Appending byte and stream

Question

I want to append byte array to stream i opened but just to pass it to hash algorithm and compute the hash, something like:

byte[] data;

using (BufferedStream bs = new BufferedStream(File.OpenRead(path), 1200000))
{
    MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();

    byte[] hash = md5.ComputeHash(data + bs);
}

I don't know how to do "data + bs" or "bs + data" part... Any idea about this?

I assume `data` has been filled by then? What are the ballpark sizes of data and the file? — H H, Dec 18 '13 at 21:23
this is just an illustration of code, not full code. Data size is 16 bytes. I want to append data array to stream and compute hash. — user216799, Dec 18 '13 at 21:28
btw file size is lets say more than 1 GB. That is why i pass stream as argument. — user216799, Dec 18 '13 at 21:34
Your code _prepends_ the data, not _appends_ it. Please be clear, it might matter. — H H, Dec 18 '13 at 21:38
And will you run this on a phone/tablet or is reading 1GB into memory no problem? — H H, Dec 18 '13 at 21:40
I need both, prepend and append. I want it to work for any file even 5 GB. — user216799, Dec 18 '13 at 21:43

score 2 · Accepted Answer · answered Dec 18 '13 at 21:43

Why wouldn't you simply do something like this:

public static byte[] MD5Hash( byte[] salt, Stream s , int blockSize )
{
  MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider() ;

  md5.Initialize();

  md5.TransformBlock(salt,0,salt.Length,salt,0) ;

  byte[] buf  = new byte[blockSize];
  int    bufl ;
  while ( (bufl=s.Read( buf , 0 , buf.Length )) > 0 )
  {
    md5.TransformBlock(buf,0,bufl,buf,0) ;
  }
  md5.TransformFinalBlock(buf,0,0) ;

  return md5.Hash ;
}

score 0 · Answer 2 · answered Dec 18 '13 at 21:23

0

Do this:

byte[] hash = md5.ComputeHash(data + ReadToEnd(bs));

And, your ReadToEnd function:

public static byte[] ReadToEnd(Stream input)
{
    byte[] buffer = new byte[16*1024];
    using (MemoryStream ms = new MemoryStream())
    {
        int read;
        while ((read = input.Read(buffer, 0, buffer.Length)) > 0)
        {
            ms.Write(buffer, 0, read);
        }
        return ms.ToArray();
    }
}

answered Dec 18 '13 at 21:23

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I think you need an `operator+` more than a `ReadToEnd()`. Anyway, with a very big file this isn't efficient/feasible. – H H Dec 18 '13 at 21:26

score 0 · Answer 3 · edited May 23 '17 at 11:52

// here is a quick approach to your original question:
List<byte> raw = new List<byte>(data);
raw.AddRange(File.ReadAllBytes("filePath.ext"));

To do this without using List (in other words arrays), use Array.Copy(...) to copy the first and second arrays into a new array of a larger size. (Personally, I prefer Lists in C#, Vectors in C++) If you have 1200000 bytes max and don't want to pull everything from the file, then you could use this code to your advantage: Best way to read a large file into a byte array in C#? where numBytes is the number of bytes you want to read in.

Appending byte and stream

3 Answers3