Error: ENOENT: no such file or directory, rename '~/.ssb/gossip.json~' -> '~/.ssb/gossip.json'

[christianbundy]

I was using Patchbay this morning and noticed that Electron and my browser froze at the same time while using scuttlebot@13.2.2. I think I tried to close Electron after a few seconds, but it may have crashed, and I found these logs:

> patchbay@7.15.6 start /home/christianbundy/src/ssbc/patchbay
> electron index.js -- --title patchbay

STARTING electron
STARTING SBOT
LOADING config
Listening on undefined:8008 (multiserver net plugin)
listening on socket unix:/home/christianbundy/.ssb/socket
ssb-friends: stream legacy api used
Trace: deprecated api used: ssb-ref.parseAddress
    at Object.parseAddress (/home/christianbundy/src/ssbc/patchbay/node_modules/ssb-ref/index.js:96:15)
    at Socket.<anonymous> (/home/christianbundy/src/ssbc/patchbay/node_modules/scuttlebot/plugins/local.js:55:22)
    at Socket.emit (events.js:182:13)
    at Socket.<anonymous> (/home/christianbundy/src/ssbc/patchbay/node_modules/broadcast-stream/index.js:51:12)
    at Socket.emit (events.js:182:13)
    at UDP.onMessage [as onmessage] (dgram.js:673:8)
{ [Error: ENOENT: no such file or directory, rename '/home/christianbundy/.ssb/gossip.json~' -> '/home/christianbundy/.ssb/gossip.json']
  errno: -2,
  code: 'ENOENT',
  syscall: 'rename',
  path: '/home/christianbundy/.ssb/gossip.json~',
  dest: '/home/christianbundy/.ssb/gossip.json' }
{ [Error: ENOENT: no such file or directory, rename '/home/christianbundy/.ssb/gossip.json~' -> '/home/christianbundy/.ssb/gossip.json']
  errno: -2,
  code: 'ENOENT',
  syscall: 'rename',
  path: '/home/christianbundy/.ssb/gossip.json~',
  dest: '/home/christianbundy/.ssb/gossip.json' }
{ [Error: ENOENT: no such file or directory, rename '/home/christianbundy/.ssb/gossip.json~' -> '/home/christianbundy/.ssb/gossip.json']
  errno: -2,
  code: 'ENOENT',
  syscall: 'rename',
  path: '/home/christianbundy/.ssb/gossip.json~',
  dest: '/home/christianbundy/.ssb/gossip.json' }
{ [Error: ENOENT: no such file or directory, rename '/home/christianbundy/.ssb/gossip.json~' -> '/home/christianbundy/.ssb/gossip.json']
  errno: -2,
  code: 'ENOENT',
  syscall: 'rename',
  path: '/home/christianbundy/.ssb/gossip.json~',
  dest: '/home/christianbundy/.ssb/gossip.json' }

I checked my gossip.json file and I think there may have been some changes made: a few of them near the top of the file have the { duration, stateChange, client, ping, failure } keys, but most of them now look like this:

{
  "host": "diefreien.club",
  "port": 8008,
  "key": "@Y2fxCQla30qvtLJufJ57Im0on1QO72H5KECXio5xQZs=.ed25519",
  "address": "net:diefreien.club:8008~shs:Y2fxCQla30qvtLJufJ57Im0on1QO72H5KECXio5xQZs=",
  "source": "pub",
  "announcers": 523,
  "duration": null
}

After a quick git grep '~' I can't seem to figure out why a rename was happening, any chance someone else knows?

[christianbundy]

/shrug

[dominictarr]

why there is a rename: writing to a temp file and renaming it to the target file gives you an atomic write https://en.wikipedia.org/wiki/Atomicity_(database_systems)

When writing a file, if the file is more than blocks it's possible that there is a failure causing the file to not be completely written. If you wrote straight to the target file, this would mean your original file is now invalid. If you write to a temp file, you can check it's all fully there and correct, then renaming it over the original file is a single operation that cannot fail part way through (it can only fully fail or fully succeed).

[christianbundy]

Oh, that makes perfect sense, thanks! I guess this was probably coming from atomic-file, which explains why I couldn't find any relevant code doing file renames in the SSBC org. Thanks again, I was convinced I'd never find an answer for this.

[dominictarr]

I learnt about that technique in this blogpost, I think: https://www.davidpashley.com/articles/writing-robust-shell-scripts/