ZyklonB: use XDG paths by default

Install plugins to /usr/share rather than /usr/lib since they're
arch-independent.  Many precedents can be found for scripted plugins
in /usr/share and fewer for /usr/lib.

Look for plugins in all XDG data directories and repurpose
the "plugin_dir" setting to override this behaviour.

This adds some complexity to the bot but unifies the project.
It might make sense to remove the "plugin_dir" setting.

CMakeLists.txt

@@ -132,8 +132,6 @@ set (HAVE_EDITLINE "${WANT_LIBEDIT}")
 set (HAVE_LUA      "${WITH_LUA}")
 
 include (GNUInstallDirs)
-# ZyklonB is currently an odd duck but degesch follows normal XDG rules
-set (zyklonb_plugin_dir ${CMAKE_INSTALL_LIBDIR}/zyklonb/plugins)
 configure_file (${PROJECT_SOURCE_DIR}/config.h.in ${PROJECT_BINARY_DIR}/config.h)
 include_directories (${PROJECT_SOURCE_DIR} ${PROJECT_BINARY_DIR})
 
@@ -187,8 +185,9 @@ add_custom_target (clang-tidy
 # Installation
 install (TARGETS zyklonb degesch kike DESTINATION ${CMAKE_INSTALL_BINDIR})
 install (FILES LICENSE DESTINATION ${CMAKE_INSTALL_DOCDIR})
+# XXX: our defaults for XDG_DATA_DIRS expect /usr/local/shore or /usr/share
 install (DIRECTORY plugins/zyklonb/
-	DESTINATION ${zyklonb_plugin_dir} USE_SOURCE_PERMISSIONS)
+	DESTINATION ${CMAKE_INSTALL_DATADIR}/zyklonb/plugins USE_SOURCE_PERMISSIONS)
 install (DIRECTORY plugins/degesch/
 	DESTINATION ${CMAKE_INSTALL_DATADIR}/degesch/plugins)
 

config.h.in

@@ -2,7 +2,7 @@
 #define CONFIG_H
 
 #define PROGRAM_VERSION "${project_version}"
-#define ZYKLONB_PLUGIN_DIR "${CMAKE_INSTALL_PREFIX}/${zyklonb_plugin_dir}"
+#define LIBDIR "${CMAKE_INSTALL_FULL_LIBDIR}"
 
 #cmakedefine HAVE_READLINE
 #cmakedefine HAVE_EDITLINE

zyklonb.c

@@ -1,7 +1,7 @@
 /*
  * zyklonb.c: the experimental IRC bot
  *
- * Copyright (c) 2014 - 2016, Přemysl Eric Janouch <p@janouch.name>
+ * Copyright (c) 2014 - 2020, Přemysl Eric Janouch <p@janouch.name>
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted.
@@ -18,7 +18,6 @@
 
 #include "config.h"
 #define PROGRAM_NAME "ZyklonB"
-#define PLUGIN_DIR ZYKLONB_PLUGIN_DIR
 
 #include "common.c"
 
@@ -49,7 +48,7 @@ static struct simple_config_item g_config_table[] =
 	{ "prefix",          ":",               "The prefix for bot commands"    },
 	{ "admin",           NULL,              "Host mask for administrators"   },
 	{ "plugins",         NULL,              "The plugins to load on startup" },
-	{ "plugin_dir",      PLUGIN_DIR,        "Where to search for plugins"    },
+	{ "plugin_dir",      NULL,              "Plugin search path override"    },
 	{ "recover",         "on",              "Whether to re-launch on crash"  },
 
 	{ NULL,              NULL,              NULL                             }
@@ -1015,21 +1014,41 @@ is_valid_plugin_name (const char *name)
 	return true;
 }
 
+static char *
+plugin_resolve_relative_filename (const char *filename)
+{
+	struct strv paths = strv_make ();
+	get_xdg_data_dirs (&paths);
+	strv_append (&paths, LIBDIR);  // Legacy, we do not compile any plugins
+	char *result = resolve_relative_filename_generic
+		(&paths, PROGRAM_NAME "/plugins/", filename);
+	strv_free (&paths);
+	return result;
+}
+
 static struct plugin *
 plugin_launch (struct bot_context *ctx, const char *name, struct error **e)
 {
+	char *path = NULL;
 	const char *plugin_dir = str_map_find (&ctx->config, "plugin_dir");
-	if (!plugin_dir)
+	if (plugin_dir)
 	{
-		error_set (e, "plugin directory not set");
+		// resolve_relative_filename_generic() won't accept relative paths,
-		return NULL;
+		// so just keep the old behaviour and expect the file to exist.
+		// We could use resolve_filename() on "plugin_dir" with paths=getcwd().
+		path = xstrdup_printf ("%s/%s", plugin_dir, name);
+	}
+	else if (!(path = plugin_resolve_relative_filename (name)))
+	{
+		error_set (e, "plugin not found");
+		goto fail_0;
 	}
 
 	int stdin_pipe[2];
 	if (pipe (stdin_pipe) == -1)
 	{
 		error_set (e, "%s: %s", "pipe", strerror (errno));
-		return NULL;
+		goto fail_0;
 	}
 
 	int stdout_pipe[2];
@@ -1079,7 +1098,7 @@ plugin_launch (struct bot_context *ctx, const char *name, struct error **e)
 		// Restore some of the signal handling
 		signal (SIGPIPE, SIG_DFL);
 
-		char *argv[] = { xstrdup_printf ("%s/%s", plugin_dir, name), NULL };
+		char *argv[] = { path, NULL };
 		execve (argv[0], argv, environ);
 
 		// We will collect the failure later via SIGCHLD
@@ -1089,6 +1108,7 @@ plugin_launch (struct bot_context *ctx, const char *name, struct error **e)
 	}
 
 	str_free (&work_dir);
+	free (path);
 
 	xclose (stdin_pipe[0]);
 	xclose (stdout_pipe[1]);
@@ -1108,6 +1128,8 @@ fail_2:
 fail_1:
 	xclose (stdin_pipe[0]);
 	xclose (stdin_pipe[1]);
+fail_0:
+	free (path);
 	return NULL;
 }