Re: C file recoginzed as image file

[Jason Rumney]

Richard Stallman wrote:
>     > Besides which, a jpg file starts with characters that don't make any
>     > sense at the start of a C file.  So if it looks like a plausible C
>     > file, it won't be treated as a jpeg.
>
>     If it looks like a plausible C file to who?
>
> To anyone who knows C.  The first two characters of a JPG file are
> character codes above 128, that would obviously be invalid in C.
>   

The user cannot see those first two characters until they load the file. 
If it is in fact a dangerous jpg file, they will not find out until too 
late. If my patch to use image-mode-maybe for magic-mode-alist is 
installed, this will not happen for file extensions that the user might 
reasonably expect to be something other than an image. But it will still 
happen for unknown file extensions, which in some cases (.thm files, or 
thumbnails without an extension) will be considered a good thing, but 
there may also be cases where a user receives a file with an unknown 
extension and opens it in Emacs to see the file contents to decide what 
type of file it is, expecting Emacs to be a safe way of checking such 
files. So maybe it would be better to define a new function 
`image-mode-confirm' which always asks the user before using image-mode 
on a file, and using that for magic-mode-alist and other uses which 
could be considered risky.