Blocking and non-blocking HTTP client interfaces.
This module defines a common interface shared by two implementations,
``simple_httpclient`` and ``curl_httpclient``. Applications may either
instantiate their chosen implementation class directly or use the
`AsyncHTTPClient` class from this module, which selects an implementation
that can be overridden with the `AsyncHTTPClient.configure` method.
The default implementation is ``simple_httpclient``, and this is expected
to be suitable for most users' needs. However, some applications may wish
to switch to ``curl_httpclient`` for reasons such as the following:
* ``curl_httpclient`` has some features not found in ``simple_httpclient``,
including support for HTTP proxies and the ability to use a specified
network interface.
* ``curl_httpclient`` is more likely to be compatible with sites that are
not-quite-compliant with the HTTP spec, or sites that use little-exercised
features of HTTP.
* ``curl_httpclient`` is faster.
* ``curl_httpclient`` was the default prior to Tornado 2.0.
Note that if you are using ``curl_httpclient``, it is highly
recommended that you use a recent version of ``libcurl`` and
``pycurl``. Currently the minimum supported version of libcurl is
7.21.1, and the minimum version of pycurl is 7.18.2. It is highly
recommended that your ``libcurl`` installation is built with
asynchronous DNS resolver (threaded or c-ares), otherwise you may
encounter various problems with request timeouts (for more
information, see
http://curl.haxx.se/libcurl/c/curl_easy_setopt.html#CURLOPTCONNECTTIMEOUTMS
and comments in curl_httpclient.py).
To select ``curl_httpclient``, call `AsyncHTTPClient.configure` at startup::
AsyncHTTPClient.configure("tornado.curl_httpclient.CurlAsyncHTTPClient")