Get FileSystem Restrictions

Question

I would like to code a function that tells me if it's possible to WRITE a file/folder to a specific path or not. I would like to do that WITHOUT actually writing any file(s) to the disk. Is there a WINAPI function for that? Thank you for your help.

Lamaism

There's no single function that will do that. If you can navigate the security API you can make a pretty good go at checking this in advance. By far the easiest way to know whether or not you can write to some location is to attempt to do so. – Zonked

I've also dealt with this kind of situation. first I based my solution on checking ACL permissions, but soon I came to realize that the only reliable way is to actually try and create a temp file using GetTempFileName API (or whatever). – Argentina

Well, i insert CD-ROM, then your program, checks ACL. You are granted the right to create your files - but the media just does not support it. Ditto for write-protected floppies, SD cards, etc. ACL is just not enough. Better try. Set Windows flags to auto-delete file on close, if you are afraid to live garbage in case of errors. – Give

See also How can I use Delphi to test if a Directory is writeable? – Argentina

@Argentina I wanted to do the same but without writing a temporary file. – Lamaism

Answer 1

You can use GetFileSecurity() and AccessCheck() functions. Read the Aaron Ballman's article on How to Check Access Rights. He provided the CanAccessFolder() function to do what you asked.

Caty

Answer 2

function CheckFileAccess(const FileName: string; const CheckedAccess: Cardinal): Cardinal;
var Token: THandle;
    Status: LongBool;
    Access: Cardinal;
    SecDescSize: Cardinal;
    PrivSetSize: Cardinal;
    PrivSet: PRIVILEGE_SET;
    Mapping: GENERIC_MAPPING;
    SecDesc: PSECURITY_DESCRIPTOR;
begin
  Result := 0;
  GetFileSecurity(PChar(Filename), OWNER_SECURITY_INFORMATION or GROUP_SECURITY_INFORMATION or DACL_SECURITY_INFORMATION, nil, 0, SecDescSize);
  SecDesc := GetMemory(SecDescSize);

  if GetFileSecurity(PChar(Filename), OWNER_SECURITY_INFORMATION or GROUP_SECURITY_INFORMATION or DACL_SECURITY_INFORMATION, SecDesc, SecDescSize, SecDescSize) then
  begin
    ImpersonateSelf(SecurityImpersonation);
    OpenThreadToken(GetCurrentThread, TOKEN_QUERY, False, Token);
    if Token <> 0 then
    begin
      Mapping.GenericRead := FILE_GENERIC_READ;
      Mapping.GenericWrite := FILE_GENERIC_WRITE;
      Mapping.GenericExecute := FILE_GENERIC_EXECUTE;
      Mapping.GenericAll := FILE_ALL_ACCESS;

      MapGenericMask(Access, Mapping);
      PrivSetSize := SizeOf(PrivSet);
      AccessCheck(SecDesc, Token, CheckedAccess, Mapping, PrivSet, PrivSetSize, Access, Status);
      CloseHandle(Token);
      if Status then
        Result := Access;
    end;
  end;

  FreeMem(SecDesc, SecDescSize);
end;

You use this like: if (CheckFileAccess(SysteemGegevens.DFImportPath, FILE_ALL_ACCESS) <> FILE_ALL_ACCESS) then

with

const
FILE_READ_DATA = $0001;
FILE_WRITE_DATA = $0002;
FILE_APPEND_DATA = $0004;
FILE_READ_EA = $0008;
FILE_WRITE_EA = $0010;
FILE_EXECUTE = $0020;
FILE_READ_ATTRIBUTES = $0080;
FILE_WRITE_ATTRIBUTES = $0100;
FILE_GENERIC_READ = (STANDARD_RIGHTS_READ or FILE_READ_DATA or
FILE_READ_ATTRIBUTES or FILE_READ_EA or SYNCHRONIZE);
FILE_GENERIC_WRITE = (STANDARD_RIGHTS_WRITE or FILE_WRITE_DATA or
FILE_WRITE_ATTRIBUTES or FILE_WRITE_EA or FILE_APPEND_DATA or SYNCHRONIZE);
FILE_GENERIC_EXECUTE = (STANDARD_RIGHTS_EXECUTE or FILE_READ_ATTRIBUTES or
FILE_EXECUTE or SYNCHRONIZE);
FILE_ALL_ACCESS = STANDARD_RIGHTS_REQUIRED or SYNCHRONIZE or $1FF;

Haematite

Could you explain what this function does, what are the input parameters and what is the result, please ? Btw., you should check results of the Windows API function calls... – Sedan

This is seems to be the ported CanAccessFolder function from the answer above. – Lamaism

TLama: Sorry, added. Benjamin: I would not know, grabbed it from our code base – Haematite

Hello, I used this function and started having printing related issues: #74229386 – Bacterin