quickwit-oss/quickwit · error

time format description should be valid

Error message

time format description should be valid

What it means

This panic fires when `time::format_description::parse_borrowed::<2>` fails to parse the hard-coded format string `[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond digits:3]Z` used by the telemetry log timestamp formatter. The string is a compile-time constant in the source, so the panic can only occur if that constant was edited to an invalid format description (bad component syntax, invalid modifier, or exceeding the 2-item inline capacity... note the string parses as one item, so capacity is not the issue). It protects the logging subsystem from silently emitting malformed timestamps.

Source

Thrown at quickwit/quickwit-telemetry-exporters/src/logs.rs:36

use serde_json::{Map, Value};
use time::format_description::BorrowedFormatItem;
use tracing::field::{Field, Visit};
use tracing::{Event, Subscriber};
use tracing_subscriber::field::RecordFields;
use tracing_subscriber::fmt::FmtContext;
use tracing_subscriber::fmt::format::{
    DefaultFields, Format, FormatEvent, FormatFields, Full, Json, JsonFields, Writer,
};
use tracing_subscriber::fmt::time::UtcTime;
use tracing_subscriber::registry::LookupSpan;

/// We do not rely on the RFC3339 implementation, because it has a nanosecond precision.
/// See discussion here: https://github.com/time-rs/time/discussions/418
pub(crate) fn time_formatter() -> UtcTime<Vec<BorrowedFormatItem<'static>>> {
    let time_format = time::format_description::parse_borrowed::<2>(
        "[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond digits:3]Z",
    )
    .expect("time format description should be valid");
    UtcTime::new(time_format)
}

pub(crate) enum EventFormat<'a> {
    Full(Format<Full, UtcTime<Vec<BorrowedFormatItem<'a>>>>),
    Json(Format<Json>),
    Ddg(DdgFormat),
}

impl EventFormat<'_> {
    /// Gets the log format from the environment variable `QW_LOG_FORMAT`.
    pub(crate) fn get_from_env() -> Self {
        match get_from_env_opt::<String>("QW_LOG_FORMAT", false)
            .as_deref()
            .map(str::to_ascii_lowercase)
            .as_deref()
        {
            Some("json") => EventFormat::Json(tracing_subscriber::fmt::format().json()),

View on GitHub (pinned to a39730c5cd)

Solutions

1. Check git history of quickwit/quickwit-telemetry-exporters/src/logs.rs — restore the original format string `[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond digits:3]Z`
2. Validate your new format string with `time::format_description::parse_borrowed::<2>(...)` in a unit test before committing it
3. If a `time` crate upgrade broke it, consult the time-rs changelog for renamed/removed format components and fix the description accordingly
4. Use `time::macros::format_description!` instead of runtime parsing to turn this panic into a compile-time error

Example fix

// before (invalid component)
"[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond digits:three]Z"
// after
"[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond digits:3]Z"

#[test]
fn time_format_is_valid() {
    time::format_description::parse_borrowed::<2>(
        "[year]-[month]-[day]T[hour]:[minute]:[second].[subsecond digits:3]Z",
    ).expect("time format description should be valid");
}

When it happens

Trigger: Calling `time_formatter()` (directly, or via `get_from_env`/`capture_full_log` which configure the tracing subscriber) after someone modified the format string literal in quickwit-telemetry-exporters/src/logs.rs to an invalid `time` crate format description.

Common situations: A contributor edits the timestamp format to change precision or timezone representation and uses invalid `time`-crate syntax (e.g. `[subsecond digits:9]` misspelled, unknown component, wrong modifier); upgrading the `time` crate to a version that removed or renamed a format component.

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• Encountered unknown command: code {other}

AI-assisted analysis of quickwit-oss/quickwit@a39730c5cd (2026-09-08). Data as JSON: /api/errors/05a05efe2201a3f8. Report an issue: GitHub.