Question

I’m working on a procedure for decrypting binary data using AesCryptoServiceProvider. For the final step, retrieving the decrypted data and returning it as an array of bytes, I’m currently using the following implementation:

let rec streamBytes (s : CryptoStream) (b : int) = seq {
    if b >= 0 then
        yield byte b
        yield! streamBytes s (s.ReadByte()) }
streamBytes cryptoStream (cryptoStream.ReadByte())
|> Seq.toArray

It works, but it doesn’t feel “correct” to me. Passing the result of CryptoStream.ReadByte() as an argument to streamBytes(), and then checking is value in that recursive call seems a bit Rube Goldberg-y. Is there a better way to be doing it?

Answer 1

Draining stream byte by byte will be very slow.

if you have .NET 4.0 then the most straightforward way will be:

open System.IO

let readAllBytes (s : Stream) = 
    let ms = new MemoryStream()
    s.CopyTo(ms)
    ms.ToArray()

else you need to reproduce CopyTo functionality manually

let readAllBytes (s : Stream) =
    let ms = new MemoryStream()
    let buf = Array.zeroCreate 8192
    let rec impl () = 
        let read = s.Read(buf, 0, buf.Length) 
        if read > 0 then 
            ms.Write(buf, 0, read)
            impl ()
    impl ()