3.11 String

The standard defines a string of n (numbered 0 through n-1) ASCII bytes to be the number n encoded as an unsigned integer (as described above), and followed by the n bytes of the string. Byte m of the string always precedes byte m+1 of the string, and byte 0 of the string always follows the string's length. If n is not a multiple of four, then the n bytes are followed by enough (0 to 3) residual zero bytes, r, to make the total byte count a multiple of four. Counted byte strings are declared as follows:

         string object<m>;
      or
         string object<>;

The constant m denotes an upper bound of the number of bytes that a string may contain. If m is not specified, as in the second declaration, it is assumed to be (2**32) - 1, the maximum length. The constant m would normally be found in a protocol specification. For example, a filing protocol may state that a file name can be no longer than 255 bytes, as follows:

         string filename<255>;

            0     1     2     3     4     5   ...
         +-----+-----+-----+-----+-----+-----+...+-----+-----+...+-----+
         |        length n       |byte0|byte1|...| n-1 |  0  |...|  0  |
         +-----+-----+-----+-----+-----+-----+...+-----+-----+...+-----+
         |<-------4 bytes------->|<------n bytes------>|<---r bytes--->|
                                 |<----n+r (where (n+r) mod 4 = 0)---->|
                                                                  STRING

It is an error to encode a length greater than the maximum described in the specification.