Websocket server » History » Revision 3
Revision 2 (Tom Clegg, 06/16/2016 08:20 PM) → Revision 3/12 (Tom Clegg, 06/17/2016 04:26 AM)
h1. Websocket server
(early draft)
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h2. Background
The Rails API server can function as a websocket server. Clients (notably Workbench, arv-mount, arv-ws) use it to listen for events without polling.
Problems with current implementation:
* Unreliable. See #9427, #8277 Unreliable
* Resource-heavy (one postgres connection per connected client, uses lots of memory)
* Logging is not very good
* Updates look like database records instead of API responses (e.g., computed fields are missing, collection manifest_text has no signatures)
* Offers an API for catching up on missed events after disconnecting/reconnecting, but this API (let alone the code) isn't enough to offer a "don't miss any events, don't send any events twice" guarantee. See #9388
#8460
h2. Desired features
Monotonically increasing event IDs, so clients can (meaningfully) request "all matching events since X"
h2. Design sketch
New server, written in Go.
One goroutine per connected client.
One database connection receiving notifications about new logs. (Possibly still N database connections serving "catch-up" messages to N clients.)
h2. Libraries
Websocket:
* https://godoc.org/golang.org/x/net/websocket
PostgreSQL:
* https://godoc.org/github.com/lib/pq via https://godoc.org/database/sql
* https://godoc.org/github.com/lib/pq#hdr-Notifications and https://godoc.org/github.com/lib/pq/listen_example
h2. Obstacles
#8565, #8566