Hi Folks,
Have you encountered the “left over data” error message? If you’ve worked with
Daffodil for more than 5 minutes, you undoubtedly have.
The problem with that error message is it gives you absolutely no clue what’s
causing the problem.
Perhaps if we start cataloging the things that triggered the error message,
then the Daffodil team will be able to provide better diagnostics. Here’s my
contribution to said catalog.
-----------------------
In recent weeks I have encountered the dreaded “left over data” error message
twice. After enormous effort I was able to figure out what the problems were in
my DFDL schema. First I need to describe my DFDL schema.
My DFDL schema consists of a series of element declarations and within each
element are declarations of subelements:
A
A.1
A.2
…
B
B.1
B.2
…
…
Each subelement is of type string and uses a regex to describe the subelement’s
data (i.e., the subelements use dfdl:lengthKind=”pattern” and
dfdl:lengthPattern=”regex”)
The first time that I got the “left over data” error message I found the cause
was due to this bug in my DFDL schema: a dfdl:lengthPattern listed the regex
alternatives in the wrong order (shortest to longest instead of longest to
shortest). The error message said that Daffodil stopped consuming input at
element G. The actual element containing the regex in wrong order was element
G.2 (Daffodil stopped consuming input pretty near the problem)
After I fixed that bug I immediately got another “left over data” error at
element J. After much more effort I found the bug: a regex erroneously had
spaces in it. In this case, the error message said that Daffodil stopped
consuming input at element J. The actual element containing the regex with
spaces was element K.5 (Daffodil stopped consuming input pretty far from the
problem)
/Roger
