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+
+:mod:`xdrlib` --- Encode and decode XDR data
+============================================
+
+.. module:: xdrlib
+   :synopsis: Encoders and decoders for the External Data Representation (XDR).
+
+
+.. 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 data member
+   :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, instance:
+       print 'packing the double failed:', instance.msg
+