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ce1e7a2f71
As currently implemented, failure of a PGEVT_RESULTCREATE callback causes the PGresult to be converted to an error result. This is intellectually inconsistent (shouldn't a failing callback likewise prevent creation of the error result? what about side-effects on the behavior seen by other event procs? why does PQfireResultCreateEvents act differently from PQgetResult?), but more importantly it destroys any promises we might wish to make about the behavior of libpq in nontrivial operating modes, such as pipeline mode. For example, it's not possible to promise that PGRES_PIPELINE_SYNC results will be returned if an event callback fails on those. With this definition, expecting applications to behave sanely in the face of possibly-failing callbacks seems like a very big lift. Hence, redefine the result of a callback failure as being simply that that event procedure won't be called any more for this PGresult (which was true already). Event procedures can still signal failure back to the application through out-of-band mechanisms, for example via their passthrough arguments. Similarly, don't let failure of a PGEVT_RESULTCOPY callback prevent PQcopyResult from succeeding. That definition allowed a misbehaving event proc to break single-row mode (our sole internal use of PQcopyResult), and it probably had equally deleterious effects for outside uses. Discussion: https://postgr.es/m/3185105.1644960083@sss.pgh.pa.us