Hello,
The PGresult structure returned on COPY ... FROM provides a handful of
information (https://www.postgresql.org/docs/13/libpq-copy.html):
number of fields expected and whether they are binary or not.
However it doesn't provide the types expected. For binary copy the
exact type is important: playing with it, it seems that no cast
whatsoever is applied and the errors reported are relatively low
level. For instance, passing an int4 value to an int8 field causes a
"protocol_violation: insufficient data left in message"; the other way
around is greeted with "invalid_binary_representation: incorrect
binary data format".
Naively, it would seem that once a "COPY ... FROM STDIN" is executed
successfully, the server has a pretty good idea of what data types it
is expecting. I'm wondering: is it absurd to ask for this info to be
returned as RowDescription and to be exposed by the libpq PQftype()?
Cheers
-- Daniele