Make try_rmfile() to delete read-only files on Windows

3 files changed, 33 insertions, 2 deletions

diff --git a/libbutl/filesystem.cxx b/libbutl/filesystem.cxx
index fd9ba75..bd91c07 100644
--- a/libbutl/filesystem.cxx
+++ b/libbutl/filesystem.cxx
@@ -299,12 +299,36 @@ namespace butl
   try_rmfile (const path& p, bool ignore_error)
   {
     rmfile_status r (rmfile_status::success);
+    const char* f (p.string ().c_str ());
 
 #ifndef _WIN32
-    if (unlink (p.string ().c_str ()) != 0)
+    int ur (unlink (f));
 #else
-    if (_unlink (p.string ().c_str ()) != 0)
+    int ur (_unlink (f));
+
+    // On Windows a file with the read-only attribute can not be deleted. This
+    // can be the reason if the deletion fails with the 'permission denied'
+    // error code. In such a case we just reset the attribute and repeat the
+    // attempt. If the attempt fails, then we try to restore the attribute.
+    //
+    if (ur != 0 && errno == EACCES)
+    {
+      DWORD a (GetFileAttributes (f));
+      if (a != INVALID_FILE_ATTRIBUTES && (a & FILE_ATTRIBUTE_READONLY) != 0 &&
+          SetFileAttributes (f, a & ~FILE_ATTRIBUTE_READONLY))
+      {
+        ur = _unlink (f);
+
+        // Restoring the attribute is unlikely to fail as we managed to reset
+        // it earlier.
+        //
+        if (ur != 0)
+          SetFileAttributes (f, a);
+      }
+    }
 #endif
+
+    if (ur != 0)
     {
       // Strangely on Linux unlink() removes a dangling symlink but returns
       // ENOENT.
diff --git a/libbutl/filesystem.mxx b/libbutl/filesystem.mxx
index 8ffbce9..a87e57b 100644
--- a/libbutl/filesystem.mxx
+++ b/libbutl/filesystem.mxx
@@ -196,6 +196,10 @@ LIBBUTL_MODEXPORT namespace butl
   //
   enum class rmfile_status {success, not_exist};
 
+  // Note that on Windows the read-only attribute is reset prior to the file
+  // removal (as it can't otherwise be deleted). In such a case the operation
+  // is not atomic.
+  //
   LIBBUTL_SYMEXPORT rmfile_status
   try_rmfile (const path&, bool ignore_error = false);
 
diff --git a/libbutl/url.txx b/libbutl/url.txx
index addfe88..e511bed 100644
--- a/libbutl/url.txx
+++ b/libbutl/url.txx
@@ -413,8 +413,11 @@ LIBBUTL_MODEXPORT namespace butl //@@ MOD Clang needs this for some reason.
 
     if (authority)
     {
+      // We can't append '//' string literal, so appending characters.
+      //
       r += '/';
       r += '/';
+
       r += authority->string ();
     }