1 files changed, 50 insertions, 0 deletions

diff --git a/cli/internal/cacheitem/filepath_windows.go b/cli/internal/cacheitem/filepath_windows.go
new file mode 100644
index 0000000..2c3b852
--- /dev/null
+++ b/cli/internal/cacheitem/filepath_windows.go
@@ -0,0 +1,50 @@
+//go:build windows
+// +build windows
+
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cacheitem
+
+func isSlash(c uint8) bool {
+	return c == '\\' || c == '/'
+}
+
+// volumeNameLen returns length of the leading volume name on Windows.
+// It returns 0 elsewhere.
+func volumeNameLen(path string) int {
+	if len(path) < 2 {
+		return 0
+	}
+	// with drive letter
+	c := path[0]
+	if path[1] == ':' && ('a' <= c && c <= 'z' || 'A' <= c && c <= 'Z') {
+		return 2
+	}
+	// is it UNC? https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
+	if l := len(path); l >= 5 && isSlash(path[0]) && isSlash(path[1]) &&
+		!isSlash(path[2]) && path[2] != '.' {
+		// first, leading `\\` and next shouldn't be `\`. its server name.
+		for n := 3; n < l-1; n++ {
+			// second, next '\' shouldn't be repeated.
+			if isSlash(path[n]) {
+				n++
+				// third, following something characters. its share name.
+				if !isSlash(path[n]) {
+					if path[n] == '.' {
+						break
+					}
+					for ; n < l; n++ {
+						if isSlash(path[n]) {
+							break
+						}
+					}
+					return n
+				}
+				break
+			}
+		}
+	}
+	return 0
+}