mirror of https://github.com/python/cpython
315 lines
12 KiB
ReStructuredText
315 lines
12 KiB
ReStructuredText
|
|
:mod:`asynchat` --- Asynchronous socket command/response handler
|
|
================================================================
|
|
|
|
.. module:: asynchat
|
|
:synopsis: Support for asynchronous command/response protocols.
|
|
.. moduleauthor:: Sam Rushing <rushing@nightmare.com>
|
|
.. sectionauthor:: Steve Holden <sholden@holdenweb.com>
|
|
|
|
|
|
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
|
|
:cfunc:`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_data(data)
|
|
|
|
Called with *data* holding an arbitrary amount of received data. The
|
|
default method, which must be overridden, raises a
|
|
:exc:`NotImplementedError` exception.
|
|
|
|
|
|
.. method:: async_chat._collect_incoming_data(data)
|
|
|
|
Sample implementation of a data collection rutine to be used in conjunction
|
|
with :meth:`_get_data` in a user-specified :meth:`found_terminator`.
|
|
|
|
|
|
.. method:: async_chat.discard_buffers()
|
|
|
|
In emergencies this method will discard any data held in the input and/or
|
|
output buffers and the producer fifo.
|
|
|
|
|
|
.. method:: async_chat.found_terminator()
|
|
|
|
Called when the incoming data stream matches the termination condition set
|
|
by :meth:`set_terminator`. The default method, which must be overridden,
|
|
raises a :exc:`NotImplementedError` exception. The buffered input data
|
|
should be available via an instance attribute.
|
|
|
|
|
|
.. method:: async_chat._get_data()
|
|
|
|
Will return and clear the data received with the sample
|
|
:meth:`_collect_incoming_data` implementation.
|
|
|
|
|
|
.. method:: async_chat.get_terminator()
|
|
|
|
Returns the current terminator for the channel.
|
|
|
|
|
|
.. method:: async_chat.handle_close()
|
|
|
|
Called when the channel is closed. The default method silently closes the
|
|
channel's socket.
|
|
|
|
|
|
.. method:: async_chat.handle_read()
|
|
|
|
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 :meth:`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, :meth:`handle_read` calls the
|
|
:meth:`found_terminator` method after calling :meth:`collect_incoming_data`
|
|
with any data preceding the terminating condition.
|
|
|
|
|
|
.. method:: async_chat.handle_write()
|
|
|
|
Called when the application may write data to the channel. The default
|
|
method calls the :meth:`initiate_send` method, which in turn will call
|
|
:meth:`refill_buffer` to collect data from the producer fifo associated
|
|
with the channel.
|
|
|
|
|
|
.. method:: async_chat.push(data)
|
|
|
|
Creates a :class:`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.
|
|
|
|
|
|
.. method:: 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 :meth:`more`
|
|
method and send the data to the remote endpoint.
|
|
|
|
|
|
.. method:: async_chat.readable()
|
|
|
|
Should return ``True`` for the channel to be included in the set of
|
|
channels tested by the :cfunc:`select` loop for readability.
|
|
|
|
|
|
.. method:: async_chat.refill_buffer()
|
|
|
|
Refills the output buffer by calling the :meth:`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.
|
|
|
|
|
|
.. method:: 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 | Description |
|
|
+===========+=============================================+
|
|
| *string* | Will call :meth:`found_terminator` when the |
|
|
| | string is found in the input stream |
|
|
+-----------+---------------------------------------------+
|
|
| *integer* | Will call :meth:`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 :meth:`found_terminator` is called.
|
|
|
|
|
|
.. method:: async_chat.writable()
|
|
|
|
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.
|
|
|
|
|
|
asynchat - Auxiliary Classes and Functions
|
|
------------------------------------------
|
|
|
|
|
|
.. class:: simple_producer(data, buffer_size=512)
|
|
|
|
A :class:`simple_producer` takes a chunk of data and an optional buffer
|
|
size. Repeated calls to its :meth:`more` method yield successive chunks of
|
|
the data no larger than *buffer_size*.
|
|
|
|
|
|
.. method:: more()
|
|
|
|
Produces the next chunk of information from the producer, or returns the
|
|
empty string.
|
|
|
|
|
|
.. class:: fifo(list=None)
|
|
|
|
Each channel maintains a :class:`fifo` holding data which has been pushed
|
|
by the application but not yet popped for writing to the channel. A
|
|
:class:`fifo` 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.
|
|
|
|
|
|
.. method:: is_empty()
|
|
|
|
Returns ``True`` if and only if the fifo is empty.
|
|
|
|
|
|
.. method:: first()
|
|
|
|
Returns the least-recently :meth:`push`\ ed item from the fifo.
|
|
|
|
|
|
.. method:: push(data)
|
|
|
|
Adds the given data (which may be a string or a producer object) to the
|
|
producer fifo.
|
|
|
|
|
|
.. method:: pop()
|
|
|
|
If the fifo is not empty, returns ``True, first()``, deleting the popped
|
|
item. Returns ``False, None`` for an empty fifo.
|
|
|
|
The :mod:`asynchat` module also defines one utility function, which may be of
|
|
use in network and textual analysis operations.
|
|
|
|
|
|
.. function:: find_prefix_at_end(haystack, needle)
|
|
|
|
Returns ``True`` if string *haystack* ends with any non-empty prefix of
|
|
string *needle*.
|
|
|
|
|
|
.. _asynchat-example:
|
|
|
|
asynchat Example
|
|
----------------
|
|
|
|
The following partial example shows how HTTP requests can be read with
|
|
:class:`async_chat`. A web server might create an
|
|
:class:`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 :meth:`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 = b""
|
|
self.set_terminator(b"\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() == b"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, b"".join(self.ibuffer))
|
|
self.handling = True
|
|
self.ibuffer = []
|
|
self.handle_request()
|