You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
279 lines
7.9 KiB
279 lines
7.9 KiB
:mod:`xdrlib` --- Encode and decode XDR data
|
|
============================================
|
|
|
|
.. module:: xdrlib
|
|
:synopsis: Encoders and decoders for the External Data Representation (XDR).
|
|
|
|
**Source code:** :source:`Lib/xdrlib.py`
|
|
|
|
.. index::
|
|
single: XDR
|
|
single: External Data Representation
|
|
|
|
--------------
|
|
|
|
The :mod:`xdrlib` module supports the External Data Representation Standard as
|
|
described in :rfc:`1014`, written by Sun Microsystems, Inc. June 1987. It
|
|
supports most of the data types described in the RFC.
|
|
|
|
The :mod:`xdrlib` module defines two classes, one for packing variables into XDR
|
|
representation, and another for unpacking from XDR representation. There are
|
|
also two exception classes.
|
|
|
|
|
|
.. class:: Packer()
|
|
|
|
:class:`Packer` is the class for packing data into XDR representation. The
|
|
:class:`Packer` class is instantiated with no arguments.
|
|
|
|
|
|
.. class:: Unpacker(data)
|
|
|
|
``Unpacker`` is the complementary class which unpacks XDR data values from a
|
|
string buffer. The input buffer is given as *data*.
|
|
|
|
|
|
.. seealso::
|
|
|
|
:rfc:`1014` - XDR: External Data Representation Standard
|
|
This RFC defined the encoding of data which was XDR at the time this module was
|
|
originally written. It has apparently been obsoleted by :rfc:`1832`.
|
|
|
|
:rfc:`1832` - XDR: External Data Representation Standard
|
|
Newer RFC that provides a revised definition of XDR.
|
|
|
|
|
|
.. _xdr-packer-objects:
|
|
|
|
Packer Objects
|
|
--------------
|
|
|
|
:class:`Packer` instances have the following methods:
|
|
|
|
|
|
.. method:: Packer.get_buffer()
|
|
|
|
Returns the current pack buffer as a string.
|
|
|
|
|
|
.. method:: Packer.reset()
|
|
|
|
Resets the pack buffer to the empty string.
|
|
|
|
In general, you can pack any of the most common XDR data types by calling the
|
|
appropriate ``pack_type()`` method. Each method takes a single argument, the
|
|
value to pack. The following simple data type packing methods are supported:
|
|
:meth:`pack_uint`, :meth:`pack_int`, :meth:`pack_enum`, :meth:`pack_bool`,
|
|
:meth:`pack_uhyper`, and :meth:`pack_hyper`.
|
|
|
|
|
|
.. method:: Packer.pack_float(value)
|
|
|
|
Packs the single-precision floating point number *value*.
|
|
|
|
|
|
.. method:: Packer.pack_double(value)
|
|
|
|
Packs the double-precision floating point number *value*.
|
|
|
|
The following methods support packing strings, bytes, and opaque data:
|
|
|
|
|
|
.. method:: Packer.pack_fstring(n, s)
|
|
|
|
Packs a fixed length string, *s*. *n* is the length of the string but it is
|
|
*not* packed into the data buffer. The string is padded with null bytes if
|
|
necessary to guaranteed 4 byte alignment.
|
|
|
|
|
|
.. method:: Packer.pack_fopaque(n, data)
|
|
|
|
Packs a fixed length opaque data stream, similarly to :meth:`pack_fstring`.
|
|
|
|
|
|
.. method:: Packer.pack_string(s)
|
|
|
|
Packs a variable length string, *s*. The length of the string is first packed
|
|
as an unsigned integer, then the string data is packed with
|
|
:meth:`pack_fstring`.
|
|
|
|
|
|
.. method:: Packer.pack_opaque(data)
|
|
|
|
Packs a variable length opaque data string, similarly to :meth:`pack_string`.
|
|
|
|
|
|
.. method:: Packer.pack_bytes(bytes)
|
|
|
|
Packs a variable length byte stream, similarly to :meth:`pack_string`.
|
|
|
|
The following methods support packing arrays and lists:
|
|
|
|
|
|
.. method:: Packer.pack_list(list, pack_item)
|
|
|
|
Packs a *list* of homogeneous items. This method is useful for lists with an
|
|
indeterminate size; i.e. the size is not available until the entire list has
|
|
been walked. For each item in the list, an unsigned integer ``1`` is packed
|
|
first, followed by the data value from the list. *pack_item* is the function
|
|
that is called to pack the individual item. At the end of the list, an unsigned
|
|
integer ``0`` is packed.
|
|
|
|
For example, to pack a list of integers, the code might appear like this::
|
|
|
|
import xdrlib
|
|
p = xdrlib.Packer()
|
|
p.pack_list([1, 2, 3], p.pack_int)
|
|
|
|
|
|
.. method:: Packer.pack_farray(n, array, pack_item)
|
|
|
|
Packs a fixed length list (*array*) of homogeneous items. *n* is the length of
|
|
the list; it is *not* packed into the buffer, but a :exc:`ValueError` exception
|
|
is raised if ``len(array)`` is not equal to *n*. As above, *pack_item* is the
|
|
function used to pack each element.
|
|
|
|
|
|
.. method:: Packer.pack_array(list, pack_item)
|
|
|
|
Packs a variable length *list* of homogeneous items. First, the length of the
|
|
list is packed as an unsigned integer, then each element is packed as in
|
|
:meth:`pack_farray` above.
|
|
|
|
|
|
.. _xdr-unpacker-objects:
|
|
|
|
Unpacker Objects
|
|
----------------
|
|
|
|
The :class:`Unpacker` class offers the following methods:
|
|
|
|
|
|
.. method:: Unpacker.reset(data)
|
|
|
|
Resets the string buffer with the given *data*.
|
|
|
|
|
|
.. method:: Unpacker.get_position()
|
|
|
|
Returns the current unpack position in the data buffer.
|
|
|
|
|
|
.. method:: Unpacker.set_position(position)
|
|
|
|
Sets the data buffer unpack position to *position*. You should be careful about
|
|
using :meth:`get_position` and :meth:`set_position`.
|
|
|
|
|
|
.. method:: Unpacker.get_buffer()
|
|
|
|
Returns the current unpack data buffer as a string.
|
|
|
|
|
|
.. method:: Unpacker.done()
|
|
|
|
Indicates unpack completion. Raises an :exc:`Error` exception if all of the
|
|
data has not been unpacked.
|
|
|
|
In addition, every data type that can be packed with a :class:`Packer`, can be
|
|
unpacked with an :class:`Unpacker`. Unpacking methods are of the form
|
|
``unpack_type()``, and take no arguments. They return the unpacked object.
|
|
|
|
|
|
.. method:: Unpacker.unpack_float()
|
|
|
|
Unpacks a single-precision floating point number.
|
|
|
|
|
|
.. method:: Unpacker.unpack_double()
|
|
|
|
Unpacks a double-precision floating point number, similarly to
|
|
:meth:`unpack_float`.
|
|
|
|
In addition, the following methods unpack strings, bytes, and opaque data:
|
|
|
|
|
|
.. method:: Unpacker.unpack_fstring(n)
|
|
|
|
Unpacks and returns a fixed length string. *n* is the number of characters
|
|
expected. Padding with null bytes to guaranteed 4 byte alignment is assumed.
|
|
|
|
|
|
.. method:: Unpacker.unpack_fopaque(n)
|
|
|
|
Unpacks and returns a fixed length opaque data stream, similarly to
|
|
:meth:`unpack_fstring`.
|
|
|
|
|
|
.. method:: Unpacker.unpack_string()
|
|
|
|
Unpacks and returns a variable length string. The length of the string is first
|
|
unpacked as an unsigned integer, then the string data is unpacked with
|
|
:meth:`unpack_fstring`.
|
|
|
|
|
|
.. method:: Unpacker.unpack_opaque()
|
|
|
|
Unpacks and returns a variable length opaque data string, similarly to
|
|
:meth:`unpack_string`.
|
|
|
|
|
|
.. method:: Unpacker.unpack_bytes()
|
|
|
|
Unpacks and returns a variable length byte stream, similarly to
|
|
:meth:`unpack_string`.
|
|
|
|
The following methods support unpacking arrays and lists:
|
|
|
|
|
|
.. method:: Unpacker.unpack_list(unpack_item)
|
|
|
|
Unpacks and returns a list of homogeneous items. The list is unpacked one
|
|
element at a time by first unpacking an unsigned integer flag. If the flag is
|
|
``1``, then the item is unpacked and appended to the list. A flag of ``0``
|
|
indicates the end of the list. *unpack_item* is the function that is called to
|
|
unpack the items.
|
|
|
|
|
|
.. method:: Unpacker.unpack_farray(n, unpack_item)
|
|
|
|
Unpacks and returns (as a list) a fixed length array of homogeneous items. *n*
|
|
is number of list elements to expect in the buffer. As above, *unpack_item* is
|
|
the function used to unpack each element.
|
|
|
|
|
|
.. method:: Unpacker.unpack_array(unpack_item)
|
|
|
|
Unpacks and returns a variable length *list* of homogeneous items. First, the
|
|
length of the list is unpacked as an unsigned integer, then each element is
|
|
unpacked as in :meth:`unpack_farray` above.
|
|
|
|
|
|
.. _xdr-exceptions:
|
|
|
|
Exceptions
|
|
----------
|
|
|
|
Exceptions in this module are coded as class instances:
|
|
|
|
|
|
.. exception:: Error
|
|
|
|
The base exception class. :exc:`Error` has a single public attribute
|
|
:attr:`msg` containing the description of the error.
|
|
|
|
|
|
.. exception:: ConversionError
|
|
|
|
Class derived from :exc:`Error`. Contains no additional instance variables.
|
|
|
|
Here is an example of how you would catch one of these exceptions::
|
|
|
|
import xdrlib
|
|
p = xdrlib.Packer()
|
|
try:
|
|
p.pack_double(8.01)
|
|
except xdrlib.ConversionError as instance:
|
|
print('packing the double failed:', instance.msg)
|
|
|