injection_points: Add injection_points_list()

This function can be used to retrieve the information about all the
injection points attached to a cluster, providing coverage for
InjectionPointList() introduced in 7b2eb72b1b.

The original proposal turned around a system function, but that would
not be backpatchable to stable branches.  It was also a bit weird to
have a system function that fails depending on if the build allows
injection points or not.

Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Reviewed-by: Rahila Syed <rahilasyed90@gmail.com>
Discussion: https://postgr.es/m/Z_xYkA21KyLEHvWR@paquier.xyz

src/test/modules/injection_points/expected/injection_points.out

@@ -39,6 +39,15 @@ SELECT injection_points_attach('TestInjectionLog2', 'notice');
  
 (1 row)
 
+SELECT point_name, library, function FROM injection_points_list()
+  ORDER BY point_name COLLATE "C";
+     point_name     |     library      |     function     
+--------------------+------------------+------------------
+ TestInjectionError | injection_points | injection_error
+ TestInjectionLog   | injection_points | injection_notice
+ TestInjectionLog2  | injection_points | injection_notice
+(3 rows)
+
 SELECT injection_points_run('TestInjectionBooh'); -- nothing
  injection_points_run 
 ----------------------
@@ -298,5 +307,12 @@ SELECT injection_points_detach('TestConditionLocal1');
  
 (1 row)
 
+-- No points should be left around.
+SELECT point_name, library, function FROM injection_points_list()
+  ORDER BY point_name COLLATE "C";
+ point_name | library | function 
+------------+---------+----------
+(0 rows)
+
 DROP EXTENSION injection_points;
 DROP FUNCTION wait_pid;

src/test/modules/injection_points/injection_points--1.0.sql

@@ -77,6 +77,18 @@ RETURNS void
 AS 'MODULE_PATHNAME', 'injection_points_detach'
 LANGUAGE C STRICT PARALLEL UNSAFE;
 
+--
+-- injection_points_list()
+--
+-- List of all the injection points currently attached.
+--
+CREATE FUNCTION injection_points_list(OUT point_name text,
+   OUT library text,
+   OUT function text)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'injection_points_list'
+LANGUAGE C STRICT VOLATILE PARALLEL RESTRICTED;
+
 --
 -- injection_points_stats_numcalls()
 --

src/test/modules/injection_points/injection_points.c

@@ -18,6 +18,7 @@
 #include "postgres.h"
 
 #include "fmgr.h"
+#include "funcapi.h"
 #include "injection_stats.h"
 #include "miscadmin.h"
 #include "nodes/pg_list.h"
@@ -545,6 +546,44 @@ injection_points_detach(PG_FUNCTION_ARGS)
 	PG_RETURN_VOID();
 }
 
+/*
+ * SQL function for listing all the injection points attached.
+ */
+PG_FUNCTION_INFO_V1(injection_points_list);
+Datum
+injection_points_list(PG_FUNCTION_ARGS)
+{
+#define NUM_INJECTION_POINTS_LIST 3
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	List	   *inj_points;
+	ListCell   *lc;
+
+	/* Build a tuplestore to return our results in */
+	InitMaterializedSRF(fcinfo, 0);
+
+	inj_points = InjectionPointList();
+
+	foreach(lc, inj_points)
+	{
+		Datum		values[NUM_INJECTION_POINTS_LIST];
+		bool		nulls[NUM_INJECTION_POINTS_LIST];
+		InjectionPointData *inj_point = lfirst(lc);
+
+		memset(values, 0, sizeof(values));
+		memset(nulls, 0, sizeof(nulls));
+
+		values[0] = PointerGetDatum(cstring_to_text(inj_point->name));
+		values[1] = PointerGetDatum(cstring_to_text(inj_point->library));
+		values[2] = PointerGetDatum(cstring_to_text(inj_point->function));
+
+		/* shove row into tuplestore */
+		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
+	}
+
+	return (Datum) 0;
+#undef NUM_INJECTION_POINTS_LIST
+}
+
 
 void
 _PG_init(void)

src/test/modules/injection_points/sql/injection_points.sql

@@ -18,6 +18,9 @@ SELECT injection_points_attach('TestInjectionError', 'error');
 SELECT injection_points_attach('TestInjectionLog', 'notice');
 SELECT injection_points_attach('TestInjectionLog2', 'notice');
 
+SELECT point_name, library, function FROM injection_points_list()
+  ORDER BY point_name COLLATE "C";
+
 SELECT injection_points_run('TestInjectionBooh'); -- nothing
 SELECT injection_points_run('TestInjectionLog2'); -- notice
 SELECT injection_points_run('TestInjectionLog2', NULL); -- notice
@@ -85,5 +88,9 @@ SELECT injection_points_detach('TestConditionError');
 SELECT injection_points_attach('TestConditionLocal1', 'error');
 SELECT injection_points_detach('TestConditionLocal1');
 
+-- No points should be left around.
+SELECT point_name, library, function FROM injection_points_list()
+  ORDER BY point_name COLLATE "C";
+
 DROP EXTENSION injection_points;
 DROP FUNCTION wait_pid;