A native erlang implementation of D-Bus

D-Bus is now largely used in a lot of applications for language-independant, object-oriented RPC system.

The erlang platform needs an erlang native implementation.

Example

Bus = system,  % or `session` or any valid D-Bus address string
dbus:start_link(Bus),
BusProxy = dbus:get_proxy(Bus),
dbus_bus:request_name(BusProxy, <<"com.example">>).

Unix file descriptor passing

Supported on unix: transports, and only there: tcp: and nonce-tcp: sockets cannot carry a descriptor at all, so NEGOTIATE_UNIX_FD is never sent over them and such a connection authenticates with agree_unix_fd = false. Capability is not agreement -- the peer still has to answer AGREE_UNIX_FD, and a message carrying descriptors on a connection where it did not is {error, unix_fd_not_negotiated} with nothing written.

A message carries its descriptors on #dbus_message.fds. The value of an h (unix_fd) in a body is an index into that list, not a descriptor; dbus_message:fd/2 resolves one. The UNIX_FDS header field is synthesised from fds while marshalling, so a caller sets fds and never the field. At most ?MAX_UNIX_FDS (16) descriptors travel with one message.

Received descriptors belong to the owner process: they are open in this OS process, they count against RLIMIT_NOFILE, and the library will not close them. Consuming one -- socket:open/1, a port program, a NIF -- or dbus_fd:close/1 is the owner's job, and dbus_fd:dup/1 is how one outlives the message it arrived with. The descriptors nobody takes delivery of are the library's and are closed with a logged warning: a message that fails to parse, descriptors arriving when AGREE_UNIX_FD was never exchanged, and the queue left over when a connection dies.

Descriptors sent stay the sender's. sendmsg(2) gives the peer a copy of the open file description, not the number, so the descriptors in a message passed to dbus_connection:send/2 are still open here when it returns.

Documentation

• API documentation
• D-Bus Specifications