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logging.rs
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logging.rs
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//! Defines the default logging behavior for Hoard, using [`tracing`].
//!
//! [`Formatter`] does the heavy lifting of formatting the output.
//!
//! [`get_subscriber`] returns a default [`SubscriberBuilder`] that can be used without any changes.
use std::collections::BTreeMap;
use std::fmt;
use std::str::FromStr;
use tracing::field::{Field, Visit};
use tracing::{Event, Level, Subscriber};
use tracing_subscriber::field::RecordFields;
use tracing_subscriber::fmt::format::Writer;
use tracing_subscriber::fmt::{
FmtContext, FormatEvent, FormatFields, FormattedFields, SubscriberBuilder,
};
use tracing_subscriber::registry::LookupSpan;
use tracing_subscriber::{EnvFilter, FmtSubscriber};
const LOG_ENV: &str = "HOARD_LOG";
const EMPTY_PREFIX: &str = " ";
struct FormatterVisitor {
message: Option<String>,
fields: BTreeMap<String, String>,
is_terse: bool,
}
impl FormatterVisitor {
fn new(is_terse: bool) -> Self {
Self {
message: None,
fields: BTreeMap::new(),
is_terse,
}
}
}
impl Visit for FormatterVisitor {
fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
if self.message.is_none() && field.name() == "message" {
self.message = Some(format!("{value:?}"));
} else {
let value = if self.is_terse {
format!("{value:?}")
} else {
format!("{value:#?}")
};
self.fields.insert(field.name().to_string(), value);
}
}
}
/// The default log formatter for Hoard.
#[derive(Clone, Debug)]
pub struct Formatter {
max_level: Level,
}
impl<'writer> FormatFields<'writer> for Formatter {
fn format_fields<R: RecordFields>(
&self,
mut writer: Writer<'writer>,
fields: R,
) -> fmt::Result {
let is_terse = matches!(self.max_level, Level::ERROR | Level::WARN | Level::INFO);
let mut visitor = FormatterVisitor::new(is_terse);
fields.record(&mut visitor);
let empty_prefix_newline = format!("\n{EMPTY_PREFIX}");
let longest_name_len = visitor.fields.keys().map(String::len).max().unwrap_or(0);
let fields = visitor
.fields
.iter()
.map(|(name, value)| {
let value = value
.split('\n')
.collect::<Vec<_>>()
.join(&empty_prefix_newline);
if is_terse {
format!("{name}={value}")
} else {
let padding = " ".repeat(longest_name_len - name.len());
format!("{padding}{name} = {value}")
}
})
.collect::<Vec<_>>();
let fields_output = if is_terse {
fields.join(", ")
} else {
let fields = fields.join(&format!("\n{EMPTY_PREFIX} "));
if fields.is_empty() {
fields
} else {
format!("\n{EMPTY_PREFIX}where {fields}")
}
};
if let Some(msg) = visitor.message {
write!(writer, "{msg}")?;
if is_terse && !fields_output.is_empty() {
write!(writer, ": ")?;
}
}
write!(writer, "{fields_output}")
}
}
#[allow(single_use_lifetimes)]
impl<S, N> FormatEvent<S, N> for Formatter
where
S: Subscriber + for<'a> LookupSpan<'a>,
N: for<'a> FormatFields<'a> + 'static,
{
fn format_event(
&self,
ctx: &FmtContext<'_, S, N>,
writer: Writer<'_>,
event: &Event<'_>,
) -> fmt::Result {
let mut writer = writer;
let metadata = event.metadata();
// Only show prefix if debug or higher verbosity, or warning/error
if self.max_level >= Level::DEBUG || metadata.level() != &Level::INFO {
write!(writer, "{} {}: ", metadata.level(), metadata.target())?;
}
// Write message
// TODO: ANSIfy?
ctx.field_format().format_fields(writer.by_ref(), event)?;
writeln!(writer)?;
// Format spans only if tracing verbosity
if matches!(self.max_level, Level::TRACE | Level::DEBUG) {
if let Some(scope) = ctx.event_scope() {
for span in scope.from_root() {
write!(writer, "{}at {}", EMPTY_PREFIX, span.name())?;
let ext = span.extensions();
let fields = ext
.get::<FormattedFields<N>>()
.expect("should never be `None`")
.to_string();
if !fields.is_empty() {
// join string matches the above write!()
let fields = fields.split('\n').collect::<Vec<_>>().join("\n ");
write!(writer, ": {fields}")?;
}
writeln!(writer)?;
}
}
// Add extra newline for easier reading
writeln!(writer)
} else {
Ok(())
}
}
}
/// Returns a [`SubscriberBuilder`] with the default settings for Hoard.
pub fn get_subscriber() -> SubscriberBuilder<Formatter, Formatter, EnvFilter> {
let max_level = {
let env_str = std::env::var(LOG_ENV).unwrap_or_else(|_| String::new());
// Get the last item that is only a level
let level_opt = env_str
.split(',')
.map(str::trim)
.rev()
.map(FromStr::from_str)
.find_map(Result::ok);
level_opt.unwrap_or({
if cfg!(debug_assertions) {
Level::DEBUG
} else {
Level::INFO
}
})
};
let env_filter = EnvFilter::try_from_env(LOG_ENV)
.unwrap_or_else(|_| EnvFilter::default().add_directive(max_level.into()));
FmtSubscriber::builder()
.with_env_filter(env_filter)
.event_format(Formatter { max_level })
.fmt_fields(Formatter { max_level })
}