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#õ :mod:`asynchat` --- Asynchronous socket command/response handler
================================================================
.. module:: asynchat
:synopsis: Support for asynchronous command/response protocols.
.. moduleauthor:: Sam Rushing
.. sectionauthor:: Steve Holden
**Source code:** :source:`Lib/asynchat.py`
--------------
This module builds on the :mod:`asyncore` infrastructure, simplifying
asynchronous clients and servers and making it easier to handle protocols
whose elements are terminated by arbitrary strings, or are of variable length.
:mod:`asynchat` defines the abstract class :class:`async_chat` that you
subclass, providing implementations of the :meth:`collect_incoming_data` and
:meth:`found_terminator` methods. It uses the same asynchronous loop as
:mod:`asyncore`, and the two types of channel, :class:`asyncore.dispatcher`
and :class:`asynchat.async_chat`, can freely be mixed in the channel map.
Typically an :class:`asyncore.dispatcher` server channel generates new
:class:`asynchat.async_chat` channel objects as it receives incoming
connection requests.
.. class:: async_chat()
This class is an abstract subclass of :class:`asyncore.dispatcher`. To make
practical use of the code you must subclass :class:`async_chat`, providing
meaningful :meth:`collect_incoming_data` and :meth:`found_terminator`
methods.
The :class:`asyncore.dispatcher` methods can be used, although not all make
sense in a message/response context.
Like :class:`asyncore.dispatcher`, :class:`async_chat` defines a set of
events that are generated by an analysis of socket conditions after a
:c:func:`select` call. Once the polling loop has been started the
:class:`async_chat` object's methods are called by the event-processing
framework with no action on the part of the programmer.
Two class attributes can be modified, to improve performance, or possibly
even to conserve memory.
.. data:: ac_in_buffer_size
The asynchronous input buffer size (default ``4096``).
.. data:: ac_out_buffer_size
The asynchronous output buffer size (default ``4096``).
Unlike :class:`asyncore.dispatcher`, :class:`async_chat` allows you to
define a first-in-first-out queue (fifo) of *producers*. A producer need
have only one method, :meth:`more`, which should return data to be
transmitted on the channel.
The producer indicates exhaustion (*i.e.* that it contains no more data) by
having its :meth:`more` method return the empty string. At this point the
:class:`async_chat` object removes the producer from the fifo and starts
using the next producer, if any. When the producer fifo is empty the
:meth:`handle_write` method does nothing. You use the channel object's
:meth:`set_terminator` method to describe how to recognize the end of, or
an important breakpoint in, an incoming transmission from the remote
endpoint.
To build a functioning :class:`async_chat` subclass your input methods
:meth:`collect_incoming_data` and :meth:`found_terminator` must handle the
data that the channel receives asynchronously. The methods are described
below.
.. method:: async_chat.close_when_done()
Pushes a ``None`` on to the producer fifo. When this producer is popped off
the fifo it causes the channel to be closed.
.. method:: async_chat.collect_incoming_da