From 5706732c55fff25f4f57b8b082c1fb89359ffd6c Mon Sep 17 00:00:00 2001
From: Lars Vahlenberg <lars.vahlenberg@gmail.com>
Date: Thu, 28 Jul 2022 23:03:06 +0200
Subject: [PATCH] Naive implementation of searching of DataDescriptor, not
 compatible with big archives (>32bit), but handles test cases.

---
 .../Common/Zip/StreamingZipFilePart.cs        | 18 ++++++++++
 src/SharpCompress/Utility.cs                  | 35 +++++++++++++++++++
 .../SharpCompress.Test/Zip/ZipArchiveTests.cs |  4 +--
 3 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/src/SharpCompress/Common/Zip/StreamingZipFilePart.cs b/src/SharpCompress/Common/Zip/StreamingZipFilePart.cs
index f287ab73..9b333038 100644
--- a/src/SharpCompress/Common/Zip/StreamingZipFilePart.cs
+++ b/src/SharpCompress/Common/Zip/StreamingZipFilePart.cs
@@ -55,6 +55,24 @@ internal BinaryReader FixStreamedFileLocation(ref RewindableStream rewindableStr
                 else
                 {
                     // We would need to search for the magic word
+                    rewindableStream.Position -= 4;
+                    var pos = rewindableStream.Position;
+                    while( Utility.Find(rewindableStream, new byte[] { 0x50,0x4b,0x07,0x08 } ) )
+                    {
+                        // We should probably check CRC32 for positive matching as well
+                        var size = rewindableStream.Position - pos;
+                        var br = new BinaryReader(rewindableStream);
+                        br.ReadUInt32();
+                        br.ReadUInt32(); // CRC32
+                        var compressed_size = br.ReadUInt32();
+                        var uncompressed_size = br.ReadUInt32();
+                        if (compressed_size == size && compressed_size == uncompressed_size )
+                        {
+                            rewindableStream.Position -= 16;
+                            break;
+                        }
+                        rewindableStream.Position -= 12;
+                    }
                 }
 
                 Skipped = true;
diff --git a/src/SharpCompress/Utility.cs b/src/SharpCompress/Utility.cs
index ee732e8d..28979d9d 100644
--- a/src/SharpCompress/Utility.cs
+++ b/src/SharpCompress/Utility.cs
@@ -165,6 +165,41 @@ public static void Skip(this Stream source)
             }
         }
 
+        public static bool Find(this Stream source, byte[] array)
+        {
+            byte[] buffer = GetTransferByteArray();
+            try
+            {
+                var pos = source.Position;
+                int count = 0;
+                var len = source.Read(buffer, 0, buffer.Length);
+                source.Position = pos + len;
+
+                do
+                {
+                    for (int i = 0; i < len; i++)
+                    {
+                        if (array[count] == buffer[i])
+                        {
+                            count++;
+                            if (count == array.Length)
+                            {
+                                source.Position = source.Position - len + i - array.Length +1;
+                                return true;
+                            }
+                        }
+                    }
+                }
+                while ((len = source.Read(buffer, 0, buffer.Length)) > 0);
+            }
+            finally
+            {
+                ArrayPool<byte>.Shared.Return(buffer);
+            }
+
+            return false;
+        }
+
         public static DateTime DosDateToDateTime(UInt16 iDate, UInt16 iTime)
         {
             int year = iDate / 512 + 1980;
diff --git a/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs b/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs
index 67653e77..eb85da5e 100644
--- a/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs
+++ b/tests/SharpCompress.Test/Zip/ZipArchiveTests.cs
@@ -751,9 +751,7 @@ public void Zip_Uncompressed_Skip_All()
                     x++;
                 }
 
-                // if we implement searching for DataDescriptor on none compressed streams
-                // this would work, see StreamingZipFilePart function FixStreamedFileLocation
-                // Assert.Equal(4, x);
+                Assert.Equal(4, x);
             }
         }
     }