Writing warn! and info! to different files

[jafioti]

I am using the rolling appender to write to files, but I would like to write warn and info messages to different paths, from two different rolling appenders. Here's what I'm doing now:

let file_appender = tracing_appender::rolling::minutely("./logs/debug", "prefix.log");
    let (non_blocking, _guard) = tracing_appender::non_blocking(file_appender);
    tracing_subscriber::fmt()
        .with_writer(non_blocking)
        .with_ansi(false)
        .with_max_level(Level::WARN)
        .init();

I tried to set a second appender as global, but you can only have one global writer at a time. Is there a way to split the output of info! to "/log/info" and warn to "/log/warn" ?

[hawkw]

Sending different kinds of events to different outputs can be accomplished with MakeWriter filtering. You can create a pair of rolling file appenders and combine them using the MakeWriterExt combinators.

In your case, to write warn and info messages to different rolling appenders, it might look something like this:

    use tracing_subscriber::fmt::writer::MakeWriterExt;

    let info_appender = tracing_appender::rolling::minutely("./logs/info", "prefix.log");
    let (info_appender, _info_guard) = tracing_appender::non_blocking(info_appender);
    let warn_appender = tracing_appender::rolling::minutely("./logs/info", "prefix.log");
    let (warn_appender, _warn_guard) = tracing_appender::non_blocking(warn_appender);

    let files = info_appender
        .with_min_level(Level::INFO)
        .or_else(warn_appender.with_max_level(Level::WARN));

    tracing_subscriber::fmt()
        .with_writer(files)
        .with_ansi(false)
        .with_max_level(Level::WARN)
        .init();

Also, note that the with_max_level filter you're adding to the subscriber itself will disable all INFO events...so the info file will be empty unless you remove that. :)

[jafioti]

Exactly what I wanted, thanks!

[hawkw]

Glad I could help!

We should probably also make it possible to combine the two files and then provide them both to a single non_blocking writer, so that you don't have to spin up a separate worker thread for each file. But, the current API doesn't really permit that yet.