Grumble, I forgot about COPY WITH OIDS. Amend that proposal as follows:
... We should use two different
magic numbers depending on whether OIDs are included in the dump or not.
If OIDs are included in the dump, the OID field immediately follows the
field-count word. It is a normal field except that it's not included
in the field-count. In particular it has a typlen --- this will allow
handling of 4-byte vs 8-byte OIDs without too much pain, and will allow
OIDs to be shown as NULL if we someday allow OIDs to be optional.
regards, tom lane