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.. include:: header.txt
====================
Connection objects
====================
Connection objects allow the sending and receiving of picklable
objects or strings. They can be thought of as message oriented
connected sockets.
Connection objects usually created using `processing.Pipe()` -- see
also `Listener and Clients <connection-ref.html>`_.
Connection objects have the following methods:
`send(obj)`
Send an object to the other end of the connection which should
be read using `recv()`.
The object must be picklable.
`recv()`
Return an object sent from the other end of the connection
using `send()`. Raises `EOFError` if there is nothing left to
receive and the other end was closed.
`fileno()`
Returns the file descriptor or handle used by the connection.
`close()`
Close the connection.
This is called automatically when the connection is garbage
collected.
`poll(timeout=0.0)`
Return whether there is any data available to be read within
`timeout` seconds.
If `timeout` is `None` then an infinite timeout is used.
Unlike the other blocking methods on Windows this method can
be interrupted by Ctrl-C.
`sendBytes(buffer)`
Send byte data from an object supporting the buffer interface
as a complete message.
Can be used to send strings or a view returned by `buffer()`.
`recvBytes()`
Return a complete message of byte data sent from the other end
of the connection as a string. Raises `EOFError` if there is
nothing left to receive and the other end was closed.
`recvBytesInto(buffer, offset=0)`
Read into `buffer` at position `offset` a complete message of
byte data sent from the other end of the connection and return
the number of bytes in the message. Raises `EOFError` if
there is nothing left to receive and the other end was closed.
`buffer` must be an object satisfying the writable buffer
interface and `offset` must be non-negative and less than
the length of `buffer` (in bytes).
If the buffer is too short then a `BufferTooShort` exception
is raised and the complete message is available as `e.args[0]`
where `e` is the exception instance.
For example:
>>> from processing import Pipe
>>> a, b = Pipe()
>>> a.send([1, 'hello', None])
>>> b.recv()
[1, 'hello', None]
>>> b.sendBytes('thank you')
>>> a.recvBytes()
'thank you'
>>> import array
>>> arr1 = array.array('i', range(5))
>>> arr2 = array.array('i', [0] * 10)
>>> a.sendBytes(arr1)
>>> count = b.recvBytesInto(arr2)
>>> assert count == len(arr1) * arr1.itemsize
>>> arr2
array('i', [0, 1, 2, 3, 4, 0, 0, 0, 0, 0])
.. warning::
The `recv()` method automatically unpickles the data it receives
which can be a security risk unless you can trust the process
which sent the message.
Therefore, unless the connection object was produced using
`Pipe()` you should only use the `recv()` and `send()` methods
after performing some sort of authentication. See `Authentication
keys <connection-ref.html#authentication-keys>`_.
.. warning::
If a process is killed while it is trying to read or write to a
pipe then the data in the pipe is likely to become corrupted
because it may become impossible to be sure where the message
boundaries lie.
.. _Prev: queue-objects.html
.. _Up: processing-ref.html
.. _Next: manager-objects.html
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