All logs output to stderr by default, including successful requests

I'm noticing that all logs, including normal, successful request logs with 200 status, are outputted to stderr by default, even though these logs do not indicate any errors.

To verify this, I ran a clean local instance of Mercure with the following command:

docker run \
    -e MERCURE_PUBLISHER_JWT_KEY='!ChangeThisMercureHubJWTSecretKey!' \
    -e MERCURE_SUBSCRIBER_JWT_KEY='!ChangeThisMercureHubJWTSecretKey!' \
    -p 80:80 \
    -p 443:443 \
    dunglas/mercure caddy run --config /etc/caddy/dev.Caddyfile \
    > stdout.txt 2> stderr.txt

When I accessed the Mercure UI in my browser and repeatedly clicked the “Subscribe to topic” button, I observed that stderr.txt was filling up with logs, while stdout.txt remained empty. This behavior suggests that all request logs, even for successful 200 responses, are being directed to stderr.

Could you confirm if this is the expected behavior, or if there’s a configuration option I might be missing to correctly separate normal request logs (to stdout) from actual error logs (to stderr)?

Thank you for your help in understanding this behavior.

Example of logs when I click 'subscribe to topic':

2024-11-12 17:15:14 {"level":"info","ts":1731428114.7049754,"logger":"http.handlers.mercure","msg":"LocalSubscriber disconnected","subscriber":{"id":"urn:uuid:d5669788-d3a9-48e3-9752-b7e08f09540c","last_event_id":"","remote_addr":"192.168.65.1:41307","topic_selectors":["https://example.com/my-private-topic","{scheme}://{+host}/demo/books/{id}.jsonld","/.well-known/mercure/subscriptions{/topic}{/subscriber}"],"topics":["https://example.com/my-private-topic"]}}
2024-11-12 17:15:14 {"level":"info","ts":1731428114.7051046,"logger":"http.log.access.log0","msg":"handled request","request":{"remote_ip":"192.168.65.1","remote_port":"41307","client_ip":"192.168.65.1","proto":"HTTP/2.0","method":"GET","host":"localhost","uri":"/.well-known/mercure?topic=https%3A%2F%2Fexample.com%2Fmy-private-topic","headers":{"Authorization":["REDACTED"],"User-Agent":["Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36"],"Sec-Ch-Ua":["\"Chromium\";v=\"130\", \"Google Chrome\";v=\"130\", \"Not?A_Brand\";v=\"99\""],"Sec-Fetch-Site":["same-origin"],"Sec-Fetch-Dest":["empty"],"Accept-Encoding":["gzip, deflate, br, zstd"],"Accept-Language":["en-US,en-DE;q=0.9,en;q=0.8,de;q=0.7,hr;q=0.6"],"Sec-Ch-Ua-Platform":["\"macOS\""],"Sec-Ch-Ua-Mobile":["?0"],"Sec-Fetch-Mode":["cors"],"Referer":["https://localhost/.well-known/mercure/ui/"],"Priority":["u=1, i"],"Accept":["text/event-stream"]},"tls":{"resumed":false,"version":772,"cipher_suite":4865,"proto":"h2","server_name":"localhost"}},"bytes_read":0,"user_id":"","duration":0.191722917,"size":2,"status":200,"resp_headers":{"Server":["Caddy"],"X-Frame-Options":["DENY"],"Content-Type":["text/event-stream"],"Pragma":["no-cache"],"X-Accel-Buffering":["no"],"Expire":["0"],"Alt-Svc":["h3=\":443\"; ma=2592000"],"X-Content-Type-Options":["nosniff"],"X-Xss-Protection":["1; mode=block"],"Content-Security-Policy":["default-src 'self' mercure.rocks cdn.jsdelivr.net"],"Connection":["keep-alive"],"Cache-Control":["private, no-cache, no-store, must-revalidate, max-age=0"]}}
2024-11-12 17:15:14 {"level":"info","ts":1731428114.7223518,"logger":"http.handlers.mercure","msg":"New subscriber","subscriber":{"id":"urn:uuid:efba2997-a2cc-4a0a-9aa3-5dd1f95db9ac","last_event_id":"","remote_addr":"192.168.65.1:41307","topic_selectors":["https://example.com/my-private-topic","{scheme}://{+host}/demo/books/{id}.jsonld","/.well-known/mercure/subscriptions{/topic}{/subscriber}"],"topics":["https://example.com/my-private-topic"]}}

dunglas / mercure

All logs output to stderr by default, including successful requests #983