Re: pnstrdup considered armed and dangerous

On 2016-10-03 14:55:24 -0700, Andres Freund wrote:
> Hi,
>
> A colleage of me just wrote innocent looking code like
> char *shardRelationName = pnstrdup(relationName, NAMEDATALEN);
> which is at the moment wrong if relationName isn't preallocated to
> NAMEDATALEN size.
>
> /*
> * pnstrdup
> * Like pstrdup(), but append null byte to a
> * not-necessarily-null-terminated input string.
> */
> char *
> pnstrdup(const char *in, Size len)
> {
> char *out = palloc(len + 1);
>
> memcpy(out, in, len);
> out[len] = '\0';
> return out;
> }
>
> isn't that a somewhat weird behaviour / implementation? Not really like
> strndup(), which one might believe to be analoguous...

I've since hit this bug again. To fix it, you'd need strnlen. The lack
of which I'd also independently hit twice. So here's a patch adding
pg_strnlen and using that to fix pnstrdup.

Greetings,

Andres Freund