17.7. asynchat
— 异步 socket 指令/响应 处理器¶
Source code: Lib/asynchat.py
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.
-
class
asynchat.
async_chat
¶ This class is an abstract subclass of
asyncore.dispatcher
. To make practical use of the code you must subclassasync_chat
, providing meaningfulcollect_incoming_data()
andfound_terminator()
methods. Theasyncore.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 aselect()
call. Once the polling loop has been started theasync_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 itsmore()
method return the empty string. At this point theasync_chat
object removes the producer from the fifo and starts using the next producer, if any. When the producer fifo is empty thehandle_write()
method does nothing. You use the channel object’sset_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 methodscollect_incoming_data()
andfound_terminator()
must handle the data that the channel receives asynchronously. The methods are described below.-
-
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.
-
async_chat.
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.
-
async_chat.
discard_buffers
()¶ In emergencies this method will discard any data held in the input and/or output buffers and the producer fifo.
-
async_chat.
found_terminator
()¶ Called when the incoming data stream matches the termination condition set by
set_terminator()
. The default method, which must be overridden, raises aNotImplementedError
exception. The buffered input data should 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 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.
-
async_chat.
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.
-
async_chat.
set_terminator
(term)¶ 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.term
描述
string
Will call
found_terminator()
when the string is found in the input streaminteger
Will call
found_terminator()
when the indicated number of characters have been receivedNone
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.
17.7.1. asynchat - Auxiliary Classes¶
-
class
asynchat.
fifo
([list=None])¶ A
fifo
holding data which has been pushed by the application but not yet popped for writing to the channel. Afifo
is a list used to hold data and/or producers until they are required. If the list argument is provided then it should contain producers or data items to be written to the channel.-
is_empty
()¶ Returns
True
if and only if the fifo is empty.
-
push
(data)¶ Adds the given data (which may be a string or a producer object) to the producer fifo.
-
pop
()¶ If the fifo is not empty, returns
True, first()
, deleting the popped item. ReturnsFalse, None
for an empty fifo.
-
17.7.2. asynchat Example¶
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.
class http_request_handler(asynchat.async_chat):
def __init__(self, sock, addr, sessions, log):
asynchat.async_chat.__init__(self, sock=sock)
self.addr = addr
self.sessions = sessions
self.ibuffer = []
self.obuffer = ""
self.set_terminator("\r\n\r\n")
self.reading_headers = True
self.handling = False
self.cgi_data = None
self.log = log
def collect_incoming_data(self, data):
"""Buffer the data"""
self.ibuffer.append(data)
def found_terminator(self):
if self.reading_headers:
self.reading_headers = False
self.parse_headers("".join(self.ibuffer))
self.ibuffer = []
if self.op.upper() == "POST":
clen = self.headers.getheader("content-length")
self.set_terminator(int(clen))
else:
self.handling = True
self.set_terminator(None)
self.handle_request()
elif not self.handling:
self.set_terminator(None) # browsers sometimes over-send
self.cgi_data = parse(self.headers, "".join(self.ibuffer))
self.handling = True
self.ibuffer = []
self.handle_request()