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6. AN EXAMPLE OF AN XDR DATA DESCRIPTION Connected: An Internet Encyclopedia
6. AN EXAMPLE OF AN XDR DATA DESCRIPTION

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6. AN EXAMPLE OF AN XDR DATA DESCRIPTION

6. AN EXAMPLE OF AN XDR DATA DESCRIPTION

Here is a short XDR data description of a thing called a "file", which might be used to transfer files from one machine to another.

         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 interpretor<MAXNAMELEN>; /* program interpretor  */
         };

         /*
          * 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       */
         };

Suppose now that there is a user named "john" who wants to store his lisp program "sillyprog" that contains just the data "(quit)". His file would be encoded as follows:

       OFFSET  HEX BYTES       ASCII    COMMENTS
       ------  ---------       -----    --------
        0      00 00 00 09     ....     -- length of filename = 9
        4      73 69 6c 6c     sill     -- filename characters
        8      79 70 72 6f     ypro     -- ... and more characters ...
       12      67 00 00 00     g...     -- ... and 3 zero-bytes of fill
       16      00 00 00 02     ....     -- filekind is EXEC = 2
       20      00 00 00 04     ....     -- length of interpretor = 4
       24      6c 69 73 70     lisp     -- interpretor characters
       28      00 00 00 04     ....     -- length of owner = 4
       32      6a 6f 68 6e     john     -- owner characters
       36      00 00 00 06     ....     -- length of file data = 6
       40      28 71 75 69     (qui     -- file data bytes ...
       44      74 29 00 00     t)..     -- ... and 2 zero-bytes of fill


Next: 7. TRADEMARKS AND OWNERS

Connected: An Internet Encyclopedia
6. AN EXAMPLE OF AN XDR DATA DESCRIPTION

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