48 lines
1.6 KiB
C#
48 lines
1.6 KiB
C#
// <copyright file="GuidV7.cs" company="MUnique">
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// Licensed under the MIT License. See LICENSE file in the project root for full license information.
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// </copyright>
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namespace MUnique.OpenMU.Persistence;
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using System.Security.Cryptography;
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/// <summary>
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/// A generator for version 7 GUIDs. Layout:
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/// The first 6 bytes is a unix timestamp in milliseconds.
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/// The 7th byte contains the version number (7) in the upper 4 bits.
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/// The rest is random.
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/// </summary>
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public static class GuidV7
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{
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/// <summary>
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/// Creates a new random guid.
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/// </summary>
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/// <returns>The new guid.</returns>
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public static Guid NewGuid() => NewGuid(DateTimeOffset.UtcNow);
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/// <summary>
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/// Creates a new random guid for the specified date.
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/// </summary>
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/// <param name="dateTimeOffset">The date time offset which is the prefix of the id.</param>
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/// <returns>The new guid.</returns>
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public static Guid NewGuid(DateTimeOffset dateTimeOffset)
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{
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// We create a buffer which is two bytes bigger than the Guid,
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// because we don't need the first two bytes of the timestamp.
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Span<byte> buffer = stackalloc byte[18];
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var uuidAsBytes = buffer[2..];
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var currentTimestamp = dateTimeOffset.ToUnixTimeMilliseconds();
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if (!BitConverter.TryWriteBytes(buffer, currentTimestamp))
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{
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throw new InvalidOperationException("Could not convert the timestamp to bytes.");
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}
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RandomNumberGenerator.Fill(uuidAsBytes[6..]);
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uuidAsBytes[6] &= 0x0F;
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uuidAsBytes[6] |= 0x70;
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return new Guid(uuidAsBytes, true);
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}
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} |