Stats in json to stdout (new command line option --json)

[AndersSpringborg]

I extended the cli with a --json argument. This argument prints the result of a run in json, after a run is finished. It blocks other INFO logs, so it's easy to interoperable with other programs. Below is an example with jq

❯ python -m locust -f examples/locustfile.py --host http://localhost:80 --headless -u 10 -t 4s --json
[
    {
        "name": "/",
        "method": "GET",
        "last_request_timestamp": 1670363796.9102132,
        "start_time": 1670363793.665749,
        "num_requests": 8,
        "num_none_requests": 0,
        "num_failures": 0,
        "total_response_time": 61.882097012130544,
        "max_response_time": 18.852641980629414,
        "min_response_time": 3.2629000197630376,
        "total_content_length": 4920,
        "response_times": {
            "19": 1,
            "9": 1,
            "4": 3,
            "10": 1,
            "3": 1,
            "8": 1
        },
        "num_reqs_per_sec": {
            "1670363793": 1,
            "1670363794": 2,
            "1670363795": 1,
            "1670363796": 4
        },
        "num_fail_per_sec": {}
    }
]

❯ python -m locust -f examples/locustfile.py --host http://localhost:80 --headless -u 10 -t 4s --json | jq .[0].response_times
{
  "11": 2,
  "10": 1,
  "4": 4,
  "9": 1
}

Locust: 2.13.2.dev11
Python: 3.10.8

[cyberw]

Nice!

I think it makes more sense to send the output directly to stdout using print() instead of using logging. That removes the need to disable logging too.

Can you also add a test case? (either an integration test in test_main.py, or in test_stats.py or whatever it is called)

[AndersSpringborg]

Yeah I'll use print instead. That seems easier to maintain too.

I think INFO logging should still be disabled, as if you run locust in kubernetes (or other orchestration software, kubernetes combines stderr and stdout in their logging api. If you have a program that parses that log, still fails if locust fails (as it gets the error or warning log)

I'll make some integrations tests too. 🤠

[cyberw]

I think the user explicitly specifying --skip-log-setup or --loglevel ERROR when you need to suppress stderr logging is better. Changing the log level as a side effect of setting --json is not what I would expect, as a user (even though it may make sense in certain cases, like yours)

[AndersSpringborg]

I've made some integration tests, and deleted the part about skipping logging.

Merry Christmas 🎄

[cyberw]

Cool stuff, thanks!

[meeech]

@cyberw @AndersSpringborg out of curiosity, why not matching ENV_VAR for this option? Any particular reason? Would a pr to add that be welcome?