Allow to override hostname() with a lua call hostname("example.com")

daemon/README.rst

@@ -369,10 +369,15 @@ Environment
 
 	env.USER -- equivalent to $USER in shell
 
-.. function:: hostname()
+.. function:: hostname([fqdn])
 
    :return: Machine hostname.
 
+   If called with a parameter, it will set kresd's internal
+   hostname. If called without a parameter, it will return kresd's
+   internal hostname, or the system's POSIX hostname (see
+   gethostname(2)) if kresd's internal hostname is unset.
+	    
 .. function:: verbose(true | false)
 
    :return: Toggle verbose logging.

daemon/engine.c

@@ -147,12 +147,56 @@ static int l_verbose(lua_State *L)
 	return 1;
 }
 
+char *engine_get_hostname(struct engine *engine) {
+	static char hostname_str[KNOT_DNAME_MAXLEN];
+	if (!engine) {
+		return NULL;
+	}
+
+	if (!engine->hostname) {
+		if (gethostname(hostname_str, sizeof(hostname_str)) != 0)
+			return NULL;
+		return hostname_str;
+	}
+	return engine->hostname;
+}
+
+int engine_set_hostname(struct engine *engine, const char *hostname) {
+	if (!engine || !hostname) {
+		return kr_error(EINVAL);
+	}
+
+	char *new_hostname = strdup(hostname);
+	if (!new_hostname) {
+		return kr_error(ENOMEM);
+	}
+	if (engine->hostname) {
+		free(engine->hostname);
+	}
+	engine->hostname = new_hostname;
+
+	return 0;
+}
+
 /** Return hostname. */
 static int l_hostname(lua_State *L)
 {
-	char host_str[KNOT_DNAME_MAXLEN];
-	gethostname(host_str, sizeof(host_str));
-	lua_pushstring(L, host_str);
+	struct engine *engine = engine_luaget(L);
+	if (lua_gettop(L) == 0) {
+		lua_pushstring(L, engine_get_hostname(engine));
+		return 1;
+	}
+	if ((lua_gettop(L) != 1) || !lua_isstring(L, 1)) {
+		lua_pushstring(L, "hostname takes at most one parameter: (\"fqdn\")");
+		lua_error(L);
+	}
+
+	if (engine_set_hostname(engine, lua_tostring(L, 1)) != 0) {
+		lua_pushstring(L, "setting hostname failed");
+		lua_error(L);
+	}
+
+	lua_pushstring(L, engine_get_hostname(engine));	
 	return 1;
 }
 

daemon/engine.h

@@ -59,6 +59,7 @@ struct engine {
     fd_array_t ipc_set;
     knot_mm_t *pool;
     uv_timer_t *updater;
+    char *hostname;
     struct lua_State *L;
 };
 
@@ -78,3 +79,7 @@ int engine_pcall(struct lua_State *L, int argc);
 
 /** Return engine light userdata. */
 struct engine *engine_luaget(struct lua_State *L);
+
+/** Set/get the per engine hostname */
+char *engine_get_hostname(struct engine *engine);
+int engine_set_hostname(struct engine *engine, const char *hostname);