[COMPRESS-724] Fix PAX 1.x sparse header alignment#775
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Do not skip an extra tar record when parsePAX1XSparseHeaders(InputStream, int) finishes reading sparse headers exactly on a record boundary. Add a regression test that keeps the first data byte visible after an aligned sparse header block. Reviewed-by: OpenAI Codex Reviewed-by: Anthropic Claude Code
garydgregory
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Jul 4, 2026
garydgregory
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Hello @OldTruckDriver
Thank you for the PR.
The tests contain too many magic numbers.
For example:
final byte[] fileData = new byte[513];
Arrays.fill(fileData, 0, 512, (byte) 'A');
fileData[512] = 'B';Above 513 and 512 are clearly related.
In pax1xSparseHeaderAlignedToSingleRecord, why 200 and 108. Either use local vars with clear names or write comments.
TY!
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Summary
Fix
TarUtils.parsePAX1XSparseHeaders(InputStream, int)so it does not skip an extra tar record when GNU PAX 1.x sparse headers end exactly on a record boundary.Details
Previously, the padding calculation used
recordSize - bytesRead % recordSize. WhenbytesReadwas already aligned torecordSize, this computed a full-record skip instead of0, advancing the stream past real entry data.This change uses modulo padding calculation so aligned sparse headers leave the stream positioned at the first data byte.
Tests
mvn -q -Dtest=org.apache.commons.compress.archivers.tar.TarUtilsTest testmvn -q