1 files changed, 90 insertions, 0 deletions
diff --git a/lib/VNLib.Data.Caching/src/FbmMessageChecksum.cs b/lib/VNLib.Data.Caching/src/FbmMessageChecksum.cs
new file mode 100644
index 0000000..5a9af31
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+++ b/lib/VNLib.Data.Caching/src/FbmMessageChecksum.cs
@@ -0,0 +1,90 @@
+/*
+* 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]);
+        }
+    }
+}