Document asyncio transport APIs
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Antoine Pitrou
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@ -242,6 +242,176 @@ buffer size reaches the low-water mark.
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Transports
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----------
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Transports are classed provided by :mod:`asyncio` in order to abstract
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various kinds of communication channels. You generally won't instantiate
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a transport yourself; instead, you will call a :class:`EventLoop` method
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which will create the transport and try to initiate the underlying
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communication channel, calling you back when it succeeds.
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Once the communication channel is established, a transport is always
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paired with a :ref:`protocol <protocol>` instance. The protocol can
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then call the transport's methods for various purposes.
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:mod:`asyncio` currently implements transports for TCP, UDP, SSL, and
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subprocess pipes. The methods available on a transport depend on
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the transport's kind.
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Methods common to all transports
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. method:: close(self)
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Close the transport. If the transport has a buffer for outgoing
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data, buffered data will be flushed asynchronously. No more data
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will be received. After all buffered data is flushed, the
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protocol's :meth:`connection_lost` method will be called with
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:const:`None` as its argument.
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.. method:: get_extra_info(name, default=None)
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Return optional transport information. *name* is a string representing
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the piece of transport-specific information to get, *default* is the
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value to return if the information doesn't exist.
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This method allows transport implementations to easily expose
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channel-specific information.
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Methods of readable streaming transports
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. method:: pause_reading()
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Pause the receiving end of the transport. No data will be passed to
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the protocol's :meth:`data_received` method until meth:`resume_reading`
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is called.
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.. method:: resume_reading()
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Resume the receiving end. The protocol's :meth:`data_received` method
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will be called once again if some data is available for reading.
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Methods of writable streaming transports
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. method:: write(data)
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Write some *data* bytes to the transport.
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This method does not block; it buffers the data and arranges for it
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to be sent out asynchronously.
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.. method:: writelines(list_of_data)
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Write a list (or any iterable) of data bytes to the transport.
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This is functionally equivalent to calling :meth:`write` on each
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element yielded by the iterable, but may be implemented more efficiently.
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.. method:: write_eof()
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Close the write end of the transport after flushing buffered data.
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Data may still be received.
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This method can raise :exc:`NotImplementedError` if the transport
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(e.g. SSL) doesn't support half-closes.
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.. method:: can_write_eof()
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Return :const:`True` if the transport supports :meth:`write_eof`,
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:const:`False` if not.
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.. method:: abort()
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Close the transport immediately, without waiting for pending operations
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to complete. Buffered data will be lost. No more data will be received.
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The protocol's :meth:`connection_lost` method will eventually be
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called with :const:`None` as its argument.
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.. method:: set_write_buffer_limits(high=None, low=None)
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Set the *high*- and *low*-water limits for write flow control.
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These two values control when call the protocol's
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:meth:`pause_writing` and :meth:`resume_writing` methods are called.
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If specified, the low-water limit must be less than or equal to the
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high-water limit. Neither *high* nor *low* can be negative.
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The defaults are implementation-specific. If only the
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high-water limit is given, the low-water limit defaults to a
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implementation-specific value less than or equal to the
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high-water limit. Setting *high* to zero forces *low* to zero as
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well, and causes :meth:`pause_writing` to be called whenever the
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buffer becomes non-empty. Setting *low* to zero causes
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:meth:`resume_writing` to be called only once the buffer is empty.
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Use of zero for either limit is generally sub-optimal as it
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reduces opportunities for doing I/O and computation
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concurrently.
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.. method:: get_write_buffer_size()
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Return the current size of the output buffer used by the transport.
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Methods of datagram transports
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. method:: sendto(data, addr=None)
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Send the *data* bytes to the remote peer given by *addr* (a
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transport-dependent target address). If *addr* is :const:`None`, the
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data is sent to the target address given on transport creation.
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This method does not block; it buffers the data and arranges for it
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to be sent out asynchronously.
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.. method:: abort()
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Close the transport immediately, without waiting for pending operations
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to complete. Buffered data will be lost. No more data will be received.
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The protocol's :meth:`connection_lost` method will eventually be
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called with :const:`None` as its argument.
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Methods of subprocess transports
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. method:: get_pid()
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Return the subprocess process id as an integer.
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.. method:: get_returncode()
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Return the subprocess returncode as an integer or :const:`None`
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if it hasn't returned, similarly to the
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:attr:`subprocess.Popen.returncode` attribute.
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.. method:: get_pipe_transport(fd)
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Return the transport for the communication pipe correspondong to the
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integer file descriptor *fd*. The return value can be a readable or
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writable streaming transport, depending on the *fd*. If *fd* doesn't
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correspond to a pipe belonging to this transport, :const:`None` is
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returned.
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.. method:: send_signal(signal)
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Send the *signal* number to the subprocess, as in
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:meth:`subprocess.Popen.send_signal`.
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.. method:: terminate()
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Ask the subprocess to stop, as in :meth:`subprocess.Popen.terminate`.
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This method is an alias for the :meth:`close` method.
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On POSIX systems, this method sends SIGTERM to the subprocess.
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On Windows, the Windows API function TerminateProcess() is called to
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stop the subprocess.
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.. method:: kill(self)
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Kill the subprocess, as in :meth:`subprocess.Popen.kill`
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On POSIX systems, the function sends SIGKILL to the subprocess.
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On Windows, this method is an alias for :meth:`terminate`.
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.. _sync:
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