
Streams (high-level API)
************************


Stream functions
================

asyncio.open_connection(host=None, port=None, *, loop=None, limit=None, **kwds)

   A wrapper for "create_connection()" returning a (reader, writer)
   pair.

   The reader returned is a "StreamReader" instance; the writer is a
   "StreamWriter" instance.

   The arguments are all the usual arguments to
   "BaseEventLoop.create_connection()" except *protocol_factory*; most
   common are positional host and port, with various optional keyword
   arguments following.

   Additional optional keyword arguments are *loop* (to set the event
   loop instance to use) and *limit* (to set the buffer limit passed
   to the "StreamReader").

   (If you want to customize the "StreamReader" and/or
   "StreamReaderProtocol" classes, just copy the code -- there's
   really nothing special here except some convenience.)

   This function is a *coroutine*.

asyncio.start_server(client_connected_cb, host=None, port=None, *, loop=None, limit=None, **kwds)

   Start a socket server, with a callback for each client connected.
   The return value is the same as "create_server()".

   The *client_connected_cb* parameter is called with two parameters:
   *client_reader*, *client_writer*.  *client_reader* is a
   "StreamReader" object, while *client_writer* is a "StreamWriter"
   object.  The *client_connected_cb* parameter can either be a plain
   callback function or a *coroutine function*; if it is a coroutine
   function, it will be automatically converted into a "Task".

   The rest of the arguments are all the usual arguments to
   "create_server()" except *protocol_factory*; most common are
   positional *host* and *port*, with various optional keyword
   arguments following.

   Additional optional keyword arguments are *loop* (to set the event
   loop instance to use) and *limit* (to set the buffer limit passed
   to the "StreamReader").

   This function is a *coroutine*.

asyncio.open_unix_connection(path=None, *, loop=None, limit=None, **kwds)

   A wrapper for "create_unix_connection()" returning a (reader,
   writer) pair.

   See "open_connection()" for information about return value and
   other details.

   This function is a *coroutine*.

   Availability: UNIX.

asyncio.start_unix_server(client_connected_cb, path=None, *, loop=None, limit=None, **kwds)

   Start a UNIX Domain Socket server, with a callback for each client
   connected.

   See "start_server()" for information about return value and other
   details.

   This function is a *coroutine*.

   Availability: UNIX.


StreamReader
============

class class asyncio.StreamReader(limit=None, loop=None)

   exception()

      Get the exception.

   feed_eof()

      Acknowledge the EOF.

   feed_data(data)

      Feed *data* bytes in the internal buffer.  Any operations
      waiting for the data will be resumed.

   set_exception(exc)

      Set the exception.

   set_transport(transport)

      Set the transport.

   read(n=-1)

      Read up to *n* bytes.  If *n* is not provided, or set to "-1",
      read until EOF and return all read bytes.

      If the EOF was received and the internal buffer is empty, return
      an empty "bytes" object.

      This method is a *coroutine*.

   readline()

      Read one line, where "line" is a sequence of bytes ending with
      "\n".

      If EOF is received, and "\n" was not found, the method will
      return the partial read bytes.

      If the EOF was received and the internal buffer is empty, return
      an empty "bytes" object.

      This method is a *coroutine*.

   readexactly(n)

      Read exactly *n* bytes. Raise an "IncompleteReadError" if the
      end of the stream is reached before *n* can be read, the
      "IncompleteReadError.partial" attribute of the exception
      contains the partial read bytes.

      This method is a *coroutine*.

   at_eof()

      Return "True" if the buffer is empty and "feed_eof()" was
      called.


StreamWriter
============

class class asyncio.StreamWriter(transport, protocol, reader, loop)

   Wraps a Transport.

   This exposes "write()", "writelines()", "can_write_eof()",
   "write_eof()", "get_extra_info()" and "close()".  It adds "drain()"
   which returns an optional "Future" on which you can wait for flow
   control.  It also adds a transport attribute which references the
   "Transport" directly.

   transport

      Transport.

   can_write_eof()

      Return "True" if the transport supports "write_eof()", "False"
      if not. See "WriteTransport.can_write_eof()".

   close()

      Close the transport: see "BaseTransport.close()".

   drain()

      Wait until the write buffer of the underlying transport is
      flushed.

      The intended use is to write:

         w.write(data)
         yield from w.drain()

      When the transport buffer is full (the protocol is paused),
      block until the buffer is (partially) drained and the protocol
      is resumed. When there is nothing to wait for, the yield-from
      continues immediately.

      This method is a *coroutine*.

   get_extra_info(name, default=None)

      Return optional transport information: see
      "BaseTransport.get_extra_info()".

   write(data)

      Write some *data* bytes to the transport: see
      "WriteTransport.write()".

   writelines(data)

      Write a list (or any iterable) of data bytes to the transport:
      see "WriteTransport.writelines()".

   write_eof()

      Close the write end of the transport after flushing buffered
      data: see "WriteTransport.write_eof()".


StreamReaderProtocol
====================

class class asyncio.StreamReaderProtocol(stream_reader, client_connected_cb=None, loop=None)

   Trivial helper class to adapt between "Protocol" and
   "StreamReader". Sublclass of "Protocol".

   *stream_reader* is a "StreamReader" instance, *client_connected_cb*
   is an optional function called with (stream_reader, stream_writer)
   when a connection is made, *loop* is the event loop instance to
   use.

   (This is a helper class instead of making "StreamReader" itself a
   "Protocol" subclass, because the "StreamReader" has other potential
   uses, and to prevent the user of the "StreamReader" to accidentally
   call inappropriate methods of the protocol.)


IncompleteReadError
===================

exception exception asyncio.IncompleteReadError

      Incomplete read error, subclass of "EOFError".

   expected

      Total number of expected bytes ("int").

   partial

      Read bytes string before the end of stream was reached
      ("bytes").


Example
=======

Simple example querying HTTP headers of the URL passed on the command
line:

   import asyncio
   import urllib.parse
   import sys

   @asyncio.coroutine
   def print_http_headers(url):
       url = urllib.parse.urlsplit(url)
       reader, writer = yield from asyncio.open_connection(url.hostname, 80)
       query = ('HEAD {url.path} HTTP/1.0\r\n'
                'Host: {url.hostname}\r\n'
                '\r\n').format(url=url)
       writer.write(query.encode('latin-1'))
       while True:
           line = yield from reader.readline()
           if not line:
               break
           line = line.decode('latin1').rstrip()
           if line:
               print('HTTP header> %s' % line)

   url = sys.argv[1]
   loop = asyncio.get_event_loop()
   task = asyncio.async(print_http_headers(url))
   loop.run_until_complete(task)
   loop.close()

Usage:

   python example.py http://example.com/path/page.html
