1 files changed, 75 insertions, 0 deletions
diff --git a/src/mscorlib/corefx/System/IO/PathInternal.CaseSensitivity.cs b/src/mscorlib/corefx/System/IO/PathInternal.CaseSensitivity.cs
new file mode 100644
index 0000000000..bea2df93b9
--- /dev/null
+++ b/src/mscorlib/corefx/System/IO/PathInternal.CaseSensitivity.cs
@@ -0,0 +1,75 @@
+// 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;
+
+namespace System.IO
+{
+    /// <summary>Contains internal path helpers that are shared between many projects.</summary>
+    internal static partial class PathInternal
+    {
+        private enum Tristate : byte
+        {
+            NotInitialized,
+            True,
+            False,
+        }
+
+        private static Tristate s_isCaseSensitive = Tristate.NotInitialized;
+
+        /// <summary>Returns a comparison that can be used to compare file and directory names for equality.</summary>
+        internal static StringComparison StringComparison
+        {
+            get
+            {
+                return IsCaseSensitive ?
+                    StringComparison.Ordinal :
+                    StringComparison.OrdinalIgnoreCase;
+            }
+        }
+
+        /// <summary>Gets whether the system is case-sensitive.</summary>
+        internal static bool IsCaseSensitive
+        {
+            get
+            {
+                // This must be lazily initialized as there are dependencies on PathInternal's static constructor
+                // being fully initialized. (GetIsCaseSensitive() calls GetFullPath() which needs to use PathInternal)
+                if (s_isCaseSensitive == Tristate.NotInitialized)
+                    s_isCaseSensitive = GetIsCaseSensitive() ? Tristate.True : Tristate.False;
+
+                return s_isCaseSensitive == Tristate.True;
+            }
+        }
+
+        /// <summary>
+        /// Determines whether the file system is case sensitive.
+        /// </summary>
+        /// <remarks>
+        /// Ideally we'd use something like pathconf with _PC_CASE_SENSITIVE, but that is non-portable, 
+        /// not supported on Windows or Linux, etc. For now, this function creates a tmp file with capital letters 
+        /// and then tests for its existence with lower-case letters.  This could return invalid results in corner 
+        /// cases where, for example, different file systems are mounted with differing sensitivities.
+        /// </remarks>
+        private static bool GetIsCaseSensitive()
+        {
+            try
+            {
+                string pathWithUpperCase = Path.Combine(Path.GetTempPath(), "CASESENSITIVETEST" + Guid.NewGuid().ToString("N"));
+                using (new FileStream(pathWithUpperCase, FileMode.CreateNew, FileAccess.ReadWrite, FileShare.None, 0x1000, FileOptions.DeleteOnClose))
+                {
+                    string lowerCased = pathWithUpperCase.ToLowerInvariant();
+                    return !File.Exists(lowerCased);
+                }
+            }
+            catch (Exception exc)
+            {
+                // In case something goes terribly wrong, we don't want to fail just because
+                // of a casing test, so we assume case-insensitive-but-preserving.
+                Debug.Fail("Casing test failed: " + exc);
+                return false;
+            }
+        }
+    }
+}