btheadset.rb

#!/usr/bin/env ruby

# bluez 4.101
# pulseaudio 4.0

require 'dbus'

bd_addr = ARGV[0]

# Connect to the headset.
# Assumes that the headset has already paired by bluez-simple-agent.
bluez_service = DBus.system_bus.service('org.bluez')
adapter_path, = bluez_service.object('/').tap(&:introspect).DefaultAdapter

adapter = bluez_service.object(adapter_path).tap(&:introspect)
device_path, = adapter.FindDevice(bd_addr)

headset = bluez_service.object(device_path).tap(&:introspect)['org.bluez.Headset']
if not headset.IsConnected.first
  headset.Connect
end

# Lookup PulseAudio's bus.
server_lookup = DBus.session_bus.service('org.PulseAudio1').object('/org/pulseaudio/server_lookup1').tap(&:introspect)['org.PulseAudio.ServerLookup1']
pulse_address = server_lookup['Address']

# Get PulseAudio object.
pulse_bus = DBus::Connection.new(pulse_address)
pulse_bus.connect
pulse_service = pulse_bus.service('org.PulseAudio1')
pulse_core = pulse_service.object('/org/pulseaudio/core1').tap(&:introspect)['org.PulseAudio.Core1']

# Set the headset as the fallback(default) sink.
sink_path, = pulse_core.GetSinkByName("bluez_sink.#{bd_addr.gsub(':', '_')}")
# Explicitly states that sink_path has ObjectPath type.
pulse_core['FallbackSink'] = ['o', sink_path]

# Set the headset as the fallback(default) source.
source_path, = pulse_core.GetSourceByName("bluez_source.#{bd_addr.gsub(':', '_')}")
# Explicitly states that source_path has ObjectPath type.
pulse_core['FallbackSource'] = ['o', source_path]