Merge pull request #611 from Thunderstr1k3/fix-zipheader-seeking

Allowing to seek empty zip files

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)
             {

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()
         {