(C# Windows) Check if a file path (relative or absolute) can be written by current user without attempting to create open or actually write anything to it. Inspired by http://stackoverflow.com/questions/1281620/checking-for-directory-and-file-write-permissions-in-net

GetFileWriteAccess.cs

using System.IO;
using System.Security.AccessControl;
using System.Security.Principal;

private bool FileCanWrite(string path)
{
  bool writeAllow = false;
  bool writeDeny = false;
  
  try
  {
    FileSystemSecurity security;
    if (File.Exists(path)) security = File.GetAccessControl(path);
    else security = Directory.GetAccessControl(Path.GetDirectoryName(Path.GetFullPath(path)));
    AuthorizationRuleCollection rules = security.GetAccessRules(true, true, typeof(NTAccount));
    WindowsPrincipal curUser = new WindowsPrincipal(WindowsIdentity.GetCurrent());
    foreach (FileSystemAccessRule rule in rules)
    {
      if (0 == (rule.FileSystemRights & (FileSystemRights.Write | FileSystemRights.WriteData))) continue;
      if (rule.IdentityReference.Value.StartsWith("S-1-"))
      {
        SecurityIdentifier sid = new SecurityIdentifier(rule.IdentityReference.Value);
        if (!curUser.IsInRole(sid)) continue;
      }
      else if (!curUser.IsInRole(rule.IdentityReference.Value)) continue;
      if (rule.AccessControlType == AccessControlType.Deny) writeDeny = true;
      else if (rule.AccessControlType == AccessControlType.Allow) writeAllow = true;
    }
  }
  catch
  {
    writeDeny = true;
  }
  return writeAllow && !writeDeny;
}