Pure Ocaml implementation of the D-Bus protocol
Library obus

This module implements manipulation of a D-Bus connection. A D-Bus connection is a channel opened with another application which also implement the D-Bus protocol. It is used to exchange D-Bus messages.

type t

Type of D-Bus connections

val compare : t -> t -> int

Same as Pervasives.compare. It allows this module to be used as argument to the functors Set.Make and Map.Make.


The following functions will return a connection which is ready to send and receive messages. You should use them only for direct connection to another application without passing through a message bus.

Otherwise you should use OBus_bus or immediately call OBus_bus.register_connection after the creation.

val of_addresses : ?switch:Lwt_switch.t -> ?shared:bool -> OBus_address.t list -> t Lwt.t

of_addresses ?switch ?shared addresses try to get a working D-Bus connection from a list of addresses. The server must be accessible from at least one of these addresses.

If shared is true and a connection to the same server is already open, then it is used instead of transport. This is the default behaviour.

val loopback : unit -> t

Create a connection with a loopback transport

val close : t -> unit Lwt.t

Close a connection.

All thread waiting for a reply will fail with the exception Connection_closed.


  • when a connection is closed, the transport it use is closed too
  • if the connection is already closed, it does nothing
val active : t -> bool React.signal

Returns whether a connection is active.

exception Connection_closed

Raised when trying to use a closed connection

exception Connection_lost

Raised when a connection has been lost

exception Transport_error of exn

Raised when something wrong happens on the backend transport of the connection

val name : t -> OBus_name.bus

Returns the unique name of the connection. This is only meaningful is the other endpoint of the connection is a message bus. If it is not the case it returns "".

val transport : t -> OBus_transport.t

transport connection get the transport associated with a connection

val can_send_basic_type : t -> OBus_value.T.basic -> bool
val can_send_single_type : t -> OBus_value.T.single -> bool
val can_send_sequence_type : t -> OBus_value.T.sequence -> bool

can_send_*_type connection typ returns whether values of the given type can be sent through the given connection.

Sending messages

These functions are the low-level functions for sending messages. They take and return a complete message description

val send_message : t -> OBus_message.t -> unit Lwt.t

send_message connection message send a message without expecting a reply.

val send_message_with_reply : t -> OBus_message.t -> OBus_message.t Lwt.t

send_message_with_reply connection message Send a message and return a thread which waits for the reply (which is a method return or an error)

val send_message_keep_serial : t -> OBus_message.t -> unit Lwt.t

Same as send_message but does not generate a serial for the message.

Warning: this is for implementing a D-Bus daemon only, not for casual use.

val send_message_keep_serial_with_reply : t -> OBus_message.t -> OBus_message.t Lwt.t

Same as send_message_with_reply but does not generate a serial for the message.

Warning: this is for implementing a D-Bus daemon only, not for casual use.

Helpers for calling methods
val method_call : connection:t -> ?destination:OBus_name.bus -> path:OBus_path.t -> ?interface:OBus_name.interface -> member:OBus_name.member -> i_args:'a OBus_value.C.sequence -> o_args:'b OBus_value.C.sequence -> 'a -> 'b Lwt.t

Calls a method using the given parameters, and waits for its reply.

val method_call_with_message : connection:t -> ?destination:OBus_name.bus -> path:OBus_path.t -> ?interface:OBus_name.interface -> member:OBus_name.member -> i_args:'a OBus_value.C.sequence -> o_args:'b OBus_value.C.sequence -> 'a -> (OBus_message.t * 'b) Lwt.t

Same as method_call, but also returns the reply message so you can extract informations from it.

val method_call_no_reply : connection:t -> ?destination:OBus_name.bus -> path:OBus_path.t -> ?interface:OBus_name.interface -> member:OBus_name.member -> i_args:'a OBus_value.C.sequence -> 'a -> unit Lwt.t

Same as method_call but does not expect a reply

General purpose filters

Filters are functions that are applied on all incoming and outgoing messages.

For incoming messages they are called before dispatching, for outgoing ones, they are called just before being sent.

type filter = OBus_message.t -> OBus_message.t option

The result of a filter must be:

  • Some msg where msg is the message given to the filter modified or not, which means that the message is replaced by this one
  • None which means that the message will be dropped, i.e. not dispatched or not sent
val incoming_filters : t -> filter Lwt_sequence.t

Filters applied on incoming messages

val outgoing_filters : t -> filter Lwt_sequence.t

Filters appllied on outgoing messages

Connection local Storage

Connection local storage allows to attach values to a connection. It is internally used by modules of obus.

type 'a key

Type of keys. Keys are used to identify a resource attached to a connection.

val new_key : unit -> 'a key

new_key () generates a new key.

val get : t -> 'a key -> 'a option

get connection key returns the data associated to key in connection, if any.

val set : t -> 'a key -> 'a option -> unit

set connection key value attach value to connection under the key key. set connection key None will remove any occurence of key from connection.

Errors handling

Note: when a filter/signal handler/method_call handler raise an exception, it is just dropped. If OBus_info.debug is set then a message is printed on stderr

val set_on_disconnect : t -> ( exn -> unit Lwt.t ) -> unit

Sets the function called when a fatal error happen or when the conection is lost.


  • the default function does nothing
  • it is not called when the connection is closed using close
  • if the connection is closed, it does nothing
val of_transport : ?switch:Lwt_switch.t -> ?guid:OBus_address.guid -> ?up:bool -> OBus_transport.t -> t

Create a D-Bus connection on the given transport. If guid is provided the connection will be shared.

up tell whether the connection is initially up or down, default is true.

A connection can be up or down. Except for connections created with of_transport, newly created connections are always up.

When a connection is down, messages will not be dispatched

val state : t -> [ `Up | `Down ] React.signal

Signal holding the current state of the connection

val set_up : t -> unit

Sets up the connection if it is not already up

val set_down : t -> unit

Sets down the connection if it is not already down