nautechsystems/nautilus_trader · error · anyhow::Error

Invalid spec pair: {kv}

Error message

Invalid spec pair: {kv}

What it means

LoggingSpec::from_spec parses a comma-separated key=value spec string into a LoggingConfig. When a key is not one of the recognized flag keys (is_colored, print_config, use_tracing, bypass_logging, fileout_sync_on_flush, buffered_stdout, etc.) the parser aborts with this error. It means the spec string contains an unrecognized key or is malformed.

Source

Thrown at crates/common/src/logging/config.rs:224

        let mut config = Self::default();

        for kv in spec.split(';') {
            let kv = kv.trim();
            if kv.is_empty() {
                continue;
            }

            let Some((k, v)) = kv.split_once('=') else {
                // Handle bare flags (without =)
                match kv.to_lowercase().as_str() {
                    "log_components_only" => config.log_components_only = true,
                    "is_colored" => config.is_colored = true,
                    "print_config" => config.print_config = true,
                    "use_tracing" => config.use_tracing = true,
                    "bypass_logging" => config.bypass_logging = true,
                    "fileout_sync_on_flush" => config.fileout_sync_on_flush = true,
                    "buffered_stdout" => config.buffered_stdout = true,
                    _ => anyhow::bail!("Invalid spec pair: {kv}"),
                }
                continue;
            };

            let k = k.trim();
            let v = v.trim();
            let k_lower = k.to_lowercase();

            match k_lower.as_str() {
                "is_colored" => {
                    config.is_colored = parse_bool_value(v);
                }
                "log_components_only" => {
                    config.log_components_only = parse_bool_value(v);
                }
                "print_config" => {
                    config.print_config = parse_bool_value(v);
                }

View on GitHub (pinned to 18893faf8b)

Solutions

1. Check the spec string and correct the key spelling to one of the supported keys (is_colored, print_config, use_tracing, bypass_logging, fileout_sync_on_flush, buffered_stdout).
2. Verify each pair is formatted `key=value` with no stray separators or whitespace-only tokens.
3. Check the version of the crate you are using: some spec keys exist only in certain releases; consult the config module docs for that version.
4. Remove options that are not supported and set them programmatically on LoggingConfig instead.

Example fix

// before
let config = LoggingSpec::from_spec("color=true,print_config")?;
// after
let config = LoggingSpec::from_spec("is_colored=true,print_config=true")?;

const VALID_KEYS: [&str; 6] = ["is_colored", "print_config", "use_tracing", "bypass_logging", "fileout_sync_on_flush", "buffered_stdout"];
fn spec_keys_valid(spec: &str) -> bool {
    spec.split(',').all(|kv| {
        let key = kv.split('=').next().unwrap_or("").trim();
        VALID_KEYS.contains(&key)
    });
}

match LoggingSpec::from_spec(spec) {
    Ok(cfg) => cfg,
    Err(e) if e.to_string().contains("Invalid spec pair") => {
        eprintln!("bad logging spec '{spec}': {e}");
        LoggingSpec::default()
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: Calling from_spec (or the higher-level env/config parsing that delegates to it) with a spec pair whose key is not in the accepted set, e.g. `color=true` instead of `is_colored=true`, or a bare token like `verbose` without `=` that falls through to the flag/pair branches and fails.

Common situations: Typos in environment-variable-driven logging config (e.g. NAUTILUS_LOG spec strings), copying spec options from documentation of a different version where a key was renamed or removed, or accidentally passing free-form text as a spec.

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

• Tracing subscriber already initialized
• Logging has been shut down and cannot be re-initialized
• Global logging sender was already published
• Logging is running without a published sender
• Failed to initialize tracing subscriber: {e}

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/679d45a63e48efd8. Report an issue: GitHub.