write the twist/twistd plugins and setup code

src/twisted/plugins/magic_wormhole_transit_relay.py

@@ -0,0 +1,8 @@
+from twisted.application.service import ServiceMaker
+
+TransitRelay = ServiceMaker(
+    "Magic-Wormhole Transit Relay", # name
+    "wormhole_transit_relay.server_tap", # module
+    "Provide the Transit Relay server for Magic-Wormhole clients.", # desc
+    "transitrelay", # tapname
+    )

src/wormhole_transit_relay/server_tap.py

@@ -0,0 +1,68 @@
+from . import transit_server
+from twisted.internet import reactor
+from twisted.python import usage
+from twisted.application.internet import StreamServerEndpointService
+from twisted.application.service import MultiService
+from twisted.internet import endpoints
+
+LONGDESC = """\
+This plugin sets up a 'Transit Relay' server for magic-wormhole. This service
+listens for TCP connections, finds pairs which present the same handshake, and
+glues the two TCP sockets together.
+
+If --usage-logfile= is provided, a line will be written to the given file after
+each connection is done. This line will be a complete JSON object (starting
+with "{" and ending with "}\n"). The keys will be:
+
+* 'started': number, seconds since epoch
+* 'total_time': number, seconds from open to last close
+* 'waiting_time': number, seconds from start to 2nd side appearing, or null
+* 'total_bytes': number, total bytes relayed (sum of both directions)
+* 'mood': string, one of: happy, lonely, errory
+
+A mood of "happy" means both sides gave a correct handshake. "lonely" means a
+second matching side never appeared (and thus 'waiting_time' will be null).
+"errory" means the first side gave an invalid handshake.
+
+If --blur-usage= is provided, then 'started' will be rounded to the given time
+interval, and 'total_bytes' will be rounded as well.
+
+If --stats-json is provided, the server will periodically write a simple JSON
+dictionary to that file (atomically), with usage since last reboot. This
+information is *not* blurred (the assumption is that it will be overwritten on
+a regular basis, and is aggregated anyways). The keys are:
+
+* active.connected: number of paired connections
+* active.waiting: number of not-yet-paired connections
+* since_reboot.bytes: sum of 'total_bytes'
+* since_reboot.total: number of completed connections
+* since_reboot.moods: dict mapping mood string to number of connections
+
+The server will write twistd.pid and twistd.log files as usual, if daemonized
+by twistd.
+"""
+
+class Options(usage.Options):
+    #synopsis = "[--port=] [--usage-logfile=] [--blur-usage=] [--stats-json=]"
+    longdesc = LONGDESC
+
+    optParameters = [
+        ("port", "p", "tcp:4001", "endpoint to listen on"),
+        ("usage-logfile", None, None, "record usage data (JSON lines)"),
+        ("blur-usage", None, None, "blur logged timestamps and data sizes"),
+        ("stats-json", None, None, "record usage since-reboot"),
+        ]
+
+    def opt_blur_usage(self, arg):
+        self["blur_usage"] = int(arg)
+
+
+def makeService(config, reactor=reactor):
+    s = MultiService()
+    t = transit_server.Transit(blur_usage=config["blur-usage"],
+                               usage_logfile=config["usage-logfile"],
+                               stats_json_path=config["stats-json"])
+    s.setServiceParent(t) # for the timer
+    ep = endpoints.serverFromString(reactor, config["port"]) # to listen
+    s.setServiceParent(StreamServerEndpointService(ep, t))
+    return s