Feature #80: D-Bus support

- Add D-Bus support. Currently 7 methods are available: "reset" (same as
  SIGUSR1), "list_win" (list the windows compton manages), "win_get"
  (get a property of the window), "win_set" (set a property of the
  window), "find_win" (find window based on client window / focus),
  "opts_get" (get the value of a compton option), and "opts_set" (set
  the value of a compton option), together with 4 signals: "win_added",
  "win_destroyed", "win_mapped", "win_unmapped".

- D-Bus support depends on libdbus.

- As there are many items and my time is tight, no much tests are done.
  Bugs to be expected.

- Create a new header file `common.h` that contains shared content.

- Fix some bugs in timeout handling.

- Update file headers in all source files.

- Re-enable --unredir-if-possible on multi-screen set-ups, as the user
  could turn if off manually anyway.

- Check if the window is mapped in `repair_win()`.

- Add ps->track_atom_lst and its handlers, to prepare for the new
  condition format.

- Known issue 1: "win_get", "win_set", "opts_get", "opts_set" support a
  very limited number of targets only. New ones will be added gradually.

- Known issue 2: Accidental drop of D-Bus connection is not handled.

- Known issue 3: Introspection does not reveal all available methods,
  because some methods have unpredictable prototypes. Still hesitating
  about what to do...

- Known issue 4: Error handling is not finished yet. Compton does not
  always reply with the correct error message (but it does print out the
  correct error message, usually).

1 files changed, 213 insertions, 0 deletions

diff --git a/dbus.h b/dbus.h
new file mode 100644
index 000000000..fb51c8cc4
--- /dev/null
+++ b/dbus.h
@@ -0,0 +1,213 @@
+/*
+ * Compton - a compositor for X11
+ *
+ * Based on `xcompmgr` - Copyright (c) 2003, Keith Packard
+ *
+ * Copyright (c) 2011-2013, Christopher Jeffrey
+ * See LICENSE for more information.
+ *
+ */
+
+#include "common.h"
+#include <ctype.h>
+
+#define CDBUS_SERVICE_NAME      "com.github.chjj.compton"
+#define CDBUS_INTERFACE_NAME    CDBUS_SERVICE_NAME
+#define CDBUS_OBJECT_NAME       "/com/github/chjj/compton"
+#define CDBUS_ERROR_PREFIX      CDBUS_INTERFACE_NAME ".error"
+#define CDBUS_ERROR_UNKNOWN     CDBUS_ERROR_PREFIX ".unknown"
+#define CDBUS_ERROR_UNKNOWN_S   "Well, I don't know what happened. Do you?"
+#define CDBUS_ERROR_BADMSG      CDBUS_ERROR_PREFIX ".bad_message"
+#define CDBUS_ERROR_BADMSG_S    "Unrecognized command. Beware compton " \
+                                "cannot make you a sandwich."
+#define CDBUS_ERROR_BADARG      CDBUS_ERROR_PREFIX ".bad_argument"
+#define CDBUS_ERROR_BADARG_S    "Something wrong in arguments?"
+#define CDBUS_ERROR_BADWIN      CDBUS_ERROR_PREFIX ".bad_window"
+#define CDBUS_ERROR_BADWIN_S    "Requested window %#010lx not found."
+#define CDBUS_ERROR_FORBIDDEN   CDBUS_ERROR_PREFIX ".forbidden"
+#define CDBUS_ERROR_FORBIDDEN_S "Incorrect password, access denied."
+
+// Window type
+typedef uint32_t cdbus_window_t;
+#define CDBUS_TYPE_WINDOW       DBUS_TYPE_UINT32
+#define CDBUS_TYPE_WINDOW_STR   DBUS_TYPE_UINT32_AS_STRING
+
+typedef uint16_t cdbus_enum_t;
+#define CDBUS_TYPE_ENUM         DBUS_TYPE_UINT16
+#define CDBUS_TYPE_ENUM_STR     DBUS_TYPE_UINT16_AS_STRING
+
+static dbus_bool_t
+cdbus_callback_add_timeout(DBusTimeout *timeout, void *data);
+
+static void
+cdbus_callback_remove_timeout(DBusTimeout *timeout, void *data);
+
+static void
+cdbus_callback_timeout_toggled(DBusTimeout *timeout, void *data);
+
+static bool
+cdbus_callback_handle_timeout(session_t *ps, timeout_t *ptmout);
+
+/**
+ * Determine the poll condition of a DBusWatch.
+ */
+static inline short
+cdbus_get_watch_cond(DBusWatch *watch) {
+  const unsigned flags = dbus_watch_get_flags(watch);
+  short condition = POLLERR | POLLHUP;
+  if (flags & DBUS_WATCH_READABLE)
+    condition |= POLLIN;
+  if (flags & DBUS_WATCH_WRITABLE)
+    condition |= POLLOUT;
+
+  return condition;
+}
+
+static dbus_bool_t
+cdbus_callback_add_watch(DBusWatch *watch, void *data);
+
+static void
+cdbus_callback_remove_watch(DBusWatch *watch, void *data);
+
+static void
+cdbus_callback_watch_toggled(DBusWatch *watch, void *data);
+
+static bool
+cdbus_apdarg_bool(session_t *ps, DBusMessage *msg, const void *data);
+
+static bool
+cdbus_apdarg_wid(session_t *ps, DBusMessage *msg, const void *data);
+
+static bool
+cdbus_apdarg_enum(session_t *ps, DBusMessage *msg, const void *data);
+
+static bool
+cdbus_apdarg_string(session_t *ps, DBusMessage *msg, const void *data);
+
+static bool
+cdbus_apdarg_wids(session_t *ps, DBusMessage *msg, const void *data);
+
+/** @name DBus signal sending
+ */
+///@{
+
+static bool
+cdbus_signal(session_t *ps, const char *name,
+    bool (*func)(session_t *ps, DBusMessage *msg, const void *data),
+    const void *data);
+
+/**
+ * Send a signal with no argument.
+ */
+static inline bool
+cdbus_signal_noarg(session_t *ps, const char *name) {
+  return cdbus_signal(ps, name, NULL, NULL);
+}
+
+/**
+ * Send a signal with a Window ID as argument.
+ */
+static inline bool
+cdbus_signal_wid(session_t *ps, const char *name, Window wid) {
+  return cdbus_signal(ps, name, cdbus_apdarg_wid, &wid);
+}
+
+///@}
+
+/** @name DBus reply sending
+ */
+///@{
+
+static bool
+cdbus_reply(session_t *ps, DBusMessage *srcmsg,
+    bool (*func)(session_t *ps, DBusMessage *msg, const void *data),
+    const void *data);
+
+static bool
+cdbus_reply_errm(session_t *ps, DBusMessage *msg);
+
+#define cdbus_reply_err(ps, srcmsg, err_name, err_format, ...) \
+  cdbus_reply_errm((ps), dbus_message_new_error_printf((srcmsg), (err_name), (err_format), ## __VA_ARGS__))
+
+/**
+ * Send a reply with no argument.
+ */
+static inline bool
+cdbus_reply_noarg(session_t *ps, DBusMessage *srcmsg) {
+  return cdbus_reply(ps, srcmsg, NULL, NULL);
+}
+
+/**
+ * Send a reply with a bool argument.
+ */
+static inline bool
+cdbus_reply_bool(session_t *ps, DBusMessage *srcmsg, bool bval) {
+  return cdbus_reply(ps, srcmsg, cdbus_apdarg_bool, &bval);
+}
+
+/**
+ * Send a reply with a wid argument.
+ */
+static inline bool
+cdbus_reply_wid(session_t *ps, DBusMessage *srcmsg, Window wid) {
+  return cdbus_reply(ps, srcmsg, cdbus_apdarg_wid, &wid);
+}
+
+/**
+ * Send a reply with a string argument.
+ */
+static inline bool
+cdbus_reply_string(session_t *ps, DBusMessage *srcmsg, const char *str) {
+  return cdbus_reply(ps, srcmsg, cdbus_apdarg_string, str);
+}
+
+/**
+ * Send a reply with a enum argument.
+ */
+static inline bool
+cdbus_reply_enum(session_t *ps, DBusMessage *srcmsg, cdbus_enum_t eval) {
+  return cdbus_reply(ps, srcmsg, cdbus_apdarg_enum, &eval);
+}
+
+///@}
+
+static bool
+cdbus_msg_get_arg(DBusMessage *msg, int count, const int type, void *pdest);
+
+/**
+ * Return a string representation of a D-Bus message type.
+ */
+static inline const char *
+cdbus_repr_msgtype(DBusMessage *msg) {
+  return dbus_message_type_to_string(dbus_message_get_type(msg));
+}
+
+/** @name Message processing
+ */
+///@{
+
+static void
+cdbus_process(session_t *ps, DBusMessage *msg);
+
+static bool
+cdbus_process_list_win(session_t *ps, DBusMessage *msg);
+
+static bool
+cdbus_process_win_get(session_t *ps, DBusMessage *msg);
+
+static bool
+cdbus_process_win_set(session_t *ps, DBusMessage *msg);
+
+static bool
+cdbus_process_find_win(session_t *ps, DBusMessage *msg);
+
+static bool
+cdbus_process_opts_get(session_t *ps, DBusMessage *msg);
+
+static bool
+cdbus_process_opts_set(session_t *ps, DBusMessage *msg);
+
+static bool
+cdbus_process_introspect(session_t *ps, DBusMessage *msg);
+
+///@}