siphon-control (Python)

Python client for the SIPhon external control plane (siphon-control.v1) — an ARI/ESL-class rail for driving handed-over calls out of process. Built with PyO3 over the async Rust client, so the wire is hidden: no manual JSON, no request-id bookkeeping.

Two connection modes

The plane runs in one of two modes; both are exposed here and share the SAME @on_call decorator and the SAME Call handle — only the transport differs.

• Inbound-persistent (ControlClient) — the app dials siphon and holds one long-lived socket (does the hello handshake). Simplest to reason about; use it for development and single-process controllers.
• Per-call-connect (ControlServer) — siphon dials the app per handed-over call, so the app is a WebSocket server. Each accepted connection owns exactly one call and the first frame is a pushed StasisStart (no hello). This is the documented production default for multi-pod controllers: because the accepting socket is the call, "the audio lands on the wrong pod" can't happen.

Inbound-persistent

import asyncio
from siphon_control import ControlClient, ControlError

client = ControlClient(app="ivr-app", token="s3cr3t",
                       url="ws://siphon:9090/control/ws")

@client.on_call
async def handle(call):
    await call.answer()
    try:
        await call.transfer("sip:agent@pbx")   # REFER, awaits correlated reply
    except ControlError as error:
        print("transfer rejected:", error.code)

async def main():
    async with client:          # closes on the way out — see Shutdown below
        await client.run()

asyncio.run(main())

Per-call-connect

import asyncio
from siphon_control import ControlServer, ControlError

server = ControlServer(app="ivr-app", token="s3cr3t", bind="0.0.0.0:8790")

@server.on_call
async def handle(call):
    await call.answer()
    try:
        await call.transfer("sip:agent@pbx")
    except ControlError as error:
        print("transfer rejected:", error.code)

async def main():
    async with server:
        await server.serve()

asyncio.run(main())

Shutdown

Both classes are async context managers, and async with is the recommended shape. close() is the same thing explicitly.

It matters more than it looks. run() / serve() are driven by a background tokio task, and every handed-over call is dispatched from another one. Nothing joins those tasks and the runtime outlives the interpreter, so an app that finishes without closing leaves them delivering results into an asyncio loop — and then into a Python — that is no longer there. Closing first means there is nothing in flight to strand.

Not closing is handled rather than fatal: a handover arriving after the loop or interpreter has gone is dropped, and a handler cancelled during teardown is not reported as a failure. That is damage control, not a substitute for closing.

API

ControlClient (inbound-persistent)

• ControlClient(app, token, url=…, protocol=1, reply_timeout_ms=…, reconnect_backoff_ms=…)
• @client.on_call — register an async (or sync) per-call handler.
• await client.connect() / await client.run() — connect / drive (reconnect + resync).
• await client.command(verb, module=None, target=None, args=None) — the generic {module, verb, target, args} primitive for any adapter (SIP today; SMPP/SS7 later).
• await client.originate(channel, to, *, media=False, sdp=None, body=None, content_type=None, …, session_timer=None) — place an outbound call under a channel id you choose; resolves to {"channel", "call_id", "sip_call_id"} once the INVITE is on the wire. Exactly one media plan (media=True, sdp= or body=). session_timer={"expires", "min_se", "refresher"} runs an RFC 4028 session timer on the call, each key left out taking the server's default. What the server would refuse raises ValueError before a frame goes out.
• await client.describe() — adapter schema.
• client.shutdown() — stop the client and unblock run().
• client.close() — shutdown, plus drop the handler so nothing else is dispatched. async with client: does this on the way out. See Shutdown above.

ControlServer (per-call-connect)

• ControlServer(app, token, bind="0.0.0.0:8790", reply_timeout_ms=…) — bind is the address the app listens on for siphon to dial; the token is validated on the incoming upgrade.
• @server.on_call — the SAME decorator + Call handle as ControlClient.
• await server.bind() — bind the listener; resolves to the bound address string (bind to …:0 to learn the ephemeral port before siphon dials in).
• server.local_addr — the bound address once bind() / serve() has run, else None.
• await server.serve() / await server.run() — accept siphon's per-call dials forever (stop by cancelling the task).
• server.close() — drop the handler so no further accepted call is dispatched. async with server: does this on the way out. See Shutdown above.

Call (shared by both modes)

• Call verbs: answer(), answer_with(code, …), progress(), reject(code, reason), hangup(reason=None), refer(to) / transfer(to), set_header(name, value), get_header(name), set_var(key, value), get_var(key), command(verb, args=None), next_event().
• Media verbs play_file(file) / dtmf(digits) raise ControlError with code == "unsupported_verb" until the server implements media.

Errors

A rejected command raises ControlError carrying a stable .code (not_found, forbidden, unsupported_verb, unauthorized, …).

Build

maturin develop        # into the active venv
maturin build --release

The target interpreter is free-threaded CPython 3.14t (the SIPhon runtime); the wheel also loads on a standard GIL build.

License

MIT