[HACKERS] libpq support for arrays and composites

One of the areas where libpq seems to be severely lacking is in handling
arrays and composites in query results. I'd like to set about rectifying
that.

Ideally this would mean that drivers using libpq could easily and
reliably deliver such objects suitably structured in their particular
languages (e.g. lists and hashes in Perl).

One complicating factor I see is that there is no protocol level support
for anything other than simple objects - each data value is simply a
stream of bytes of a known length. We would therefore need some pretty
robust processing to pick apart structured objects.

We'll need a new API to handle such objects. I'm thinking of something like:

PQarray * PQgetArray( const PGresult *res, int row_number, int
column_number);
int PQgetArrayNDims(PQarray * array);
int PQgetArrayLower(PQarray * array, int dim);
int PQgetArrayUpper(PQarray * array, int dim);
int PQgetArrayElementLength(PQarray * array, int dim1, ...);
bool PQgetArrayElementIsNull(PQarray * array, int dim1, ...);
char * PQgetArrayElement(PQarray * array, int dim1, ...);

PQcomposite * PQgetComposite(const PGresult *res, int row_number, int
column_number);
PQcomposite * PQgetArrayElementComposite(PQarray * array, int dim1, ...);
int PQgetCompositeNFields(PQcomposite * composite);
char * PQgetCompositeFName(PQcomposite * composite, int fnumber);
int PQgetCompositeFNumber(PQcomposite * composite, char * fname);
Oid PQgetCOmpositeFType(PQcomposite * composite, int fnumber);
int PQgetCompositeFieldLength(PQcomposite * , int fnumber);
bool PQgetCompositeFieldIsNull(PQcomposite * composite, int fnumber);
char * PQgetCompositeField(PQcomposite * composite, int fnumber);

Not sure if we need analogs for PQfformat, PQfmod or PQfsize - I suspect
not, but right now I'm just thinking out loud.

Thoughts? Is this worth doing?

cheers

andrew

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