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//! Field formatters for [`tracing_subscriber`].
use std::error::Error;
use std::fmt::Debug;
use tracing::field::Field;
use tracing_subscriber::field::{RecordFields, Visit, VisitOutput};
use tracing_subscriber::fmt::format::{DefaultVisitor, FormatFields, Writer};
/// Visits only `dyn Error`.
struct ErrorVisitor<'a>(&'a mut dyn Visit);
// this just wraps an existing visitor, so if the trait methods gain a return type in the future,
// we want to just pass it through
#[allow(clippy::semicolon_if_nothing_returned)]
impl<'a> Visit for ErrorVisitor<'a> {
// do nothing
fn record_debug(&mut self, _field: &Field, _value: &dyn Debug) {}
fn record_f64(&mut self, _field: &Field, _value: f64) {}
fn record_i64(&mut self, _field: &Field, _value: i64) {}
fn record_u64(&mut self, _field: &Field, _value: u64) {}
fn record_i128(&mut self, _field: &Field, _value: i128) {}
fn record_u128(&mut self, _field: &Field, _value: u128) {}
fn record_bool(&mut self, _field: &Field, _value: bool) {}
fn record_str(&mut self, _field: &Field, _value: &str) {}
fn record_bytes(&mut self, _field: &Field, _value: &[u8]) {}
// format the error and use the inner visitor
fn record_error(&mut self, field: &Field, value: &(dyn Error + 'static)) {
use std::fmt;
use tor_error::ErrorReport as _;
/// Wrapper to add a `Debug` impl to something that implements `Display`.
struct DisplayToDebug<T: fmt::Display>(T);
impl<T: fmt::Display> fmt::Debug for DisplayToDebug<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&self.0, f)
}
}
// use `ErrorReport` to format the error
self.0.record_debug(field, &DisplayToDebug(value.report()))
}
}
/// Visits everything but `dyn Error`.
struct NonErrorVisitor<'a>(&'a mut dyn Visit);
// this just wraps an existing visitor, so if the trait methods gain a return type in the future,
// we want to just pass it through
#[allow(clippy::semicolon_if_nothing_returned)]
impl<'a> Visit for NonErrorVisitor<'a> {
// use the inner visitor
fn record_debug(&mut self, field: &Field, value: &dyn Debug) {
self.0.record_debug(field, value)
}
fn record_f64(&mut self, field: &Field, value: f64) {
self.0.record_f64(field, value)
}
fn record_i64(&mut self, field: &Field, value: i64) {
self.0.record_i64(field, value)
}
fn record_u64(&mut self, field: &Field, value: u64) {
self.0.record_u64(field, value)
}
fn record_i128(&mut self, field: &Field, value: i128) {
self.0.record_i128(field, value)
}
fn record_u128(&mut self, field: &Field, value: u128) {
self.0.record_u128(field, value)
}
fn record_bool(&mut self, field: &Field, value: bool) {
self.0.record_bool(field, value)
}
fn record_str(&mut self, field: &Field, value: &str) {
self.0.record_str(field, value)
}
fn record_bytes(&mut self, field: &Field, value: &[u8]) {
self.0.record_bytes(field, value)
}
// do nothing
fn record_error(&mut self, _field: &Field, _value: &(dyn Error + 'static)) {}
}
/// Log error fields after other fields.
pub(crate) struct ErrorsLastFieldFormatter;
impl<'writer> FormatFields<'writer> for ErrorsLastFieldFormatter {
fn format_fields<R: RecordFields>(
&self,
mut writer: Writer<'writer>,
fields: R,
) -> std::fmt::Result {
// we use a visitor from `tracing_subscriber` for formatting fields
let mut visitor = DefaultVisitor::new(writer.by_ref(), /* is_empty= */ true);
// record non-error fields first, then record error fields
fields.record(&mut NonErrorVisitor(&mut visitor));
fields.record(&mut ErrorVisitor(&mut visitor));
visitor.finish()?;
Ok(())
}
}
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