client: expose user-facing api from doublezerod

[packethog]

The first use case for this would be for the "yolo" mode multihoming proposal from Anza where a healthcheck script could either poll/subscribe to tunnel session state from doublezerod and be notified of session state changes to fail the validator over to a different external interface.

[alexpyattaev]

Our proposal is that the doublezerod process would use (approximately) the following mechanism:

• On startup, create a named pipe in /run/doublezero_event in SEQPACKET mode
• Set permissions appropriately to make sure unpriviledged processes can connect and receive messages
• When a client connects to the pipe, the server accepts connection and sends a JSON message with version and any other reasonable metadata about itself. This message must include a key describing current service status
• When an event of interest occurs, the server pushes a JSON with machine-readable event description to all connected clients.

For example, the messages could look like:

{"version":"1.2.3.", "online":true}
{"event":"switch failure", "mitigation":"reconnecting", "online": false }
{"event":"connection success",  "online":true }

Additional keys may be added as needed later.

[alexpyattaev]

A really crude demo for the server-side of the seqpacket setup

server

import socket
import os
import threading
import time

SOCKET_PATH = '/tmp/seqpacket.sock'

if os.path.exists(SOCKET_PATH):
    os.remove(SOCKET_PATH)

def handle_client(conn):
    with conn:
        print(conn)
        while True:
            time.sleep(1.0)
            conn.send(b'{"online":true}')

with socket.socket(socket.AF_UNIX, socket.SOCK_SEQPACKET) as server_sock:
    server_sock.bind(SOCKET_PATH)
    server_sock.listen()
    print("Server listening on", SOCKET_PATH)

    while True:
        conn, _ = server_sock.accept()
        conn.send(b'{"version":"1.2.3", "online":true}')
        t = threading.Thread(target=handle_client, args=(conn,))
        t.start()

client

import socket
import time

SOCKET_PATH = '/tmp/seqpacket.sock'
with socket.socket(socket.AF_UNIX, socket.SOCK_SEQPACKET) as client_sock:
    client_sock.connect(SOCKET_PATH)
    while True:
        print(client_sock.recv(1024))
        time.sleep(1.0)

[packethog]

Would you be open to using a streaming http conn as the transport over a STREAM socket named pipe? The reason I ask is we already open a sock file at /var/run/doublezerod/doublezerod.sock that our CLI uses to interact with the daemon via http and it would be nice to be able add a /events endpoint instead of a separate solution for this use case. The payloads we currently accept are all json encoded as well.

[alexpyattaev]

I think it would work equally well. @nbridge-jump would that work on your end?