Merge pull request #1505 from SteamRE/vzip-cleanup

Add tests for DepotChunk, validate PK zip magic

SteamKit2/SteamKit2/Steam/CDN/DepotChunk.cs

@@ -53,16 +53,30 @@ public static int Process( DepotManifest.ChunkData info, ReadOnlySpan<byte> data
             try
             {
                 var written = aes.DecryptCbc( data[ iv.Length.. ], iv, buffer, PaddingMode.PKCS7 );
-                var decryptedStream = new MemoryStream( buffer, 0, written );
 
-                if ( buffer.Length > 1 && buffer[ 0 ] == 'V' && buffer[ 1 ] == 'Z' )
+                if ( buffer.Length < 16 )
                 {
+                    throw new InvalidDataException( $"Not enough data in the decrypted depot chunk (was {buffer.Length} bytes)." );
+                }
+
+                if ( buffer[ 0 ] == 'V' && buffer[ 1 ] == 'S' && buffer[ 2 ] == 'Z' && buffer[ 3 ] == 'a' ) // Zstd
+                {
+                    throw new NotImplementedException( "Zstd compressed chunks are not yet implemented in SteamKit." );
+                }
+                else if ( buffer[ 0 ] == 'V' && buffer[ 1 ] == 'Z' && buffer[ 2 ] == 'a' ) // LZMA
+                {
+                    using var decryptedStream = new MemoryStream( buffer, 0, written );
                     writtenDecompressed = VZipUtil.Decompress( decryptedStream, destination, verifyChecksum: false );
                 }
-                else
+                else if ( buffer[ 0 ] == 'P' && buffer[ 1 ] == 'K' && buffer[ 2 ] == 0x03 && buffer[ 3 ] == 0x04 ) // PKzip
                 {
+                    using var decryptedStream = new MemoryStream( buffer, 0, written );
                     writtenDecompressed = ZipUtil.Decompress( decryptedStream, destination, verifyChecksum: false );
                 }
+                else
+                {
+                    throw new InvalidDataException( $"Unexpected depot chunk compression (first four bytes are {Convert.ToHexString( buffer.AsSpan( 0, 4 ) )})." );
+                }
             }
             finally
             {

SteamKit2/SteamKit2/Util/VZipUtil.cs

@@ -12,19 +12,19 @@ static class VZipUtil
         private const int HeaderLength = 7; // magic + version + timestamp/crc
         private const int FooterLength = 10; // crc + decompressed size + magic
 
-        private const char Version = 'a';
+        private const byte Version = (byte)'a';
 
         public static int Decompress( MemoryStream ms, byte[] destination, bool verifyChecksum = true )
         {
             using BinaryReader reader = new BinaryReader( ms );
             if ( reader.ReadUInt16() != VZipHeader )
             {
-                throw new Exception( "Expecting VZipHeader at start of stream" );
+                throw new InvalidDataException( "Expecting VZipHeader at start of stream" );
             }
 
-            if ( reader.ReadChar() != Version )
+            if ( reader.ReadByte() != Version )
             {
-                throw new Exception( "Expecting VZip version 'a'" );
+                throw new InvalidDataException( "Expecting VZip version 'a'" );
             }
 
             // Sometimes this is a creation timestamp (e.g. for Steam Client VZips).
@@ -45,7 +45,7 @@ public static int Decompress( MemoryStream ms, byte[] destination, bool verifyCh
 
             if ( reader.ReadUInt16() != VZipFooter )
             {
-                throw new Exception( "Expecting VZipFooter at end of stream" );
+                throw new InvalidDataException( "Expecting VZipFooter at end of stream" );
             }
 
             if ( destination.Length < sizeDecompressed )

SteamKit2/SteamKit2/Util/ZipUtil.cs

@@ -35,7 +35,7 @@ public static int Decompress( MemoryStream ms, byte[] destination, bool verifyCh
 
             if ( verifyChecksum && Crc32.HashToUInt32( destination.AsSpan()[ ..sizeDecompressed ] ) != entry.Crc32 )
             {
-                throw new Exception( "Checksum validation failed for decompressed file" );
+                throw new InvalidDataException( "Checksum validation failed for decompressed file" );
             }
 
             return sizeDecompressed;

SteamKit2/Tests/DepotChunkFacts.cs

@@ -0,0 +1,78 @@
+using System;
+using System.IO;
+using System.IO.Hashing;
+using System.Reflection;
+using System.Security.Cryptography;
+using SteamKit2;
+using SteamKit2.CDN;
+using Xunit;
+
+namespace Tests
+{
+    public class DepotChunkFacts
+    {
+        [Fact]
+        public void DecryptsAndDecompressesDepotChunkPKZip()
+        {
+            var assembly = Assembly.GetExecutingAssembly();
+            using var stream = assembly.GetManifestResourceStream( "Tests.Files.depot_440_chunk_bac8e2657470b2eb70d6ddcd6c07004be8738697.bin" );
+            using var ms = new MemoryStream();
+            stream.CopyTo( ms );
+            var chunkData = ms.ToArray();
+
+            var chunk = new DepotManifest.ChunkData(
+                id: [], // id is not needed here
+                checksum: 2130218374,
+                offset: 0,
+                comp_length: 320,
+                uncomp_length: 544
+            );
+
+            var destination = new byte[ chunk.UncompressedLength ];
+            var writtenLength = DepotChunk.Process( chunk, chunkData, destination, [
+                0x44, 0xCE, 0x5C, 0x52, 0x97, 0xA4, 0x15, 0xA1,
+                0xA6, 0xF6, 0x9C, 0x85, 0x60, 0x37, 0xA5, 0xA2,
+                0xFD, 0xD8, 0x2C, 0xD4, 0x74, 0xFA, 0x65, 0x9E,
+                0xDF, 0xB4, 0xD5, 0x9B, 0x2A, 0xBC, 0x55, 0xFC
+            ] );
+
+            Assert.Equal( chunk.CompressedLength, ( uint )chunkData.Length );
+            Assert.Equal( chunk.UncompressedLength, ( uint )writtenLength );
+
+            var hash = Convert.ToHexString( SHA1.HashData( destination ) );
+            Assert.Equal( "BAC8E2657470B2EB70D6DDCD6C07004BE8738697", hash );
+        }
+
+        [Fact]
+        public void DecryptsAndDecompressesDepotChunkVZip()
+        {
+            var assembly = Assembly.GetExecutingAssembly();
+            using var stream = assembly.GetManifestResourceStream( "Tests.Files.depot_232250_chunk_7b8567d9b3c09295cdbf4978c32b348d8e76c750.bin" );
+            using var ms = new MemoryStream();
+            stream.CopyTo( ms );
+            var chunkData = ms.ToArray();
+
+            var chunk = new DepotManifest.ChunkData(
+                id: [], // id is not needed here
+                checksum: 2894626744,
+                offset: 0,
+                comp_length: 304,
+                uncomp_length: 798
+            );
+
+            var destination = new byte[ chunk.UncompressedLength ];
+            var writtenLength = DepotChunk.Process( chunk, chunkData, destination, [
+                0xE5, 0xF6, 0xAE, 0xD5, 0x5E, 0x9E, 0xCE, 0x42,
+                0x9E, 0x56, 0xB8, 0x13, 0xFB, 0xF6, 0xBF, 0xE9,
+                0x24, 0xF3, 0xCF, 0x72, 0x97, 0x2F, 0xDB, 0xD0,
+                0x57, 0x1F, 0xFC, 0xAD, 0x9F, 0x2F, 0x7D, 0xAA,
+            ] );
+
+            Assert.Equal( chunk.CompressedLength, ( uint )chunkData.Length );
+            Assert.Equal( chunk.UncompressedLength, ( uint )writtenLength );
+
+            var hash = Convert.ToHexString( SHA1.HashData( destination ) );
+            Assert.Equal( "7B8567D9B3C09295CDBF4978C32B348D8E76C750", hash );
+        }
+    }
+}

SteamKit2/Tests/Files/.gitattributes

@@ -0,0 +1,2 @@
+*.bin binary
+*.manifest binary

SteamKit2/Tests/Files/depot_232250_chunk_7b8567d9b3c09295cdbf4978c32b348d8e76c750.bin

@@ -0,0 +1,2 @@
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