From 8dd81c77f14cc30c967a1d9f11c3525562d65fe0 Mon Sep 17 00:00:00 2001
From: Andrey Novosad <Andrey.Novosad@adacta-fintech.com>
Date: Wed, 22 Jul 2026 17:17:41 +0300
Subject: [PATCH] fix: Add XLSX signature to MicrosoftOffice365Document (fixes
 #59)

Add the signature 50 4B 03 04 14 00 06 08 08 00 to the list of recognized
Office 365 document signatures. This signature is used by some XLSX files
(e.g. saved by non-Microsoft editors) and should be recognized as XLSX
instead of generic ZIP files.

Fixes #59
---
 .../FileTypeChecker.Tests.csproj                 |   3 +++
 FileTypeChecker.Tests/FileTypeValidatorTests.cs  |   1 +
 FileTypeChecker.Tests/files/test-issue-59.xlsx   | Bin 0 -> 1578 bytes
 .../Types/MicrosoftOffice365Document.cs          |   1 +
 4 files changed, 5 insertions(+)
 create mode 100644 FileTypeChecker.Tests/files/test-issue-59.xlsx

diff --git a/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj b/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj
index 1ce0499..e700479 100644
--- a/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj
+++ b/FileTypeChecker.Tests/FileTypeChecker.Tests.csproj
@@ -125,6 +125,9 @@
     <None Update="files\test-issue-41.xlsx">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="files\test-issue-59.xlsx">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Update="files\file_example_AVI_480_750kB.avi">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
diff --git a/FileTypeChecker.Tests/FileTypeValidatorTests.cs b/FileTypeChecker.Tests/FileTypeValidatorTests.cs
index 0b90eb8..c3ace14 100644
--- a/FileTypeChecker.Tests/FileTypeValidatorTests.cs
+++ b/FileTypeChecker.Tests/FileTypeValidatorTests.cs
@@ -409,6 +409,7 @@ public void Is_ShouldDistinguishOpenDocumentTypesOnSmallBuffers()
         [TestCase("FileTypeCheckerLogo-150.heic", typeof(HighEfficiencyImageFile))]
         [TestCase("issue311docx.testfile", typeof(MicrosoftOffice365Document))]
         [TestCase("test-issue-41.xlsx", typeof(MicrosoftOffice365Document))]
+        [TestCase("test-issue-59.xlsx", typeof(MicrosoftOffice365Document))]
         [TestCase("file_example_AVI_480_750kB.avi", typeof(AudioVideoInterleaveVideoFormat))]
         [TestCase("file_example_WAV_1MG.wav", typeof(WaveformAudioFileFormat))]
         [TestCase("test.m4a", typeof(M4a))]
diff --git a/FileTypeChecker.Tests/files/test-issue-59.xlsx b/FileTypeChecker.Tests/files/test-issue-59.xlsx
new file mode 100644
index 0000000000000000000000000000000000000000..964cc6aeb86ef7f0ca525178982ab69c7a9956f6
GIT binary patch
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diff --git a/FileTypeChecker/Types/MicrosoftOffice365Document.cs b/FileTypeChecker/Types/MicrosoftOffice365Document.cs
index 800228d..4be6703 100644
--- a/FileTypeChecker/Types/MicrosoftOffice365Document.cs
+++ b/FileTypeChecker/Types/MicrosoftOffice365Document.cs
@@ -14,6 +14,7 @@ public class MicrosoftOffice365Document : FileType, IFileType
             new(new byte[] { 0x50, 0x4B, 0x03, 0x04, 0x14, 0x00, 0x08, 0x08, 0x08, 0x00 }),
             new(new byte[] { 0x50, 0x4B, 0x03, 0x04, 0x14, 0x00, 0x00, 0x08, 0x08, 0x00 }),
             new(new byte[] { 0x50, 0x4B, 0x03, 0x04, 0x14, 0x00, 0x00, 0x00, 0x08, 0x00 }),
+            new(new byte[] { 0x50, 0x4B, 0x03, 0x04, 0x14, 0x00, 0x06, 0x08, 0x08, 0x00 }),
             new(new byte[] { 0x50, 0x4B, 0x03, 0x04, 0x14, 0x00, 0x06, 0x00 }),
             new(new byte[] { 0x50, 0x4B, 0x03, 0x04, 0x14, 0x00, 0x00, 0x00, 0x00, 0x00, 0xC8 })
         };