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use tracing::{span::Attributes, Id, Subscriber};
use tracing_subscriber::{layer::Context, registry::LookupSpan, Layer};
pub const PREFIX_LOG_SPAN: &str = "substrate-log-prefix";
pub struct PrefixLayer;
impl<S> Layer<S> for PrefixLayer
where
S: Subscriber + for<'a> LookupSpan<'a>,
{
fn new_span(&self, attrs: &Attributes<'_>, id: &Id, ctx: Context<'_, S>) {
let span = match ctx.span(id) {
Some(span) => span,
None => {
debug_assert!(
false,
"newly created span with ID {:?} did not exist in the registry; this is a bug!",
id
);
return
},
};
if span.name() != PREFIX_LOG_SPAN {
return
}
let mut extensions = span.extensions_mut();
if extensions.get_mut::<Prefix>().is_none() {
let mut s = String::new();
let mut v = PrefixVisitor(&mut s);
attrs.record(&mut v);
if !s.is_empty() {
let fmt_fields = Prefix(s);
extensions.insert(fmt_fields);
}
}
}
}
struct PrefixVisitor<'a, W: std::fmt::Write>(&'a mut W);
macro_rules! write_node_name {
($method:ident, $type:ty, $format:expr) => {
fn $method(&mut self, field: &tracing::field::Field, value: $type) {
if field.name() == "name" {
let _ = write!(self.0, $format, value);
}
}
};
}
impl<'a, W: std::fmt::Write> tracing::field::Visit for PrefixVisitor<'a, W> {
write_node_name!(record_debug, &dyn std::fmt::Debug, "[{:?}] ");
write_node_name!(record_str, &str, "[{}] ");
write_node_name!(record_i64, i64, "[{}] ");
write_node_name!(record_u64, u64, "[{}] ");
write_node_name!(record_bool, bool, "[{}] ");
}
#[derive(Debug)]
pub(crate) struct Prefix(String);
impl Prefix {
pub(crate) fn as_str(&self) -> &str {
self.0.as_str()
}
}