1 files changed, 43 insertions, 0 deletions
diff --git a/src/cmd/go/internal/web/url_windows.go b/src/cmd/go/internal/web/url_windows.go
new file mode 100644
index 0000000..2a65ec8
--- /dev/null
+++ b/src/cmd/go/internal/web/url_windows.go
@@ -0,0 +1,43 @@
+// Copyright 2019 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 web
+
+import (
+	"errors"
+	"path/filepath"
+	"strings"
+)
+
+func convertFileURLPath(host, path string) (string, error) {
+	if len(path) == 0 || path[0] != '/' {
+		return "", errNotAbsolute
+	}
+
+	path = filepath.FromSlash(path)
+
+	// We interpret Windows file URLs per the description in
+	// https://blogs.msdn.microsoft.com/ie/2006/12/06/file-uris-in-windows/.
+
+	// The host part of a file URL (if any) is the UNC volume name,
+	// but RFC 8089 reserves the authority "localhost" for the local machine.
+	if host != "" && host != "localhost" {
+		// A common "legacy" format omits the leading slash before a drive letter,
+		// encoding the drive letter as the host instead of part of the path.
+		// (See https://blogs.msdn.microsoft.com/freeassociations/2005/05/19/the-bizarre-and-unhappy-story-of-file-urls/.)
+		// We do not support that format, but we should at least emit a more
+		// helpful error message for it.
+		if filepath.VolumeName(host) != "" {
+			return "", errors.New("file URL encodes volume in host field: too few slashes?")
+		}
+		return `\\` + host + path, nil
+	}
+
+	// If host is empty, path must contain an initial slash followed by a
+	// drive letter and path. Remove the slash and verify that the path is valid.
+	if vol := filepath.VolumeName(path[1:]); vol == "" || strings.HasPrefix(vol, `\\`) {
+		return "", errors.New("file URL missing drive letter")
+	}
+	return path[1:], nil
+}