Dry run through input function for a given built-in data type

Hello

Our business is writing a small batch insert engine with constraint
aware validation (pg_version(): PostgreSQL 9.2.10 on
x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat
4.4.7-11), 64-bit)

The the goal is to run abstracted multi-line INSERT/UPDATES and return a
result set detailing what was successfully inserted and what
domain/constraint violations would have happened if an attempt were to
be made at inserting those bad rows.

Everything happens in a single big auto generated CTE cascade to
mitigate the risk of race conditions (serializable isolation on top of
that would be our last resort).

Metadata is retrieved from pg_catalog, custom table and domain CHECK
expression are nicely turned into boolean compliance states, EXISTS()
calls do all the required look-aside for foreign keys existence and so
on. Everything is working as intended so far.

Ironically, I'm hitting a wall when it comes to native types. The only
ways I've found to reliably create the validation SQL expression is to
either hard code it or attempt a cast in a PL/PGSQL function and catch
the exception (much slower).

Is there any cleaner way to, say, only run the validation part of a type
input function to infer domain compatibility? Or maybe is there a
built-in dictionary of regular expressions? Or else?

Many thanks guys

F