Allow reading and writing messages from sockets in async mode

examples/async_socket_message_client.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+
+import asyncio
+import argparse
+import capnp
+
+import addressbook_capnp
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(
+        usage="Connects to the Example thread server \
+at the given address and does some RPCs"
+    )
+    parser.add_argument("host", help="HOST:PORT")
+
+    return parser.parse_args()
+
+
+async def writeAddressBook(stream, bob_id):
+    addresses = addressbook_capnp.AddressBook.new_message()
+    people = addresses.init("people", 1)
+
+    bob = people[0]
+    bob.id = bob_id
+    bob.name = "Bob"
+    bob.email = "bob@example.com"
+    bobPhones = bob.init("phones", 2)
+    bobPhones[0].number = "555-4567"
+    bobPhones[0].type = "home"
+    bobPhones[1].number = "555-7654"
+    bobPhones[1].type = "work"
+    bob.employment.unemployed = None
+
+    await addresses.write_async(stream)
+
+
+async def main(host):
+    host, port = host.split(":")
+    stream = await capnp.AsyncIoStream.create_connection(host=host, port=port)
+
+    await writeAddressBook(stream, 0)
+
+    message = await addressbook_capnp.AddressBook.read_async(stream)
+    print(message)
+    assert message.people[0].name == "Alice"
+    assert message.people[0].id == 0
+
+    await writeAddressBook(stream, 1)
+
+
+if __name__ == "__main__":
+    args = parse_args()
+    asyncio.run(main(args.host))