Handshake and lifecycle

The handshake

The daemon speaks first. The adapter stays silent until it receives initialize; a frame sent before that is a violation.

daemon:  {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocols":[1],"host":{"name":"oxidepmd","version":"0.4.0"},"adapter":{"name":"notifier","version":"0.1.0"},"kind":"service","grant":{"level":"read","scope":"all"},"paths":{"state":"/home/u/.oxidepm/adapters/state/notifier"},"limits":{"max_line":262144,"max_in_flight":32,"event_queue":1024}}}
adapter: {"jsonrpc":"2.0","id":1,"result":{"protocol":1,"name":"notifier","version":"0.1.0"}}
daemon:  {"jsonrpc":"2.0","method":"initialized","params":{}}

The version numbers in this example are illustrative. The daemon puts its own version in host.version.

The adapter must answer within 10 seconds, with the highest protocol it shares with protocols, and its own name and version.
The daemon compares name and version with what it has on record. A difference means the executable is not what was installed: the adapter is killed and marked failed (tampered) and does not start again.
A protocol that is not in the offered list, or an error -32022 (optionally with data.supported), marks the adapter failed (incompatible).
After a good reply, the daemon sends the notification initialized. A service then receives events. A tool is idle until a request arrives.
A silent or broken handshake ends the process. It counts as a crash, and the supervisor restarts it with a growing delay until it gives up.

adapter: {"jsonrpc":"2.0","id":1,"error":{"code":-32022,"message":"unsupported protocol","data":{"supported":[1],"code":"E_ADAPTER_PROTOCOL"}}}

Staying alive

A service is sent ping every 15 seconds and has 5 seconds to answer. Three misses in a row kill it. A tool is not pinged: it is started for a request, kept warm for 30 seconds, and asked to exit when idle.

daemon:  {"jsonrpc":"2.0","id":2,"method":"ping","params":{}}
adapter: {"jsonrpc":"2.0","id":2,"result":{}}

Timeouts and cancellation

Every wait for an adapter is a timer in the daemon. The adapter's cooperation is not needed.
When a deadline passes, or the caller goes away, the daemon forgets the request at once, sends cancel {id} and remembers the id. A reply with that id (a late answer, or error -32024 from an adapter that obeyed the cancel) is dropped and counted, without a strike. An id that was never issued is a strike.
When the connection ends for any reason, every request in flight fails with E_ADAPTER_CRASHED.

Shutdown

When the adapter is stopped, the daemon sends shutdown and waits up to 2 seconds. It then closes the adapter's standard input (the adapter must also exit when its input closes), waits until 2 seconds are over, sends SIGTERM to the adapter's process group, waits until 5 seconds are over in all, and then sends SIGKILL. The total is fixed. Queued events are written first, for up to a second.