities on web.run_app finalization. #3497

Improved Documentation

  • Add documentation for aiohttp.web.HTTPException. #3490


3.5.1 (2018-12-24)

  • Fix a regression about ClientSession._requote_redirect_url modification in debug mode.

3.5.0 (2018-12-22)


  • The library type annotations are checked in strict mode now.

  • Add support for setting cookies for individual request (#2387)

  • Application.add_domain implementation (#2809)

  • The default app in the request returned by test_utils.make_mocked_request can now have objects assigned to it and retrieved using the [] operator. (#3174)

  • Make request.url accessible when transport is closed. (#3177)

  • Add zlib_executor_size argument to Response constructor to allow compression to run in a background executor to avoid blocking the main thread and potentially triggering health check failures. (#3205)

  • Enable users to set ClientTimeout in aiohttp.request (#3213)

  • Don’t raise a warning if NETRC environment variable is not set and ~/.netrc file doesn’t exist. (#3267)

  • Add default logging handler to web.run_app If the Application.debug` flag is set and the default logger aiohttp.access is used, access logs will now be output using a stderr StreamHandler if no handlers are attached. Furthermore, if the default logger has no log level set, the log level will be set to DEBUG. (#3324)

  • Add method argument to session.ws_connect(). Sometimes server API requires a different HTTP method for WebSocket connection establishment. For example, Docker exec needs POST. (#3378)

  • Create a task per request handling. (#3406)


  • Enable passing access_log_class via handler_args (#3158)

  • Return empty bytes with end-of-chunk marker in empty stream reader. (#3186)

  • Accept CIMultiDictProxy instances for headers argument in web.Response constructor. (#3207)

  • Don’t uppercase HTTP method in parser (#3233)

  • Make method match regexp RFC-7230 compliant (#3235)

  • Add app.pre_frozen state to properly handle startup signals in sub-applications. (#3237)

  • Enhanced parsing and validation of helpers.BasicAuth.decode. (#3239)

  • Change imports from collections module in preparation for 3.8. (#3258)

  • Ensure Host header is added first to ClientRequest to better replicate browser (#3265)

  • Fix forward compatibility with Python 3.8: importing ABCs directly from the collections module will not be supported anymore. (#3273)

  • Keep the query string by normalize_path_middleware. (#3278)

  • Fix missing parameter raise_for_status for aiohttp.request() (#3290)

  • Bracket IPv6 addresses in the HOST header (#3304)

  • Fix default message for server ping and pong frames. (#3308)

  • Fix tests/ typo and tests/autobahn/ duplicate loop def. (#3337)

  • Fix false-negative indicator end_of_HTTP_chunk in StreamReader.readchunk function (#3361)

  • Release HTTP response before raising status exception (#3364)

  • Fix task cancellation when sendfile() syscall is used by static file handling. (#3383)

  • Fix stack trace for asyncio.TimeoutError which was not logged, when it is caught in the handler. (#3414)

Improved Documentation

  • Improve documentation of Application.make_handler parameters. (#3152)

  • Fix BaseRequest.raw_headers doc. (#3215)

  • Fix typo in TypeError exception reason in web.Application._handle (#3229)

  • Make server access log format placeholder %b documentation reflect behavior and docstring. (#3307)

Deprecations and Removals

  • Deprecate modification of session.requote_redirect_url (#2278)

  • Deprecate stream.unread_data() (#3260)

  • Deprecated use of boolean in resp.enable_compression() (#3318)

  • Encourage creation of aiohttp public objects inside a coroutine (#3331)

  • Drop dead Connection.detach() and Connection.writer. Both methods were broken for more than 2 years. (#3358)

  • Deprecate app.loop, request.loop, client.loop and connector.loop properties. (#3374)

  • Deprecate explicit debug argument. Use asyncio debug mode instead. (#3381)

  • Deprecate body parameter in HTTPException (and derived classes) constructor. (#3385)

  • Deprecate bare connector close, use async with connector: and await connector.close() instead. (#3417)

  • Deprecate obsolete read_timeout and conn_timeout in ClientSession constructor. (#3438)


  • #3341, #3351

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