[VikramAditya33]

This change calculates the checksum through zimReader over the logical range from the beginning of the archive to the stored checksum. Multipart traversal, physical offsets, and part sizes are therefore handled by the existing reader abstraction.

The regression test creates a valid ZIM and embeds it as several non-aligned parts with unrelated bytes before and between them. The test fails with the previous implementation and passes with this fix.

Using the 64KiB buffer, on a 1 GiB ZIM stored in tmpfs, seven validation runs improved from a median of 2.145 seconds at approximately 477 MiB/s to 1.554 seconds at approximately 659 MiB/s which is a 27.6% reduction in validation time, or about a 1.38x speedup.

Fixes #1131

[VikramAditya33]

@kelson42 @veloman-yunkan PTAL

[codecov]

Codecov Report

❌ Patch coverage is 63.63636% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.76%. Comparing base (6a49d7d) to head (afdde72).

Files with missing lines	Patch %	Lines
src/fileimpl.cpp	63.63%	1 Missing and 3 partials ⚠️

❌ Your patch check has failed because the patch coverage (63.63%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1135      +/-   ##
==========================================
+ Coverage   56.63%   56.76%   +0.12%     
==========================================
  Files         100      100              
  Lines        5064     5056       -8     
  Branches     2246     2239       -7     
==========================================
+ Hits         2868     2870       +2     
+ Misses        715      714       -1     
+ Partials     1481     1472       -9     

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[Copilot]

🟢 Approval recommended

All reviewed files are covered, with no unresolved blocking issues.

Pull request overview

Fixes checksum validation for multipart and embedded ZIM files by hashing through the logical reader view.

Changes:

• Uses a 64 KiB buffer for checksum validation.
• Centralizes the checksum buffer-size constant.
• Adds regression coverage for non-aligned multipart archives.

File summaries

File	Description
test/archive.cpp	Adds multipart checksum regression coverage.
src/writer/creator.cpp	Uses the shared buffer constant.
src/fileimpl.cpp	Hashes the logical archive range through zimReader.
src/constants.h	Defines the shared checksum buffer size.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Lite

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[VikramAditya33]

@veloman-yunkan I've simplified the tests as suggested.

[veloman-yunkan]

@VikramAditya33 Please update the description of the PR to agree with the actual code.

[veloman-yunkan]

Thank you for your contribution!