duplicati/Duplicati/Library/Snapshots/SnapshotUtility.cs

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using System;
using System.Collections.Generic;
using System.IO;
using System.Runtime.Versioning;
using Duplicati.Library.Common.IO;

namespace Duplicati.Library.Snapshots
{
    /// <summary>
    /// Simple helper to initialize and load a snapshot implementation for the current OS
    /// </summary>
    public static class SnapshotUtility
    {
        /// <summary>
        /// Loads a snapshot implementation for the current OS
        /// </summary>
        /// <param name="paths">The list of paths to create snapshots of</param>
        /// <param name="options">A set of commandline options</param>
        /// <param name="followSymlinks">Whether to follow symlinks</param>
        /// <returns>The ISnapshotService implementation</returns>
        public static ISnapshotService CreateSnapshot(IEnumerable<string> paths, Dictionary<string, string> options, bool followSymlinks)
        {
            if (OperatingSystem.IsLinux())
            {
                return CreateLinuxSnapshot(paths, followSymlinks);
            }
            else if (OperatingSystem.IsWindows())
            {
                return CreateWindowsSnapshot(paths, options, followSymlinks);
            }
            else
            {
                throw new NotSupportedException("Unsupported Operating System");
            }
        }

        /// <summary>
        /// Creates a snapshot implementation that does not use snapshots (i.e., regular file access)
        /// </summary>
        /// <param name="paths">The list of paths to create snapshots of</param>
        /// <param name="ignoreAdvisoryLocking">Flag to ignore advisory locking</param>
        /// <param name="followSymlinks">Whether to follow symlinks</param>
        /// <returns>The ISnapshotService implementation</returns>
        public static ISnapshotService CreateNoSnapshot(IEnumerable<string> paths, bool ignoreAdvisoryLocking, bool followSymlinks)
        {
            if (OperatingSystem.IsMacOS() || OperatingSystem.IsLinux())
                return new NoSnapshotLinux(paths, ignoreAdvisoryLocking, followSymlinks);
            else if (OperatingSystem.IsWindows())
                return new NoSnapshotWindows(paths, followSymlinks);
            else
                throw new NotSupportedException("Unsupported Operating System");

        }

        // The two loader methods below guard against the type system attempting to load types
        // related to the OS specific implementations which may not be present for
        // the operation system we are not running on (i.e. prevent loading AlphaVSS on Linux)

        /// <summary>
        /// Loads a snapshot implementation for Linux
        /// </summary>
        /// <param name="folders">The list of folders to create snapshots of</param>
        /// <param name="followSymlinks">Whether to follow symlinks</param>
        /// <returns>The ISnapshotService implementation</returns>
        [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
        [SupportedOSPlatform("linux")]
        [SupportedOSPlatform("macOS")]
        private static ISnapshotService CreateLinuxSnapshot(IEnumerable<string> folders, bool followSymlinks)
        {
            return new LinuxSnapshot(folders, followSymlinks);
        }

        /// <summary>
        /// Loads a snapshot implementation for Windows
        /// </summary>
        /// <param name="folders">The list of folders to create snapshots of</param>
        /// <param name="options">A set of commandline options</param>
        /// <param name="followSymlinks">Whether to follow symlinks</param>
        /// <returns>The ISnapshotService implementation</returns>
        [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
        [SupportedOSPlatform("windows")]
        private static ISnapshotService CreateWindowsSnapshot(IEnumerable<string> folders, Dictionary<string, string> options, bool followSymlinks)
        {
            return new WindowsSnapshot(folders, options, followSymlinks);
        }

        /// <summary>
        /// Extension method for ISnapshotService which determines whether the given path is a symlink.
        /// </summary>
        /// <param name="snapshot">ISnapshotService implementation</param>
        /// <param name="path">File or folder path</param>
        /// <param name="attributes">File attributes</param>
        /// <returns>Whether the path is a symlink</returns>
        public static bool IsSymlink(this ISnapshotService snapshot, string path, FileAttributes attributes)
        {
            // Not all reparse points are symlinks.
            // For example, on Windows 10 Fall Creator's Update, the OneDrive folder (and all subfolders)
            // are reparse points, which allows the folder to hook into the OneDrive service and download things on-demand.
            // If we can't find a symlink target for the current path, we won't treat it as a symlink.
            return (attributes & FileAttributes.ReparsePoint) == FileAttributes.ReparsePoint && !string.IsNullOrEmpty(snapshot.GetSymlinkTarget(path));
        }

        /// <summary>
        /// Extension method for ISystemIO which determines whether the given path is a symlink.
        /// </summary>
        /// <param name="systemIO">ISystemIO implementation</param>
        /// <param name="path">File or folder path</param>
        /// <returns>Whether the path is a symlink</returns>
        public static bool IsSymlink(this ISystemIO systemIO, string path)
        {
            return systemIO.IsSymlink(path, systemIO.GetFileAttributes(path));
        }

        /// <summary>
        /// Extension method for ISystemIO which determines whether the given path is a symlink.
        /// </summary>
        /// <param name="systemIO">ISystemIO implementation</param>
        /// <param name="path">File or folder path</param>
        /// <param name="attributes">File attributes</param>
        /// <returns>Whether the path is a symlink</returns>
        public static bool IsSymlink(this ISystemIO systemIO, string path, FileAttributes attributes)
        {
            // Not all reparse points are symlinks.
            // For example, on Windows 10 Fall Creator's Update, the OneDrive folder (and all subfolders)
            // are reparse points, which allows the folder to hook into the OneDrive service and download things on-demand.
            // If we can't find a symlink target for the current path, we won't treat it as a symlink.
            return (attributes & FileAttributes.ReparsePoint) == FileAttributes.ReparsePoint && !string.IsNullOrEmpty(systemIO.GetSymlinkTarget(path));
        }
    }
}