Use TryComputeHash to remove more allocations.

Author: bgrainger

src/MySqlConnector/Core/ServerSession.cs

@@ -580,7 +580,7 @@ private async Task<PayloadData> SwitchAuthenticationAsync(ConnectionSettings cs,
 				return await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
 
 			case "caching_sha2_password":
-				var scrambleBytes = AuthenticationUtility.CreateScrambleResponse(Utility.TrimZeroByte(switchRequest.Data), cs.Password);
+				var scrambleBytes = AuthenticationUtility.CreateScrambleResponse(Utility.TrimZeroByte(switchRequest.Data.AsSpan()), cs.Password);
 				payload = new PayloadData(scrambleBytes);
 				await SendReplyAsync(payload, ioBehavior, cancellationToken).ConfigureAwait(false);
 				payload = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);

src/MySqlConnector/Protocol/Serialization/AuthenticationUtility.cs

@@ -23,7 +23,9 @@ public static byte[] HashPassword(ReadOnlySpan<byte> challenge, string password)
 			Span<byte> combined = stackalloc byte[40];
 			challenge.CopyTo(combined);
 
-			var passwordBytes = Encoding.UTF8.GetBytes(password);
+			var passwordByteCount = Encoding.UTF8.GetByteCount(password);
+			Span<byte> passwordBytes = stackalloc byte[passwordByteCount];
+			Encoding.UTF8.GetBytes(password.AsSpan(), passwordBytes);
 			Span<byte> hashedPassword = stackalloc byte[20];
 			sha1.TryComputeHash(passwordBytes, hashedPassword, out _);
 			sha1.TryComputeHash(hashedPassword, combined.Slice(20), out _);
@@ -36,7 +38,7 @@ public static byte[] HashPassword(ReadOnlySpan<byte> challenge, string password)
 			return hashedPassword.ToArray();
 		}
 
-		public static byte[] CreateScrambleResponse(byte[] nonce, string password)
+		public static byte[] CreateScrambleResponse(ReadOnlySpan<byte> nonce, string password)
 		{
 			var scrambleResponse = string.IsNullOrEmpty(password)
 				? Utility.EmptyByteArray
@@ -45,23 +47,26 @@ public static byte[] CreateScrambleResponse(byte[] nonce, string password)
 			return scrambleResponse;
 		}
 
-		private static byte[] HashPasswordWithNonce(byte[] nonce, string password)
+		private static byte[] HashPasswordWithNonce(ReadOnlySpan<byte> nonce, string password)
 		{
 			using var sha256 = SHA256.Create();
-			var passwordBytes = Encoding.UTF8.GetBytes(password);
-			var hashedPassword = sha256.ComputeHash(passwordBytes);
+			var passwordByteCount = Encoding.UTF8.GetByteCount(password);
+			Span<byte> passwordBytes = stackalloc byte[passwordByteCount];
+			Encoding.UTF8.GetBytes(password.AsSpan(), passwordBytes);
 
-			var doubleHashedPassword = sha256.ComputeHash(hashedPassword);
-			var combined = new byte[doubleHashedPassword.Length + nonce.Length];
+			Span<byte> hashedPassword = stackalloc byte[32];
+			sha256.TryComputeHash(passwordBytes, hashedPassword, out _);
 
-			Buffer.BlockCopy(doubleHashedPassword, 0, combined, 0, doubleHashedPassword.Length);
-			Buffer.BlockCopy(nonce, 0, combined, doubleHashedPassword.Length, nonce.Length);
+			Span<byte> combined = stackalloc byte[32 + nonce.Length];
+			sha256.TryComputeHash(hashedPassword, combined, out _);
+			nonce.CopyTo(combined.Slice(32));
 
-			var xorBytes = sha256.ComputeHash(combined);
+			Span<byte> xorBytes = stackalloc byte[32];
+			sha256.TryComputeHash(combined, xorBytes, out _);
 			for (int i = 0; i < hashedPassword.Length; i++)
 				hashedPassword[i] ^= xorBytes[i];
 
-			return hashedPassword;
+			return hashedPassword.ToArray();
 		}
 	}
 }

src/MySqlConnector/Utilities/Utility.cs

@@ -391,6 +391,9 @@ public static byte[] TrimZeroByte(byte[] value)
 			return value;
 		}
 
+		public static ReadOnlySpan<byte> TrimZeroByte(ReadOnlySpan<byte> value) =>
+			value[value.Length - 1] == 0 ? value.Slice(0, value.Length - 1) : value;
+
 #if NET45
 		public static bool TryGetBuffer(this MemoryStream memoryStream, out ArraySegment<byte> buffer)
 		{