This module builds on the 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. asynchat defines the abstract class
async_chat that you subclass, providing implementations of the
collect_incoming_data() and found_terminator()
methods. It uses the same asynchronous loop as asyncore, and
the two types of channel, asyncore.dispatcher and
asynchat.async_chat, can freely be mixed in the channel map.
Typically an asyncore.dispatcher server channel generates new
asynchat.async_chat channel objects as it receives incoming
connection requests.
-
This class is an abstract subclass of asyncore.dispatcher. To make
practical use of the code you must subclass async_chat, providing
meaningful collect_incoming_data() and found_terminator()
methods. The asyncore.dispatcher methods can be
used, although not all make sense in a message/response context.
Like asyncore.dispatcher, async_chat defines a set of events
that are generated by an analysis of socket conditions after a
select() call. Once the polling loop has been started the
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.
- ac_in_buffer_size
-
The asynchronous input buffer size (default
4096 ).
- ac_out_buffer_size
-
The asynchronous output buffer size (default
4096 ).
Unlike asyncore.dispatcher, async_chat allows you to define
a first-in-first-out queue (fifo) of producers. A producer need have
only one method, 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 more() method return the empty string. At
this point the async_chat object removes the producer from the fifo
and starts using the next producer, if any. When the producer fifo is empty
the handle_write() method does nothing. You use the channel object's
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 async_chat subclass your
input methods collect_incoming_data() and
found_terminator() must handle the data that the channel receives
asynchronously. The methods are described below.
-
Pushes a
None on to the producer fifo. When this producer is
popped off the fifo it causes the channel to be closed.
collect_incoming_data( |
data) |
-
Called with data holding an arbitrary amount of received data.
The default method, which must be overridden, raises a NotImplementedError exception.
-
In emergencies this method will discard any data held in the input and/or
output buffers and the producer fifo.
-
Called when the incoming data stream matches the termination condition
set by set_terminator. The default method, which must be overridden,
raises a NotImplementedError exception. The buffered input data should
be available via an instance attribute.
-
Returns the current terminator for the channel.
-
Called when the channel is closed. The default method silently closes
the channel's socket.
-
Called when a read event fires on the channel's socket in the
asynchronous loop. The default method checks for the termination
condition established by set_terminator(), which can be either
the appearance of a particular string in the input stream or the receipt
of a particular number of characters. When the terminator is found,
handle_read calls the found_terminator() method after
calling collect_incoming_data() with any data preceding the
terminating condition.
-
Called when the application may write data to the channel.
The default method calls the initiate_send() method, which in turn
will call refill_buffer() to collect data from the producer
fifo associated with the channel.
-
Creates a simple_producer object (see below) containing the data and
pushes it on to the channel's
producer_fifo to ensure its
transmission. This is all you need to do to have the channel write
the data out to the network, although it is possible to use your
own producers in more complex schemes to implement encryption and
chunking, for example.
push_with_producer( |
producer) |
-
Takes a producer object and adds it to the producer fifo associated with
the channel. When all currently-pushed producers have been exhausted
the channel will consume this producer's data by calling its
more() method and send the data to the remote endpoint.
-
Should return
True for the channel to be included in the set of
channels tested by the select() loop for readability.
-
Refills the output buffer by calling the more() method of the
producer at the head of the fifo. If it is exhausted then the
producer is popped off the fifo and the next producer is activated.
If the current producer is, or becomes,
None then the channel
is closed.
-
Sets the terminating condition to be recognised on the channel.
term
may be any of three types of value, corresponding to three different ways
to handle incoming protocol data.
term |
Description |
string |
Will call found_terminator() when the
string is found in the input stream |
integer |
Will call found_terminator() when the
indicated number of characters have been received |
None |
The channel continues to collect data forever |
Note that any data following the terminator will be available for reading by
the channel after found_terminator() is called.
-
Should return
True as long as items remain on the producer fifo,
or the channel is connected and the channel's output buffer is non-empty.
Release 2.5.2, documentation updated on 21st February, 2008.
See About this document... for information on suggesting changes.
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