oppi.li
1excuse - mount jetstream as a character device on linux
2
3CUSE is FUSE's little brother, and it allows mounting a
4single character device file in /dev, with the device driver
5being implemented in userspace.
6
7unlike typical files, character devices like /dev/urandom
8are not seekable. they only support a streaming interface:
9
10 λ cat /dev/urandom # random numbers
11
12excuse simply mounts a websocket connection to an atproto
13jetstream as a userspace character device:
14
15 λ sudo RUST_LOG=info excuse
16 [2025-09-21 INFO excuse] Initializing CUSE at /dev/jetstream
17 [2025-09-21 INFO excuse] /dev/jetstream is now 0644
18
19in another terminal:
20
21 λ cat /dev/jetstream | jq
22 {
23 "did": "did:plc:s6zjj6aw652mmvsrs573j6ti",
24 "time_us": 1758442606746247,
25 "kind": "commit",
26 "commit": { ... }
27 }
28 .
29 .
30 .
31
32you will notice a couple of optimizations:
33
34 - the websocket is only opened when the file has readers,
35 and is closed when all readers are closed
36 - the same connection is shared by all readers
37 - the data is buffered and not sent byte by byte
38
39it is a bit of a gimmick however, you can do this easily
40with websocat:
41
42 λ websocat wss://jetstream1.us-east.fire.hose.cam/subscribe