standby clone: don't assume existence of "user" in upstream conninfo

Usually a seperate user (typically "repmgr") is set up specifically to manage
the repmgr metadata, however there's no compelling requirement to do this, and
it's possible the database owner (usually: "postgres") will be used, in which
case it's possible the username will be left out of the conninfo string.

Addresses GitHub #437.

dbutils.c

@@ -371,6 +371,37 @@ get_conninfo_value(const char *conninfo, const char *keyword, char *output)
 }
 
 
+/*
+ * Get a default conninfo value for the provided parameter, and copy
+ * it to the 'output' buffer.
+ *
+ * Returns true on success, or false on failure (provided keyword not found).
+ *
+ */
+bool
+get_conninfo_default_value(const char *param, char *output, int maxlen)
+{
+	PQconninfoOption *defs = NULL;
+	PQconninfoOption *def = NULL;
+	bool found = false;
+
+	defs = PQconndefaults();
+
+	for (def = defs; def->keyword; def++)
+	{
+		if (strncmp(def->keyword, param, maxlen) == 0)
+		{
+			strncpy(output, def->val, maxlen);
+			found = true;
+		}
+	}
+
+	PQconninfoFree(defs);
+
+	return found;
+}
+
+
 void
 initialize_conninfo_params(t_conninfo_param_list *param_list, bool set_defaults)
 {

dbutils.h

@@ -357,7 +357,7 @@ void		close_connection(PGconn **conn);
 
 /* conninfo manipulation functions */
 bool		get_conninfo_value(const char *conninfo, const char *keyword, char *output);
-
+bool		get_conninfo_default_value(const char *param, char *output, int maxlen);
 void		initialize_conninfo_params(t_conninfo_param_list *param_list, bool set_defaults);
 void		free_conninfo_params(t_conninfo_param_list *param_list);
 void		copy_conninfo_params(t_conninfo_param_list *dest_list, t_conninfo_param_list *source_list);
@@ -369,6 +369,7 @@ bool		parse_conninfo_string(const char *conninfo_str, t_conninfo_param_list *par
 char	   *param_list_to_string(t_conninfo_param_list *param_list);
 bool		has_passfile(void);
 
+
 /* transaction functions */
 bool		begin_transaction(PGconn *conn);
 bool		commit_transaction(PGconn *conn);

repmgr-action-standby.c

@@ -4078,13 +4078,25 @@ check_source_server()
 		if (record_status == RECORD_FOUND)
 		{
 			t_conninfo_param_list upstream_conninfo = T_CONNINFO_PARAM_LIST_INITIALIZER;
+			char	   *upstream_conninfo_user;
 
 			initialize_conninfo_params(&upstream_conninfo, false);
 			parse_conninfo_string(node_record.conninfo, &upstream_conninfo, NULL, false);
 
 			strncpy(recovery_conninfo_str, node_record.conninfo, MAXLEN);
 			strncpy(upstream_repluser, node_record.repluser, NAMEDATALEN);
-			strncpy(upstream_user, param_get(&upstream_conninfo, "user"), NAMEDATALEN);
+
+			upstream_conninfo_user = param_get(&upstream_conninfo, "user");
+			if (upstream_conninfo_user != NULL)
+			{
+				strncpy(upstream_user, upstream_conninfo_user, NAMEDATALEN);
+			}
+			else
+			{
+				get_conninfo_default_value("user", upstream_user, NAMEDATALEN);
+			}
+
+			log_verbose(LOG_DEBUG, "upstream_user is \"%s\"", upstream_user);
 
 			upstream_conninfo_found = true;
 		}