Replace sequence of bytes in binary file

Question

What is the best method to replace sequence of bytes in binary file to the same length of other bytes? The binary files will be pretty large, about 50 mb and should not be loade

Answer 1

    public static void BinaryReplace(string sourceFile, byte[] sourceSeq, string targetFile, byte[] targetSeq)
    {
        FileStream sourceStream = File.OpenRead(sourceFile);
        FileStream targetStream = File.Create(targetFile);

        try
        {
            int b;
            long foundSeqOffset = -1;
            int searchByteCursor = 0;

            while ((b=sourceStream.ReadByte()) != -1)
            {
                if (sourceSeq[searchByteCursor] == b)
                {
                    if (searchByteCursor == sourceSeq.Length - 1)
                    {
                        targetStream.Write(targetSeq, 0, targetSeq.Length);
                        searchByteCursor = 0;
                        foundSeqOffset = -1;
                    }
                    else 
                    {
                        if (searchByteCursor == 0)
                        {
                            foundSeqOffset = sourceStream.Position - 1;
                        }

                        ++searchByteCursor;
                    }
                }
                else
                {
                    if (searchByteCursor == 0)
                    {
                        targetStream.WriteByte((byte) b);
                    }
                    else
                    {
                        targetStream.WriteByte(sourceSeq[0]);
                        sourceStream.Position = foundSeqOffset + 1;
                        searchByteCursor = 0;
                        foundSeqOffset = -1;
                    }
                }
            }
        }
        finally
        {
            sourceStream.Dispose();
            targetStream.Dispose();
        }
    }