Exception in generate_sample with 0 as sample size

[Gaurav Arora]

I was trying to input sample size as 0 to generate function and this lead to an exception. We should probably handle this case

Continuing. Exception: basic_string::replace: pos (which is 18446744073709551615) > this->size() (which is 2) [Inferior 1 (process 3121) exited with code 01]

Exception occurs at ​https://github.com/xapian/xapian/blob/356ea64fa21c7d6d5974e5e8dac796c000fe84e6/xapian-applications/omega/sample.cc#L54 line

output.replace(maxlen - ind.size(), string::npos, ind);

Size of ind is 3 as i sent "..." and maxlen is zero, so it tries to access -ve index of string. Which should be prevented.

Probably better to return an empty string if sample size provided is smaller than ind. But i am waiting for feedback from community before proposing and writing a patch

[Olly Betts]

Returning an empty string sounds good to me.

It'd be good to check that the dynamic snippet code in core handles this case sensibly too.

[Olly Betts]

Patch in ​https://github.com/xapian/xapian/pull/191

[Olly Betts]

Fixed in git master by d21a213e95c8a010da8bb7031160a66100ba07c0. Leaving open until backported.

[Olly Betts]

It'd be good to check that the dynamic snippet code in core handles this case sensibly too.

I don't see anything in xapian-core/tests/api_snippets.cc testing what happens if the requested snippet length is 0 or a sufficiently small value that there's no useful snippet to show, so that would be a useful addition still.

[Olly Betts]

Backported for 1.4.6 in 65039dc1e7da321ccd29559e012a9917d535a003.

Created #759 for adding similar tests for MSet::snippet() in xapian-core.