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GuidUtility
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// Source: https://github.com/LogosBible/Logos.Utility/blob/master/src/Logos.Utility/GuidUtility.cs | |
using System; | |
using System.Security.Cryptography; | |
using System.Text; | |
/// <summary> | |
/// Helper methods for working with <see cref="Guid"/>. | |
/// </summary> | |
static class GuidUtility | |
{ | |
/// <summary> | |
/// Creates a name-based UUID using the algorithm from RFC 4122 §4.3. | |
/// </summary> | |
/// <param name="namespaceId">The ID of the namespace.</param> | |
/// <param name="name">The name (within that namespace).</param> | |
/// <param name="version">The version number of the UUID to create; this value must be either | |
/// 3 (for MD5 hashing) or 5 (for SHA-1 hashing).</param> | |
/// <returns>A UUID derived from the namespace and name.</returns> | |
/// <remarks>See <a href="http://code.logos.com/blog/2011/04/generating_a_deterministic_guid.html">Generating a deterministic GUID</a>.</remarks> | |
public static Guid Create(Guid namespaceId, string name, int version = VersionSHA1) | |
{ | |
if (name == null) throw new ArgumentNullException(nameof(name)); | |
if (version != VersionMD5 && version != VersionSHA1) throw new ArgumentOutOfRangeException(nameof(version), $"version must be either {VersionMD5} or {VersionSHA1}."); | |
// convert the name to a sequence of octets (as defined by the standard or conventions of its namespace) (step 3) | |
// ASSUME: UTF-8 encoding is always appropriate | |
byte[] nameBytes = Encoding.UTF8.GetBytes(name); | |
// convert the namespace UUID to network order (step 3) | |
byte[] namespaceBytes = namespaceId.ToByteArray(); | |
SwapByteOrder(namespaceBytes); | |
// compute the hash of the name space ID concatenated with the name (step 4) | |
byte[] hash; | |
using (var algorithm = version == VersionMD5 ? (HashAlgorithm)MD5.Create() : SHA1.Create()) | |
{ | |
algorithm.TransformBlock(namespaceBytes, 0, namespaceBytes.Length, null, 0); | |
algorithm.TransformFinalBlock(nameBytes, 0, nameBytes.Length); | |
hash = algorithm.Hash!; | |
} | |
// most bytes from the hash are copied straight to the bytes of the new GUID (steps 5-7, 9, 11-12) | |
byte[] newGuid = new byte[16]; | |
Array.Copy(hash, 0, newGuid, 0, 16); | |
// set the four most significant bits (bits 12 through 15) of the time_hi_and_version field to the appropriate 4-bit version number from Section 4.1.3 (step 8) | |
newGuid[6] = (byte)((newGuid[6] & 0x0F) | (version << 4)); | |
// set the two most significant bits (bits 6 and 7) of the clock_seq_hi_and_reserved to zero and one, respectively (step 10) | |
newGuid[8] = (byte)((newGuid[8] & 0x3F) | 0x80); | |
// convert the resulting UUID to local byte order (step 13) | |
SwapByteOrder(newGuid); | |
return new Guid(newGuid); | |
} | |
/// <summary> | |
/// The namespace for fully-qualified domain names (from RFC 4122, Appendix C). | |
/// </summary> | |
public static readonly Guid DnsNamespace = new Guid("6ba7b810-9dad-11d1-80b4-00c04fd430c8"); | |
/// <summary> | |
/// The namespace for URLs (from RFC 4122, Appendix C). | |
/// </summary> | |
public static readonly Guid UrlNamespace = new Guid("6ba7b811-9dad-11d1-80b4-00c04fd430c8"); | |
/// <summary> | |
/// The namespace for ISO OIDs (from RFC 4122, Appendix C). | |
/// </summary> | |
public static readonly Guid IsoOidNamespace = new Guid("6ba7b812-9dad-11d1-80b4-00c04fd430c8"); | |
// Converts a GUID (expressed as a byte array) to/from network order (MSB-first). | |
static void SwapByteOrder(byte[] guid) | |
{ | |
SwapBytes(guid, 0, 3); | |
SwapBytes(guid, 1, 2); | |
SwapBytes(guid, 4, 5); | |
SwapBytes(guid, 6, 7); | |
} | |
static void SwapBytes(byte[] guid, int left, int right) | |
{ | |
byte temp = guid[left]; | |
guid[left] = guid[right]; | |
guid[right] = temp; | |
} | |
const int VersionMD5 = 3; | |
const int VersionSHA1 = 5; | |
} |
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