Implement retrieval of remote postgis version

scripts-available/CDB_FederatedServerDiagnostics.sql

@@ -41,12 +41,40 @@ $$
 LANGUAGE PLPGSQL VOLATILE PARALLEL UNSAFE;
 
 
+--
+-- Get the PostGIS extension version of a remote PG server
+--
 CREATE OR REPLACE FUNCTION @extschema@.__CDB_FS_Foreign_PostGIS_Version_PG(server_internal name)
 RETURNS text
 AS $$
+DECLARE
+    -- Import pg_settings from pg_catalog
+    remote_schema name := 'pg_catalog';
+    remote_table name := 'pg_extension';
+    local_schema name := @extschema@.__CDB_FS_Create_Schema(server_internal, remote_schema);
+    role_name name := @extschema@.__CDB_FS_Generate_Server_Role_Name(server_internal);
+    remote_postgis_version text;
 BEGIN
-    -- TODO implement
-    RETURN '4.0';
+    -- Import the foreign pg_extension table
+    IF NOT EXISTS (
+        SELECT * FROM pg_class
+        WHERE relnamespace = (SELECT oid FROM pg_namespace WHERE nspname = local_schema)
+        AND relname = remote_table
+    ) THEN
+        EXECUTE format('IMPORT FOREIGN SCHEMA %I LIMIT TO (%I) FROM SERVER %I INTO %I',
+                    remote_schema, remote_table, server_internal, local_schema);
+    END IF;
+
+    BEGIN
+        EXECUTE format('
+            SELECT extversion FROM %I.%I WHERE extname = ''postgis'';
+        ', local_schema, remote_table) INTO remote_postgis_version;
+    EXCEPTION WHEN OTHERS THEN
+        RAISE EXCEPTION 'Not enough permissions to access the server "%"',
+                        @extschema@.__CDB_FS_Extract_Server_Name(server_internal);
+    END;
+
+    RETURN remote_postgis_version;
 END
 $$
 LANGUAGE PLPGSQL VOLATILE PARALLEL UNSAFE;

test/CDB_FederatedServerDiagnostics.sql

@@ -22,6 +22,10 @@ SELECT 'C1', cartodb.CDB_Federated_Server_Register_PG(server => 'loopback'::text
         "password": "cdb_fs_passwd"
     }
 }'::jsonb);
+
+\c cdb_fs_tester postgres
+CREATE EXTENSION postgis;
+\c contrib_regression postgres
 \set QUIET off