Add pg_get_acl() to get the ACL for a database object

This function returns the ACL for a database object, specified by
catalog OID and object OID.  This is useful to be able to
retrieve the ACL associated to an object specified with a
(class_id,objid) couple, similarly to the other functions for object
identification, when joined with pg_depend or pg_shdepend.

Original idea by Álvaro Herrera.

Bump catalog version.

Author: Joel Jacobson
Reviewed-by: Isaac Morland, Michael Paquier, Ranier Vilela
Discussion: https://postgr.es/m/80b16434-b9b1-4c3d-8f28-569f21c2c102@app.fastmail.com

Author: michaelpq

doc/src/sgml/func.sgml

@@ -26587,6 +26587,21 @@ SELECT currval(pg_get_serial_sequence('sometable', 'id'));
      </thead>
 
      <tbody>
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_get_acl</primary>
+        </indexterm>
+        <function>pg_get_acl</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type> )
+        <returnvalue>aclitem[]</returnvalue>
+       </para>
+       <para>
+        Returns the <acronym>ACL</acronym> for a database object, specified
+        by catalog OID and object OID. This function returns
+        <literal>NULL</literal> values for undefined objects.
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
@@ -26700,6 +26715,32 @@ SELECT currval(pg_get_serial_sequence('sometable', 'id'));
     </tgroup>
    </table>
 
+   <para>
+    <function>pg_get_acl</function> is useful for retrieving and inspecting
+    the privileges associated with database objects without looking at
+    specific catalogs. For example, to retrieve all the granted privileges
+    on objects in the current database:
+<programlisting>
+postgres=# SELECT
+    (pg_identify_object(s.classid,s.objid,s.objsubid)).*,
+    pg_catalog.pg_get_acl(s.classid,s.objid) AS acl
+FROM pg_catalog.pg_shdepend AS s
+JOIN pg_catalog.pg_database AS d
+    ON d.datname = current_database() AND
+       d.oid = s.dbid
+JOIN pg_catalog.pg_authid AS a
+    ON a.oid = s.refobjid AND
+       s.refclassid = 'pg_authid'::regclass
+WHERE s.deptype = 'a';
+-[ RECORD 1 ]-----------------------------------------
+type     | table
+schema   | public
+name     | testtab
+identity | public.testtab
+acl      | {postgres=arwdDxtm/postgres,foo=r/postgres}
+</programlisting>
+   </para>
+
   </sect2>
 
   <sect2 id="functions-info-comment">

src/backend/catalog/objectaddress.c

@@ -4362,6 +4362,54 @@ pg_identify_object_as_address(PG_FUNCTION_ARGS)
 	PG_RETURN_DATUM(HeapTupleGetDatum(htup));
 }
 
+/*
+ * SQL-level callable function to obtain the ACL of a specified object, given
+ * its catalog OID and object OID.
+ */
+Datum
+pg_get_acl(PG_FUNCTION_ARGS)
+{
+	Oid			classId = PG_GETARG_OID(0);
+	Oid			objectId = PG_GETARG_OID(1);
+	Oid			catalogId;
+	AttrNumber	Anum_acl;
+	Relation	rel;
+	HeapTuple	tup;
+	Datum		datum;
+	bool		isnull;
+
+	/* for "pinned" items in pg_depend, return null */
+	if (!OidIsValid(classId) && !OidIsValid(objectId))
+		PG_RETURN_NULL();
+
+	/* for large objects, the catalog to look at is pg_largeobject_metadata */
+	catalogId = (classId == LargeObjectRelationId) ?
+		LargeObjectMetadataRelationId : classId;
+	Anum_acl = get_object_attnum_acl(catalogId);
+
+	/* return NULL if no ACL field for this catalog */
+	if (Anum_acl == InvalidAttrNumber)
+		PG_RETURN_NULL();
+
+	rel = table_open(catalogId, AccessShareLock);
+
+	tup = get_catalog_object_by_oid(rel, get_object_attnum_oid(catalogId),
+									objectId);
+	if (!HeapTupleIsValid(tup))
+	{
+		table_close(rel, AccessShareLock);
+		PG_RETURN_NULL();
+	}
+
+	datum = heap_getattr(tup, Anum_acl, RelationGetDescr(rel), &isnull);
+	table_close(rel, AccessShareLock);
+
+	if (isnull)
+		PG_RETURN_NULL();
+
+	PG_RETURN_DATUM(datum);
+}
+
 /*
  * Return a palloc'ed string that describes the type of object that the
  * passed address is for.

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202407012
+#define CATALOG_VERSION_NO	202407041
 
 #endif

src/include/catalog/pg_proc.dat

@@ -6362,6 +6362,11 @@
   proname => 'pg_describe_object', provolatile => 's', prorettype => 'text',
   proargtypes => 'oid oid int4', prosrc => 'pg_describe_object' },
 
+{ oid => '6347', descr => 'get ACL for SQL object',
+  proname => 'pg_get_acl', provolatile => 's', prorettype => '_aclitem',
+  proargtypes => 'oid oid', proargnames => '{classid,objid}',
+  prosrc => 'pg_get_acl' },
+
 { oid => '3839',
   descr => 'get machine-parseable identification of SQL object',
   proname => 'pg_identify_object', provolatile => 's', prorettype => 'record',

src/test/regress/expected/privileges.out

@@ -213,10 +213,39 @@ SELECT * FROM atest1;
 (0 rows)
 
 CREATE TABLE atest2 (col1 varchar(10), col2 boolean);
+SELECT pg_get_acl('pg_class'::regclass, 'atest2'::regclass::oid);
+ pg_get_acl 
+------------
+ 
+(1 row)
+
 GRANT SELECT ON atest2 TO regress_priv_user2;
 GRANT UPDATE ON atest2 TO regress_priv_user3;
 GRANT INSERT ON atest2 TO regress_priv_user4 GRANTED BY CURRENT_USER;
 GRANT TRUNCATE ON atest2 TO regress_priv_user5 GRANTED BY CURRENT_ROLE;
+SELECT unnest(pg_get_acl('pg_class'::regclass, 'atest2'::regclass::oid));
+                     unnest                     
+------------------------------------------------
+ regress_priv_user1=arwdDxtm/regress_priv_user1
+ regress_priv_user2=r/regress_priv_user1
+ regress_priv_user3=w/regress_priv_user1
+ regress_priv_user4=a/regress_priv_user1
+ regress_priv_user5=D/regress_priv_user1
+(5 rows)
+
+-- Invalid inputs
+SELECT pg_get_acl('pg_class'::regclass, 0); -- null
+ pg_get_acl 
+------------
+ 
+(1 row)
+
+SELECT pg_get_acl(0, 0); -- null
+ pg_get_acl 
+------------
+ 
+(1 row)
+
 GRANT TRUNCATE ON atest2 TO regress_priv_user4 GRANTED BY regress_priv_user5;  -- error
 ERROR:  grantor must be current user
 SET SESSION AUTHORIZATION regress_priv_user2;

src/test/regress/sql/privileges.sql

@@ -183,10 +183,16 @@ GRANT SELECT ON atest1 TO regress_priv_user3, regress_priv_user4;
 SELECT * FROM atest1;
 
 CREATE TABLE atest2 (col1 varchar(10), col2 boolean);
+SELECT pg_get_acl('pg_class'::regclass, 'atest2'::regclass::oid);
 GRANT SELECT ON atest2 TO regress_priv_user2;
 GRANT UPDATE ON atest2 TO regress_priv_user3;
 GRANT INSERT ON atest2 TO regress_priv_user4 GRANTED BY CURRENT_USER;
 GRANT TRUNCATE ON atest2 TO regress_priv_user5 GRANTED BY CURRENT_ROLE;
+SELECT unnest(pg_get_acl('pg_class'::regclass, 'atest2'::regclass::oid));
+
+-- Invalid inputs
+SELECT pg_get_acl('pg_class'::regclass, 0); -- null
+SELECT pg_get_acl(0, 0); -- null
 
 GRANT TRUNCATE ON atest2 TO regress_priv_user4 GRANTED BY regress_priv_user5;  -- error