fix: Report error using OTel convention

Author: cijothomas

opentelemetry-appender-tracing/CHANGELOG.md

@@ -48,6 +48,10 @@ when conversion is feasible. Otherwise stored as
 allocation when values can be represented in their original types.
 - Byte arrays are stored as `opentelemetry::logs::AnyValue::Bytes` instead
 of string.
+- `Error` fields are reported using attribute named "exception.message". For
+  example, the below will now report an attribute named "exception.message",
+  instead of previously reporting the user provided attribute "error".
+  `error!(....error = &OTelSdkError::AlreadyShutdown as &dyn std::error::Error...)`
 - perf - small perf improvement by avoiding string allocation of `target`
 
 ## 0.28.1

opentelemetry-appender-tracing/src/layer.rs

@@ -80,6 +80,18 @@ impl<LR: LogRecord> tracing::field::Visit for EventVisitor<'_, LR> {
         }
     }
 
+    fn record_error(
+        &mut self,
+        _field: &tracing_core::Field,
+        value: &(dyn std::error::Error + 'static),
+    ) {
+        self.log_record.add_attribute(
+            Key::new("exception.message"),
+            AnyValue::from(value.to_string()),
+        );
+        // No ability to get exception.stacktrace or exception.type from the error today.
+    }
+
     fn record_bytes(&mut self, field: &tracing_core::Field, value: &[u8]) {
         self.log_record
             .add_attribute(Key::new(field.name()), AnyValue::from(value));
@@ -247,7 +259,7 @@ mod tests {
     use opentelemetry::trace::{TraceContextExt, TraceFlags, Tracer};
     use opentelemetry::InstrumentationScope;
     use opentelemetry::{logs::AnyValue, Key};
-    use opentelemetry_sdk::error::OTelSdkResult;
+    use opentelemetry_sdk::error::{OTelSdkError, OTelSdkResult};
     use opentelemetry_sdk::logs::{InMemoryLogExporter, LogProcessor};
     use opentelemetry_sdk::logs::{LogBatch, LogExporter};
     use opentelemetry_sdk::logs::{SdkLogRecord, SdkLoggerProvider};
@@ -355,7 +367,7 @@ mod tests {
         let big_u64value: u64 = u64::MAX;
         let small_usizevalue: usize = 42;
         let big_usizevalue: usize = usize::MAX;
-        error!(name: "my-event-name", target: "my-system", event_id = 20, bytes = &b"abc"[..], small_u64value, big_u64value, small_usizevalue, big_usizevalue, user_name = "otel", user_email = "[email protected]");
+        error!(name: "my-event-name", target: "my-system", event_id = 20, bytes = &b"abc"[..], error = &OTelSdkError::AlreadyShutdown as &dyn std::error::Error, small_u64value, big_u64value, small_usizevalue, big_usizevalue, user_name = "otel", user_email = "[email protected]");
         assert!(logger_provider.force_flush().is_ok());
 
         // Assert TODO: move to helper methods
@@ -386,9 +398,9 @@ mod tests {
 
         // Validate attributes
         #[cfg(not(feature = "experimental_metadata_attributes"))]
-        assert_eq!(log.record.attributes_iter().count(), 8);
+        assert_eq!(log.record.attributes_iter().count(), 9);
         #[cfg(feature = "experimental_metadata_attributes")]
-        assert_eq!(log.record.attributes_iter().count(), 12);
+        assert_eq!(log.record.attributes_iter().count(), 13);
         assert!(attributes_contains(
             &log.record,
             &Key::new("event_id"),
@@ -404,6 +416,11 @@ mod tests {
             &Key::new("user_email"),
             &AnyValue::String("[email protected]".into())
         ));
+        assert!(attributes_contains(
+            &log.record,
+            &Key::new("exception.message"),
+            &AnyValue::String(OTelSdkError::AlreadyShutdown.to_string().into())
+        ));
         assert!(attributes_contains(
             &log.record,
             &Key::new("small_u64value"),

opentelemetry-appender-tracing/src/lib.rs

@@ -1 +1,8 @@
+/// This module provides integration/bridge between OpenTelemetry and the `tracing` crate.
+/// TODO: Fill details
+/// 1. How is this different from tracing-opentelemetry crate?
+/// 2. How to use this crate?
+/// 3. What are the stability guarantees? How are fields mapped?
+/// 4. What are the limitations?
+/// 
 pub mod layer;