From 65987f5970892f7fc8bc353f87fe8b7363e0b06d Mon Sep 17 00:00:00 2001
From: albertony <12441419+albertony@users.noreply.github.com>
Date: Fri, 28 Oct 2022 21:00:22 +0200
Subject: [PATCH] lib/file: improve error message for create dir on
 non-existent network host on windows (#6420)

---
 lib/file/mkdir_windows.go      | 16 +++++++++-------
 lib/file/mkdir_windows_test.go | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/lib/file/mkdir_windows.go b/lib/file/mkdir_windows.go
index 36ccadd9c..73a82ac62 100644
--- a/lib/file/mkdir_windows.go
+++ b/lib/file/mkdir_windows.go
@@ -11,8 +11,9 @@ import (
 
 // MkdirAll creates a directory named path, along with any necessary parents.
 //
-// Improves os.MkdirAll by avoiding trying to create a folder \\? when the
-// volume of a given extended length path does not exist.
+// Improves os.MkdirAll by avoiding trying to create a folder `\\?` when the
+// volume of a given extended length path does not exist, and `\\?\UNC` when
+// a network host name does not exist.
 //
 // Based on source code from golang's os.MkdirAll
 // (https://github.com/golang/go/blob/master/src/os/path.go)
@@ -37,7 +38,6 @@ func MkdirAll(path string, perm os.FileMode) error {
 	}
 	if i > 0 {
 		path = path[:i]
-
 		if path == filepath.VolumeName(path) {
 			// Make reference to a drive's root directory include the trailing slash.
 			// In extended-length form without trailing slash ("\\?\C:"), os.Stat
@@ -53,10 +53,12 @@ func MkdirAll(path string, perm os.FileMode) error {
 				j--
 			}
 			if j > 1 {
-				// Create parent.
-				err = MkdirAll(path[:j-1], perm)
-				if err != nil {
-					return err
+				if path[:j-1] != `\\?\UNC` {
+					// Create parent.
+					err = MkdirAll(path[:j-1], perm)
+					if err != nil {
+						return err
+					}
 				}
 			}
 		}
diff --git a/lib/file/mkdir_windows_test.go b/lib/file/mkdir_windows_test.go
index e6daf1d49..6b574b792 100644
--- a/lib/file/mkdir_windows_test.go
+++ b/lib/file/mkdir_windows_test.go
@@ -128,3 +128,21 @@ func TestMkdirAllOnUnusedDrive(t *testing.T) {
 	errormsg = fmt.Sprintf("mkdir \\\\?\\%s\\: The system cannot find the path specified.", path)
 	checkMkdirAllSubdirs(t, `\\?\`+path, false, errormsg)
 }
+
+// Testing paths on unknown network host
+// This is an additional difference from golang's os.MkdirAll. With our
+// first fix, stopping it from recursing extended-length paths down to
+// the "\\?" prefix, it would now stop at `\\?\UNC`, because that is what
+// filepath.VolumeName returns (which is wrong, that is not a volume name!),
+// and still return a nonifnromative error:
+// "mkdir \\?\UNC\\: The filename, directory name, or volume label syntax is incorrect."
+// Our version stops the recursion at level before this, and reports:
+// "mkdir \\?\UNC\0.0.0.0: The specified path is invalid."
+func TestMkdirAllOnUnusedNetworkHost(t *testing.T) {
+	path := `\\0.0.0.0\share`
+	errormsg := fmt.Sprintf("mkdir %s\\: The format of the specified network name is invalid.", path)
+	checkMkdirAllSubdirs(t, path, false, errormsg)
+	path = `\\?\UNC\0.0.0.0\share`
+	errormsg = `mkdir \\?\UNC\0.0.0.0: The specified path is invalid.`
+	checkMkdirAllSubdirs(t, path, false, errormsg)
+}