From: Daniel Berger <djberg96@...>
Date: 2006-05-29T12:12:57+09:00
Subject: Re: String segfault with wide character function, Windows

Daniel Berger wrote:
> Ruby 1.8.4 (one click)
> Windows XP
> 
> Check this out segfault:
> 
> # strtest.rb
> require 'Win32API'
> 
> GetFullPathNameW = Win32API.new('kernel32','GetFullPathNameW','PLPP', 'L')
> 
> path = "C:\\test"
> buf  = 0.chr * 260
> 
> if GetFullPathNameW.call(path, buf.size, buf, 0) == 0
>    puts "Failed"
> end
> 
> #p buf
> p buf.split("\0\0").first # boom!
> 
> # Result
> strtest.rb:13: [BUG] Segmentation fault
> ruby 1.8.4 (2005-12-24) [i386-mswin32]
> 
> This application has requested the Runtime to terminate it in an unusual 
> way. Please contact the application's support team for more information.
> 
> I noticed that if I dropped the 'buf' to 245 or fewer characters, it 
> works ok.  Also, it segfaults on just about any op that modifies buf, 
> not just String#split.
> 
> Any ideas?
> 
> Thanks,
> 
> Dan
> 
> 

The solution was found by Heesob, which I have pasted below (taken from 
the win32utils-devel mailing list):

I have found out what is the problem.
It's not bug of Ruby or Windows, it is only bug of code.

First try this:

require 'Win32API'
GetFullPathNameW = Win32API.new('kernel32','GetFullPathNameW','PLPP', 'L')
for i in 1..100
path = "c:\\test"
buf  = 0.chr * 260
if GetFullPathNameW.call(path, buf.size, buf, 0) == 0
     puts "Failed"
end
p buf.split("\0\0").first
end

It will cause various errors like
uninitialized constant GetFullPathNameW (NameError)
or
segfault.

Next, try this:

require 'Win32API'
GetFullPathNameW = Win32API.new('kernel32','GetFullPathNameW','PLPP', 'L')
for i in 1..100
path = "c:\\test"
buf  = 0.chr * 260
# buf.size/2 -> actual length of buf
if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0
     puts "Failed"
end
p buf.split("\0\0").first
end

It runs Ok. but the result is not correct.

Next , try this:

require 'Win32API'
GetFullPathNameW = Win32API.new('kernel32','GetFullPathNameW','PLPP', 'L')
for i in 1..100
# append \0 to path
path = "c:\\test\0"
buf  = 0.chr * 260
# buf.size/2 -> actual length of buf in unicode string
if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0
     puts "Failed"
end
p buf.split("\0\0").first
end

It runs ok. The result is correct.

Finally, the complete and correct code is like this:

require 'Win32API'
GetFullPathNameW = Win32API.new('kernel32','GetFullPathNameW','PLPP', 'L')
for i in 1..100
path = "c\0:\0\\\0t\0e\0s\0t\0\0"
buf  = 0.chr * 260
# buf.size/2 -> actual length of buf in unicode string
if GetFullPathNameW.call(path, buf.size/2, buf, 0) == 0
     puts "Failed"
end
buf = buf.split("\0\0").first
buf = (buf.size % 2).zero? ? buf : buf+"\0"
p buf
end

Remeber, Ruby's string is terminated with "\0" implicitly, but UTF16
string requires double "\0".
For ascii chars, it happens trailing three "\0"  : one for ascii char
and two for string termination.

Regards,

Park Heesob