UA-.NETStandard/Libraries/Opc.Ua.Client/FileSystem/TemporaryFileTransferClient.cs

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using System;
using System.Threading;
using System.Threading.Tasks;

namespace Opc.Ua.Client.FileSystem
{
    /// <summary>
    /// Client for the OPC UA <c>TemporaryFileTransferType</c>
    /// (Part 5 §C.5). Wraps the
    /// <see cref="TemporaryFileTransferTypeClient"/> proxy and exposes
    /// the read/commit lifecycles as <see cref="UaFileStream"/> /
    /// <see cref="UaTemporaryWriteFile"/> values.
    /// </summary>
    /// <remarks>
    /// <para>
    /// The temporary-file-transfer pattern is intentionally separate
    /// from <see cref="FileSystemClient"/> because its lifecycle does
    /// not fit the <see cref="System.IO"/> abstraction: the server
    /// allocates a transient file, the client streams data through it,
    /// and a final commit (or rollback) signals the server to either
    /// publish or discard the result.
    /// </para>
    /// <para>
    /// <see cref="UaTemporaryWriteFile"/> owns the close lifecycle for
    /// the underlying handle: exactly one terminal call is made,
    /// either <see cref="UaTemporaryWriteFile.CommitAsync"/> (which
    /// invokes <c>CloseAndCommit</c>) or
    /// <see cref="UaTemporaryWriteFile.DisposeAsync"/> (which falls
    /// back to <c>Close</c>). The wrapped <see cref="System.IO.Stream"/>
    /// itself does NOT close the server handle on disposal.
    /// </para>
    /// </remarks>
    public sealed class TemporaryFileTransferClient
    {
        /// <summary>
        /// Creates a new client rooted at the supplied
        /// <c>TemporaryFileTransferType</c> object.
        /// </summary>
        /// <param name="session">The OPC UA session.</param>
        /// <param name="temporaryFileTransferObjectId">NodeId of the
        /// <c>TemporaryFileTransferType</c> instance.</param>
        /// <param name="options">Optional configuration; defaults are
        /// applied when <c>null</c>.</param>
        public TemporaryFileTransferClient(
            ISession session,
            NodeId temporaryFileTransferObjectId,
            FileSystemClientOptions? options = null)
        {
            Session = session ?? throw new ArgumentNullException(nameof(session));
            if (temporaryFileTransferObjectId.IsNull)
            {
                throw new ArgumentNullException(nameof(temporaryFileTransferObjectId));
            }
            ObjectId = temporaryFileTransferObjectId;
            Options = (options ?? new FileSystemClientOptions()).Clone();
            Options.Validate();
            Proxy = new TemporaryFileTransferTypeClient(
                session,
                temporaryFileTransferObjectId,
                session.MessageContext.Telemetry);
        }

        /// <summary>The session.</summary>
        public ISession Session { get; }

        /// <summary>The NodeId of the underlying
        /// <c>TemporaryFileTransferType</c> object.</summary>
        public NodeId ObjectId { get; }

        /// <summary>The (cloned, immutable) configuration.</summary>
        public FileSystemClientOptions Options { get; }

        /// <summary>The underlying generated proxy.</summary>
        public TemporaryFileTransferTypeClient Proxy { get; }

        /// <summary>
        /// Asks the server to generate a temporary file for reading.
        /// Returns a <see cref="UaFileStream"/> wrapping the server
        /// handle; disposing the stream issues <c>Close</c> per the
        /// regular <c>FileType</c> lifecycle.
        /// </summary>
        /// <param name="generateOptions">Server-defined generation
        /// options; pass <c>default</c> for "no options".</param>
        /// <param name="ct">Cancellation token.</param>
        public async ValueTask<UaFileStream> GenerateFileForReadAsync(
            Variant generateOptions = default,
            CancellationToken ct = default)
        {
            (NodeId fileNodeId, uint handle, _) = await Proxy
                .GenerateFileForReadAsync(generateOptions, ct)
                .ConfigureAwait(false);

            var fileProxy = new FileTypeClient(
                Session,
                fileNodeId,
                Session.MessageContext.Telemetry);

            try
            {
                return new UaFileStream(
                    fileProxy,
                    handle,
                    UaFileMode.Read,
                    initialLength: 0,
                    initialPosition: 0,
                    chunkSize: Options.ChunkSize);
            }
            catch
            {
                try
                {
                    await fileProxy.CloseAsync(handle, CancellationToken.None)
                        .ConfigureAwait(false);
                }
                catch
                {
                    // Best-effort cleanup.
                }
                throw;
            }
        }

        /// <summary>
        /// Asks the server to allocate a temporary file for writing.
        /// The returned <see cref="UaTemporaryWriteFile"/> owns the
        /// close lifecycle: call
        /// <see cref="UaTemporaryWriteFile.CommitAsync"/> to publish
        /// the file or rely on <see cref="UaTemporaryWriteFile.DisposeAsync"/>
        /// to roll back.
        /// </summary>
        /// <param name="generateOptions">Server-defined generation
        /// options.</param>
        /// <param name="ct">Cancellation token.</param>
        public async ValueTask<UaTemporaryWriteFile> GenerateFileForWriteAsync(
            Variant generateOptions = default,
            CancellationToken ct = default)
        {
            (NodeId fileNodeId, uint handle) = await Proxy
                .GenerateFileForWriteAsync(generateOptions, ct)
                .ConfigureAwait(false);

            var fileProxy = new FileTypeClient(
                Session,
                fileNodeId,
                Session.MessageContext.Telemetry);

            return new UaTemporaryWriteFile(
                Proxy,
                fileProxy,
                fileNodeId,
                handle,
                Options.ChunkSize);
        }
    }
}