First version of the function WIP

scripts-available/CDB_ForeignTable.sql

@@ -150,8 +150,10 @@ LANGUAGE plpgsql VOLATILE PARALLEL UNSAFE;
 --      "host": "myhostname.us-east-2.rds.amazonaws.com",
 --      "port": "5432"
 --    },
---    "user": "fdw_user",
---    "password": "secret"
+--    "user_mapping": {
+--      "user": "fdw_user",
+--      "password": "secret"
+--    }
 -- ');
 --
 -- Underneath it will:
@@ -169,8 +171,71 @@ LANGUAGE plpgsql VOLATILE PARALLEL UNSAFE;
 --   * The publicuser: GRANT amazon TO publicuser;
 CREATE OR REPLACE FUNCTION @extschema@.CDB_SetUp_Foreign_Server(fdw_name NAME, config json)
 RETURNS void AS $$
--- TODO Code here
-$$ LANGUAGE SQL VOLATILE PARALLEL UNSAFE;
+DECLARE
+  row record;
+  option record;
+BEGIN
+  -- TODO: refactor with original function
+  -- This function tries to be as idempotent as possible, by not creating anything more than once
+  -- (not even using IF NOT EXIST to avoid throwing warnings)
+  IF NOT EXISTS ( SELECT * FROM pg_extension WHERE extname = 'postgres_fdw') THEN
+    CREATE EXTENSION postgres_fdw;
+  END IF;
+  -- Create FDW first if it does not exist
+  IF NOT EXISTS ( SELECT * FROM pg_foreign_server WHERE srvname = fdw_name)
+    THEN
+    EXECUTE FORMAT('CREATE SERVER %I FOREIGN DATA WRAPPER postgres_fdw', fdw_name);
+  END IF;
+
+  -- Set FDW settings
+  FOR row IN SELECT p.key, p.value from lateral json_each_text(config->'server') p
+    LOOP
+      IF NOT EXISTS (WITH a AS (select split_part(unnest(srvoptions), '=', 1) as options from pg_foreign_server where srvname=fdw_name) SELECT * from a where options = row.key)
+        THEN
+        EXECUTE FORMAT('ALTER SERVER %I OPTIONS (ADD %I %L)', fdw_name, row.key, row.value);
+      ELSE
+        EXECUTE FORMAT('ALTER SERVER %I OPTIONS (SET %I %L)', fdw_name, row.key, row.value);
+      END IF;
+    END LOOP;
+
+    -- Create specific role for this
+    IF NOT EXISTS ( SELECT 1 FROM pg_roles WHERE rolname = fdw_name) THEN
+       EXECUTE format('CREATE ROLE %I NOLOGIN', fdw_name);
+    END IF;
+
+    -- Create user mapping
+    IF NOT EXISTS ( SELECT * FROM pg_user_mappings WHERE srvname = fdw_name AND usename = fdw_name ) THEN
+        EXECUTE FORMAT ('CREATE USER MAPPING FOR %I SERVER %I', fdw_name, fdw_name);
+    END IF;
+
+    -- Update user mapping settings
+    FOR option IN SELECT o.key, o.value from lateral json_each_text('user_mapping') o LOOP
+        IF NOT EXISTS (WITH a AS (select split_part(unnest(umoptions), '=', 1) as options from pg_user_mappings WHERE srvname = fdw_name AND usename = fdw_name) SELECT * from a where options = option.key) THEN
+          EXECUTE FORMAT('ALTER USER MAPPING FOR %I SERVER %I OPTIONS (ADD %I %L)', fdw_name, fdw_name, option.key, option.value);
+        ELSE
+          EXECUTE FORMAT('ALTER USER MAPPING FOR %I SERVER %I OPTIONS (SET %I %L)', fdw_name, fdw_name, option.key, option.value);
+        END IF;
+      END LOOP;
+    END LOOP;
+
+    -- Grant usage on the wrapper and server to the fdw role
+    EXECUTE FORMAT ('GRANT USAGE ON FOREIGN DATA WRAPPER postgres_fdw TO %I', fdw_name);
+    EXECUTE FORMAT ('GRANT USAGE ON FOREIGN ON FOREIGN SERVER %I TO %I', fdw_name, fdw_name);
+
+    -- Create schema if it does not exist.
+    IF NOT EXISTS ( SELECT * from pg_namespace WHERE nspname=fdw_name) THEN
+      EXECUTE FORMAT ('CREATE SCHEMA %I', fdw_name);
+    END IF;
+
+    -- Give the fdw role usage permisions over the schema
+    EXECUTE FORMAT ('GRANT USAGE ON SCHEMA %I TO %I', fdw_name, fdw_name);
+
+    -- Grant the fdw role to the caller, and permissions to grant it to others
+    EXECUTE FORMAT ('GRANT %I TO %I WITH ADMIN OPTION', fdw_name, session_user);
+
+    -- TODO: Bring here the remote cdb_tablemetadata
+
+$$ LANGUAGE plpgsql VOLATILE PARALLEL UNSAFE SECURITY DEFINER;
 
 CREATE OR REPLACE FUNCTION @extschema@._cdb_dbname_of_foreign_table(reloid oid)
 RETURNS TEXT AS $$