Advanced Usage¶
Customizing pool behavior¶
The PoolManager
class automatically handles creating
ConnectionPool
instances for each host as needed. By
default, it will keep a maximum of 10 ConnectionPool
instances. If you’re making requests to many different hosts it might improve
performance to increase this number:
>>> import urllib3
>>> http = urllib3.PoolManager(num_pools=50)
However, keep in mind that this does increase memory and socket consumption.
Similarly, the ConnectionPool
class keeps a pool
of individual HTTPConnection
instances. These connections
are used during an individual request and returned to the pool when the request
is complete. By default only one connection will be saved for re-use. If you
are making many requests to the same host simultaneously it might improve
performance to increase this number:
>>> import urllib3
>>> http = urllib3.PoolManager(maxsize=10)
# Alternatively
>>> http = urllib3.HTTPConnectionPool('google.com', maxsize=10)
The behavior of the pooling for ConnectionPool
is
different from PoolManager
. By default, if a new
request is made and there is no free connection in the pool then a new
connection will be created. However, this connection will not be saved if more
than maxsize
connections exist. This means that maxsize
does not
determine the maximum number of connections that can be open to a particular
host, just the maximum number of connections to keep in the pool. However, if you specify block=True
then there can be at most maxsize
connections
open to a particular host:
>>> http = urllib3.PoolManager(maxsize=10, block=True)
# Alternatively
>>> http = urllib3.HTTPConnectionPool('google.com', maxsize=10, block=True)
Any new requests will block until a connection is available from the pool. This is a great way to prevent flooding a host with too many connections in multi-threaded applications.
Streaming and IO¶
When dealing with large responses it’s often better to stream the response content:
>>> import urllib3
>>> http = urllib3.PoolManager()
>>> r = http.request(
... 'GET',
... 'http://httpbin.org/bytes/1024',
... preload_content=False)
>>> for chunk in r.stream(32):
... print(chunk)
b'...'
b'...'
...
>>> r.release_conn()
Setting preload_content
to False
means that urllib3 will stream the
response content. stream()
lets you iterate over
chunks of the response content.
Note
When using preload_content=False
, you should call
release_conn()
to release the http connection
back to the connection pool so that it can be re-used.
However, you can also treat the HTTPResponse
instance as
a file-like object. This allows you to do buffering:
>>> r = http.request(
... 'GET',
... 'http://httpbin.org/bytes/1024',
... preload_content=False)
>>> r.read(4)
b'\x88\x1f\x8b\xe5'
Calls to read()
will block until more response
data is available.
>>> import io
>>> reader = io.BufferedReader(r, 8)
>>> reader.read(4)
>>> r.release_conn()
You can use this file-like object to do things like decode the content using
codecs
:
>>> import codecs
>>> reader = codecs.getreader('utf-8')
>>> r = http.request(
... 'GET',
... 'http://httpbin.org/ip',
... preload_content=False)
>>> json.load(reader(r))
{'origin': '127.0.0.1'}
>>> r.release_conn()
Proxies¶
You can use ProxyManager
to tunnel requests through an
HTTP proxy:
>>> import urllib3
>>> proxy = urllib3.ProxyManager('http://localhost:3128/')
>>> proxy.request('GET', 'http://google.com/')
The usage of ProxyManager
is the same as
PoolManager
.
You can use SOCKSProxyManager
to connect to SOCKS4 or
SOCKS5 proxies. In order to use SOCKS proxies you will need to install
PySocks or install urllib3 with the
socks
extra:
pip install urllib3[socks]
Once PySocks is installed, you can use
SOCKSProxyManager
:
>>> from urllib3.contrib.socks import SOCKSProxyManager
>>> proxy = SOCKSProxyManager('socks5://localhost:8889/')
>>> proxy.request('GET', 'http://google.com/')
Custom SSL certificates¶
Instead of using certifi you can provide your
own certificate authority bundle. This is useful for cases where you’ve
generated your own certificates or when you’re using a private certificate
authority. Just provide the full path to the certificate bundle when creating a
PoolManager
:
>>> import urllib3
>>> http = urllib3.PoolManager(
... cert_reqs='CERT_REQUIRED',
... ca_certs='/path/to/your/certificate_bundle')
When you specify your own certificate bundle only requests that can be
verified with that bundle will succeed. It’s recommended to use a separate
PoolManager
to make requests to URLs that do not need
the custom certificate.
Client certificates¶
You can also specify a client certificate. This is useful when both the server
and the client need to verify each other’s identity. Typically these
certificates are issued from the same authority. To use a client certificate,
provide the full path when creating a PoolManager
:
>>> http = urllib3.PoolManager(
... cert_file='/path/to/your/client_cert.pem',
... cert_reqs='CERT_REQUIRED',
... ca_certs='/path/to/your/certificate_bundle')
If you have an encrypted client certificate private key you can use
the key_password
parameter to specify a password to decrypt the key.
>>> http = urllib3.PoolManager(
... cert_file='/path/to/your/client_cert.pem',
... cert_reqs='CERT_REQUIRED',
... key_file='/path/to/your/client.key',
... key_password='keyfile_password')
If your key isn’t encrypted the key_password
parameter isn’t required.
Certificate validation and Mac OS X¶
Apple-provided Python and OpenSSL libraries contain a patches that make them automatically check the system keychain’s certificates. This can be surprising if you specify custom certificates and see requests unexpectedly succeed. For example, if you are specifying your own certificate for validation and the server presents a different certificate you would expect the connection to fail. However, if that server presents a certificate that is in the system keychain then the connection will succeed.
This article has more in-depth analysis and explanation.
SSL Warnings¶
urllib3 will issue several different warnings based on the level of certificate verification support. These warnings indicate particular situations and can be resolved in different ways.
InsecureRequestWarning
- This happens when a request is made to an HTTPS URL without certificate verification enabled. Follow the certificate verification guide to resolve this warning.
InsecurePlatformWarning
- This happens on Python 2 platforms that have an outdated
ssl
module. These olderssl
modules can cause some insecure requests to succeed where they should fail and secure requests to fail where they should succeed. Follow the pyOpenSSL guide to resolve this warning.
SNIMissingWarning
- This happens on Python 2 versions older than 2.7.9. These older versions lack SNI support. This can cause servers to present a certificate that the client thinks is invalid. Follow the pyOpenSSL guide to resolve this warning.
Making unverified HTTPS requests is strongly discouraged, however, if you
understand the risks and wish to disable these warnings, you can use disable_warnings()
:
>>> import urllib3
>>> urllib3.disable_warnings()
Alternatively you can capture the warnings with the standard logging
module:
>>> logging.captureWarnings(True)
Finally, you can suppress the warnings at the interpreter level by setting the
PYTHONWARNINGS
environment variable or by using the
-W flag.
Google App Engine¶
urllib3 supports Google App Engine with some caveats.
If you’re using the Flexible environment, you do not have to do
any configuration- urllib3 will just work. However, if you’re using the
Standard environment then
you either have to use urllib3.contrib.appengine
’s
AppEngineManager
or use the Sockets API
To use AppEngineManager
:
>>> from urllib3.contrib.appengine import AppEngineManager
>>> http = AppEngineManager()
>>> http.request('GET', 'https://google.com/')
To use the Sockets API, add the following to your app.yaml and use
PoolManager
as usual:
env_variables:
GAE_USE_SOCKETS_HTTPLIB : 'true'
For more details on the limitations and gotchas, see
urllib3.contrib.appengine
.
Brotli Encoding¶
Brotli is a compression algorithm created by Google with better compression
than gzip and deflate and is supported by urllib3 if the
brotlipy package is installed.
You may also request the package be installed via the urllib3[brotli]
extra:
python -m pip install urllib3[brotli]
Here’s an example using brotli encoding via the Accept-Encoding
header:
>>> from urllib3 import PoolManager
>>> http = PoolManager()
>>> http.request('GET', 'https://www.google.com/', headers={'Accept-Encoding': 'br'})
Decrypting captured TLS sessions with Wireshark¶
Python 3.8 and higher support logging of TLS pre-master secrets. With these secrets tools like Wireshark can decrypt captured network traffic.
To enable this simply define environment variable SSLKEYLOGFILE:
export SSLKEYLOGFILE=/path/to/keylogfile.txt
Then configure the key logfile in Wireshark, see Wireshark TLS Decryption for instructions.