C# – Conversion from byte array to base64 and back

base64bytearraycencodingtype conversion

I am trying to:

Generate a byte array.
Convert that byte array to base64
Convert that base64 string back to a byte array.

I've tried out a few solutions, for example those in this question.

For some reason the initial and final byte arrays do not match. Here is the code used:

using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
    {
         byte[] originalArray = new byte[32];
         rng.GetBytes(key);
         string temp_inBase64 = Convert.ToBase64String(originalArray);
         byte[] temp_backToBytes = Encoding.UTF8.GetBytes(temp_inBase64);
    }

My questions are:

Why do "originalArray" and "temp_backToBytes" not match? (originalArray has length of 32, temp_backToBytes has a length of 44, but their values are also different)
Is it possible to convert back and forth, and if so, how do I accomplish this?

Best Answer

The reason the encoded array is longer by about a quarter is that base-64 encoding uses only six bits out of every byte; that is its reason of existence - to encode arbitrary data, possibly with zeros and other non-printable characters, in a way suitable for exchange through ASCII-only channels, such as e-mail.

The way you get your original array back is by using Convert.FromBase64String:

 byte[] temp_backToBytes = Convert.FromBase64String(temp_inBase64);

Related Solutions

Java – Create ArrayList from array

new ArrayList<>(Arrays.asList(array));

C# – Creating a byte array from a stream

It really depends on whether or not you can trust s.Length. For many streams, you just don't know how much data there will be. In such cases - and before .NET 4 - I'd use code like this:

public static byte[] ReadFully(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();
    }
}

With .NET 4 and above, I'd use Stream.CopyTo, which is basically equivalent to the loop in my code - create the MemoryStream, call stream.CopyTo(ms) and then return ms.ToArray(). Job done.

I should perhaps explain why my answer is longer than the others. Stream.Read doesn't guarantee that it will read everything it's asked for. If you're reading from a network stream, for example, it may read one packet's worth and then return, even if there will be more data soon. BinaryReader.Read will keep going until the end of the stream or your specified size, but you still have to know the size to start with.

The above method will keep reading (and copying into a MemoryStream) until it runs out of data. It then asks the MemoryStream to return a copy of the data in an array. If you know the size to start with - or think you know the size, without being sure - you can construct the MemoryStream to be that size to start with. Likewise you can put a check at the end, and if the length of the stream is the same size as the buffer (returned by MemoryStream.GetBuffer) then you can just return the buffer. So the above code isn't quite optimised, but will at least be correct. It doesn't assume any responsibility for closing the stream - the caller should do that.

See this article for more info (and an alternative implementation).

Best Answer

Related Solutions

Java – Create ArrayList from array

C# – Creating a byte array from a stream

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