[Shane32]

Loading an XLSX whose entries use 64-bit ZIP data descriptors without local ZIP64 size markers can throw BadReadException because the streaming reader advances to the wrong offset. Read package entries through the bundled ZipFile.Read central-directory reader while preserving CRC checks, temporary-stream disposal, and InvalidDataException for invalid packages.

Adds a 1,764-byte synthetic workbook containing only Sheet1!A1 = "test", with regression tests for reading and saving/reopening it. Both tests reproduce the failure before the fix, so no external workbook data is needed.

Validation:

• Full test suite passed on .NET Core 2.1, .NET Core 3.1, .NET 6, .NET 8, .NET Framework 4.6.2, 4.8, and 4.8.1: 8,194 passed, 1,519 skipped, zero failures.
• Debug solution build passed across all configured targets.

Summary by CodeRabbit

• Bug Fixes
  • Fixed compatibility with workbooks that use ZIP64 data descriptors, allowing them to be opened and saved reliably.
  • Loading a workbook now leaves the supplied input stream readable.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 2e3bbe31-b13e-4134-92f6-a501338e8688

📥 Commits

Reviewing files that changed from the base of the PR and between 686684b and a9bbab6.

⛔ Files ignored due to path filters: 1

• EPPlusTest/Workbooks/test-zip64-descriptor.xlsx is excluded by !**/*.xlsx

📒 Files selected for processing: 3

• EPPlus/Packaging/ZipPackage.cs
• EPPlusTest/EPPlusTest.Core.csproj
• EPPlusTest/ExcelPackageTests.cs

Included review availability: This review used your included allowance. Your plan provides up to 1 included review per hour; 0 remain after this review.

📝 Walkthrough

ZIP package loading now uses ZipFile.Read and extracts archive entries. Tests cover opening and reloading a ZIP64 data-descriptor workbook.

Changes: ZIP64 Archive Reading

Layer / File(s)	Summary
Archive entry loading EPPlus/Packaging/ZipPackage.cs	ZipPackage(Stream) reads entries through ZipFile.Read and extracts nonempty entries. It wraps ZIP parsing exceptions as InvalidDataException.
ZIP64 workbook validation EPPlusTest/EPPlusTest.Core.csproj, EPPlusTest/ExcelPackageTests.cs	The test project copies the ZIP64 workbook fixture. Tests check worksheet and cell data after opening and reloading, and verify that the input stream remains readable.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant ZipPackage
  participant ZipFile
  participant ZipEntry
  participant MemoryStream
  ZipPackage->>ZipFile: Read archive stream
  ZipFile-->>ZipPackage: Return archive entries
  ZipPackage->>ZipEntry: Extract each nonempty entry
  ZipEntry->>MemoryStream: Write extracted contents

Loading

Suggested reviewers: jankallman

Merge Risk: ⚪ Minimal · up to a9bba

The change switches package loading to the central-directory ZIP reader to fix XLSX files with 64-bit data descriptors, and adds regression tests for opening and saving such a workbook. No actionable merge-blocking risk remains.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: fixing XLSX loading for 64-bit ZIP data descriptors.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

• Fix all pre-merge checks with AI

✨ Finishing Touches: 💡 1

📝 Generate docstrings: 💡

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[Copilot]

🟢 Approval recommended

Review found no blocking defects, with fixture validation and regression coverage supporting the targeted reader change.

No open issues 🎉

What changed in this PR

Fixes XLSX loading for entries with 64-bit ZIP data descriptors by using the bundled central-directory reader.

Changes:

• Replaces streaming ZIP reads while preserving CRC validation, temporary-stream disposal, and invalid-package handling.
• Adds loading and save/reopen regression tests.
• Configures the synthetic workbook fixture to copy to test output.

File	Description
EPPlusTest/​ExcelPackageTests.cs	Adds ZIP64 descriptor regression tests and an input-stream ownership assertion.
EPPlusTest/​EPPlusTest.Core.csproj	Copies the workbook fixture to test output.
EPPlus/​Packaging/​ZipPackage.cs	Uses central-directory ZIP reading and entry extraction.

_{Review effort: Balanced}