Re: utf8 library may cause heap corruption

[Kim Alvefur <zash@...>]

On Thu, Feb 09, 2017 at 02:30:39PM +0200, Dirk Laurie wrote:
> 2017-02-09 14:05 GMT+02:00 云风 Cloud Wu <cloudwu@gmail.com>:
> 
> > But there is another problem.
> >
> > local s = "\xE4\xBA"
> > assert(utf8.len(s, 1, 2) == utf8.len(s .. "\x91",1,2)) -- failed
> 
> Why is this a problem? It should fail. s is not a valid UTF8 codepoint
> ("\xE4" promises three bytes, but there are only two). When you
> supply the extra byte, there is one valid codepoint. starting between
> charaters 1 and 2.

The manual says:
> Returns the number of UTF-8 characters in string s that **start**
> between positions i and j (both inclusive).

Extra emphasis on **start**. The 3 byte does sequence starts within the
range given.


-- 
Zash

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