Problem when calling the buffer function from MobilityDB

[ezimanyi]

I get an error when calling the C function

Datum buffer(PG_FUNCTION_ARGS)

with only two arguments, the third one being optional

ERROR:  invalid memory alloc request size 18446744073709551613

The problem is solved when I modify the function as follows

PG_FUNCTION_INFO_V1(buffer);
Datum buffer(PG_FUNCTION_ARGS)
{
  [...]
  text *params_text;

  if (PG_NARGS() > 2)
  {
    params_text = PG_GETARG_TEXT_P(2);
  }
  else
  {
    // params_text = palloc(VARHDRSZ); <- ORIGINAL DEFINITION
    // SET_VARSIZE(params_text, 0);
    params_text = cstring_to_text(""); // <- PROPOSED SOLUTION
  }
  [...]
}

[robe]

pramsey have an opinion on this?

[strk]

The code in cstring_to_text("") does:

    int len = strlen(""); /* Should be 0 */
    text       *result = (text *) palloc(len + VARHDRSZ);

    SET_VARSIZE(result, len + VARHDRSZ);
    memcpy(VARDATA(result), s, len);

    return result;

So what we're missing is basically the VARHDRSZ in the SET_VARSIZE call (we're passing 0 rather than 0 + VARHDRSZ).

The patch is safe and more readable than doing this "manually", so I'd go for it.

[Regina Obe <lr@…>]

In ff1be8a/git:

Handle null arg. Patch from Esteban Zimanyi, MobilityDB. References #4982 for PostGIS 3.1.4

[Regina Obe <lr@…>]

In e2a545c1/git:

Handle null arg. Patch from Esteban Zimanyi, MobilityDB. Closes #4982 for PostGIS 3.2.0