i am trying to using tracing & tracing_subscriber with axum

it's my code snippet

main function:

fn main() -> Result<(), io::Error> {
    let rt = runtime::Builder::new_current_thread()
        .enable_io()
        .enable_time()
        .build()?;
    tracing_subscriber::fmt().event_format(format().json()).init();
     if let Err(e) = rt.block_on(axum_main()) {
        e.source();
    }
    Ok(())
}

and the function of axum_main()

let app: Router<()> = Router::new().route(
        "/",
        routing::get(|| {
            async {
                tracing::info!("wowo here");
                "HELLO,world"
            }.instrument(tracing::info_span!("hello_span"))
        }),
    );

    let addr: SocketAddr = "192.168.42.200:9090".parse().unwrap();
    let socket = TcpSocket::new_v4()?;

    #[cfg(all(unix, not(target_os = "solaris"), not(target_os = "illumos")))]
    {
        socket.set_reuseport(true)?;
        socket.set_reuseaddr(true)?;
    }
    socket.bind(addr)?;
    let listener = socket.listen(1024)?;

    let r = axum::serve(listener, app.into_make_service()).await?;

    Ok(r)

it's really a simple code, but when i use cargo run, and visit http://192.168.42.200:9090/ it report a panic with:

thread 'main' panicked at /root/.cargo/registry/src/rsproxy-e3de039b2554c837/tracing-subscriber-0.3.19/src/fmt/format/json.rs:197:49:
span 'hello_span' had malformed fields! this is a bug.
  error: EOF while parsing a value at line 1 column 0
  fields: FormattedFields { fields: "", formatter: tracing_subscriber::fmt::format::DefaultFields, was_ansi: true }
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/std/src/panicking.rs:692:5
   1: core::panicking::panic_fmt
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/panicking.rs:75:14
   2: <tracing_subscriber::fmt::format::json::SerializableSpan<Span,N> as serde::ser::Serialize>::serialize
             at /root/.cargo/registry/src/rsproxy-e3de039b2554c837/tracing-subscriber-0.3.19/src/fmt/format/json.rs:197:49
   3: <serde_json::ser::Compound<W,F> as serde::ser::SerializeMap>::serialize_value

The Goal: How can i resolve it (i want my log event output as json)? or Am I using it improperly?

when i switch this line: tracing_subscriber::fmt().event_format(format().json()).init() to tracing_subscriber::fmt().event_format(format()pact()).init() everythings works well

appendix: my Cargo.toml dependencies:

[dependencies]
axum = "0.8.1"
tokio = { version = "1.44.1", features = ["macros", "rt"] }
tracing = "0.1.41"
tracing-subscriber = {version = "0.3.19",features = ["env-filter","chrono","json"]}

i am trying to using tracing & tracing_subscriber with axum

it's my code snippet

main function:

fn main() -> Result<(), io::Error> {
    let rt = runtime::Builder::new_current_thread()
        .enable_io()
        .enable_time()
        .build()?;
    tracing_subscriber::fmt().event_format(format().json()).init();
     if let Err(e) = rt.block_on(axum_main()) {
        e.source();
    }
    Ok(())
}

and the function of axum_main()

let app: Router<()> = Router::new().route(
        "/",
        routing::get(|| {
            async {
                tracing::info!("wowo here");
                "HELLO,world"
            }.instrument(tracing::info_span!("hello_span"))
        }),
    );

    let addr: SocketAddr = "192.168.42.200:9090".parse().unwrap();
    let socket = TcpSocket::new_v4()?;

    #[cfg(all(unix, not(target_os = "solaris"), not(target_os = "illumos")))]
    {
        socket.set_reuseport(true)?;
        socket.set_reuseaddr(true)?;
    }
    socket.bind(addr)?;
    let listener = socket.listen(1024)?;

    let r = axum::serve(listener, app.into_make_service()).await?;

    Ok(r)

it's really a simple code, but when i use cargo run, and visit http://192.168.42.200:9090/ it report a panic with:

thread 'main' panicked at /root/.cargo/registry/src/rsproxy.cn-e3de039b2554c837/tracing-subscriber-0.3.19/src/fmt/format/json.rs:197:49:
span 'hello_span' had malformed fields! this is a bug.
  error: EOF while parsing a value at line 1 column 0
  fields: FormattedFields { fields: "", formatter: tracing_subscriber::fmt::format::DefaultFields, was_ansi: true }
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/std/src/panicking.rs:692:5
   1: core::panicking::panic_fmt
             at /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/panicking.rs:75:14
   2: <tracing_subscriber::fmt::format::json::SerializableSpan<Span,N> as serde::ser::Serialize>::serialize
             at /root/.cargo/registry/src/rsproxy.cn-e3de039b2554c837/tracing-subscriber-0.3.19/src/fmt/format/json.rs:197:49
   3: <serde_json::ser::Compound<W,F> as serde::ser::SerializeMap>::serialize_value

The Goal: How can i resolve it (i want my log event output as json)? or Am I using it improperly?

when i switch this line: tracing_subscriber::fmt().event_format(format().json()).init() to tracing_subscriber::fmt().event_format(format()pact()).init() everythings works well

appendix: my Cargo.toml dependencies:

[dependencies]
axum = "0.8.1"
tokio = { version = "1.44.1", features = ["macros", "rt"] }
tracing = "0.1.41"
tracing-subscriber = {version = "0.3.19",features = ["env-filter","chrono","json"]}

• rust
• rust-axum
• rust-tracing

1 Answer 1

Use this instead:

tracing_subscriber::fmt().json().init();

From this issue, the panic "is an unfortunate consequence of having separate field and event formatters". The JSON event formatter is expecting the JSON fields to be formatted a specific way, but you didn't have the matching .fmt_fields(...). The above does that all in one.