shadowsocks/shadowsocks-rust · error

logging

Error message

logging

What it means

Panic while building the log4rs Config object in init_with_config: the builder chain .build(...) returned Err (e.g. duplicate logger names or an invalid appender/logger setup) and expect('logging') panics. This is the first of the two expect calls, on config construction rather than initialization.

Solutions

1. Ensure the programmatically built Config has unique logger and appender names
2. Print/log the generated config on failure instead of a bare expect
3. Validate the LogConfig inputs (level, format) before building the log4rs config
4. Check shadowsocks-rust updates for changes in init_with_config's builder logic

Example fix

// before
.build(Root::builder().appender("console").build(l2))
.expect("logging");
// after
.build(Root::builder().appender("console").build(l2))
.unwrap_or_else(|e| {
    eprintln!("invalid logging config: {}", e);
    std::process::exit(1);
})

// ensure logger/appender names passed into the builder are unique before building
assert_unique(&["shadowsocks_rust", "shadowsocks", "shadowsocks_service"]);

// build() returns Result and init_with_config expects it; wrap init in a fallible helper
let config = builder.build(root).map_err(|e| LoggingInitError(e))?;

When it happens

Trigger: init_with_config constructs a Config with appenders/loggers whose names collide or are invalid, causing ConfigBuilder::build to error before log4rs::init_config is reached.

Common situations: Bin-name-derived logger names duplicating the root/other loggers; programmatic LogConfig values producing zero or conflicting appenders; refactors changing logger name strings (shadowsocks_rust, shadowsocks, shadowsocks_service) into collisions.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• init logging with file
• dns
• Failed to create file writer for logging
• method
• missing manager config

AI-assisted analysis of shadowsocks/shadowsocks-rust@8eb0f0a65b (2026-09-09). Data as JSON: /api/errors/c8658e63f19951d2. Report an issue: GitHub.

Appendix: source

Thrown at src/logging/log4rs.rs:67

    let (l1, l2) = match debug_level {
        0 => (LevelFilter::Info, LevelFilter::Off),
        1 => (LevelFilter::Debug, LevelFilter::Off),
        2 => (LevelFilter::Trace, LevelFilter::Off),
        3 => (LevelFilter::Trace, LevelFilter::Debug),
        _ => (LevelFilter::Off, LevelFilter::Trace),
    };

    let config = match debug_level {
        0..=3 => logging_builder
            .logger(Logger::builder().build(bin_name, l1))
            .logger(Logger::builder().build("shadowsocks_rust", l1))
            .logger(Logger::builder().build("shadowsocks", l1))
            .logger(Logger::builder().build("shadowsocks_service", l1)),
        _ => logging_builder,
    }
    .build(Root::builder().appender("console").build(l2))
    .expect("logging");

    log4rs::init_config(config).expect("logging");
}

View on GitHub (pinned to 8eb0f0a65b)