bug in regEnumKeys (System.Win32.Registry)

[MagnusTherning]

The following code throws a segmentation fault:

module Main where

import System.Win32.Registry

listRegistry p = do
    putStrLn $ "HKLM\\" ++ p
    hkey <- regOpenKey hKEY_LOCAL_MACHINE p
    sub_paths <- regEnumKeys hkey
    let full_subs = map ((p ++ "\\") ++) sub_paths
    mapM_ listRegistry full_subs
    
main = do
    mapM_ listRegistry ["SOFTWARE\\JavaSoft"]

[MagnusTherning]

Hmm, I didn't really intend the code to look like that. I've stuck it in hpaste:  http://hpaste.org/5666

Hopefully it'll survive there long enough.

[igloo]

I can reproduce this, but it doesn't always segfault for me.

[igloo]

Fixed:

Sun Apr  6 21:50:51 BST 2008  Ian Lynagh <igloo@earth.li>
  * malloc a big enough buffer for the registry functions. Fixes trac #2097.
  We were mallocing a byte per tchar, but tchars are normally 2 bytes big...
  I think they are at most 4 bytes, so we now malloc 4 * #tchars. Not sure
  if there is a proper function I should be using for this?

[MagnusTherning]

Replying to igloo:

Fixed: {{{ Sun Apr 6 21:50:51 BST 2008 Ian Lynagh <igloo@…> * malloc a big enough buffer for the registry functions. Fixes trac #2097. We were mallocing a byte per tchar, but tchars are normally 2 bytes big... I think they are at most 4 bytes, so we now malloc 4 * #tchars. Not sure if there is a proper function I should be using for this? }}}

One way to be sure is to switch to using wide characters explicitly, i.e. to use RegOpenKeyExW rather than RegOpenKeyEx?.

[igloo]

Replying to MagnusTherning:

Replying to igloo:

Fixed: {{{ Sun Apr 6 21:50:51 BST 2008 Ian Lynagh <igloo@…> * malloc a big enough buffer for the registry functions. Fixes trac #2097. We were mallocing a byte per tchar, but tchars are normally 2 bytes big... I think they are at most 4 bytes, so we now malloc 4 * #tchars. Not sure if there is a proper function I should be using for this? }}}

One way to be sure is to switch to using wide characters explicitly, i.e. to use RegOpenKeyExW rather than RegOpenKeyEx?.

We are using wide characters explicitly (RegEnumKeyW); the question is how large a buffer to pass as the third argument.

[MagnusTherning]

Replying to igloo:

We are using wide characters explicitly (RegEnumKeyW); the question is how large a buffer to pass as the third argument.

All right, maybe I should have been a bit more clear :-) AFAIK the use of TCHAR is something that allows the programmer to switch between Unicode (in Windows parlance) and ASCII at compile time. If the "W functions" are used explicitly I think it'd be better to also use wchar_t explicitly rather than hide them behind TCHARs.

According to Wikipedia "unicode" means UTF-16 on Windows, so allowing up to 4 bytes per character will be enough, though likely a bit wasteful.

[igloo]

I've merged the patch now, and I'm pretty sure it's safe, if not optimal, so I'm closing the ticket. Patches to improve it are of course welcomed!