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December 2018

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clarification on behavior of DFDL encodingErrorPolicy='error' and pre-decoding by implementations
by Mike Beckerle 06 Dec '18

06 Dec '18

The DFDL spec isn't clear on when encodingErrorPolicy 'error' is allowed to cause an error, and when one must be suppressed, if the implementation pre-decodes data into characters. Example: Suppose you have what turns out to be 8 characters of text, followed by some binary data. Suppose a DFDL implementation happens to always try to fill a buffer of 64 decoded characters, just for efficiency reasons. Depending on what is in the binary data, this may parse the 8 characters of text without error, but subsequently hit a decode error, because it has strayed into binary data past the text. There is no actual decode error in the data stream, because parsing should determine there are only 8 characters of text, and then switch to parsing the binary data using binary means. The DFDL spec doesn't say this isn't allowed to cause a decode error. Perhaps it is implied somewhere? But I didn't find it. The DFDL spec does point out that for asserts/discriminators with testKind pattern, that pattern matching may cause decode errors. But again, suppose the regex matching library an implementation uses happens to pre-fetch and pre-decode a bunch of characters, but the regex matching library then finds a match that is quite short, and stops well before the characters that were pre-decoded that caused a decode error. It would seem to me that this sort of pre-decoding should not cause decode errors. but the DFDL spec doesn't state that explicitly. comments? Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy <http://www.ogf.org/About/abt_policies.php>

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