11.16.1 Packer Objects

Packer is the class for packing data into XDR representation. The Packer class is instantiated with no arguments.

get_buffer()

Returns the current pack buffer as a string.

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: pack_uint, pack_int, pack_enum, pack_bool, pack_uhyper, and pack_hyper.

The following methods pack floating point numbers, however they require C library support. Without the optional C built-in module, both of these methods will raise an xdrlib.ConversionError exception. See the note at the end of this chapter for details.

pack_float(value)

Packs the single-precision floating point number value.

pack_double(value)

Packs the double-precision floating point number value.

The following methods support packing strings, bytes, and opaque data:

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.

pack_fopaque(n, data)

Packs a fixed length opaque data stream, similarly to pack_fstring.

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 pack_fstring.

pack_opaque(data)

Packs a variable length opaque data string, similarly to pack_string.

pack_bytes(bytes)

Packs a variable length byte stream, similarly to pack_string.

The following methods support packing arrays and lists:

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.

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 ValueError exception is raised if len(array) is not equal to n. As above, pack_item is the function used to pack each element.

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 pack_farray above.