Re: Undefined behavior in utf8_decode()

> May be an argument about whether the utf8 lib should detect invalid  
strings,
> or if it's the users job to sanitise before use. 

I suppose the first one, the Lua 5.5 Reference Manual says:

> If it finds any invalid byte sequence, returns fail plus the position of 
the first invalid byte.

Sergey

On Monday, February 16, 2026 at 7:53:45 PM UTC+3 Scott Morgan wrote:

On 16/02/2026 15:05, Sergey Bronnikov wrote: 
> 
> make MYCFLAGS=-fsanitize=undefined MYLDFLAGS=-fsanitize=undefined 
> echo "dXRmOC5sZW4n2b0B/4+Pj4+Pj48AACc=" | base64 --decode | ./lua - 
> 

d9 bd 01 ff 8f 8f 8f 8f 8f 8f 8f 00 00 

That doesn't appear to be valid UTF8 (0xff shouldn't appear in UTF8 
bytes[1]) 

May be an argument about whether the utf8 lib should detect invalid 
strings, or if it's the users job to sanitise before use. 

Scott 

[1] https://www.rfc-editor.org/rfc/rfc3629#page-3 
> The octet values C0, C1, F5 to FF never appear 

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