Optimize DepotManifest Serialization

SteamKit2/SteamKit2/Types/DepotManifest.cs

@@ -219,25 +219,6 @@ public bool DecryptFilenames(byte[] encryptionKey)
             return true;
         }
 
-        /// <summary>
-        /// Serializes depot manifest and saves the output to a file.
-        /// </summary>
-        /// <param name="filename">Output file name.</param>
-        /// <returns><c>true</c> if serialization was successful; otherwise, <c>false</c>.</returns>
-        public bool SaveToFile( string filename )
-        {
-            using var fs = File.Open( filename, FileMode.Create );
-            using var bw = new BinaryWriter( fs );
-            var data = Serialize();
-            if ( data != null )
-            {
-                bw.Write( data );
-                return true;
-            }
-
-            return false;
-        }
-
         /// <summary>
         /// Loads binary manifest from a file and deserializes it.
         /// </summary>
@@ -371,12 +352,34 @@ void ParseProtobufManifestMetadata(ContentManifestMetadata metadata)
             EncryptedCRC = metadata.crc_encrypted;
         }
 
-        byte[]? Serialize()
+        class ChunkIdComparer : IEqualityComparer<byte[]>
+        {
+            public bool Equals( byte[]? x, byte[]? y )
+            {
+                if ( ReferenceEquals( x, y ) ) return true;
+                if ( x == null || y == null ) return false;
+                return x.SequenceEqual( y );
+            }
+
+            public int GetHashCode( byte[] obj )
+            {
+                ArgumentNullException.ThrowIfNull( obj );
+
+                // ChunkID is SHA-1, so we can just use the first 4 bytes
+                return BitConverter.ToInt32( obj, 0 );
+            }
+        }
+
+        /// <summary>
+        /// Serializes the depot manifest into the provided output stream.
+        /// </summary>
+        /// <param name="output">The stream to which the serialized depot manifest will be written.</param>
+        public void Serialize( Stream output )
         {
             DebugLog.Assert( Files != null, nameof( DepotManifest ), "Files was null when attempting to serialize manifest." );
 
             var payload = new ContentManifestPayload();
-            var uniqueChunks = new List<byte[]>();
+            var uniqueChunks = new HashSet<byte[]>( new ChunkIdComparer() );
 
             foreach ( var file in Files )
             {
@@ -409,10 +412,7 @@ void ParseProtobufManifestMetadata(ContentManifestMetadata metadata)
                     protochunk.cb_compressed = chunk.CompressedLength;
 
                     protofile.chunks.Add( protochunk );
-                    if ( !uniqueChunks.Exists( x => x.SequenceEqual( chunk.ChunkID! ) ) )
-                    {
-                        uniqueChunks.Add( chunk.ChunkID! );
-                    }
+                    uniqueChunks.Add( chunk.ChunkID! );
                 }
 
                 payload.mappings.Add( protofile );
@@ -450,8 +450,7 @@ void ParseProtobufManifestMetadata(ContentManifestMetadata metadata)
                 }
             }
 
-            using var ms = new MemoryStream();
-            using var bw = new BinaryWriter( ms );
+            using var bw = new BinaryWriter( output, Encoding.Default, true );
 
             // Write Protobuf payload
             using ( var ms_payload = new MemoryStream() )
@@ -477,8 +476,6 @@ void ParseProtobufManifestMetadata(ContentManifestMetadata metadata)
 
             // Write EOF marker
             bw.Write( DepotManifest.PROTOBUF_ENDOFMANIFEST_MAGIC );
-
-            return ms.ToArray();
         }
     }
 }