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subscriber: record error sources in fmt layer with JSON format #3317

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af13a08
record error sources for json format
stijnherfst Jun 17, 2025
4e06dad
format
stijnherfst Jun 17, 2025
32c00ed
fix missing .into()
stijnherfst Jun 17, 2025
d457290
Merge branch 'main' into json-record-error
stijnherfst Jun 23, 2025
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37 changes: 37 additions & 0 deletions tracing-serde/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -441,6 +441,43 @@ where
self.state = self.serializer.serialize_entry(field.name(), &value)
}
}

fn record_error(&mut self, field: &Field, value: &(dyn std::error::Error + 'static)) {
if self.state.is_ok() {
self.state = self
.serializer
.serialize_entry(field.name(), &format_args!("{}", value));

if self.state.is_ok() {
if let Some(source) = value.source() {
#[derive(Clone, Copy)]
struct ErrorSourceSerializeSeq<'a> {
current: &'a (dyn std::error::Error + 'static),
}

impl serde::Serialize for ErrorSourceSerializeSeq<'_> {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: serde::Serializer,
{
let mut seq = serializer.serialize_seq(None)?;
let mut curr = Some(self.current);
while let Some(curr_err) = curr {
seq.serialize_element(&format_args!("{}", curr_err))?;
curr = curr_err.source();
}
seq.end()
}
}

self.state = self.serializer.serialize_entry(
&format_args!("{}.sources", field.name()),
&ErrorSourceSerializeSeq { current: source },
);
}
}
}
}
}

/// Implements `tracing_core::field::Visit` for some `serde::ser::SerializeStruct`.
Expand Down
127 changes: 114 additions & 13 deletions tracing-subscriber/src/fmt/format/json.rs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ use crate::{
};
use serde::ser::{SerializeMap, Serializer as _};
use serde_json::Serializer;
use std::borrow::Cow;
use std::{
collections::BTreeMap,
fmt::{self, Write},
Expand Down Expand Up @@ -405,7 +406,7 @@ impl<'a> FormatFields<'a> for JsonFields {
// then, we could store fields as JSON values, and add to them
// without having to parse and re-serialize.
let mut new = String::new();
let map: BTreeMap<&'_ str, serde_json::Value> =
let map: BTreeMap<Cow<'_, str>, serde_json::Value> =
serde_json::from_str(current).map_err(|_| fmt::Error)?;
let mut v = JsonVisitor::new(&mut new);
v.values = map;
Expand All @@ -422,7 +423,7 @@ impl<'a> FormatFields<'a> for JsonFields {
/// [visitor]: crate::field::Visit
/// [`MakeVisitor`]: crate::field::MakeVisitor
pub struct JsonVisitor<'a> {
values: BTreeMap<&'a str, serde_json::Value>,
values: BTreeMap<Cow<'a, str>, serde_json::Value>,
writer: &'a mut dyn Write,
}

Expand Down Expand Up @@ -460,7 +461,7 @@ impl crate::field::VisitOutput<fmt::Result> for JsonVisitor<'_> {
let mut ser_map = serializer.serialize_map(None)?;

for (k, v) in self.values {
ser_map.serialize_entry(k, &v)?;
ser_map.serialize_entry(&*k, &v)?;
}

ser_map.end()
Expand Down Expand Up @@ -492,42 +493,63 @@ impl field::Visit for JsonVisitor<'_> {
}
};

self.values.insert(field.name(), value);
self.values.insert(field.name().into(), value);
}

/// Visit a double precision floating point value.
fn record_f64(&mut self, field: &Field, value: f64) {
self.values
.insert(field.name(), serde_json::Value::from(value));
.insert(field.name().into(), serde_json::Value::from(value));
}

/// Visit a signed 64-bit integer value.
fn record_i64(&mut self, field: &Field, value: i64) {
self.values
.insert(field.name(), serde_json::Value::from(value));
.insert(field.name().into(), serde_json::Value::from(value));
}

/// Visit an unsigned 64-bit integer value.
fn record_u64(&mut self, field: &Field, value: u64) {
self.values
.insert(field.name(), serde_json::Value::from(value));
.insert(field.name().into(), serde_json::Value::from(value));
}

/// Visit a boolean value.
fn record_bool(&mut self, field: &Field, value: bool) {
self.values
.insert(field.name(), serde_json::Value::from(value));
.insert(field.name().into(), serde_json::Value::from(value));
}

/// Visit a string value.
fn record_str(&mut self, field: &Field, value: &str) {
self.values
.insert(field.name(), serde_json::Value::from(value));
.insert(field.name().into(), serde_json::Value::from(value));
}

fn record_bytes(&mut self, field: &Field, value: &[u8]) {
self.values
.insert(field.name(), serde_json::Value::from(value));
.insert(field.name().into(), serde_json::Value::from(value));
}

fn record_error(&mut self, field: &Field, value: &(dyn std::error::Error + 'static)) {
self.values.insert(
field.name().into(),
serde_json::Value::from(value.to_string()),
);

if let Some(source) = value.source() {
let mut sources = Vec::new();
let mut curr = Some(source);
while let Some(curr_err) = curr {
sources.push(serde_json::Value::from(curr_err.to_string()));
curr = curr_err.source();
}

self.values.insert(
format!("{}.sources", field.name()).into(),
serde_json::Value::Array(sources),
);
}
}

fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
Expand All @@ -536,12 +558,14 @@ impl field::Visit for JsonVisitor<'_> {
#[cfg(feature = "tracing-log")]
name if name.starts_with("log.") => (),
name if name.starts_with("r#") => {
self.values
.insert(&name[2..], serde_json::Value::from(format!("{:?}", value)));
self.values.insert(
(&name[2..]).into(),
serde_json::Value::from(format!("{:?}", value)),
);
}
name => {
self.values
.insert(name, serde_json::Value::from(format!("{:?}", value)));
.insert(name.into(), serde_json::Value::from(format!("{:?}", value)));
}
};
}
Expand Down Expand Up @@ -827,6 +851,83 @@ mod test {
});
}

#[test]
fn json_field_record_error() {
let buffer = MockMakeWriter::default();
let subscriber = crate::fmt()
.json()
.with_writer(buffer.clone())
.with_span_events(FmtSpan::NEW)
.finish();

#[derive(Debug)]
struct Error {
message: &'static str,
source: Option<Box<Error>>,
}

impl std::fmt::Display for Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}", self.message)
}
}

impl std::error::Error for Error {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
self.source.as_ref().map(|e| e.as_ref() as _)
}
}

let error = Error {
message: "outer",
source: Some(
Error {
message: "middle",
source: Some(
Error {
message: "inner",
source: None,
}
.into(),
),
}
.into(),
),
};

with_default(subscriber, || {
// Event: `tracing_serde::SerdeMapVisitor`
{
tracing::info!(error = &error as &dyn std::error::Error, "event");
let event = parse_as_json(&buffer);

println!("event {:#?}", event);

assert_eq!(event["fields"]["message"], "event");
assert_eq!(event["fields"]["error"], "outer");
assert_eq!(
event["fields"]["error.sources"].as_array().unwrap().len(),
2
);
assert_eq!(event["fields"]["error.sources"][0], "middle");
assert_eq!(event["fields"]["error.sources"][1], "inner");
}

// Span: `tracing_subscriber::fmt::json::JsonVisitor`
{
let _span =
tracing::info_span!("parent_span", error = &error as &dyn std::error::Error);
let event = parse_as_json(&buffer);

assert_eq!(event["span"]["name"], "parent_span");
assert_eq!(event["span"]["error"], "outer");
assert_eq!(event["span"]["error.sources"].as_array().unwrap().len(), 2);
assert_eq!(event["span"]["error.sources"][0], "middle");
assert_eq!(event["span"]["error.sources"][1], "inner");
}
})
}

fn parse_as_json(buffer: &MockMakeWriter) -> serde_json::Value {
let buf = String::from_utf8(buffer.buf().to_vec()).unwrap();
let json = buf
Expand Down