distbuild: allow daemons to bind to ephemeral ports

You can bind to an ephemeral port by passing 0 as the port number.
To work out which port you actually got, you need to call getsockname().

To facilitate being able to spawn multiple copies of the daemons for
testing environments, you can pass a -file option, which will make the
daemon write which port it actually bound to.

If this path is a fifo, reading from it in the spawner process will
allow synchronisation of only spawning services that require that port to
be ready after it is.

2 files changed, 28 insertions, 3 deletions

diff --git a/distbuild/sockserv.py b/distbuild/sockserv.py
index a5215e79..68991a93 100644
--- a/distbuild/sockserv.py
+++ b/distbuild/sockserv.py
@@ -26,15 +26,20 @@ class ListenServer(StateMachine):
 
     '''Listen for new connections on a port, send events for them.'''
 
-    def __init__(self, addr, port, machine, extra_args=None):
+    def __init__(self, addr, port, machine, extra_args=None, port_file=''):
         StateMachine.__init__(self, 'listening')
         self._addr = addr
         self._port = port
         self._machine = machine
         self._extra_args = extra_args or []
+        self._port_file = port_file
         
     def setup(self):
         src = ListeningSocketEventSource(self._addr, self._port)
+        if self._port_file:
+            host, port = src.sock.getsockname()
+            with open(self._port_file, 'w') as f:
+                f.write(port)
         self.mainloop.add_event_source(src)
 
         spec = [
diff --git a/morphlib/plugins/distbuild_plugin.py b/morphlib/plugins/distbuild_plugin.py
index 50ab7eeb..7e8188dd 100644
--- a/morphlib/plugins/distbuild_plugin.py
+++ b/morphlib/plugins/distbuild_plugin.py
@@ -121,6 +121,11 @@ class WorkerDaemon(cliapp.Plugin):
             'listen for connections on PORT',
             default=3434,
             group=group_distbuild)
+        self.app.settings.string(
+            ['worker-daemon-port-file'],
+            'write port used by worker-daemon to FILE',
+            default='',
+            group=group_distbuild)
         self.app.add_subcommand(
             'worker-daemon',
             self.worker_daemon,
@@ -136,7 +141,9 @@ class WorkerDaemon(cliapp.Plugin):
 
         address = self.app.settings['worker-daemon-address']
         port = self.app.settings['worker-daemon-port']
-        router = distbuild.ListenServer(address, port, distbuild.JsonRouter)
+        port_file = self.app.settings['worker-daemon-port-file']
+        router = distbuild.ListenServer(address, port, distbuild.JsonRouter,
+                                        port_file=port_file)
         loop = distbuild.MainLoop()
         loop.add_state_machine(router)
         loop.run()
@@ -156,6 +163,11 @@ class ControllerDaemon(cliapp.Plugin):
             'listen for initiator connections on PORT',
             default=7878,
             group=group_distbuild)
+        self.app.settings.string(
+            ['controller-initiator-port-file'],
+            'write the port to listen for initiator connections to FILE',
+            default='',
+            group=group_distbuild)
 
         self.app.settings.string(
             ['controller-helper-address'],
@@ -167,6 +179,11 @@ class ControllerDaemon(cliapp.Plugin):
             'listen for helper connections on PORT',
             default=5656,
             group=group_distbuild)
+        self.app.settings.string(
+            ['controller-helper-port-file'],
+            'write the port to listen for helper connections to FILE',
+            default='',
+            group=group_distbuild)
 
         self.app.settings.string_list(
             ['worker'],
@@ -218,8 +235,10 @@ class ControllerDaemon(cliapp.Plugin):
         listener_specs = [
             # address, port, class to initiate on connection, class init args
             ('controller-helper-address', 'controller-helper-port', 
+             'controller-helper-port-file',
              distbuild.HelperRouter, []),
             ('controller-initiator-address', 'controller-initiator-port',
+             'controller-initiator-port-file',
              distbuild.InitiatorConnection, 
              [artifact_cache_server, morph_instance]),
         ]
@@ -229,9 +248,10 @@ class ControllerDaemon(cliapp.Plugin):
         queuer = distbuild.WorkerBuildQueuer()
         loop.add_state_machine(queuer)
 
-        for addr, port, sm, extra_args in listener_specs:
+        for addr, port, port_file, sm, extra_args in listener_specs:
             addr = self.app.settings[addr]
             port = self.app.settings[port]
+            port_file = self.app.settings[port_file]
             listener = distbuild.ListenServer(
                 addr, port, sm, extra_args=extra_args)
             loop.add_state_machine(listener)