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/*
* Copyright (c) 2024 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Data.Caching
* File: FbmMessageChecksum.cs
*
* FbmMessageChecksum.cs is part of VNLib.Data.Caching which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Data.Caching is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* VNLib.Data.Caching is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see https://www.gnu.org/licenses/.
*/
using System;
using System.Buffers.Binary;
using System.Diagnostics;
using VNLib.Utils;
using VNLib.Hashing.Checksums;
using VNLib.Net.Messaging.FBM;
using static VNLib.Data.Caching.Constants;
namespace VNLib.Data.Caching
{
/// <summary>
/// Utility class for verifying and writing checksums for FBM messages
/// </summary>
public static class FbmMessageChecksum
{
/// <summary>
/// Verifies the checksum of the supplied data using the FNV1a algorithm
/// </summary>
/// <param name="checksum">The checksum base32 encoded string of the checksum data</param>
/// <param name="data">The data to compute the checksum on</param>
/// <returns>True if the checksum of the data matches the supplied one</returns>
public static bool VerifyFnv1aChecksum(ReadOnlySpan<char> checksum, ReadOnlySpan<byte> data)
{
//Convert the checksum to bytes
Span<byte> asBytes = stackalloc byte[sizeof(ulong)];
ERRNO byteSize = VnEncoding.TryFromBase32Chars(checksum, asBytes);
Debug.Assert(byteSize == sizeof(ulong), "Failed to convert checksum to bytes");
//Compute the checksum of the supplied data
ulong computed = FNV1a.Compute64(data);
//Compare the checksums
return BinaryPrimitives.ReadUInt64BigEndian(asBytes) == computed;
}
/// <summary>
/// Writes the FNV1a checksum of the supplied data to the message header buffer
/// </summary>
/// <param name="message">The FBM message to write the checksum headers to</param>
/// <param name="data">The message data to compute the checksum of</param>
/// <exception cref="ArgumentNullException"></exception>
public static void WriteFnv1aChecksum(IFBMMessage message, ReadOnlySpan<byte> data)
{
ArgumentNullException.ThrowIfNull(message);
//Compute the checksum of the data
ulong checksum = FNV1a.Compute64(data);
Span<byte> asBytes = stackalloc byte[sizeof(ulong)];
Span<char> asChars = stackalloc char[16];
//get big endian bytes
BinaryPrimitives.WriteUInt64BigEndian(asBytes, checksum);
ERRNO charSize = VnEncoding.TryToBase32Chars(asBytes, asChars);
Debug.Assert(charSize > 0, "Failed to convert checksum to base32");
//Write the checksum and type to the response
message.WriteHeader(ChecksumType, ChecksumTypes.Fnv1a);
message.WriteHeader(ChecksumValue, asChars[..(int)charSize]);
}
}
}
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