Fix sticky permissions

Author: franzpoeschel

include/openPMD/auxiliary/Filesystem.hpp

@@ -21,6 +21,7 @@
 #pragma once
 
 #include <string>
+#include <sys/types.h>
 #include <vector>
 
 #include "openPMD/config.hpp"
@@ -66,6 +67,10 @@ namespace auxiliary
      */
     std::vector<std::string> list_directory(std::string const &path);
 
+    std::string get_parent(std::string const &path);
+
+    mode_t get_permissions(std::string const &path);
+
     /** Create all required directories to have a reachable given absolute or
      * relative path.
      *

src/auxiliary/Filesystem.cpp

@@ -96,6 +96,44 @@ std::vector<std::string> list_directory(std::string const &path)
     return ret;
 }
 
+std::string get_parent(std::string const &path)
+{
+    std::string parent = path;
+    size_t pos = parent.find_last_of(directory_separator);
+    if (pos != std::string::npos)
+    {
+        parent = parent.substr(0, pos);
+        if (parent.empty())
+            parent = "/";
+    }
+    else
+    {
+        parent.clear();
+    }
+    return parent;
+}
+
+mode_t get_permissions(std::string const &path)
+{
+    std::string parent = get_parent(path);
+    if (parent.empty())
+    {
+        return 0;
+    }
+    if (!directory_exists(parent))
+    {
+        return 0;
+    }
+
+    struct stat s;
+    if (stat(parent.c_str(), &s) != 0)
+    {
+        return 0;
+    }
+
+    return s.st_mode & 07777;
+}
+
 bool create_directories(std::string const &path)
 {
     if (directory_exists(path))
@@ -106,10 +144,12 @@ bool create_directories(std::string const &path)
         return CreateDirectory(p.c_str(), nullptr);
     };
 #else
+    // preserve sticky and setgid from parent
+    mode_t parentPerms = get_permissions(path) & (S_ISVTX | S_ISGID);
     mode_t mask = umask(0);
     umask(mask);
-    auto mk = [mask](std::string const &p) -> bool {
-        return (0 == mkdir(p.c_str(), 0777 & ~mask));
+    auto mk = [parentPerms, mask](std::string const &p) -> bool {
+        return (0 == mkdir(p.c_str(), (0777 & ~mask) | parentPerms));
     };
 #endif
     std::istringstream ss(path);