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
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
Two class attributes can be modified, to improve
performance, or possibly even to conserve memory.
The asynchronous input buffer size (default 4096).
The asynchronous output buffer size (default 4096).
Unlike asyncore.dispatcher, async_chat allows you to define
a FIFO queue 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 bytes object. At this point the async_chat object removes the
producer from the queue and starts using the next producer, if any. When the
producer queue 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
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 queue. When this producer
is popped off the queue it causes the channel to be closed.
Called with data holding an arbitrary amount of received
data. The default method, which must be overridden, raises a
In emergencies this method will discard any data held in the
input and/or output buffers and the producer queue.
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.
Pushes data on to the channel’s queue 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.
Takes a producer object and adds it to the producer queue
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.
Sets the terminating condition to be recognized on the
channel. term may be any of three types of value, corresponding to three
different ways to handle incoming protocol data.
Will call found_terminator() when the string is found in the
Will call found_terminator() when the indicated number of
characters have been received
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.
The following partial example shows how HTTP requests can be
read with async_chat. A web server might create an http_request_handler object
for each incoming client connection. Notice that initially the channel
terminator is set to match the blank line at the end of the HTTP headers, and a
flag indicates that the headers are being read.
Once the headers have been read, if the request is of type
POST (indicating that further data are present in the input stream) then the
Content-Length: header is used to set a numeric terminator to read the right
amount of data from the channel.
The handle_request() method is called once all relevant
input has been marshalled, after setting the channel terminator to None to
ensure that any extraneous data sent by the web client are ignored.
sock, addr, sessions, log):
self.ibuffer = 
self.reading_headers = True
self.log = log
self.reading_headers = False
self.ibuffer = 
self.op.upper() == b"POST":
self.handling = True
browsers sometimes over-send
self.cgi_data = parse(self.headers, b"".join(self.ibuffer))
self.handling = True