duplicati/Duplicati/Library/Utility/BackendExtensions.cs

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#nullable enable

using System;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Duplicati.Library.Interface;

namespace Duplicati.Library.Utility;

/// <summary>
/// Contains extension methods for the IBackend interfaces
/// </summary>
public static class BackendExtensions
{
    /// <summary>
    /// The test file name used to test access permissions
    /// </summary>
    public const string TEST_FILE_NAME = "duplicati-access-privileges-test.tmp";

    /// <summary>
    /// The test file content used to test access permissions
    /// </summary>
    public const string TEST_FILE_CONTENT = "This file is used by Duplicati to test access permissions and can be safely deleted.";

    /// <summary>
    /// Tests a backend by invoking the List() method.
    /// As long as the iteration can either complete or find at least one file without throwing, the test is successful
    /// </summary>
    /// <param name="backend">Backend to test</param>
    /// <param name="cancelToken">Cancellation token</param>
    public static async Task TestReadWritePermissionsAsync(this IBackend backend, CancellationToken cancellationToken)
    {
        // Remove the file if it exists
        var connected = false;
        try
        {
            await foreach (var entry in backend
                               .ListAsync(cancellationToken)
                               .WithCancellation(cancellationToken)
                               .ConfigureAwait(false))
            {
                if (entry.Name != TEST_FILE_NAME)
                    continue;

                connected = true;
                await backend.DeleteAsync(TEST_FILE_NAME, cancellationToken).ConfigureAwait(false);
                break;
            }
        }
        catch (Exception e)
            // Don't catch FolderMissingException or FileMissingException
            // so we can pass those through to the caller
            when (e is not FolderMissingException && e is not FileMissingException)
        {
            if (connected)
                throw new TestAfterConnectException(Strings.BackendExtensions.ErrorDeleteFile(TEST_FILE_NAME, e.Message), "TestPreparationError", e);

            throw new UserInformationException(Strings.BackendExtensions.ErrorListContent(e.Message), "TestPreparationError", e);
        }

        // Test write permissions
        try
        {
            if (backend is IStreamingBackend streamingBackend && streamingBackend.SupportsStreaming)
            {
                using (var testStream = new MemoryStream(Encoding.UTF8.GetBytes(TEST_FILE_CONTENT)))
                    await streamingBackend.PutAsync(TEST_FILE_NAME, testStream, cancellationToken).ConfigureAwait(false);
            }
            else
            {
                using var tempfile = new TempFile();
                File.WriteAllText(tempfile, TEST_FILE_CONTENT);
                await backend.PutAsync(TEST_FILE_NAME, tempfile, cancellationToken).ConfigureAwait(false);
            }
        }
        catch (Exception e)
            // Don't catch FolderMissingException List may return empty results
            // even if the folder is missing, and we report that exception up the chain
            when (e is not FolderMissingException)
        {
            throw new TestAfterConnectException(Strings.BackendExtensions.ErrorWriteFile(TEST_FILE_NAME, e.Message), "TestWriteError", e);
        }

        // Test read permissions
        try
        {
            if (backend is IStreamingBackend streamingBackend && streamingBackend.SupportsStreaming)
            {
                using var testStream = new MemoryStream();
                await streamingBackend.GetAsync(TEST_FILE_NAME, testStream, cancellationToken).ConfigureAwait(false);
                var readValue = Encoding.UTF8.GetString(testStream.ToArray());
                if (readValue != TEST_FILE_CONTENT)
                    throw new Exception("Test file corrupted.");
            }
            else
            {
                using var tempfile = new TempFile();
                await backend.GetAsync(TEST_FILE_NAME, tempfile, cancellationToken).ConfigureAwait(false);
                var readValue = File.ReadAllText(tempfile);
                if (readValue != TEST_FILE_CONTENT)
                    throw new Exception("Test file corrupted.");
            }
        }
        catch (Exception e)
        {
            try { await backend.DeleteAsync(TEST_FILE_NAME, cancellationToken).ConfigureAwait(false); }
            catch { } // Ignore delete errors here, report the read error instead

            throw new TestAfterConnectException(Strings.BackendExtensions.ErrorReadFile(TEST_FILE_NAME, e.Message), "TestReadError", e);
        }

        // Cleanup
        try
        {
            await backend.DeleteAsync(TEST_FILE_NAME, cancellationToken).ConfigureAwait(false);
        }
        catch (Exception e)
        {
            throw new TestAfterConnectException(Strings.BackendExtensions.ErrorDeleteFile(TEST_FILE_NAME, e.Message), "TestCleanupError", e);
        }
    }
}