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using System;
using System.Security.Cryptography;
namespace Hazel.Crypto
{
/// <summary>
/// Streams data into a SHA256 digest
/// </summary>
public class Sha256Stream : IDisposable
{
/// <summary>
/// Size of the SHA256 digest in bytes
/// </summary>
public const int DigestSize = 32;
private SHA256 hash = SHA256.Create();
private bool isHashFinished = false;
struct EmptyArray
{
public static readonly byte[] Value = new byte[0];
}
/// <summary>
/// Create a new instance of a SHA256 stream
/// </summary>
public Sha256Stream()
{
}
/// <summary>
/// Release resources associated with the stream
/// </summary>
public void Dispose()
{
this.hash?.Dispose();
this.hash = null;
GC.SuppressFinalize(this);
}
/// <summary>
/// Reset the stream to its initial state
/// </summary>
public void Reset()
{
this.hash?.Dispose();
this.hash = SHA256.Create();
this.isHashFinished = false;
}
/// <summary>
/// Add data to the stream
/// </summary>
public void AddData(ByteSpan data)
{
while (data.Length > 0)
{
int offset = this.hash.TransformBlock(data.GetUnderlyingArray(), data.Offset, data.Length, null, 0);
data = data.Slice(offset);
}
}
/// <summary>
/// Calculate the final hash of the stream data
/// </summary>
/// <param name="output">
/// Target span to which the hash will be written
/// </param>
public void CopyOrCalculateFinalHash(ByteSpan output)
{
if (output.Length != DigestSize)
{
throw new ArgumentException($"Expected a span of {DigestSize} bytes. Got a span of {output.Length} bytes", nameof(output));
}
if (this.isHashFinished == false)
{
this.hash.TransformFinalBlock(EmptyArray.Value, 0, 0);
this.isHashFinished = true;
}
new ByteSpan(this.hash.Hash).CopyTo(output);
}
}
}
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