Deserialization of a file

Mr. Vage · July 16th, 2007, 12:17 PM

I have a file with an object serialized with System.Runtime.Serialization.Formatters.Binary.Bin aryFormatter. To ensure that the file is written properly, I append a 64 character checksum to the end. I can pull out and verify the checksum, but I can't figure out how to get the BinaryFormatter to deserialize the data. I can't have it deserialize the file stream, because it has the checksum at the end.

If I:

Open the file
Read it with a StreamReader
Output the stream to a string
Remove the checksum
Convert the string to a byte[] using System.Text.Encoding.Ascii.GetBytes()
Put the bytes into a MemoryStream
Deserialize the MemoryStream

I get this error:

Code:

System.Runtime.Serialization.SerializationException:
Binary stream '0' does not contain a valid BinaryHeader. Possible causes are invalid stream or object version change between serialization and deserialization.

planoie · July 16th, 2007, 02:08 PM

What about manually reading in the stream, removing the last 64 bytes then deserialize?

-Peter

Mr. Vage · July 16th, 2007, 08:11 PM

But that's what I'm doing. Here is my entire method:

Code:

private void loadChecksummedFile(object obj, string fileExension)
{
    FileStream fs = new FileStream(m_filePath + "." + fileExension, FileMode.Open, FileAccess.ReadWrite);
    BinaryFormatter bf = new BinaryFormatter();
    StreamReader sr = new StreamReader(fs);
    MemoryStream ms;
    MD5 checksum = MD5.Create();
    string fileString;
    string checksumInFile;
    byte[] data;
    string newChecksum;

    fileString = sr.ReadToEnd(); // Read the file into a string
    checksumInFile = fileString.Substring(fileString.Length - 64, 64); // Pull out the checksum
    data = System.Text.Encoding.ASCII.GetBytes(fileString.Substring(0, fileString.Length - 64)); //Take the string (minus the 
                                                                                                //checksum) and put it in a byte[]
    // Compute the checksum and compare
    newChecksum = checksumToString(checksum.ComputeHash(data)); 
    if(checksumInFile == newChecksum)
    {
        ms = new MemoryStream(data); //Put the byte[] of data into a memory stream because BinaryFormatter can only Deserialize 
                                     //streams
        obj = (object[]) bf.Deserialize(ms); //Error occurs here
    }
    else
        //TODO: Load the backup

    fs.Close(); 
}