libink/finit: properties, and org.finit on the system bus

Runlevel and version are state, not actions, so they belong behind
org.freedesktop.DBus.Properties rather than another method each.

Finit also claims org.finit on the system bus when it finds one, so
ordinary D-Bus clients can reach it without knowing about
/run/finit/bus.  Opportunistic on purpose: no dbus-daemon is a normal
state for the systems Finit runs on, not an error to report.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

libink/builtin.c

@@ -104,24 +104,53 @@ static void xprintf(struct xbuf *x, const char *fmt, ...)
 	x->off += (size_t)n;
 }
 
+/*
+ * Advance past one single complete type in a D-Bus signature:
+ * a basic type code, 'a' + element type, or a bracketed group.
+ * Signatures come from our own vtables, so trust them; an
+ * unterminated group just stops at NUL.
+ */
+static const char *sig_next(const char *p)
+{
+	while (*p == 'a')	/* array prefixes, then element type */
+		p++;
+	if (*p == '(' || *p == '{') {
+		char close = *p == '(' ? ')' : '}';
+
+		for (p++; *p && *p != close; p = sig_next(p))
+			;
+	}
+	return *p ? p + 1 : p;	/* NUL: unterminated group, stop here */
+}
+
+static void emit_args(struct xbuf *x, const char *sig, const char *dir)
+{
+	const char *p, *e;
+
+	for (p = sig; p && *p; p = e) {
+		e = sig_next(p);
+		xprintf(x, "      <arg type=\"%.*s\" direction=\"%s\"/>\n",
+			(int)(e - p), p, dir);
+	}
+}
+
 /* Emit a single <method> stanza for one method definition. */
 static void emit_method(struct xbuf *x, const link_method_t *m)
 {
-	const char *p;
-
 	xprintf(x, "    <method name=\"%s\">\n", m->name);
-	for (p = m->in_sig ? m->in_sig : ""; *p; p++)
-		xprintf(x, "      <arg type=\"%c\" direction=\"in\"/>\n", *p);
-	for (p = m->out_sig ? m->out_sig : ""; *p; p++)
-		xprintf(x, "      <arg type=\"%c\" direction=\"out\"/>\n", *p);
+	emit_args(x, m->in_sig, "in");
+	emit_args(x, m->out_sig, "out");
 	xprintf(x, "    </method>\n");
 }
 
-/* Introspection limitation: emit_method prints one <arg> per
- * character of the signature, which is wrong for compound types
- * (an "a(ss)" arg appears as four args).  Good enough for the
- * "s", "u", "as" signatures we expose today; replace with a
- * signature parser when the first compound argument lands. */
+static void emit_property(struct xbuf *x, const link_property_t *p)
+{
+	/* Setters are not implemented, so every property advertises
+	 * access="read" today.  When Properties.Set lands, switch on
+	 * a writable flag. */
+	xprintf(x, "    <property name=\"%s\" type=\"%s\" access=\"read\"/>\n",
+		p->name, p->sig ? p->sig : "s");
+}
 
 static const char STANDARD_INTERFACES_XML[] =
 	"  <interface name=\"org.freedesktop.DBus.Introspectable\">\n"
@@ -134,6 +163,17 @@ static const char STANDARD_INTERFACES_XML[] =
 	"    <method name=\"GetMachineId\">\n"
 	"      <arg name=\"machine_uuid\" type=\"s\" direction=\"out\"/>\n"
 	"    </method>\n"
+	"  </interface>\n"
+	"  <interface name=\"org.freedesktop.DBus.Properties\">\n"
+	"    <method name=\"Get\">\n"
+	"      <arg name=\"interface\" type=\"s\" direction=\"in\"/>\n"
+	"      <arg name=\"property\"  type=\"s\" direction=\"in\"/>\n"
+	"      <arg name=\"value\"     type=\"v\" direction=\"out\"/>\n"
+	"    </method>\n"
+	"    <method name=\"GetAll\">\n"
+	"      <arg name=\"interface\" type=\"s\" direction=\"in\"/>\n"
+	"      <arg name=\"props\"     type=\"a{sv}\" direction=\"out\"/>\n"
+	"    </method>\n"
 	"  </interface>\n";
 
 /* Is `child` a path under `parent`?  If so, write the first segment
@@ -197,11 +237,16 @@ static int handle_introspect(link_connection_t *conn, const struct link_msg *m)
 		const link_method_t *meth;
 
 		TAILQ_FOREACH(e, &o->vtables, link) {
+			const link_property_t *prop;
+
 			xprintf(&x, "  <interface name=\"%s\">\n",
 				e->vt->interface);
 			if (e->vt->methods)
 				for (meth = e->vt->methods; meth->name; meth++)
 					emit_method(&x, meth);
+			if (e->vt->properties)
+				for (prop = e->vt->properties; prop->name; prop++)
+					emit_property(&x, prop);
 			xprintf(&x, "  </interface>\n");
 		}
 	}
@@ -231,6 +276,129 @@ static int handle_introspect(link_connection_t *conn, const struct link_msg *m)
 	return send_string_reply(conn, m, xml);
 }
 
+/* ---------- Properties.Get / GetAll ---------- */
+
+/* Find the (object, vtable-entry) pair matching `path` and `interface`.
+ * Returns NULL if the path is unknown or the interface isn't exposed
+ * on it. */
+static struct link_vtable_entry *
+find_vtable(link_connection_t *conn, const char *path, const char *interface)
+{
+	struct link_object *o;
+
+	if (!path || !interface)
+		return NULL;
+	TAILQ_FOREACH(o, &conn->server->objects, link) {
+		struct link_vtable_entry *e;
+
+		if (strcmp(o->path, path) != 0)
+			continue;
+		TAILQ_FOREACH(e, &o->vtables, link) {
+			if (strcmp(e->vt->interface, interface) == 0)
+				return e;
+		}
+	}
+	return NULL;
+}
+
+static int handle_properties_get(link_connection_t *conn, const struct link_msg *m)
+{
+	const char *iface, *prop_name;
+	struct link_reader r;
+	struct link_writer w;
+	struct link_vtable_entry *e;
+	const link_property_t   *p;
+	ssize_t blen;
+
+	if (!m->signature || strcmp(m->signature, "ss") != 0)
+		return __send_error(conn, m,
+			"org.freedesktop.DBus.Error.InvalidArgs",
+			"Properties.Get takes (interface, property)");
+
+	__r_init(&r, m->body, m->body_avail);
+	if (__r_string(&r, &iface) < 0 || __r_string(&r, &prop_name) < 0)
+		return __send_error(conn, m,
+			"org.freedesktop.DBus.Error.InvalidArgs",
+			"Malformed argument");
+
+	e = find_vtable(conn, m->path, iface);
+	if (!e || !e->vt->properties)
+		return __send_error(conn, m,
+			"org.freedesktop.DBus.Error.UnknownInterface",
+			"No such interface on this object");
+
+	for (p = e->vt->properties; p->name; p++) {
+		if (strcmp(p->name, prop_name) != 0)
+			continue;
+		if (!p->getter)
+			break;
+		__w_init(&w, conn->txbuf, sizeof(conn->txbuf));
+		if (p->getter(&w, e->userdata) != 0 || (blen = __w_finish(&w)) < 0)
+			return __send_error(conn, m,
+				"org.freedesktop.DBus.Error.Failed",
+				"Property getter failed");
+		return __send_method_return(conn, m, "v",
+					   conn->txbuf, (size_t)blen);
+	}
+
+	return __send_error(conn, m,
+		"org.freedesktop.DBus.Error.UnknownProperty",
+		"No such property on this interface");
+}
+
+static int handle_properties_get_all(link_connection_t *conn, const struct link_msg *m)
+{
+	const char *iface;
+	struct link_reader r;
+	struct link_writer w;
+	struct link_vtable_entry *e;
+	const link_property_t   *p;
+	ssize_t blen;
+
+	if (!m->signature || strcmp(m->signature, "s") != 0)
+		return __send_error(conn, m,
+			"org.freedesktop.DBus.Error.InvalidArgs",
+			"Properties.GetAll takes one string");
+
+	__r_init(&r, m->body, m->body_avail);
+	if (__r_string(&r, &iface) < 0)
+		return __send_error(conn, m,
+			"org.freedesktop.DBus.Error.InvalidArgs",
+			"Malformed argument");
+
+	e = find_vtable(conn, m->path, iface);
+	if (!e)
+		return __send_error(conn, m,
+			"org.freedesktop.DBus.Error.UnknownInterface",
+			"No such interface on this object");
+
+	__w_init(&w, conn->txbuf, sizeof(conn->txbuf));
+	__w_array_begin(&w, '{');
+	if (e->vt->properties) {
+		for (p = e->vt->properties; p->name; p++) {
+			if (!p->getter)
+				continue;
+			__w_struct_begin(&w);
+			__w_string(&w, p->name);
+			if (p->getter(&w, e->userdata) != 0)
+				return __send_error(conn, m,
+					"org.freedesktop.DBus.Error.Failed",
+					"Property getter failed");
+			__w_struct_end(&w);
+		}
+	}
+	__w_array_end(&w);
+
+	blen = __w_finish(&w);
+	if (blen < 0)
+		return __send_error(conn, m,
+			"org.freedesktop.DBus.Error.Failed",
+			"Reply too large");
+
+	return __send_method_return(conn, m, "a{sv}",
+				   conn->txbuf, (size_t)blen);
+}
+
 /* ---------- AddMatch / RemoveMatch ---------- */
 
 static int handle_add_match(link_connection_t *conn, const struct link_msg *m)
@@ -310,5 +478,11 @@ int __handle_builtin(link_connection_t *conn, const struct link_msg *m)
 	if (member_is(m, "org.freedesktop.DBus.Introspectable", "Introspect"))
 		return handle_introspect(conn, m);
 
+	if (member_is(m, "org.freedesktop.DBus.Properties", "Get"))
+		return handle_properties_get(conn, m);
+
+	if (member_is(m, "org.freedesktop.DBus.Properties", "GetAll"))
+		return handle_properties_get_all(conn, m);
+
 	return -1;	/* not a built-in */
 }