XDR Data Description

The following example is a short XDR data description of a file data structure that might be used to transfer files from one machine to another.

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Example C–2 XDR File Data Structure

const MAXUSERNAME = 32;/* max length of a user name */
const MAXFILELEN = 65535;  /* max length of a file */
const MAXNAMELEN = 255;    /* max length of a file name */

/* Types of files: */
enum filekind {
 	TEXT = 0, /* ascii data */
 	DATA = 1, /* raw data */
 	EXEC = 2  /* executable */
 };

/* File information, per kind of file: */
union filetype switch (filekind kind) {
 	case TEXT:
 		void;                           /* no extra information */
 	case DATA:
 		string creator<MAXNAMELEN>;     /* data creator */
 	case EXEC:
 		string interpreter<MAXNAMELEN>; /*proginterptr*/
};

/* A complete file: */
struct file {
 	string filename<MAXNAMELEN>;        /* name of file */
 	filetype type;                      /* info about file */
 	string owner<MAXUSERNAME>;          /* owner of file */
 	opaque data<MAXFILELEN>;            /* file data */
};

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Suppose now that a user named linda wants to store her LISP program sillyprog that contains just the data "quit." Her file would be encoded as listed in the following table.

Table C–1 XDR Data Description Example

Offset	Hex Bytes	ASCII	Description
0	00 00 00 09	–	Length of file name = 9
4	73 69 6c 6c	sill	File name characters
8	79 70 72 6f	ypro	More characters
12	67 00 00 00	g	3 zero-bytes of fill
16	00 00 00 02	–	Filekind is EXEC = 2
20	00 00 00 04	–	Length of interpreter = 4
24	6c 69 73 70	lisp	Interpreter characters
28	00 00 00 04	–	Length of owner = 4
32	6a 6f 68 6e	linda	Owner characters
36	00 00 00 06	–	Length of file data = 6
40	28 71 75 69	(qu	File data bytes
44	74 29 00 00	t)	2 zero-bytes of fill