Add SQL functions to monitor the directory contents of replication slots

This commit adds a set of functions able to look at the contents of
various paths related to replication slots:
- pg_ls_logicalsnapdir, for pg_logical/snapshots/
- pg_ls_logicalmapdir, for pg_logical/mappings/
- pg_ls_replslotdir, for pg_replslot/<slot_name>/

These are intended to be used by monitoring tools.  Unlike pg_ls_dir(),
execution permission can be granted to non-superusers.  Roles members of
pg_monitor gain have access to those functions.

Bump catalog version.

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Justin Pryzby
Discussion: https://postgr.es/m/CALj2ACWsfizZjMN6bzzdxOk1ADQQeSw8HhEjhmVXn_Pu+7VzLw@mail.gmail.com

src/backend/catalog/system_functions.sql

@@ -701,6 +701,12 @@ REVOKE EXECUTE ON FUNCTION pg_ls_dir(text,boolean,boolean) FROM public;
 
 REVOKE EXECUTE ON FUNCTION pg_log_backend_memory_contexts(integer) FROM PUBLIC;
 
+REVOKE EXECUTE ON FUNCTION pg_ls_logicalsnapdir() FROM PUBLIC;
+
+REVOKE EXECUTE ON FUNCTION pg_ls_logicalmapdir() FROM PUBLIC;
+
+REVOKE EXECUTE ON FUNCTION pg_ls_replslotdir(text) FROM PUBLIC;
+
 --
 -- We also set up some things as accessible to standard roles.
 --
@@ -715,6 +721,12 @@ GRANT EXECUTE ON FUNCTION pg_ls_tmpdir() TO pg_monitor;
 
 GRANT EXECUTE ON FUNCTION pg_ls_tmpdir(oid) TO pg_monitor;
 
+GRANT EXECUTE ON FUNCTION pg_ls_logicalsnapdir() TO pg_monitor;
+
+GRANT EXECUTE ON FUNCTION pg_ls_logicalmapdir() TO pg_monitor;
+
+GRANT EXECUTE ON FUNCTION pg_ls_replslotdir(text) TO pg_monitor;
+
 GRANT pg_read_all_settings TO pg_monitor;
 
 GRANT pg_read_all_stats TO pg_monitor;

src/backend/utils/adt/genfile.c

@@ -29,6 +29,7 @@
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "postmaster/syslogger.h"
+#include "replication/slot.h"
 #include "storage/fd.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
@@ -720,3 +721,46 @@ pg_ls_archive_statusdir(PG_FUNCTION_ARGS)
 {
 	return pg_ls_dir_files(fcinfo, XLOGDIR "/archive_status", true);
 }
+
+/*
+ * Function to return the list of files in the pg_logical/snapshots directory.
+ */
+Datum
+pg_ls_logicalsnapdir(PG_FUNCTION_ARGS)
+{
+	return pg_ls_dir_files(fcinfo, "pg_logical/snapshots", false);
+}
+
+/*
+ * Function to return the list of files in the pg_logical/mappings directory.
+ */
+Datum
+pg_ls_logicalmapdir(PG_FUNCTION_ARGS)
+{
+	return pg_ls_dir_files(fcinfo, "pg_logical/mappings", false);
+}
+
+/*
+ * Function to return the list of files in the pg_replslot/<replication_slot>
+ * directory.
+ */
+Datum
+pg_ls_replslotdir(PG_FUNCTION_ARGS)
+{
+	text	   *slotname_t;
+	char		path[MAXPGPATH];
+	char	   *slotname;
+
+	slotname_t = PG_GETARG_TEXT_PP(0);
+
+	slotname = text_to_cstring(slotname_t);
+
+	if (!SearchNamedReplicationSlot(slotname, true))
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("replication slot \"%s\" does not exist",
+						slotname)));
+
+	snprintf(path, sizeof(path), "pg_replslot/%s", slotname);
+	return pg_ls_dir_files(fcinfo, path, false);
+}

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202111171
+#define CATALOG_VERSION_NO	202111231
 
 #endif

src/include/catalog/pg_proc.dat

@@ -11623,6 +11623,28 @@
   proallargtypes => '{oid,text,int8,timestamptz}', proargmodes => '{i,o,o,o}',
   proargnames => '{tablespace,name,size,modification}',
   prosrc => 'pg_ls_tmpdir_1arg' },
+{ oid => '9858',
+  descr => 'list of files in the pg_logical/snapshots directory',
+  proname => 'pg_ls_logicalsnapdir', procost => '10', prorows => '20',
+  proretset => 't', provolatile => 'v', prorettype => 'record',
+  proargtypes => '', proallargtypes => '{text,int8,timestamptz}',
+  proargmodes => '{o,o,o}', proargnames => '{name,size,modification}',
+  prosrc => 'pg_ls_logicalsnapdir' },
+{ oid => '9859',
+  descr => 'list of files in the pg_logical/mappings directory',
+  proname => 'pg_ls_logicalmapdir', procost => '10', prorows => '20',
+  proretset => 't', provolatile => 'v', prorettype => 'record',
+  proargtypes => '', proallargtypes => '{text,int8,timestamptz}',
+  proargmodes => '{o,o,o}', proargnames => '{name,size,modification}',
+  prosrc => 'pg_ls_logicalmapdir' },
+{ oid => '9860',
+  descr => 'list of files in the pg_replslot/slot_name directory',
+  proname => 'pg_ls_replslotdir', procost => '10', prorows => '20',
+  proretset => 't', provolatile => 'v', prorettype => 'record',
+  proargtypes => 'text', proallargtypes => '{text,text,int8,timestamptz}',
+  proargmodes => '{i,o,o,o}',
+  proargnames => '{slot_name,name,size,modification}',
+  prosrc => 'pg_ls_replslotdir' },
 
 # hash partitioning constraint function
 { oid => '5028', descr => 'hash partition CHECK constraint',

src/test/regress/expected/misc_functions.out

@@ -243,6 +243,56 @@ select count(*) > 0 from
  t
 (1 row)
 
+--
+-- Test replication slot directory functions
+--
+CREATE ROLE regress_slot_dir_funcs;
+-- Not available by default.
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalsnapdir()', 'EXECUTE');
+ has_function_privilege 
+------------------------
+ f
+(1 row)
+
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalmapdir()', 'EXECUTE');
+ has_function_privilege 
+------------------------
+ f
+(1 row)
+
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_replslotdir(text)', 'EXECUTE');
+ has_function_privilege 
+------------------------
+ f
+(1 row)
+
+GRANT pg_monitor TO regress_slot_dir_funcs;
+-- Role is now part of pg_monitor, so these are available.
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalsnapdir()', 'EXECUTE');
+ has_function_privilege 
+------------------------
+ t
+(1 row)
+
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalmapdir()', 'EXECUTE');
+ has_function_privilege 
+------------------------
+ t
+(1 row)
+
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_replslotdir(text)', 'EXECUTE');
+ has_function_privilege 
+------------------------
+ t
+(1 row)
+
+DROP ROLE regress_slot_dir_funcs;
 --
 -- Test adding a support function to a subject function
 --

src/test/regress/sql/misc_functions.sql

@@ -91,6 +91,27 @@ select count(*) > 0 from
    where spcname = 'pg_default') pts
   join pg_database db on pts.pts = db.oid;
 
+--
+-- Test replication slot directory functions
+--
+CREATE ROLE regress_slot_dir_funcs;
+-- Not available by default.
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalsnapdir()', 'EXECUTE');
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalmapdir()', 'EXECUTE');
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_replslotdir(text)', 'EXECUTE');
+GRANT pg_monitor TO regress_slot_dir_funcs;
+-- Role is now part of pg_monitor, so these are available.
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalsnapdir()', 'EXECUTE');
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_logicalmapdir()', 'EXECUTE');
+SELECT has_function_privilege('regress_slot_dir_funcs',
+  'pg_ls_replslotdir(text)', 'EXECUTE');
+DROP ROLE regress_slot_dir_funcs;
+
 --
 -- Test adding a support function to a subject function
 --