parse_json - differs parsing floats

[guusvw]

Hey dear VRL-folks 👋
I hope this is not a double posting, I only found issues regards parse_json for large ints, I'm having an issues as well for floats.

We're getting a JSON which contains the field ts and has in our test case the value 1626175065.5934923
after passing it to parse_json the object has the value of 1626175065.5934925, the last digit differs by 2.
I know, floats are hard & annoying, but is there some way to avoid/fix it?

$ message = "{\"level\":\"info\",\"ts\":1626175065.5934923,\"msg\":\"|200|   32.603µs /healthcheck\",\"statusCode\":200,\"request\":306,\"latency\":0.000032603,\"avgLatency\":0.004298489,\"ipPort\":\"1.1.1.1:12345\",\"method\":\"GET\",\"host\":\"1.1.1.1:8080\",\"path\":\"/healthcheck\",\"referer\":\"\"}"
"{\"level\":\"info\",\"ts\":1626175065.5934923,\"msg\":\"|200|   32.603µs /healthcheck\",\"statusCode\":200,\"request\":306,\"latency\":0.000032603,\"avgLatency\":0.004298489,\"ipPort\":\"1.1.1.1:12345\",\"method\":\"GET\",\"host\":\"1.1.1.1:8080\",\"path\":\"/healthcheck\",\"referer\":\"\"}"

$ obj, err = parse_json(message)

{ "avgLatency": 0.004298489, "host": "1.1.1.1:8080", "ipPort": "1.1.1.1:12345", "latency": 0.000032603, "level": "info", "method": "GET", "msg": "|200|   32.603µs /healthcheck", "path": "/healthcheck", "referer": "", "request": 306, "statusCode": 200, "ts": 1626175065.5934925 }

❯ bin/vector-0.36.1 --version
vector 0.36.1 (x86_64-apple-darwin 2857180 2024-03-11 14:32:52.417737479)

[jszwedko]

Hmm, interesting. I know floats have issues with representing certain numbers, but this doesn't appear to be the case for the specific example given: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=3d538d9f2ae192da51693bc12fdcfbfa

I believe we just defer to serde_json for deserialization, though, so I'm not sure why it is not preserving the precision.

[drmason13]

I jumped on this after seeing that it is in fact solvable through a feature in serde_json.
It's a non-default feature, and has been for almost 4 years now. I'm sure we won't be the only ones caught by this :)