Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | :mod:`asynchat` --- Asynchronous socket command/response handler |
| 2 | ================================================================ |
| 3 | |
| 4 | .. module:: asynchat |
| 5 | :synopsis: Support for asynchronous command/response protocols. |
Terry Jan Reedy | fa089b9 | 2016-06-11 15:02:54 -0400 | [diff] [blame] | 6 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 7 | .. moduleauthor:: Sam Rushing <rushing@nightmare.com> |
Josiah Carlson | 35bf9bf | 2008-07-07 04:24:24 +0000 | [diff] [blame] | 8 | .. sectionauthor:: Steve Holden <sholden@holdenweb.com> |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 9 | |
Raymond Hettinger | ead4975 | 2011-01-24 16:28:06 +0000 | [diff] [blame] | 10 | **Source code:** :source:`Lib/asynchat.py` |
| 11 | |
Guido van Rossum | 16591f4 | 2016-10-25 08:49:13 -0700 | [diff] [blame] | 12 | .. deprecated:: 3.6 |
| 13 | Please use :mod:`asyncio` instead. |
| 14 | |
Raymond Hettinger | ead4975 | 2011-01-24 16:28:06 +0000 | [diff] [blame] | 15 | -------------- |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 16 | |
Guido van Rossum | 4da459c | 2013-11-22 12:27:45 -0800 | [diff] [blame] | 17 | .. note:: |
| 18 | |
| 19 | This module exists for backwards compatibility only. For new code we |
| 20 | recommend using :mod:`asyncio`. |
Guido van Rossum | aa40775 | 2013-11-22 11:57:35 -0800 | [diff] [blame] | 21 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 22 | This module builds on the :mod:`asyncore` infrastructure, simplifying |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 23 | asynchronous clients and servers and making it easier to handle protocols |
| 24 | whose elements are terminated by arbitrary strings, or are of variable length. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 25 | :mod:`asynchat` defines the abstract class :class:`async_chat` that you |
| 26 | subclass, providing implementations of the :meth:`collect_incoming_data` and |
| 27 | :meth:`found_terminator` methods. It uses the same asynchronous loop as |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 28 | :mod:`asyncore`, and the two types of channel, :class:`asyncore.dispatcher` |
| 29 | and :class:`asynchat.async_chat`, can freely be mixed in the channel map. |
| 30 | Typically an :class:`asyncore.dispatcher` server channel generates new |
| 31 | :class:`asynchat.async_chat` channel objects as it receives incoming |
| 32 | connection requests. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 33 | |
| 34 | |
| 35 | .. class:: async_chat() |
| 36 | |
| 37 | This class is an abstract subclass of :class:`asyncore.dispatcher`. To make |
| 38 | practical use of the code you must subclass :class:`async_chat`, providing |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 39 | meaningful :meth:`collect_incoming_data` and :meth:`found_terminator` |
| 40 | methods. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 41 | The :class:`asyncore.dispatcher` methods can be used, although not all make |
| 42 | sense in a message/response context. |
| 43 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 44 | Like :class:`asyncore.dispatcher`, :class:`async_chat` defines a set of |
| 45 | events that are generated by an analysis of socket conditions after a |
Georg Brandl | 60203b4 | 2010-10-06 10:11:56 +0000 | [diff] [blame] | 46 | :c:func:`select` call. Once the polling loop has been started the |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 47 | :class:`async_chat` object's methods are called by the event-processing |
| 48 | framework with no action on the part of the programmer. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 49 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 50 | Two class attributes can be modified, to improve performance, or possibly |
| 51 | even to conserve memory. |
| 52 | |
| 53 | |
| 54 | .. data:: ac_in_buffer_size |
| 55 | |
| 56 | The asynchronous input buffer size (default ``4096``). |
| 57 | |
| 58 | |
| 59 | .. data:: ac_out_buffer_size |
| 60 | |
| 61 | The asynchronous output buffer size (default ``4096``). |
| 62 | |
| 63 | Unlike :class:`asyncore.dispatcher`, :class:`async_chat` allows you to |
Serhiy Storchaka | 98019e1 | 2016-05-16 09:10:43 +0300 | [diff] [blame] | 64 | define a :abbr:`FIFO (first-in, first-out)` queue of *producers*. A producer need |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 65 | have only one method, :meth:`more`, which should return data to be |
| 66 | transmitted on the channel. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 67 | The producer indicates exhaustion (*i.e.* that it contains no more data) by |
Serhiy Storchaka | 5e028ae | 2014-02-06 21:10:41 +0200 | [diff] [blame] | 68 | having its :meth:`more` method return the empty bytes object. At this point |
Serhiy Storchaka | 98019e1 | 2016-05-16 09:10:43 +0300 | [diff] [blame] | 69 | the :class:`async_chat` object removes the producer from the queue and starts |
| 70 | using the next producer, if any. When the producer queue is empty the |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 71 | :meth:`handle_write` method does nothing. You use the channel object's |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 72 | :meth:`set_terminator` method to describe how to recognize the end of, or |
| 73 | an important breakpoint in, an incoming transmission from the remote |
| 74 | endpoint. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 75 | |
| 76 | To build a functioning :class:`async_chat` subclass your input methods |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 77 | :meth:`collect_incoming_data` and :meth:`found_terminator` must handle the |
| 78 | data that the channel receives asynchronously. The methods are described |
| 79 | below. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 80 | |
| 81 | |
| 82 | .. method:: async_chat.close_when_done() |
| 83 | |
Serhiy Storchaka | 98019e1 | 2016-05-16 09:10:43 +0300 | [diff] [blame] | 84 | Pushes a ``None`` on to the producer queue. When this producer is popped off |
| 85 | the queue it causes the channel to be closed. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 86 | |
| 87 | |
| 88 | .. method:: async_chat.collect_incoming_data(data) |
| 89 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 90 | Called with *data* holding an arbitrary amount of received data. The |
| 91 | default method, which must be overridden, raises a |
| 92 | :exc:`NotImplementedError` exception. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 93 | |
| 94 | |
| 95 | .. method:: async_chat.discard_buffers() |
| 96 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 97 | In emergencies this method will discard any data held in the input and/or |
Serhiy Storchaka | 98019e1 | 2016-05-16 09:10:43 +0300 | [diff] [blame] | 98 | output buffers and the producer queue. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 99 | |
| 100 | |
| 101 | .. method:: async_chat.found_terminator() |
| 102 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 103 | Called when the incoming data stream matches the termination condition set |
| 104 | by :meth:`set_terminator`. The default method, which must be overridden, |
| 105 | raises a :exc:`NotImplementedError` exception. The buffered input data |
| 106 | should be available via an instance attribute. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 107 | |
| 108 | |
| 109 | .. method:: async_chat.get_terminator() |
| 110 | |
| 111 | Returns the current terminator for the channel. |
| 112 | |
| 113 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 114 | .. method:: async_chat.push(data) |
| 115 | |
Serhiy Storchaka | 98019e1 | 2016-05-16 09:10:43 +0300 | [diff] [blame] | 116 | Pushes data on to the channel's queue to ensure its transmission. |
Giampaolo RodolĂ | 8130290 | 2010-04-29 20:45:01 +0000 | [diff] [blame] | 117 | This is all you need to do to have the channel write the data out to the |
| 118 | network, although it is possible to use your own producers in more complex |
| 119 | schemes to implement encryption and chunking, for example. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 120 | |
| 121 | |
| 122 | .. method:: async_chat.push_with_producer(producer) |
| 123 | |
Serhiy Storchaka | 98019e1 | 2016-05-16 09:10:43 +0300 | [diff] [blame] | 124 | Takes a producer object and adds it to the producer queue associated with |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 125 | the channel. When all currently-pushed producers have been exhausted the |
| 126 | channel will consume this producer's data by calling its :meth:`more` |
| 127 | method and send the data to the remote endpoint. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 128 | |
| 129 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 130 | .. method:: async_chat.set_terminator(term) |
| 131 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 132 | Sets the terminating condition to be recognized on the channel. ``term`` |
| 133 | may be any of three types of value, corresponding to three different ways |
| 134 | to handle incoming protocol data. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 135 | |
| 136 | +-----------+---------------------------------------------+ |
| 137 | | term | Description | |
| 138 | +===========+=============================================+ |
| 139 | | *string* | Will call :meth:`found_terminator` when the | |
| 140 | | | string is found in the input stream | |
| 141 | +-----------+---------------------------------------------+ |
| 142 | | *integer* | Will call :meth:`found_terminator` when the | |
| 143 | | | indicated number of characters have been | |
| 144 | | | received | |
| 145 | +-----------+---------------------------------------------+ |
| 146 | | ``None`` | The channel continues to collect data | |
| 147 | | | forever | |
| 148 | +-----------+---------------------------------------------+ |
| 149 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 150 | Note that any data following the terminator will be available for reading |
| 151 | by the channel after :meth:`found_terminator` is called. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 152 | |
| 153 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 154 | .. _asynchat-example: |
| 155 | |
| 156 | asynchat Example |
| 157 | ---------------- |
| 158 | |
| 159 | The following partial example shows how HTTP requests can be read with |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 160 | :class:`async_chat`. A web server might create an |
| 161 | :class:`http_request_handler` object for each incoming client connection. |
| 162 | Notice that initially the channel terminator is set to match the blank line at |
| 163 | the end of the HTTP headers, and a flag indicates that the headers are being |
| 164 | read. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 165 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 166 | Once the headers have been read, if the request is of type POST (indicating |
| 167 | that further data are present in the input stream) then the |
| 168 | ``Content-Length:`` header is used to set a numeric terminator to read the |
| 169 | right amount of data from the channel. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 170 | |
| 171 | The :meth:`handle_request` method is called once all relevant input has been |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 172 | marshalled, after setting the channel terminator to ``None`` to ensure that |
| 173 | any extraneous data sent by the web client are ignored. :: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 174 | |
Giampaolo Rodola' | 0fb41b5 | 2012-05-15 15:46:00 +0200 | [diff] [blame] | 175 | |
| 176 | import asynchat |
| 177 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 178 | class http_request_handler(asynchat.async_chat): |
| 179 | |
Benjamin Peterson | 9bc9351 | 2008-09-22 22:10:59 +0000 | [diff] [blame] | 180 | def __init__(self, sock, addr, sessions, log): |
| 181 | asynchat.async_chat.__init__(self, sock=sock) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 182 | self.addr = addr |
| 183 | self.sessions = sessions |
| 184 | self.ibuffer = [] |
Josiah Carlson | 1893ce7 | 2008-07-07 04:23:14 +0000 | [diff] [blame] | 185 | self.obuffer = b"" |
| 186 | self.set_terminator(b"\r\n\r\n") |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 187 | self.reading_headers = True |
| 188 | self.handling = False |
| 189 | self.cgi_data = None |
| 190 | self.log = log |
| 191 | |
| 192 | def collect_incoming_data(self, data): |
| 193 | """Buffer the data""" |
| 194 | self.ibuffer.append(data) |
| 195 | |
| 196 | def found_terminator(self): |
| 197 | if self.reading_headers: |
| 198 | self.reading_headers = False |
Serhiy Storchaka | 5e028ae | 2014-02-06 21:10:41 +0200 | [diff] [blame] | 199 | self.parse_headers(b"".join(self.ibuffer)) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 200 | self.ibuffer = [] |
Josiah Carlson | 1893ce7 | 2008-07-07 04:23:14 +0000 | [diff] [blame] | 201 | if self.op.upper() == b"POST": |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 202 | clen = self.headers.getheader("content-length") |
| 203 | self.set_terminator(int(clen)) |
| 204 | else: |
| 205 | self.handling = True |
| 206 | self.set_terminator(None) |
| 207 | self.handle_request() |
| 208 | elif not self.handling: |
Serhiy Storchaka | dba9039 | 2016-05-10 12:01:23 +0300 | [diff] [blame] | 209 | self.set_terminator(None) # browsers sometimes over-send |
Josiah Carlson | 1893ce7 | 2008-07-07 04:23:14 +0000 | [diff] [blame] | 210 | self.cgi_data = parse(self.headers, b"".join(self.ibuffer)) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 211 | self.handling = True |
| 212 | self.ibuffer = [] |
| 213 | self.handle_request() |