Add paths of extensions to pg_available_extensions

Add a new "location" column to the pg_available_extensions and
pg_available_extension_versions views, exposing the directory where
the extension is located.

The default system location is shown as '$system', the same value
that can be used to configure the extension_control_path GUC.

User-defined locations are only visible for super users, otherwise
'<insufficient privilege>' is returned as a column value, the same
behaviour that we already use in pg_stat_activity.

I failed to resist the temptation to do a little extra editorializing of
the TAP test script.

Catalog version bumped.

Author: Matheus Alcantara <mths.dev@pm.me>
Reviewed-By: Chao Li <li.evan.chao@gmail.com>
Reviewed-By: Rohit Prasad <rohit.prasad@arm.com>
Reviewed-By: Michael Banck <mbanck@gmx.net>
Reviewed-By: Manni Wood <manni.wood@enterprisedb.com>
Reviewed-By: Euler Taveira <euler@eulerto.com>
Reviewed-By: Quan Zongliang <quanzongliang@yeah.net>

doc/src/sgml/system-views.sgml

@@ -599,6 +599,20 @@
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>location</structfield> <type>text</type>
+      </para>
+      <para>
+       The location where the extension is installed. If it is in the standard
+       system location, then the value will be <literal>$system</literal>,
+       while if it is found in the path specified by the
+       <link linkend="guc-extension-control-path"><structname>extension_control_path</structname></link>
+       GUC then the full path will be shown.
+       Only superusers can see this information.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>comment</structfield> <type>text</type>
@@ -723,6 +737,20 @@
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>location</structfield> <type>text</type>
+      </para>
+       <para>
+       The location where the extension is installed. If it is in the standard
+       system location, then the value will be <literal>$system</literal>,
+       while if it is found in the path specified by the
+       <link linkend="guc-extension-control-path"><structname>extension_control_path</structname></link>
+       GUC then the full path will be shown.
+       Only superusers can see this information.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>comment</structfield> <type>text</type>

src/backend/catalog/system_views.sql

@@ -412,14 +412,14 @@ CREATE VIEW pg_cursors AS
 
 CREATE VIEW pg_available_extensions AS
     SELECT E.name, E.default_version, X.extversion AS installed_version,
-           E.comment
+           E.location, E.comment
       FROM pg_available_extensions() AS E
            LEFT JOIN pg_extension AS X ON E.name = X.extname;
 
 CREATE VIEW pg_available_extension_versions AS
     SELECT E.name, E.version, (X.extname IS NOT NULL) AS installed,
            E.superuser, E.trusted, E.relocatable,
-           E.schema, E.requires, E.comment
+           E.schema, E.requires, E.location, E.comment
       FROM pg_available_extension_versions() AS E
            LEFT JOIN pg_extension AS X
              ON E.name = X.extname AND E.version = X.extversion;

src/backend/commands/extension.c

@@ -126,6 +126,21 @@ typedef struct
 	ParseLoc	stmt_len;		/* length in bytes; 0 means "rest of string" */
 } script_error_callback_arg;
 
+/*
+ * A location based on the extension_control_path GUC.
+ *
+ * The macro field stores the name of a macro (for example “$system”) that
+ * the extension_control_path processing supports, and which can be replaced
+ * by a system value stored in loc.
+ *
+ * For non-system paths the macro field is NULL.
+ */
+typedef struct
+{
+	char	   *macro;
+	char	   *loc;
+} ExtensionLocation;
+
 /* Local functions */
 static List *find_update_path(List *evi_list,
 							  ExtensionVersionInfo *evi_start,
@@ -140,7 +155,8 @@ static Oid	get_required_extension(char *reqExtensionName,
 								   bool is_create);
 static void get_available_versions_for_extension(ExtensionControlFile *pcontrol,
 												 Tuplestorestate *tupstore,
-												 TupleDesc tupdesc);
+												 TupleDesc tupdesc,
+												 ExtensionLocation *location);
 static Datum convert_requires_to_datum(List *requires);
 static void ApplyExtensionUpdates(Oid extensionOid,
 								  ExtensionControlFile *pcontrol,
@@ -157,6 +173,29 @@ static ExtensionControlFile *new_ExtensionControlFile(const char *extname);
 
 char	   *find_in_paths(const char *basename, List *paths);
 
+/*
+ *  Return the extension location. If the current user doesn't have sufficient
+ *  privilege, don't show the location.
+ */
+static char *
+get_extension_location(ExtensionLocation *loc)
+{
+	/* We only want to show extension paths for superusers. */
+	if (superuser())
+	{
+		/* Return the macro value if present to avoid showing system paths. */
+		if (loc->macro != NULL)
+			return loc->macro;
+		else
+			return loc->loc;
+	}
+	else
+	{
+		/* Similar to pg_stat_activity for unprivileged users */
+		return "<insufficient privilege>";
+	}
+}
+
 /*
  * get_extension_oid - given an extension name, look up the OID
  *
@@ -354,7 +393,11 @@ get_extension_control_directories(void)
 
 	if (strlen(Extension_control_path) == 0)
 	{
-		paths = lappend(paths, system_dir);
+		ExtensionLocation *location = palloc_object(ExtensionLocation);
+
+		location->macro = NULL;
+		location->loc = system_dir;
+		paths = lappend(paths, location);
 	}
 	else
 	{
@@ -366,6 +409,7 @@ get_extension_control_directories(void)
 			int			len;
 			char	   *mangled;
 			char	   *piece = first_path_var_separator(ecp);
+			ExtensionLocation *location = palloc_object(ExtensionLocation);
 
 			/* Get the length of the next path on ecp */
 			if (piece == NULL)
@@ -382,15 +426,21 @@ get_extension_control_directories(void)
 			 * suffix if it is a custom extension control path.
 			 */
 			if (strcmp(piece, "$system") == 0)
+			{
+				location->macro = pstrdup(piece);
 				mangled = substitute_path_macro(piece, "$system", system_dir);
+			}
 			else
+			{
+				location->macro = NULL;
 				mangled = psprintf("%s/extension", piece);
-
+			}
 			pfree(piece);
 
 			/* Canonicalize the path based on the OS and add to the list */
 			canonicalize_path(mangled);
-			paths = lappend(paths, mangled);
+			location->loc = mangled;
+			paths = lappend(paths, location);
 
 			/* Break if ecp is empty or move to the next path on ecp */
 			if (ecp[len] == '\0')
@@ -2215,9 +2265,9 @@ pg_available_extensions(PG_FUNCTION_ARGS)
 
 	locations = get_extension_control_directories();
 
-	foreach_ptr(char, location, locations)
+	foreach_ptr(ExtensionLocation, location, locations)
 	{
-		dir = AllocateDir(location);
+		dir = AllocateDir(location->loc);
 
 		/*
 		 * If the control directory doesn't exist, we want to silently return
@@ -2229,13 +2279,13 @@ pg_available_extensions(PG_FUNCTION_ARGS)
 		}
 		else
 		{
-			while ((de = ReadDir(dir, location)) != NULL)
+			while ((de = ReadDir(dir, location->loc)) != NULL)
 			{
 				ExtensionControlFile *control;
 				char	   *extname;
 				String	   *extname_str;
-				Datum		values[3];
+				Datum		values[4];
-				bool		nulls[3];
+				bool		nulls[4];
 
 				if (!is_extension_control_filename(de->d_name))
 					continue;
@@ -2259,7 +2309,7 @@ pg_available_extensions(PG_FUNCTION_ARGS)
 					found_ext = lappend(found_ext, extname_str);
 
 				control = new_ExtensionControlFile(extname);
-				control->control_dir = pstrdup(location);
+				control->control_dir = pstrdup(location->loc);
 				parse_extension_control_file(control, NULL);
 
 				memset(values, 0, sizeof(values));
@@ -2273,11 +2323,15 @@ pg_available_extensions(PG_FUNCTION_ARGS)
 					nulls[1] = true;
 				else
 					values[1] = CStringGetTextDatum(control->default_version);
+
+				/* location */
+				values[2] = CStringGetTextDatum(get_extension_location(location));
+
 				/* comment */
 				if (control->comment == NULL)
-					nulls[2] = true;
+					nulls[3] = true;
 				else
-					values[2] = CStringGetTextDatum(control->comment);
+					values[3] = CStringGetTextDatum(control->comment);
 
 				tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
 									 values, nulls);
@@ -2313,9 +2367,9 @@ pg_available_extension_versions(PG_FUNCTION_ARGS)
 
 	locations = get_extension_control_directories();
 
-	foreach_ptr(char, location, locations)
+	foreach_ptr(ExtensionLocation, location, locations)
 	{
-		dir = AllocateDir(location);
+		dir = AllocateDir(location->loc);
 
 		/*
 		 * If the control directory doesn't exist, we want to silently return
@@ -2327,7 +2381,7 @@ pg_available_extension_versions(PG_FUNCTION_ARGS)
 		}
 		else
 		{
-			while ((de = ReadDir(dir, location)) != NULL)
+			while ((de = ReadDir(dir, location->loc)) != NULL)
 			{
 				ExtensionControlFile *control;
 				char	   *extname;
@@ -2356,12 +2410,13 @@ pg_available_extension_versions(PG_FUNCTION_ARGS)
 
 				/* read the control file */
 				control = new_ExtensionControlFile(extname);
-				control->control_dir = pstrdup(location);
+				control->control_dir = pstrdup(location->loc);
 				parse_extension_control_file(control, NULL);
 
 				/* scan extension's script directory for install scripts */
 				get_available_versions_for_extension(control, rsinfo->setResult,
-													 rsinfo->setDesc);
+													 rsinfo->setDesc,
+													 location);
 			}
 
 			FreeDir(dir);
@@ -2378,7 +2433,8 @@ pg_available_extension_versions(PG_FUNCTION_ARGS)
 static void
 get_available_versions_for_extension(ExtensionControlFile *pcontrol,
 									 Tuplestorestate *tupstore,
-									 TupleDesc tupdesc)
+									 TupleDesc tupdesc,
+									 ExtensionLocation *location)
 {
 	List	   *evi_list;
 	ListCell   *lc;
@@ -2391,8 +2447,8 @@ get_available_versions_for_extension(ExtensionControlFile *pcontrol,
 	{
 		ExtensionVersionInfo *evi = (ExtensionVersionInfo *) lfirst(lc);
 		ExtensionControlFile *control;
-		Datum		values[8];
+		Datum		values[9];
-		bool		nulls[8];
+		bool		nulls[9];
 		ListCell   *lc2;
 
 		if (!evi->installable)
@@ -2428,11 +2484,15 @@ get_available_versions_for_extension(ExtensionControlFile *pcontrol,
 			nulls[6] = true;
 		else
 			values[6] = convert_requires_to_datum(control->requires);
+
+		/* location */
+		values[7] = CStringGetTextDatum(get_extension_location(location));
+
 		/* comment */
 		if (control->comment == NULL)
-			nulls[7] = true;
+			nulls[8] = true;
 		else
-			values[7] = CStringGetTextDatum(control->comment);
+			values[8] = CStringGetTextDatum(control->comment);
 
 		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
 
@@ -2473,7 +2533,7 @@ get_available_versions_for_extension(ExtensionControlFile *pcontrol,
 					values[6] = convert_requires_to_datum(control->requires);
 					nulls[6] = false;
 				}
-				/* comment stays the same */
+				/* comment and location stay the same */
 
 				tuplestore_putvalues(tupstore, tupdesc, values, nulls);
 			}
@@ -3903,7 +3963,8 @@ find_in_paths(const char *basename, List *paths)
 
 	foreach(cell, paths)
 	{
-		char	   *path = lfirst(cell);
+		ExtensionLocation *location = lfirst(cell);
+		char	   *path = location->loc;
 		char	   *full;
 
 		Assert(path != NULL);

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202512301
+#define CATALOG_VERSION_NO	202601011
 
 #endif

src/include/catalog/pg_proc.dat

@@ -10750,16 +10750,16 @@
 { oid => '3082', descr => 'list available extensions',
   proname => 'pg_available_extensions', procost => '10', prorows => '100',
   proretset => 't', provolatile => 's', prorettype => 'record',
-  proargtypes => '', proallargtypes => '{name,text,text}',
+  proargtypes => '', proallargtypes => '{name,text,text,text}',
-  proargmodes => '{o,o,o}', proargnames => '{name,default_version,comment}',
+  proargmodes => '{o,o,o,o}', proargnames => '{name,default_version,location,comment}',
   prosrc => 'pg_available_extensions' },
 { oid => '3083', descr => 'list available extension versions',
   proname => 'pg_available_extension_versions', procost => '10',
   prorows => '100', proretset => 't', provolatile => 's',
   prorettype => 'record', proargtypes => '',
-  proallargtypes => '{name,text,bool,bool,bool,name,_name,text}',
+  proallargtypes => '{name,text,bool,bool,bool,name,_name,text,text}',
-  proargmodes => '{o,o,o,o,o,o,o,o}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o}',
-  proargnames => '{name,version,superuser,trusted,relocatable,schema,requires,comment}',
+  proargnames => '{name,version,superuser,trusted,relocatable,schema,requires,location,comment}',
   prosrc => 'pg_available_extension_versions' },
 { oid => '3084', descr => 'list an extension\'s version update paths',
   proname => 'pg_extension_update_paths', procost => '10', prorows => '100',

src/test/modules/test_extensions/t/001_extension_control_path.pl

@@ -25,6 +25,11 @@ my $ext_name2 = "test_custom_ext_paths_using_directory";
 mkpath("$ext_dir/$ext_name2");
 create_extension($ext_name2, $ext_dir, $ext_name2);
 
+# Make windows path use Unix slashes as canonicalize_path() is called when
+# collecting extension control paths. See get_extension_control_directories().
+my $ext_dir_canonicalized = $ext_dir;
+$ext_dir_canonicalized =~ s!\\!/!g if $windows_os;
+
 # Use the correct separator and escape \ when running on Windows.
 my $sep = $windows_os ? ";" : ":";
 $node->append_conf(
@@ -35,6 +40,10 @@ extension_control_path = '\$system$sep@{[ $windows_os ? ($ext_dir =~ s/\\/\\\\/g
 # Start node
 $node->start;
 
+# Create an user to test permissions to read extension locations.
+my $user = "user01";
+$node->safe_psql('postgres', "CREATE USER $user");
+
 my $ecp = $node->safe_psql('postgres', 'show extension_control_path;');
 
 is($ecp, "\$system$sep$ext_dir$sep$ext_dir2",
@@ -46,48 +55,65 @@ $node->safe_psql('postgres', "CREATE EXTENSION $ext_name2");
 my $ret = $node->safe_psql('postgres',
 	"select * from pg_available_extensions where name = '$ext_name'");
 is( $ret,
-	"test_custom_ext_paths|1.0|1.0|Test extension_control_path",
+	"test_custom_ext_paths|1.0|1.0|$ext_dir_canonicalized/extension|Test extension_control_path",
-	"extension is installed correctly on pg_available_extensions");
+	"extension is shown correctly in pg_available_extensions");
 
 $ret = $node->safe_psql('postgres',
 	"select * from pg_available_extension_versions where name = '$ext_name'");
 is( $ret,
-	"test_custom_ext_paths|1.0|t|t|f|t|||Test extension_control_path",
+	"test_custom_ext_paths|1.0|t|t|f|t|||$ext_dir_canonicalized/extension|Test extension_control_path",
-	"extension is installed correctly on pg_available_extension_versions");
+	"extension is shown correctly in pg_available_extension_versions");
 
 $ret = $node->safe_psql('postgres',
 	"select * from pg_available_extensions where name = '$ext_name2'");
 is( $ret,
-	"test_custom_ext_paths_using_directory|1.0|1.0|Test extension_control_path",
+	"test_custom_ext_paths_using_directory|1.0|1.0|$ext_dir_canonicalized/extension|Test extension_control_path",
-	"extension is installed correctly on pg_available_extensions");
+	"extension is shown correctly in pg_available_extensions");
 
 $ret = $node->safe_psql('postgres',
 	"select * from pg_available_extension_versions where name = '$ext_name2'"
 );
 is( $ret,
-	"test_custom_ext_paths_using_directory|1.0|t|t|f|t|||Test extension_control_path",
+	"test_custom_ext_paths_using_directory|1.0|t|t|f|t|||$ext_dir_canonicalized/extension|Test extension_control_path",
-	"extension is installed correctly on pg_available_extension_versions");
+	"extension is shown correctly in pg_available_extension_versions");
 
-# Ensure that extensions installed on $system is still visible when using with
+# Test that a non-superuser is not able to read the extension location in
+# pg_available_extensions
+$ret = $node->safe_psql('postgres',
+	"select location from pg_available_extensions where name = '$ext_name2'",
+	connstr => "user=$user");
+is( $ret,
+	"<insufficient privilege>",
+	"extension location is hidden in pg_available_extensions for users with insufficient privilege");
+
+# Test that a non-superuser is not able to read the extension location in
+# pg_available_extension_versions
+$ret = $node->safe_psql('postgres',
+	"select location from pg_available_extension_versions where name = '$ext_name2'",
+	connstr => "user=$user");
+is( $ret,
+	"<insufficient privilege>",
+	"extension location is hidden in pg_available_extension_versions for users with insufficient privilege");
+
+# Ensure that extensions installed in $system are still visible when used with
 # custom extension control path.
 $ret = $node->safe_psql('postgres',
 	"select count(*) > 0 as ok from pg_available_extensions where name = 'plpgsql'"
 );
 is($ret, "t",
-	"\$system extension is installed correctly on pg_available_extensions");
+	"\$system extension is shown correctly in pg_available_extensions");
-
 
 $ret = $node->safe_psql('postgres',
 	"set extension_control_path = ''; select count(*) > 0 as ok from pg_available_extensions where name = 'plpgsql'"
 );
 is($ret, "t",
-	"\$system extension is installed correctly on pg_available_extensions with empty extension_control_path"
+	"\$system extension is shown correctly in pg_available_extensions with empty extension_control_path"
 );
 
 # Test with an extension that does not exists
 my ($code, $stdout, $stderr) =
   $node->psql('postgres', "CREATE EXTENSION invalid");
-is($code, 3, 'error to create an extension that does not exists');
+is($code, 3, 'error creating an extension that does not exist');
 like($stderr, qr/ERROR:  extension "invalid" is not available/);
 
 sub create_extension

src/test/regress/expected/rules.out

@@ -1310,14 +1310,16 @@ pg_available_extension_versions| SELECT e.name,
     e.relocatable,
     e.schema,
     e.requires,
+    e.location,
     e.comment
-   FROM (pg_available_extension_versions() e(name, version, superuser, trusted, relocatable, schema, requires, comment)
+   FROM (pg_available_extension_versions() e(name, version, superuser, trusted, relocatable, schema, requires, location, comment)
      LEFT JOIN pg_extension x ON (((e.name = x.extname) AND (e.version = x.extversion))));
 pg_available_extensions| SELECT e.name,
     e.default_version,
     x.extversion AS installed_version,
+    e.location,
     e.comment
-   FROM (pg_available_extensions() e(name, default_version, comment)
+   FROM (pg_available_extensions() e(name, default_version, location, comment)
      LEFT JOIN pg_extension x ON ((e.name = x.extname)));
 pg_backend_memory_contexts| SELECT name,
     ident,

src/tools/pgindent/typedefs.list

@@ -800,6 +800,7 @@ ExtensibleNodeEntry
 ExtensibleNodeMethods
 ExtensionControlFile
 ExtensionInfo
+ExtensionLocation
 ExtensionVersionInfo
 FDWCollateState
 FD_SET
@@ -1583,7 +1584,6 @@ LoadStmt
 LocalBufferLookupEnt
 LocalPgBackendStatus
 LocalTransactionId
-Location
 LocationIndex
 LocationLen
 LockAcquireResult