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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Diagnostics;
using System.Runtime.InteropServices;
namespace System.IO
{
/// <summary>Contains internal path helpers that are shared between many projects.</summary>
internal static partial class PathInternal
{
/// <summary>
/// Returns true if the path uses the extended syntax (\\?\)
/// </summary>
internal static bool IsExtended(ref StringBuffer path)
{
// While paths like "//?/C:/" will work, they're treated the same as "\\.\" paths.
// Skipping of normalization will *only* occur if back slashes ('\') are used.
return path.Length >= DevicePrefixLength
&& path[0] == '\\'
&& (path[1] == '\\' || path[1] == '?')
&& path[2] == '?'
&& path[3] == '\\';
}
/// <summary>
/// Gets the length of the root of the path (drive, share, etc.).
/// </summary>
internal unsafe static int GetRootLength(ref StringBuffer path)
{
if (path.Length == 0) return 0;
fixed (char* value = path.UnderlyingArray)
{
return GetRootLength(value, path.Length);
}
}
/// <summary>
/// Returns true if the path uses any of the DOS device path syntaxes. ("\\.\", "\\?\", or "\??\")
/// </summary>
internal static bool IsDevice(ref StringBuffer path)
{
// If the path begins with any two separators is will be recognized and normalized and prepped with
// "\??\" for internal usage correctly. "\??\" is recognized and handled, "/??/" is not.
return IsExtended(ref path)
||
(
path.Length >= DevicePrefixLength
&& IsDirectorySeparator(path[0])
&& IsDirectorySeparator(path[1])
&& (path[2] == '.' || path[2] == '?')
&& IsDirectorySeparator(path[3])
);
}
/// <summary>
/// Returns true if the path specified is relative to the current drive or working directory.
/// Returns false if the path is fixed to a specific drive or UNC path. This method does no
/// validation of the path (URIs will be returned as relative as a result).
/// </summary>
/// <remarks>
/// Handles paths that use the alternate directory separator. It is a frequent mistake to
/// assume that rooted paths (Path.IsPathRooted) are not relative. This isn't the case.
/// "C:a" is drive relative- meaning that it will be resolved against the current directory
/// for C: (rooted, but relative). "C:\a" is rooted and not relative (the current directory
/// will not be used to modify the path).
/// </remarks>
internal static bool IsPartiallyQualified(ref StringBuffer path)
{
if (path.Length < 2)
{
// It isn't fixed, it must be relative. There is no way to specify a fixed
// path with one character (or less).
return true;
}
if (IsDirectorySeparator(path[0]))
{
// There is no valid way to specify a relative path with two initial slashes or
// \? as ? isn't valid for drive relative paths and \??\ is equivalent to \\?\
return !(path[1] == '?' || IsDirectorySeparator(path[1]));
}
// The only way to specify a fixed path that doesn't begin with two slashes
// is the drive, colon, slash format- i.e. C:\
return !((path.Length >= 3)
&& (path[1] == VolumeSeparatorChar)
&& IsDirectorySeparator(path[2]));
}
}
}
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