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//-----------------------------------------------------------------------
// <copyright file="UniqueId.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------
namespace System.IdentityModel
{
using System;
using System.Globalization;
using System.IdentityModel;
using System.Security.Cryptography;
using System.Text;
/// <summary>
/// Generates unique IDs.
/// </summary>
internal static class UniqueId
{
private const int RandomSaltSize = 16;
// We use UUIDs as the basis for our unique identifiers. UUIDs
// cannot be used in xml:id-typed fields, because xml:id
// is made from the NCNAME production in XML Schema.
//
// An NCNAME looks like this: (simlified out complex unicode)
// [A-Za-z_][A-Za-z0-9.-_]*
//
// A UUID looks like this:
// [0-9A-Fa-f]{8}-(?:[0-9A-Fa-f]{4}-){3}[0-9A-Fa-f]{12}
//
// The problem arises when the UUID begins with [0-9], which
// violates the NCNAME production.
//
// This is fixed trivially by prepending an underscore.
private const string NcNamePrefix = "_";
// In some cases we need UniqueId to be a valid URI. In this
// case we use the urn:uuid: namespace established by
// RFC4122. Note that in this case it is not appropriate to
// use the auto-incrementing optimization, as the resulting
// value is no longer properly a UUID.
private const string UuidUriPrefix = "urn:uuid:";
// For non-random identifiers, we optimize the generation of
// unique ids by calculating only one UUID per program invocation
// and adding a 64-bit auto-incrementing value for each id
// that is needed.
private static readonly string reusableUuid = GetRandomUuid();
// The format of the optimized NCNAMEs produced is:
// _[0-9A-Fa-f]{8}-(?:[0-9A-Fa-f]{4}-){3}[0-9A-Fa-f]{12}-[A-Za-z0-9]{8}
//
// In other words: underscore + UUID + hyphen + 64-bit auto-incrementing id
private static readonly string optimizedNcNamePrefix = NcNamePrefix + reusableUuid + "-";
/// <summary>
/// Creates a unique ID suitable for use in an xml:id field. The value is
/// not hard to guess but is unique.
/// </summary>
/// <returns>The unique ID.</returns>
public static string CreateUniqueId()
{
return optimizedNcNamePrefix + GetNextId();
}
/// <summary>
/// Creates a unique ID similar to that created by CreateNonRandomId,
/// but instead of an underscore, the supplied prefix is used.
/// </summary>
/// <param name="prefix">The prefix to use.</param>
/// <returns>The unique ID, with the given prefix.</returns>
public static string CreateUniqueId(string prefix)
{
if (string.IsNullOrEmpty(prefix))
{
throw DiagnosticUtility.ExceptionUtility.ThrowHelperArgumentNull("prefix");
}
return prefix + reusableUuid + "-" + GetNextId();
}
/// <summary>
/// Creates a unique, random ID suitable for use in an xml:id field. The
/// value is hard to guess and unique.
/// </summary>
/// <returns>The unique ID.</returns>
public static string CreateRandomId()
{
return NcNamePrefix + GetRandomUuid();
}
/// <summary>
/// Creates a unique, random ID similar to that created by CreateRandomId,
/// but instead of an underscore, the supplied prefix is used.
/// </summary>
/// <param name="prefix">The prefix to use.</param>
/// <returns>The random URI.</returns>
public static string CreateRandomId(string prefix)
{
if (string.IsNullOrEmpty(prefix))
{
throw DiagnosticUtility.ExceptionUtility.ThrowHelperArgumentNull("prefix");
}
return prefix + GetRandomUuid();
}
/// <summary>
/// Creates a unique, random ID suitable for use as a URI. The value is
/// hard to guess and unique. The URI is in the urn:uuid: namespace.
/// </summary>
/// <returns>The random URI.</returns>
public static Uri CreateRandomUri()
{
return new Uri(UuidUriPrefix + GetRandomUuid());
}
private static string GetNextId()
{
RandomNumberGenerator rng = RandomNumberGenerator.Create();
byte[] id = new byte[RandomSaltSize];
rng.GetBytes(id);
StringBuilder builder = new StringBuilder();
for (int i = 0; i < id.Length; i++)
{
builder.AppendFormat("{0:X2}", id[i]);
}
return builder.ToString();
}
private static string GetRandomUuid()
{
return Guid.NewGuid().ToString("D", CultureInfo.InvariantCulture);
}
}
}
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