noise: Initial version of the noise chat plugin

Based on the WhatSat idea by @joostjager, this plugin implements a simple chat
protocol based on top of `createonion` and `sendonion`.

noise/test_chat.py

@@ -0,0 +1,54 @@
+from pyln.testing.fixtures import *
+from pyln.testing.utils import wait_for
+from pprint import pprint
+
+plugin = os.path.join(os.path.dirname(__file__), 'noise.py')
+
+
+def test_sendmsg(node_factory, executor):
+    opts = [{'plugin': plugin}, {}, {'plugin': plugin}]
+    l1, l2, l3 = node_factory.line_graph(3, wait_for_announce=True, opts=opts)
+
+    recv = executor.submit(l3.rpc.recvmsg)
+    l1.rpc.sendmsg(l3.info['id'], "Hello world!")
+
+    # This one is tailing the incoming messages
+    m1 = recv.result(10)
+
+    # This one should get the same result:
+    m2 = l3.rpc.recvmsg(last_id=-1)
+    # They should be the same :-)
+    assert(m1 == m2)
+
+
+def test_sendmsg_retry(node_factory, executor):
+    opts = [{'plugin': plugin}, {}, {'fee-base': 10000}, {'plugin': plugin}]
+    l1, l2, l3, l4 = node_factory.line_graph(4, opts=opts)
+    l5 = node_factory.get_node()
+
+    l2.openchannel(l5, 10**6)
+    l5.openchannel(l4, 10**6)
+
+    def gossip_synced(nodes):
+        for a, b in zip(nodes[:-1], nodes[1:]):
+            if a.rpc.listchannels() != b.rpc.listchannels():
+                return False
+        return True
+
+    wait_for(lambda: gossip_synced([l1, l2, l3, l4, l5]))
+
+    # Now stop l5 so the first attempt will fail.
+    l5.stop()
+
+    recv = executor.submit(l4.rpc.recvmsg)
+
+    send = executor.submit(l1.rpc.sendmsg, l4.info['id'], "Hello world!")
+
+    l1.daemon.wait_for_log(r'Retrying delivery')
+
+    sres = send.result(10)
+    assert(sres['attempt'] == 2)
+    pprint(sres)
+    print(recv.result(10))
+
+    msg = l4.rpc.recvmsg(last_id=-1)