asynchat — Asynchronous socket command/response handler¶

Source code:Lib/asynchat.py

This module builds on theasyncore infrastructure, simplifyingasynchronous clients and servers and making it easier to handle protocolswhose elements are terminated by arbitrary strings, or are of variable length.asynchat defines the abstract classasync_chat that yousubclass, providing implementations of thecollect_incoming_data() andfound_terminator() methods. It uses the same asynchronous loop asasyncore, and the two types of channel,asyncore.dispatcherandasynchat.async_chat, can freely be mixed in the channel map.Typically anasyncore.dispatcher server channel generates newasynchat.async_chat channel objects as it receives incomingconnection requests.

classasynchat.async_chat¶

This class is an abstract subclass ofasyncore.dispatcher. To makepractical use of the code you must subclassasync_chat, providingmeaningfulcollect_incoming_data() andfound_terminator()methods.Theasyncore.dispatcher methods can be used, although not all makesense in a message/response context.

Likeasyncore.dispatcher,async_chat defines a set ofevents that are generated by an analysis of socket conditions after aselect() call. Once the polling loop has been started theasync_chat object’s methods are called by the event-processingframework with no action on the part of the programmer.

Two class attributes can be modified, to improve performance, or possiblyeven to conserve memory.

ac_in_buffer_size¶

The asynchronous input buffer size (default4096).

ac_out_buffer_size¶

The asynchronous output buffer size (default4096).

Unlikeasyncore.dispatcher,async_chat allows you todefine aFIFO queue ofproducers. A producer needhave only one method,more(), which should return data to betransmitted on the channel.The producer indicates exhaustion (i.e. that it contains no more data) byhaving itsmore() method return the empty bytes object. At this pointtheasync_chat object removes the producer from the queue and startsusing the next producer, if any. When the producer queue is empty thehandle_write() method does nothing. You use the channel object’sset_terminator() method to describe how to recognize the end of, oran important breakpoint in, an incoming transmission from the remoteendpoint.

To build a functioningasync_chat subclass your input methodscollect_incoming_data() andfound_terminator() must handle thedata that the channel receives asynchronously. The methods are describedbelow.

async_chat.close_when_done()¶

Pushes aNone on to the producer queue. When this producer is popped offthe queue it causes the channel to be closed.

async_chat.collect_incoming_data(data)¶

Called withdata holding an arbitrary amount of received data. Thedefault method, which must be overridden, raises aNotImplementedError exception.

async_chat.discard_buffers()¶

In emergencies this method will discard any data held in the input and/oroutput buffers and the producer queue.

async_chat.found_terminator()¶

Called when the incoming data stream matches the termination condition setbyset_terminator(). The default method, which must be overridden,raises aNotImplementedError exception. The buffered input datashould be available via an instance attribute.

async_chat.get_terminator()¶

Returns the current terminator for the channel.

async_chat.push(data)¶

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 thenetwork, although it is possible to use your own producers in more complexschemes to implement encryption and chunking, for example.

async_chat.push_with_producer(producer)¶

Takes a producer object and adds it to the producer queue associated withthe channel. When all currently-pushed producers have been exhausted thechannel will consume this producer’s data by calling itsmore()method and send the data to the remote endpoint.

async_chat.set_terminator(term)¶

Sets the terminating condition to be recognized on the channel.termmay be any of three types of value, corresponding to three different waysto handle incoming protocol data.

term	Description
string	Will callfound_terminator() when thestring is found in the input stream
integer	Will callfound_terminator() when theindicated number of characters have beenreceived
None	The channel continues to collect dataforever

Note that any data following the terminator will be available for readingby the channel afterfound_terminator() is called.

importasynchatclasshttp_request_handler(asynchat.async_chat):def__init__(self,sock,addr,sessions,log):asynchat.async_chat.__init__(self,sock=sock)self.addr=addrself.sessions=sessionsself.ibuffer=[]self.obuffer=b""self.set_terminator(b"\r\n\r\n")self.reading_headers=Trueself.handling=Falseself.cgi_data=Noneself.log=logdefcollect_incoming_data(self,data):"""Buffer the data"""self.ibuffer.append(data)deffound_terminator(self):ifself.reading_headers:self.reading_headers=Falseself.parse_headers(b"".join(self.ibuffer))self.ibuffer=[]ifself.op.upper()==b"POST":clen=self.headers.getheader("content-length")self.set_terminator(int(clen))else:self.handling=Trueself.set_terminator(None)self.handle_request()elifnotself.handling:self.set_terminator(None)# browsers sometimes over-sendself.cgi_data=parse(self.headers,b"".join(self.ibuffer))self.handling=Trueself.ibuffer=[]self.handle_request()