ReadOnlyPermissionSet.cs

using System.Collections;
using System.Runtime.Serialization;

namespace System.Security
{
    [Serializable]
    public sealed class ReadOnlyPermissionSet : PermissionSet
    {
        private SecurityElement m_originXml;

        [NonSerialized]
        private bool m_deserializing;

        public override bool IsReadOnly => true;

        public ReadOnlyPermissionSet(SecurityElement permissionSetXml)
        {
            if (permissionSetXml == null)
            {
                throw new ArgumentNullException("permissionSetXml");
            }
            m_originXml = permissionSetXml.Copy();
            base.FromXml(m_originXml);
        }

        [OnDeserializing]
        private void OnDeserializing(StreamingContext ctx)
        {
            m_deserializing = true;
        }

        [OnDeserialized]
        private void OnDeserialized(StreamingContext ctx)
        {
            m_deserializing = false;
        }

        public override PermissionSet Copy()
        {
            return new ReadOnlyPermissionSet(m_originXml);
        }

        public override SecurityElement ToXml()
        {
            return m_originXml.Copy();
        }

        protected override IEnumerator GetEnumeratorImpl()
        {
            return new ReadOnlyPermissionSetEnumerator(base.GetEnumeratorImpl());
        }

        protected override IPermission GetPermissionImpl(Type permClass)
        {
            return base.GetPermissionImpl(permClass)?.Copy();
        }

        protected override IPermission AddPermissionImpl(IPermission perm)
        {
            throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_ModifyROPermSet"));
        }

        public override void FromXml(SecurityElement et)
        {
            if (m_deserializing)
            {
                base.FromXml(et);
                return;
            }
            throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_ModifyROPermSet"));
        }

        protected override IPermission RemovePermissionImpl(Type permClass)
        {
            throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_ModifyROPermSet"));
        }

        protected override IPermission SetPermissionImpl(IPermission perm)
        {
            throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_ModifyROPermSet"));
        }
    }
}