[config] warn if mod_authn_ldap,mysql not listed

warn if mod_authn_ldap is not listed in server.modules in lighttpd.conf
but auth.backend = "ldap" is in lighttpd.conf

warn if mod_authn_mysql is not listed in server.modules in lighttpd.conf
but auth.backend = "mysql" is in lighttpd.conf

A future release of lighttpd 1.4.x will cease automatically loading
these modules.  After that, lighttpd will fail to start up if
auth.backend requires one of these modules and the module is not loaded.

(The purpose of this change is to remove from the lighttpd core server
 the dependencies on LDAP or MariaDB libraries.)

src/configfile.c

@@ -25,6 +25,21 @@
 #include <glob.h>
 
 
+static void config_warn_authn_module (server *srv, const char *module) {
+	size_t len = strlen(module);
+	for (size_t i = 0; i < srv->config_context->used; ++i) {
+		const data_config *config = (data_config const*)srv->config_context->data[i];
+		const data_unset *du = array_get_element(config->value, "auth.backend");
+		if (NULL != du && du->type == TYPE_STRING) {
+			data_string *ds = (data_string *)du;
+			if (buffer_is_equal_string(ds->value, module, len)) {
+				log_error_write(srv, __FILE__, __LINE__, "SSSsSSS", "Warning: please add \"mod_authn_", module, "\" to server.modules list in lighttpd.conf.  A future release of lighttpd 1.4.x will not automatically load mod_authn_", module, "and lighttpd will fail to start up since your lighttpd.conf uses auth.backend = \"", module, "\".");
+				return;
+			}
+		}
+	}
+}
+
 static int config_insert(server *srv) {
 	size_t i;
 	int ret = 0;
@@ -437,6 +452,7 @@ static int config_insert(server *srv) {
 				ds = data_string_init();
 				buffer_copy_string_len(ds->value, CONST_STR_LEN("mod_authn_ldap"));
 				array_insert_unique(srv->srvconf.modules, (data_unset *)ds);
+				config_warn_authn_module(srv, "ldap");
 			      #endif
 			}
 			if (append_mod_authn_mysql) {
@@ -444,6 +460,7 @@ static int config_insert(server *srv) {
 				ds = data_string_init();
 				buffer_copy_string_len(ds->value, CONST_STR_LEN("mod_authn_mysql"));
 				array_insert_unique(srv->srvconf.modules, (data_unset *)ds);
+				config_warn_authn_module(srv, "mysql");
 			      #endif
 			}
 		}