HTTP Client

Make a Request

Begin by importing the aiohttp module:

import aiohttp

Now, let’s try to get a web-page. For example let’s get GitHub’s public time-line

with aiohttp.ClientSession() as session:
    async with session.get('') as resp:
        print(await resp.text())

Now, we have a ClientSession called session and a ClientResponse object called resp. We can get all the information we need from the response. The mandatory parameter of ClientSession.get() coroutine is an HTTP url.

In order to make an HTTP POST request use coroutine:'', data=b'data')

Other HTTP methods are available as well:

session.put('', data=b'data')
session.patch('', data=b'data')

Passing Parameters In URLs

You often want to send some sort of data in the URL’s query string. If you were constructing the URL by hand, this data would be given as key/value pairs in the URL after a question mark, e.g. Requests allows you to provide these arguments as a dict, using the params keyword argument. As an example, if you wanted to pass key1=value1 and key2=value2 to, you would use the following code:

params = {'key1': 'value1', 'key2': 'value2'}
async with session.get('',
                       params=params) as resp:
    assert resp.url == ''

You can see that the URL has been correctly encoded by printing the URL.

For sending data with multiple values for the same key MultiDict may be used as well.

It is also possible to pass a list of 2 item tuples as parameters, in that case you can specify multiple values for each key:

params = [('key', 'value1'), ('key', 'value2')]
async with session.get('',
                       params=params) as r:
    assert r.url == ''

You can also pass str content as param, but beware - content is not encoded by library. Note that + is not encoded:

async with session.get('',
                       params='key=value+1') as r:
        assert r.url = ''

Response Content

We can read the content of the server’s response. Consider the GitHub time-line again:

async with session.get('') as resp:
    print(await resp.text())

will printout something like:


aiohttp will automatically decode the content from the server. You can specify custom encoding for the text() method:

await resp.text(encoding='windows-1251')

Binary Response Content

You can also access the response body as bytes, for non-text requests:


The gzip and deflate transfer-encodings are automatically decoded for you.

JSON Response Content

There’s also a built-in JSON decoder, in case you’re dealing with JSON data:

async with session.get('') as resp:
    print(await resp.json())

In case that JSON decoding fails, json() will raise an exception. It is possible to specify custom encoding and decoder functions for the json() call.

Streaming Response Content

While methods read(), json() and text() are very convenient you should use them carefully. All these methods load the whole response in memory. For example if you want to download several gigabyte sized files, these methods will load all the data in memory. Instead you can use the content attribute. It is an instance of the aiohttp.StreamReader class. The gzip and deflate transfer-encodings are automatically decoded for you:

async with session.get('') as resp:

In general, however, you should use a pattern like this to save what is being streamed to a file:

with open(filename, 'wb') as fd:
    while True:
        chunk = await
        if not chunk:

It is not possible to use read(), json() and text() after explicit reading from content.

Releasing Response

Don’t forget to release response after use. This will ensure explicit behavior and proper connection pooling.

The easiest way to correctly response releasing is async with statement:

async with session.get(url) as resp:

But explicit release() call also may be used:

await resp.release()

But it’s not necessary if you use read(), json() and text() methods. They do release connection internally but better don’t rely on that behavior.

Custom Headers

If you need to add HTTP headers to a request, pass them in a dict to the headers parameter.

For example, if you want to specify the content-type for the previous example:

import json
url = ''
payload = {'some': 'data'}
headers = {'content-type': 'application/json'}


Custom Cookies

To send your own cookies to the server, you can use the cookies parameter:

url = ''
cookies = dict(cookies_are='working')

async with session.get(url, cookies=cookies) as resp:
    assert await resp.json() == {"cookies":
                                     {"cookies_are": "working"}}

More complicated POST requests

Typically, you want to send some form-encoded data — much like an HTML form. To do this, simply pass a dictionary to the data argument. Your dictionary of data will automatically be form-encoded when the request is made:

payload = {'key1': 'value1', 'key2': 'value2'}
async with'',
                        data=payload) as resp:
    print(await resp.text())
  "form": {
    "key2": "value2",
    "key1": "value1"

If you want to send data that is not form-encoded you can do it by passing a str instead of a dict. This data will be posted directly.

For example, the GitHub API v3 accepts JSON-Encoded POST/PATCH data:

import json
url = ''
payload = {'some': 'data'}

async with, data=json.dumps(payload)) as resp:

POST a Multipart-Encoded File

To upload Multipart-encoded files:

url = ''
files = {'file': open('report.xls', 'rb')}

await, data=files)

You can set the filename, content_type explicitly:

url = ''
data = FormData()
               open('report.xls', 'rb'),

await, data=data)

If you pass a file object as data parameter, aiohttp will stream it to the server automatically. Check StreamReader for supported format information.

Streaming uploads

aiohttp supports multiple types of streaming uploads, which allows you to send large files without reading them into memory.

As a simple case, simply provide a file-like object for your body:

with open('massive-body', 'rb') as f:
   await'http://some.url/streamed', data=f)

Or you can provide an coroutine that yields bytes objects:

def my_coroutine():
   chunk = yield from read_some_data_from_somewhere()
   if not chunk:
   yield chunk


yield expression is forbidden inside async def.


It is not a standard coroutine as it yields values so it can not be used like yield from my_coroutine(). aiohttp internally handles such coroutines.

Also it is possible to use a StreamReader object. Lets say we want to upload a file from another request and calculate the file SHA1 hash:

async def feed_stream(resp, stream):
    h = hashlib.sha256()

    while True:
        chunk = await resp.content.readany()
        if not chunk:

    return h.hexdigest()

resp = session.get('')
stream = StreamReader()
loop.create_task('', data=stream))

file_hash = await feed_stream(resp, stream)

Because the response content attribute is a StreamReader, you can chain get and post requests together (aka HTTP pipelining):

r = await session.get, '')

Uploading pre-compressed data

To upload data that is already compressed before passing it to aiohttp, call the request function with compress=False and set the used compression algorithm name (usually deflate or zlib) as the value of the Content-Encoding header:

async def my_coroutine(session, headers, my_data):
    data = zlib.compress(my_data)
    headers = {'Content-Encoding': 'deflate'}
    async with'',


To tweak or change transport layer of requests you can pass a custom connector to ClientSession and family. For example:

conn = aiohttp.TCPConnector()
session = aiohttp.ClientSession(connector=aiohttp.TCPConnector())

See also

Connectors section for more information about different connector types and configuration options.

Limiting connection pool size

To limit amount of simultaneously opened connection to the same endpoint ((host, port, is_ssl) triple) you can pass limit parameter to connector:

conn = aiohttp.TCPConnector(limit=30)

The example limits amount of parallel connections to 30.

SSL control for TCP sockets

TCPConnector constructor accepts mutually exclusive verify_ssl and ssl_context params.

By default it uses strict checks for HTTPS protocol. Certification checks can be relaxed by passing verify_ssl=False:

conn = aiohttp.TCPConnector(verify_ssl=False)
session = aiohttp.ClientSession(connector=conn)
r = await session.get('')

If you need to setup custom ssl parameters (use own certification files for example) you can create a ssl.SSLContext instance and pass it into the connector:

sslcontext = ssl.create_default_context(cafile='/path/to/ca-bundle.crt')
conn = aiohttp.TCPConnector(ssl_context=sslcontext)
session = aiohttp.ClientSession(connector=conn)
r = await session.get('')

You may also verify certificates via MD5, SHA1, or SHA256 fingerprint:

# Attempt to connect to
# with a pin to a bogus certificate:
bad_md5 = b'\xa2\x06G\xad\xaa\xf5\xd8\\J\x99^by;\x06='
conn = aiohttp.TCPConnector(fingerprint=bad_md5)
session = aiohttp.ClientSession(connector=conn)
exc = None
    r = yield from session.get('')
except FingerprintMismatch as e:
    exc = e
assert exc is not None
assert exc.expected == bad_md5

# cert's actual md5
assert == b'\xca;I\x9cuv\x8es\x138N$?\x15\xca\xcb'

Note that this is the fingerprint of the DER-encoded certificate. If you have the certificate in PEM format, you can convert it to DER with e.g. openssl x509 -in crt.pem -inform PEM -outform DER > crt.der.

Tip: to convert from a hexadecimal digest to a binary byte-string, you can use binascii.unhexlify:

md5_hex = 'ca3b499c75768e7313384e243f15cacb'
from binascii import unhexlify
assert unhexlify(md5_hex) == b'\xca;I\x9cuv\x8es\x138N$?\x15\xca\xcb'

Unix domain sockets

If your HTTP server uses UNIX domain sockets you can use UnixConnector:

conn = aiohttp.UnixConnector(path='/path/to/socket')
session = aiohttp.ClientSession(connector=conn)

Proxy support

aiohttp supports proxy. You have to use ProxyConnector:

conn = aiohttp.ProxyConnector(proxy="")
session = aiohttp.ClientSession(connector=conn)
async with session.get('') as resp:

ProxyConnector also supports proxy authorization:

conn = aiohttp.ProxyConnector(
    proxy_auth=aiohttp.BasicAuth('user', 'pass'))
session = aiohttp.ClientSession(connector=conn)
async with session.get('') as r:
    assert r.status == 200

Authentication credentials can be passed in proxy URL:

conn = aiohttp.ProxyConnector(

Response Status Codes

We can check the response status code:

async with session.get('') as resp:
    assert resp.status == 200

Response Headers

We can view the server’s response ClientResponse.headers using a CIMultiDictProxy:

>>> resp.headers
 'CONTENT-TYPE': 'application/json',
 'DATE': 'Tue, 15 Jul 2014 16:49:51 GMT',
 'SERVER': 'gunicorn/18.0',
 'CONNECTION': 'keep-alive'}

The dictionary is special, though: it’s made just for HTTP headers. According to RFC 7230, HTTP Header names are case-insensitive. It also supports multiple values for the same key as HTTP protocol does.

So, we can access the headers using any capitalization we want:

>>> resp.headers['Content-Type']

>>> resp.headers.get('content-type')

All headers converted from binary data using UTF-8 with surrogateescape option. That works fine on most cases but sometimes unconverted data is needed if a server uses nonstandard encoding. While these headers are malformed from RFC 7230 perspective they are may be retrieved by using ClientResponse.raw_headers property:

>>> resp.raw_headers
((b'SERVER', b'nginx'),
 (b'DATE', b'Sat, 09 Jan 2016 20:28:40 GMT'),
 (b'CONTENT-TYPE', b'text/html; charset=utf-8'),
 (b'CONTENT-LENGTH', b'12150'),
 (b'CONNECTION', b'keep-alive'))

Response Cookies

If a response contains some Cookies, you can quickly access them:

url = ''
async with session.get(url) as resp:


Response cookies contain only values, that were in Set-Cookie headers of the last request in redirection chain. To gather cookies between all redirection requests you can use aiohttp.ClientSession object.

Response History

If a request was redirected, it is possible to view previous responses using the history attribute:

>>> resp = await session.get('')
>>> resp
<ClientResponse( [200]>
>>> resp.history
(<ClientResponse( [301]>,)

If no redirects occurred or allow_redirects is set to False, history will be an empty sequence.


New in version 0.15.

aiohttp works with client websockets out-of-the-box.

You have to use the aiohttp.ClientSession.ws_connect() coroutine for client websocket connection. It accepts a url as a first parameter and returns ClientWebSocketResponse, with that object you can communicate with websocket server using response’s methods:

session = aiohttp.ClientSession()
async with session.ws_connect('') as ws:

    async for msg in ws:
        if == aiohttp.MsgType.text:
            if == 'close cmd':
                await ws.close()
                ws.send_str( + '/answer')
        elif == aiohttp.MsgType.closed:
        elif == aiohttp.MsgType.error:

You must use the only websocket task for both reading (e.g await ws.receive() or async for msg in ws:) and writing but may have multiple writer tasks which can only send data asynchronously (by ws.send_str('data') for example).


The example wraps a client call in Timeout context manager, adding timeout for both connecting and response body reading procedures:

with aiohttp.Timeout(0.001):
    async with aiohttp.get('') as r:
        await r.text()
blog comments powered by Disqus