/*-------------------------------------------------------------------------
 *
 * pg_largeobject.c
 *   routines to support manipulation of the pg_largeobject relation
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *   src/backend/catalog/pg_largeobject.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/table.h"
#include "catalog/catalog.h"
#include "catalog/indexing.h"
#include "catalog/pg_largeobject.h"
#include "catalog/pg_largeobject_metadata.h"
#include "miscadmin.h"
#include "utils/acl.h"
#include "utils/fmgroids.h"
#include "utils/rel.h"


/*
 * Create a large object having the given LO identifier.
 *
 * We create a new large object by inserting an entry into
 * pg_largeobject_metadata without any data pages, so that the object
 * will appear to exist with size 0.
 */
Oid
LargeObjectCreate(Oid loid)
{
 Relation pg_lo_meta;
 HeapTuple ntup;
 Oid   loid_new;
 Datum  values[Natts_pg_largeobject_metadata];
 bool  nulls[Natts_pg_largeobject_metadata];
 Oid   ownerId;
 Acl     *lomacl;

 pg_lo_meta = table_open(LargeObjectMetadataRelationId,
       RowExclusiveLock);

 /*
  * Insert metadata of the largeobject
 */
 memset(values, 0, sizeof(values));
 memset(nulls, false, sizeof(nulls));

 if (OidIsValid(loid))
  loid_new = loid;
 else
  loid_new = GetNewOidWithIndex(pg_lo_meta,
           LargeObjectMetadataOidIndexId,
           Anum_pg_largeobject_metadata_oid);
 ownerId = GetUserId();
 lomacl = get_user_default_acl(OBJECT_LARGEOBJECT, ownerId, InvalidOid);

 values[Anum_pg_largeobject_metadata_oid - 1] = ObjectIdGetDatum(loid_new);
 values[Anum_pg_largeobject_metadata_lomowner - 1]
  = ObjectIdGetDatum(ownerId);

 if (lomacl != NULL)
  values[Anum_pg_largeobject_metadata_lomacl - 1]
   = PointerGetDatum(lomacl);
 else
  nulls[Anum_pg_largeobject_metadata_lomacl - 1] = true;

 ntup = heap_form_tuple(RelationGetDescr(pg_lo_meta),
         values, nulls);

 CatalogTupleInsert(pg_lo_meta, ntup);

 heap_freetuple(ntup);

 table_close(pg_lo_meta, RowExclusiveLock);

 /* dependencies on roles mentioned in default ACL */
 recordDependencyOnNewAcl(LargeObjectRelationId, loid_new, 0,
        ownerId, lomacl);

 return loid_new;
}

/*
 * Drop a large object having the given LO identifier.  Both the data pages
 * and metadata must be dropped.
 */
void
LargeObjectDrop(Oid loid)
{
 Relation pg_lo_meta;
 Relation pg_largeobject;
 ScanKeyData skey[1];
 SysScanDesc scan;
 HeapTuple tuple;

 pg_lo_meta = table_open(LargeObjectMetadataRelationId,
       RowExclusiveLock);

 pg_largeobject = table_open(LargeObjectRelationId,
        RowExclusiveLock);

 /*
  * Delete an entry from pg_largeobject_metadata
 */
 ScanKeyInit(&skey[0],
    Anum_pg_largeobject_metadata_oid,
    BTEqualStrategyNumber, F_OIDEQ,
    ObjectIdGetDatum(loid));

 scan = systable_beginscan(pg_lo_meta,
         LargeObjectMetadataOidIndexId, true,
         NULL, 1, skey);

 tuple = systable_getnext(scan);
 if (!HeapTupleIsValid(tuple))
  ereport(ERROR,
    (errcode(ERRCODE_UNDEFINED_OBJECT),
     errmsg("large object %u does not exist", loid)));

 CatalogTupleDelete(pg_lo_meta, &tuple->t_self);

 systable_endscan(scan);

 /*
  * Delete all the associated entries from pg_largeobject
 */
 ScanKeyInit(&skey[0],
    Anum_pg_largeobject_loid,
    BTEqualStrategyNumber, F_OIDEQ,
    ObjectIdGetDatum(loid));

 scan = systable_beginscan(pg_largeobject,
         LargeObjectLOidPNIndexId, true,
         NULL, 1, skey);
 while (HeapTupleIsValid(tuple = systable_getnext(scan)))
 {
  CatalogTupleDelete(pg_largeobject, &tuple->t_self);
 }

 systable_endscan(scan);

 table_close(pg_largeobject, RowExclusiveLock);

 table_close(pg_lo_meta, RowExclusiveLock);
}

/*
 * LargeObjectExists
 *
 * We don't use the system cache for large object metadata, for fear of
 * using too much local memory.
 *
 * This function always scans the system catalog using an up-to-date snapshot,
 * so it should not be used when a large object is opened in read-only mode
 * (because large objects opened in read only mode are supposed to be viewed
 * relative to the caller's snapshot, whereas in read-write mode they are
 * relative to a current snapshot).
 */
bool
LargeObjectExists(Oid loid)
{
 return LargeObjectExistsWithSnapshot(loid, NULL);
}

/*
 * Same as LargeObjectExists(), except snapshot to read with can be specified.
 */
bool
LargeObjectExistsWithSnapshot(Oid loid, Snapshot snapshot)
{
 Relation pg_lo_meta;
 ScanKeyData skey[1];
 SysScanDesc sd;
 HeapTuple tuple;
 bool  retval = false;

 ScanKeyInit(&skey[0],
    Anum_pg_largeobject_metadata_oid,
    BTEqualStrategyNumber, F_OIDEQ,
    ObjectIdGetDatum(loid));

 pg_lo_meta = table_open(LargeObjectMetadataRelationId,
       AccessShareLock);

 sd = systable_beginscan(pg_lo_meta,
       LargeObjectMetadataOidIndexId, true,
       snapshot, 1, skey);

 tuple = systable_getnext(sd);
 if (HeapTupleIsValid(tuple))
  retval = true;

 systable_endscan(sd);

 table_close(pg_lo_meta, AccessShareLock);

 return retval;
}