CodePagesEncodingProvider.cs

Go to the documentation of this file.

using System.Collections.Generic;
using System.Threading;
 
namespace System.Text;
 
public sealed class CodePagesEncodingProvider : EncodingProvider
{
    private static readonly EncodingProvider s_singleton = new CodePagesEncodingProvider();
 
    private readonly Dictionary<int, Encoding> _encodings = new Dictionary<int, Encoding>();
 
    private readonly ReaderWriterLockSlim _cacheLock = new ReaderWriterLockSlim();
 
    public static EncodingProvider Instance => s_singleton;
 
    private static int SystemDefaultCodePage
    {
        get
        {
            if (!global::Interop.Kernel32.TryGetACPCodePage(out var codePage))
            {
                return 0;
            }
            return codePage;
        }
    }
 
    internal CodePagesEncodingProvider()
    {
    }
 
    public override Encoding? GetEncoding(int codepage)
    {
        if (codepage < 0 || codepage > 65535)
        {
            return null;
        }
        if (codepage == 0)
        {
            int systemDefaultCodePage = SystemDefaultCodePage;
            if (systemDefaultCodePage == 0)
            {
                return null;
            }
            return GetEncoding(systemDefaultCodePage);
        }
        Encoding value = null;
        _cacheLock.EnterUpgradeableReadLock();
        try
        {
            if (_encodings.TryGetValue(codepage, out value))
            {
                return value;
            }
            switch (BaseCodePageEncoding.GetCodePageByteSize(codepage))
            {
            case 1:
                value = new SBCSCodePageEncoding(codepage);
                break;
            case 2:
                value = new DBCSCodePageEncoding(codepage);
                break;
            default:
                value = GetEncodingRare(codepage);
                if (value == null)
                {
                    return null;
                }
                break;
            }
            _cacheLock.EnterWriteLock();
            try
            {
                if (_encodings.TryGetValue(codepage, out var value2))
                {
                    return value2;
                }
                _encodings.Add(codepage, value);
                return value;
            }
            finally
            {
                _cacheLock.ExitWriteLock();
            }
        }
        finally
        {
            _cacheLock.ExitUpgradeableReadLock();
        }
    }
 
    public override Encoding? GetEncoding(string name)
    {
        int codePageFromName = System.Text.EncodingTable.GetCodePageFromName(name);
        if (codePageFromName == 0)
        {
            return null;
        }
        return GetEncoding(codePageFromName);
    }
 
    private static Encoding GetEncodingRare(int codepage)
    {
        Encoding result = null;
        switch (codepage)
        {
        case 57002:
        case 57003:
        case 57004:
        case 57005:
        case 57006:
        case 57007:
        case 57008:
        case 57009:
        case 57010:
        case 57011:
            result = new ISCIIEncoding(codepage);
            break;
        case 10008:
            result = new DBCSCodePageEncoding(10008, 20936);
            break;
        case 10003:
            result = new DBCSCodePageEncoding(10003, 20949);
            break;
        case 54936:
            result = new GB18030Encoding();
            break;
        case 50220:
        case 50221:
        case 50222:
        case 50225:
        case 52936:
            result = new ISO2022Encoding(codepage);
            break;
        case 50227:
        case 51936:
            result = new DBCSCodePageEncoding(codepage, 936);
            break;
        case 51932:
            result = new EUCJPEncoding();
            break;
        case 51949:
            result = new DBCSCodePageEncoding(codepage, 20949);
            break;
        case 38598:
            result = new SBCSCodePageEncoding(codepage, 28598);
            break;
        }
        return result;
    }
 
    public override IEnumerable<EncodingInfo> GetEncodings()
    {
        return BaseCodePageEncoding.GetEncodings(this);
    }
}