HPCC-35567 Fix invalid JSON spray split points on small files.

[jakesmith]

The creation of split points for small JSON files was causing what should have been trailing empty split points to contain huge lengths due to unsigned underflow.
This was caused by the JSOM partitioner incorrectly resetting the cursor inputOffset which in turn was used to calculate length on all furture splits.

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[github-actions]

Jira Issue: https://hpccsystems.atlassian.net//browse/HPCC-35567

Jirabot Action Result:
Assigning user: [email protected]
Workflow Transition To: Merge Pending
Updated PR

[Copilot]

Pull request overview

This PR fixes a bug in JSON spray split point calculation for small files where unsigned integer underflow was causing trailing empty split points to have incorrectly large lengths. The root cause was the JSON partitioner incorrectly resetting the cursor.inputOffset to 0, which was then used to calculate split point lengths.

Key Changes

• Modified the conditional logic for when cursor.inputOffset is reset to 0 to preserve its value when EOF is encountered
• Added defensive assertex check to guard against length underflow
• Improved code clarity by introducing an intermediate variable for the adjusted start offset calculation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dali/ft/daftformat.ipp	Modified findSplitPoint to conditionally reset cursor.inputOffset only for first split or before EOF check, preserving the offset value when EOF is reached
dali/ft/daftformat.cpp	Added defensive assertion and intermediate variable to prevent unsigned underflow when calculating partition point lengths

[ghalliday]

@jakesmith 1 question

[ghalliday]

Is this correct for the case !foundRowEnd?

[jakesmith]

no, I agree it is not.
I don't think correct if !checkFoundRowStartRes either..