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Compaq FTAM Responder Support of
ISO FTAM Functions
OSI/FTAM Responder Manual—425199-001
4-10
Maximum-String-Length Checking of Data Values
Maximum-String-Length Checking of Data Values
The responder enforces strict rules on maximum-string-length checking. Every data
value received or sent by the responder is checked according to the rules described
below.
Write Operations
When writing data to the Guardian file system from the remote initiator, the responder
checks the length of each string against the maximum-string-length value established for
the file (the value proposed in the contents-type parameter of the open request or
returned in the open confirm). The responder first removes any escape sequences
contained in each string it receives before enforcing the maximum-string-length
limitation.
If the string length is greater than the proposed maximum-string-length value, or if the
string significance is fixed and the string length is less than the proposed value, the
responder returns a cancel request containing diagnostic message 1007, indicating an
unspecific FTAM protocol error.
Read Operations
The responder does no escape-sequence checking on the data it retrieves from the VFS
and sends to the remote initiator; it simply counts all bytes and packages them into
strings. For read operations on FTAM-3 files with a string-significance value of fixed,
the responder does check for strings whose length is smaller than the maximum-string-
length value. If any such strings are found, the responder returns a cancel request
containing diagnostic message 5027, indicating a bad read.
Limits on Small String-Length Values With Large PDUs
When the Compaq responder receives data from a remote initiator, it decodes the data
and stores it, as a sequence of strings, in an internal buffer with a maximum size of
25 KB. According to the NIST FTAM Phase 2 agreements, P-DATA carrying encoded
FTAM PDUs or data elements cannot exceed 16 KB; however, string-header
information in the buffer can cause the data in the buffer to be much larger than the
maximum size of the encoded data. Because each string in the buffer includes a fixed
number of bytes of header information, packing small strings into a large PDU can cause
the 25 KB buffer size to be exceeded.
During data decoding, the responder checks the length of the data. If the decoded data
cannot be accommodated in the 25 KB buffer, the responder generates a provider abort.
To avoid exceeding the buffer-size limit for writes to the Compaq responder, you can
either send a smaller number of strings per PDU or send larger strings. Sending larger
Note. Though a default value for each parameter is proposed, if there is a user-defined default
value for a particular combination of a file type and file code, that user-defined value will over-
ride the system default.