From 3e32e3d7b149a4e519e817ea578943d4096bb642 Mon Sep 17 00:00:00 2001
From: Christian <Christian@enlightensciences.de>
Date: Thu, 2 Sep 2021 13:54:32 +0200
Subject: [PATCH] Allowing to seek empty zip files

---
 .../Common/Zip/SeekableZipHeaderFactory.cs    |  3 ++-
 .../SharpCompress.Test/Zip/ZipArchiveTests.cs | 22 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/SharpCompress/Common/Zip/SeekableZipHeaderFactory.cs b/src/SharpCompress/Common/Zip/SeekableZipHeaderFactory.cs
index 86eb7d081..b24f045ba 100644
--- a/src/SharpCompress/Common/Zip/SeekableZipHeaderFactory.cs
+++ b/src/SharpCompress/Common/Zip/SeekableZipHeaderFactory.cs
@@ -117,7 +117,8 @@ private static void SeekBackToHeader(Stream stream, BinaryReader reader)
             // Search in reverse
             Array.Reverse(seek);
 
-            var max_search_area = len - MINIMUM_EOCD_LENGTH;
+            // don't exclude the minimum eocd region, otherwise you fail to locate the header in empty zip files
+            var max_search_area = len; // - MINIMUM_EOCD_LENGTH;
 
             for( int pos_from_end = 0; pos_from_end < max_search_area; ++pos_from_end)
             {
diff --git a/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs b/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs
index ec710c761..6412ff750 100644
--- a/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs
+++ b/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs
@@ -290,6 +290,28 @@ public void Zip_Create_New()
             Directory.Delete(SCRATCH_FILES_PATH, true);
         }
 
+        /// <summary>
+        /// Creates an empty zip file and attempts to read it right afterwards. 
+        /// Ensures that parsing file headers works even in that case
+        /// </summary>
+        [Fact]
+        public void Zip_Create_Empty_And_Read()
+        {
+            var archive = ZipArchive.Create();
+
+            var archiveStream = new MemoryStream();
+
+            archive.SaveTo(archiveStream, CompressionType.LZMA);
+
+            archiveStream.Position = 0;
+
+            var readArchive = ArchiveFactory.Open(archiveStream);
+
+            var count = readArchive.Entries.Count();
+
+            Assert.Equal(0, count);
+        }
+
         [Fact]
         public void Zip_Create_New_Add_Remove()
         {