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Fix: prevent SIGFPE crash in JoinFile when file segments are empty#772

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dnzbk merged 1 commit intonzbgetcom:developfrom
MikeBlom:bugfix/fix-joinfile-divide-by-zero
Apr 5, 2026
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Fix: prevent SIGFPE crash in JoinFile when file segments are empty#772
dnzbk merged 1 commit intonzbgetcom:developfrom
MikeBlom:bugfix/fix-joinfile-divide-by-zero

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@MikeBlom MikeBlom commented Apr 5, 2026 •
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Description

Fixes #773 — a divide-by-zero crash (SIGFPE) in UnpackController::JoinFile() that occurs when split file segments (e.g., .7z.001, .7z.002) are zero-byte or corrupt.

When totalSize is calculated as 0 from empty fragments, the progress calculation on line 530:

m_postInfo->SetStageProgress(int(written * 1000 / totalSize));

triggers a SIGFPE, crashing NZBGet. Since NZBGet resumes post-processing on startup, this causes a crash loop that prevents the application from starting at all.

The fix adds a guard to return early with an error message when totalSize <= 0, preventing the divide-by-zero.

Lib changes

None.

Testing

  • Reproduced the crash on Arch Linux x86_64 with NZBGet v26.0 and v26.1-testing
  • Confirmed the crash occurs in UnpackController::JoinFile via coredumpctl info: 
    Signal: 8 (FPE)
#0  _ZN16UnpackController8JoinFileEPKc (/usr/bin/nzbget + 0xfcb94)
#1  _ZN16UnpackController17JoinSplittedFilesEv (/usr/bin/nzbget + 0xfd0bd)
  • With the fix, NZBGet logs an error for the empty segments and continues running normally

@MikeBlom
Fix: prevent SIGFPE crash in JoinFile when file segments are empty
b0a683a 
When joining split files (e.g., .7z.001, .7z.002), totalSize is
calculated from fragment sizes. If all fragments are zero-byte or
corrupt, totalSize becomes 0 and the progress calculation
(written * 1000 / totalSize) triggers a divide-by-zero SIGFPE,
crashing nzbget on every startup as it resumes post-processing.

Add a guard to return early with an error message when totalSize <= 0.
@MikeBlom MikeBlom mentioned this pull request Apr 5, 2026
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@dnzbk dnzbk self-assigned this Apr 5, 2026
@dnzbk dnzbk self-requested a review April 5, 2026 14:17
@dnzbk dnzbk removed their assignment Apr 5, 2026
dnzbk
dnzbk approved these changes Apr 5, 2026
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Good catch, thank you

@dnzbk dnzbk merged commit 6e48519 into nzbgetcom:develop Apr 5, 2026
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@BrewTestBot BrewTestBot mentioned this pull request Apr 7, 2026
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dnzbk pushed a commit that referenced this pull request Apr 9, 2026
@MikeBlom @dnzbk
Fix: prevent SIGFPE crash in JoinFile when file segments are empty (#772
7661159 
)
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SIGFPE crash in UnpackController::JoinFile when split file segments are empty

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@MikeBlom @dnzbk