Compaq FTAM Responder Support of | Maximum-String-Length Checking of Data Values |
ISO FTAM Functions | |
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.
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
OSI/FTAM Responder Manual—425199-001
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