Re: Portability concerns over pq_sendbyte?

Hi,

On 2018-06-13 22:02:13 +0100, Andrew Gierth wrote:
> >>>>> "Andres" == Andres Freund  writes:
> 
>  >> unsigned char x = 128;
>  >> pq_sendbyte(&buf, x);
>  >> 
>  >> which I believe is not well-defined since pq_sendbyte takes an int8,
>  >> and conversions of unrepresentable values to _signed_ integer types
>  >> are (iirc) implementation-dependent.
> 
>  Andres> It's not implementation defined in postgres' dialect of C - we
>  Andres> rely on accurate signed->unsigned conversions in a number of
>  Andres> places.
> 
> Converting signed integer to unsigned is ok as I understand it - what's
> happening here is the reverse, converting an unrepresentable unsigned
> value to a signed type.

Err, yes, I was thinking about that conversion. Sorry for the confusion.


>  >> There are also some cases where pq_sendint16 is being called for an
>  >> unsigned value or a value that might exceed 32767.
> 
>  Andres> Hm, which case were you thinking of here? The calls usually are
>  Andres> exactly the types that the wire protocol expects, no?
> 
> There are cases where it's not actually clear what the wire protocol
> expects - I'm thinking in particular of the number of entries in a list
> of parameter types/formats.

But that didn't change around the pq_send* changes?  So I'm not sure I
understand how this is related?  I mean I'm all for documenting the wire
protocol more extensively, but we can't just change the width?

Greetings,

Andres Freund