libsystemd-bus: add lightweight object vtable implementation for exposing objects on the bus

This adds a lightweight scheme how to define interfaces in static fixed
arrays which then can be easily registered on a bus connection. This
makes it much easier to write bus services.

This automatically handles implementation of the Properties,
ObjectManager, and Introspection bus interfaces.

1 files changed, 200 insertions, 0 deletions

diff --git a/src/libsystemd-bus/bus-introspect.c b/src/libsystemd-bus/bus-introspect.c
new file mode 100644
index 0000000000..8dc9a2de15
--- /dev/null
+++ b/src/libsystemd-bus/bus-introspect.c
@@ -0,0 +1,200 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "util.h"
+#include "sd-bus-protocol.h"
+#include "bus-introspect.h"
+#include "bus-signature.h"
+#include "bus-internal.h"
+
+int introspect_begin(struct introspect *i) {
+        assert(i);
+
+        zero(*i);
+
+        i->f = open_memstream(&i->introspection, &i->size);
+        if (!i->f)
+                return -ENOMEM;
+
+        fputs(SD_BUS_INTROSPECT_DOCTYPE
+              "<node>\n", i->f);
+
+        return 0;
+}
+
+int introspect_write_default_interfaces(struct introspect *i, bool object_manager) {
+        assert(i);
+
+        fputs(SD_BUS_INTROSPECT_INTERFACE_PEER
+              SD_BUS_INTROSPECT_INTERFACE_INTROSPECTABLE
+              SD_BUS_INTROSPECT_INTERFACE_PROPERTIES, i->f);
+
+        if (object_manager)
+                fputs(SD_BUS_INTROSPECT_INTERFACE_OBJECT_MANAGER, i->f);
+
+        return 0;
+}
+
+int introspect_write_child_nodes(struct introspect *i, Set *s, const char *prefix) {
+        char *node;
+
+        assert(i);
+        assert(prefix);
+
+        while ((node = set_steal_first(s))) {
+                const char *e;
+
+                e = object_path_startswith(node, prefix);
+                if (e)
+                        fprintf(i->f, " <node name=\"%s\"/>\n", e);
+
+                free(node);
+        }
+
+        return 0;
+}
+
+static void introspect_write_flags(struct introspect *i, int type, int flags) {
+        if (flags & SD_BUS_VTABLE_DEPRECATED)
+                fputs("   <annotation name=\"org.freedesktop.DBus.Deprecated\" value=\"true\"/>\n", i->f);
+
+        if (type == _SD_BUS_VTABLE_METHOD && flags & SD_BUS_VTABLE_METHOD_NO_REPLY)
+                fputs("   <annotation name=\"org.freedesktop.DBus.Method.NoReply\" value=\"true\"/>\n", i->f);
+
+        if (type == _SD_BUS_VTABLE_PROPERTY || type == _SD_BUS_VTABLE_WRITABLE_PROPERTY) {
+                if (!(flags & SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE))
+                        fputs("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"false\"/>\n", i->f);
+                else if (flags & SD_BUS_VTABLE_PROPERTY_INVALIDATE_ONLY)
+                        fputs("   <annotation name=\"org.freedesktop.DBus.Property.EmitsChangedSignal\" value=\"invalidates\"/>\n", i->f);
+        }
+}
+
+static int introspect_write_arguments(struct introspect *i, const char *signature, const char *direction) {
+        int r;
+
+        for (;;) {
+                size_t l;
+
+                if (!*signature)
+                        return 0;
+
+                r = signature_element_length(signature, &l);
+                if (r < 0)
+                        return r;
+
+                fprintf(i->f, "   <arg type=\"%.*s\"", (int) l, signature);
+
+                if (direction)
+                        fprintf(i->f, " direction=\"%s\">\n", direction);
+                else
+                        fputs(">\n", i->f);
+
+                signature += l;
+        }
+}
+
+int introspect_write_interface(struct introspect *i, const char *interface, const sd_bus_vtable *v) {
+        assert(i);
+        assert(interface);
+        assert(v);
+
+        fprintf(i->f, " <interface name=\"%s\">\n", interface);
+
+        for (; v->type != _SD_BUS_VTABLE_END; v++) {
+
+                switch (v->type) {
+
+                case _SD_BUS_VTABLE_START:
+                        if (v->flags & SD_BUS_VTABLE_DEPRECATED)
+                                fputs("  <annotation name=\"org.freedesktop.DBus.Deprecated\" value=\"true\"/>\n", i->f);
+                        break;
+
+                case _SD_BUS_VTABLE_METHOD:
+                        fprintf(i->f, "  <method name=\"%s\">\n", v->method.member);
+                        introspect_write_arguments(i, v->method.signature, "in");
+                        introspect_write_arguments(i, v->method.result, "out");
+                        introspect_write_flags(i, v->type, v->flags);
+                        fputs("  </method>\n", i->f);
+                        break;
+
+                case _SD_BUS_VTABLE_PROPERTY:
+                case _SD_BUS_VTABLE_WRITABLE_PROPERTY:
+                        fprintf(i->f, "  <property name=\"%s\" type=\"%s\" access=\"%s\">\n",
+                                v->property.member,
+                                v->property.signature,
+                                v->type == _SD_BUS_VTABLE_WRITABLE_PROPERTY ? "readwrite" : "read");
+                        introspect_write_flags(i, v->type, v->flags);
+                        fputs("  </property>\n", i->f);
+                        break;
+
+                case _SD_BUS_VTABLE_SIGNAL:
+                        fprintf(i->f, "  <signal name=\"%s\">\n", v->signal.member);
+                        introspect_write_arguments(i, v->signal.signature, NULL);
+                        introspect_write_flags(i, v->type, v->flags);
+                        fputs("  </signal>\n", i->f);
+                        break;
+                }
+
+        }
+
+        fputs(" </interface>\n", i->f);
+        return 0;
+}
+
+int introspect_finish(struct introspect *i, sd_bus *bus, sd_bus_message *m, sd_bus_message **reply) {
+        sd_bus_message *q;
+        int r;
+
+        assert(i);
+        assert(m);
+        assert(reply);
+
+        fputs("</node>\n", i->f);
+        fflush(i->f);
+
+        if (ferror(i->f))
+                return -ENOMEM;
+
+        r = sd_bus_message_new_method_return(bus, m, &q);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_append(q, "s", i->introspection);
+        if (r < 0) {
+                sd_bus_message_unref(q);
+                return r;
+        }
+
+        *reply = q;
+        return 0;
+}
+
+void introspect_free(struct introspect *i) {
+        assert(i);
+
+        if (i->f)
+                fclose(i->f);
+
+        if (i->introspection)
+                free(i->introspection);
+
+        zero(*i);
+}