Re: [Bug-wget] Contribution on bug #45037

[Ángel González]

On 16/05/15 22:10, Ander Juaristi Alamos wrote:
> > Hello,
> >
> > I found another task where I want to contribute, the issue with 45037.
> > For what I understand, and read in the mailling list, the problem occur inftp.c
> > ftp_loop_internal ->  remove_link.
> >
> > But what I don't understand, is why each time he try to remove
> > the symbolic link. What is the purpose of this statement, in overall context of 
> > code.
> As Tim pointed out, the purpose is not to overwrite the content of the file the 
> link points to.
> If README was a regular file and then you passed "-O README", it's okay to 
> overwrite it (I don't
> know what's Wget default behavior here, if it prompts the user or whatever), 
> because the user is supposed
> to be aware of such action. But if README was a symlink, passing "-O README" 
> could be a malicious
> action, as Angel said. If you want an example of such an action and its 
> consequences,
> google for "Symlink race".
>
> > That was here, because that was a feature, and now a bug, because some others 
> > statements was removed ?
> >
> > If for example I have a symbolic link README in local, and try to download 
> > another file, with the
> > same name README remotely, with -O foo, normally, my symbolic link README 
> > should not be modified.
> Exactly. Looking at the code, my guess is that the person who wrote it didn't 
> take into account that
> the user could have passed the "-O" option (or maybe it wasn't yet implemented 
> then, who knows). He or she
> just picked the name of the downloaded file.
The -O option already existed in d5be8ecc (and probably in Geturl, too).


> > But now if I pass -O README, the symbolic link will be removed because it's a 
> > redirection ?
> > so It's not possible to just renamed it ?
> It sounds like that's exactly what should be done. Treat the symlink as if it 
> was a local file: if a symlink
> exists with the same name as the downloaded file, rename the downloaded file to 
> README.1, for instance.
Actually, instead of _renaming_ it, you should just create it with the 
right name.


> > Sorry if my questions are silly, but I'am starting in the code of wget, and my 
> > knowledge are weak.
> Something this project has taught me is that there's no silly question. It's 
> better to ask even though you're
> not really sure (and you've made some research on your own before :D) than keep 
> quiet and make wrong assumptions by yourself.

+1 Perfectly explained, Ander


Loïc, the interesting thing is that the rest of us don't really know why 
things where done that way, either. That piece of code has been there 
since the first svn revision, in 1999 (wget 1.5.3) and very few people 
contributing back then are still active nowadays. Moreover, much more 
difficult than being "there" is to remember exactly why it was added!