MailHeaderInfo.cs

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using System.Collections.Generic;
 
namespace System.Net.Mail;
 
internal static class MailHeaderInfo
{
    private readonly struct HeaderInfo
    {
        public readonly string NormalizedName;
 
        public readonly bool IsSingleton;
 
        public readonly MailHeaderID ID;
 
        public readonly bool IsUserSettable;
 
        public readonly bool AllowsUnicode;
 
        public HeaderInfo(MailHeaderID id, string name, bool isSingleton, bool isUserSettable, bool allowsUnicode)
        {
            ID = id;
            NormalizedName = name;
            IsSingleton = isSingleton;
            IsUserSettable = isUserSettable;
            AllowsUnicode = allowsUnicode;
        }
    }
 
    private static readonly HeaderInfo[] s_headerInfo = new HeaderInfo[33]
    {
        new HeaderInfo(MailHeaderID.Bcc, "Bcc", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.Cc, "Cc", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.Comments, "Comments", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ContentDescription, "Content-Description", isSingleton: true, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ContentDisposition, "Content-Disposition", isSingleton: true, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ContentID, "Content-ID", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.ContentLocation, "Content-Location", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ContentTransferEncoding, "Content-Transfer-Encoding", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.ContentType, "Content-Type", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.Date, "Date", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.From, "From", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.Importance, "Importance", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.InReplyTo, "In-Reply-To", isSingleton: true, isUserSettable: true, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.Keywords, "Keywords", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.Max, "Max", isSingleton: false, isUserSettable: true, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.MessageID, "Message-ID", isSingleton: true, isUserSettable: true, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.MimeVersion, "MIME-Version", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.Priority, "Priority", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.References, "References", isSingleton: true, isUserSettable: true, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.ReplyTo, "Reply-To", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ResentBcc, "Resent-Bcc", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ResentCc, "Resent-Cc", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ResentDate, "Resent-Date", isSingleton: false, isUserSettable: true, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.ResentFrom, "Resent-From", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ResentMessageID, "Resent-Message-ID", isSingleton: false, isUserSettable: true, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.ResentSender, "Resent-Sender", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.ResentTo, "Resent-To", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.Sender, "Sender", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.Subject, "Subject", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.To, "To", isSingleton: true, isUserSettable: false, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.XPriority, "X-Priority", isSingleton: true, isUserSettable: false, allowsUnicode: false),
        new HeaderInfo(MailHeaderID.XReceiver, "X-Receiver", isSingleton: false, isUserSettable: true, allowsUnicode: true),
        new HeaderInfo(MailHeaderID.XSender, "X-Sender", isSingleton: true, isUserSettable: true, allowsUnicode: true)
    };
 
    private static readonly Dictionary<string, int> s_headerDictionary = CreateHeaderDictionary();
 
    private static Dictionary<string, int> CreateHeaderDictionary()
    {
        Dictionary<string, int> dictionary = new Dictionary<string, int>(33, StringComparer.OrdinalIgnoreCase);
        for (int i = 0; i < s_headerInfo.Length; i++)
        {
            dictionary.Add(s_headerInfo[i].NormalizedName, i);
        }
        return dictionary;
    }
 
    internal static string GetString(MailHeaderID id)
    {
        if (id == MailHeaderID.Unknown || id == (MailHeaderID)33)
        {
            return null;
        }
        return s_headerInfo[(int)id].NormalizedName;
    }
 
    internal static bool IsUserSettable(string name)
    {
        if (s_headerDictionary.TryGetValue(name, out var value))
        {
            return s_headerInfo[value].IsUserSettable;
        }
        return true;
    }
 
    internal static bool IsSingleton(string name)
    {
        if (s_headerDictionary.TryGetValue(name, out var value))
        {
            return s_headerInfo[value].IsSingleton;
        }
        return false;
    }
 
    internal static string NormalizeCase(string name)
    {
        if (!s_headerDictionary.TryGetValue(name, out var value))
        {
            return name;
        }
        return s_headerInfo[value].NormalizedName;
    }
 
    internal static bool AllowsUnicode(string name)
    {
        if (s_headerDictionary.TryGetValue(name, out var value))
        {
            return s_headerInfo[value].AllowsUnicode;
        }
        return true;
    }
}