Re: noupcol code cleanup

Well, I went through this again myself, and fixed a lot of stuff. I'm
going to drop this thread, but didn't want the last chunk of code I
posted to be so crappy. This is what I have come up with, FWIW:

#include "executor/spi.h" /* this is what you need to work with SPI */
#include "commands/trigger.h" /* and triggers */
#include "utils/lsyscache.h" /* for get_typlenbyval */

extern Datum noupcols (PG_FUNCTION_ARGS);

/*
noupcols () -- revoke permission on column(s)

e.g.

CREATE FUNCTION noupcols ()
RETURNS opaque
AS '/usr/lib/postgresql/lib/noupcols.so'
LANGUAGE 'C';

CREATE TRIGGER person_noupcols
BEFORE UPDATE ON person
FOR EACH ROW
EXECUTE PROCEDURE noupcols( 'name_last', 'id' );

Based on code from contrib/noup.c

The approach adopted here is to set the values of all of the columns
specified by noupcols to their old values.
*/

PG_FUNCTION_INFO_V1 (noupcols);

Datum
noupcols (PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *) fcinfo->context;
Trigger *trigger; /* to get trigger name */
Relation rel; /* triggered relation */
char **args; /* arguments: column names */
int ncols; /* # of args specified in CREATE TRIGGER */
int *colindices; /* array of column indices to modify */
Datum *oldcolvals; /* old column values */
Datum *newcolval; /* new column value */
HeapTuple oldtuple = NULL; /* tuple before being modified */
HeapTuple newtuple = NULL; /* new tuple after user-specified update */
HeapTuple newnewtuple = NULL; /* tuple to return, after restoring newtuple's protected columns to their old values */
TupleDesc tupdesc; /* tuple description */
bool isnull; /* to know is some column NULL or not */
Oid oid; /* is Datum of type ByVal? */
bool typByVal; /* is Datum of type ByVal? */
int16 typLen; /* Datum size */
int ret;
int i;

if (!CALLED_AS_TRIGGER (fcinfo))
elog(ERROR, "noup: not fired by trigger manager");

if (TRIGGER_FIRED_FOR_STATEMENT (trigdata->tg_event))
elog (ERROR, "noup: can't process STATEMENT events");

if (TRIGGER_FIRED_BY_INSERT (trigdata->tg_event))
elog (ERROR, "noup: can't process INSERT events");

else if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
elog (ERROR, "noup: can't process DELETE events");

oldtuple = trigdata->tg_trigtuple;
newtuple = trigdata->tg_newtuple;

trigger = trigdata->tg_trigger;
rel = trigdata->tg_relation;

tupdesc = rel->rd_att;

ncols = trigger->tgnargs;
args = trigger->tgargs;

colindices = (int *) palloc (ncols * sizeof (int));

/* Connect to SPI manager */
if ((ret = SPI_connect()) < 0)
elog (ERROR, "noupcol: SPI_connect returned %d", ret);

/* Allocate space to place column values */
oldcolvals = (Datum*) palloc (ncols * sizeof (Datum));
newcolval = (Datum*) palloc (sizeof (Datum));

/* For each column ... */
for (i = 0; i < ncols; i++)
{
/* get index of column in tuple */
colindices[i] = SPI_fnumber (tupdesc, args[i]);

/* Bad guys may give us un-existing column in CREATE TRIGGER */
if (colindices[i] == SPI_ERROR_NOATTRIBUTE) {
elog (ERROR, "noupcols: there is no attribute '%s' in relation '%s'",
args[i],
SPI_getrelname (rel));
}

/* Get previous value of column */
oldcolvals[i] = SPI_getbinval (oldtuple, tupdesc, colindices[i], &isnull);
*newcolval = SPI_getbinval (newtuple, tupdesc, colindices[i], &isnull);

/* need this for datumIsEqual, below */
oid = SPI_gettypeid (tupdesc, colindices[i]);
get_typlenbyval (oid, &typLen, &typByVal );

/* if an update is attempted on a locked column, post a notification that it isn't allowed */
if (! datumIsEqual (oldcolvals[i], *newcolval, typByVal, typLen)) {
elog (NOTICE, "noupcols: attribute '%s' in relation '%s' is locked",
args[i],
SPI_getrelname (rel));
}
}

/* Restore protected columns to their old values */
newnewtuple = SPI_modifytuple (rel, newtuple, ncols, colindices, oldcolvals, NULL);

if (SPI_result == SPI_ERROR_ARGUMENT) {
elog (ERROR, "noupcols: bad argument to SPI_modifytuple\n");
}

if (SPI_result == SPI_ERROR_NOATTRIBUTE) {
elog (ERROR, "noupcols: bad attribute value passed to SPI_modifytuple\n");
}

pfree (oldcolvals);
pfree (newcolval);
pfree (colindices);
SPI_finish ();

return PointerGetDatum (newnewtuple);
}

--
Ron Peterson -o)
Network & Systems Manager /\\
Mount Holyoke College _\_v
http://www.mtholyoke.edu/~rpeterso ----