PeerConnection: fix listening for signals (#44), with test and example

the fix is dirty, will move code to PeerConnection

Author: mvidner

examples/no-bus/pulseaudio.rb

@@ -28,3 +28,23 @@ def peer_address
 obj = no_svc["/org/pulseaudio/core1"]
 ifc = obj["org.PulseAudio.Core1"]
 puts "PA version: #{ifc["Version"]}"
+
+puts "Waiting for volume changes, try adjusting it. Ctrl-C to exit."
+
+vol_ifc = "org.PulseAudio.Core1.Device"
+vol_member = "VolumeUpdated"
+# PA needs explicit enabling of signals
+ifc.ListenForSignal("#{vol_ifc}.#{vol_member}", [])
+
+match_rule = DBus::MatchRule.new
+match_rule.interface = vol_ifc
+match_rule.member = vol_member
+conn.add_match(match_rule) do |msg|
+  # a single argument that is an array
+  volumes = msg.params[0]
+  puts "VolumeUpdated: #{volumes.join(", ")}"
+end
+
+loop = DBus::Main.new
+loop << conn
+loop.run

lib/dbus/bus.rb

@@ -369,7 +369,7 @@ def add_match(match_rule, &slot)
       # don't ask for the same match if we override it
       unless @signal_matchrules.key?(mrs)
         DBus.logger.debug "Asked for a new match"
-        proxy.AddMatch(mrs)
+        proxy.AddMatch(mrs) if @unique_name
       end
       @signal_matchrules[mrs] = slot
     end
@@ -383,7 +383,7 @@ def remove_match(match_rule)
 
       # FIXME: if we do try, the Error.MatchRuleNotFound is *not* raised
       # and instead is reported as "no return code for nil"
-      proxy.RemoveMatch(mrs)
+      proxy.RemoveMatch(mrs) if @unique_name
     end
 
     # @api private

spec/connection_spec.rb

@@ -5,13 +5,33 @@
 require "dbus"
 
 describe DBus::PeerConnection do
+  let(:address) { ENV["DBUS_SESSION_BUS_ADDRESS"] }
+  subject { described_class.new(address) }
+
   describe "#peer_service" do
     it "returns a PeerService with a nil name" do
-      address = ENV["DBUS_SESSION_BUS_ADDRESS"]
-      pconn = described_class.new(address)
-      svc = pconn.peer_service
+      svc = subject.peer_service
       expect(svc).to be_a(DBus::ProxyService)
       expect(svc.name).to be_nil
     end
   end
+
+  describe "#add_match, #remove_match" do
+    it "doesn't crash trying to call AddMatch, RemoveMatch" do
+      mr = DBus::MatchRule.new
+      mr.member = "StateUpdated"
+      mr.interface = "org.PulseAudio.Core1.Device"
+      handler = ->(_msg) {}
+
+      # Cheating a bit with the mocking:
+      # a PulseAudio peer connection would error with
+      # > DBus::Error: Method "AddMatch" with signature "s" on interface
+      # > "org.freedesktop.DBus" doesn't exist
+      # but here we do have a bus at the other end, which replies with
+      # > DBus::Error: Client tried to send a message other than Hello without being registered
+      # where "registering" is a libdbus-1 thing meaning "internal bookkeeping and send Hello"
+      expect { subject.add_match(mr, &handler) }.to_not raise_error
+      expect { subject.remove_match(mr) }.to_not raise_error
+    end
+  end
 end