feat: otel feature, writing the OTel trace ID

tracing-subscriber/Cargo.toml

@@ -36,6 +36,7 @@ valuable = ["tracing-core/valuable", "valuable_crate", "valuable-serde", "tracin
 # Enables support for local time when using the `time` crate timestamp
 # formatters.
 local-time = ["time/local-offset"]
+otel = ["opentelemetry"]
 
 [dependencies]
 tracing-core = { path = "../tracing-core", version = "0.1.30", default-features = false }
@@ -64,6 +65,9 @@ parking_lot = { version = "0.12.1", optional = true }
 sharded-slab = { version = "0.1.4", optional = true }
 thread_local = { version = "1.1.4", optional = true }
 
+# otel
+opentelemetry = { version = "0.19", optional = true, default-features = false }
+
 [target.'cfg(tracing_unstable)'.dependencies]
 valuable_crate = { package = "valuable", version = "0.1.0", optional = true, default-features = false }
 valuable-serde = { version = "0.1.0", optional = true, default-features = false }

tracing-subscriber/src/fmt/fmt_layer.rs

@@ -311,10 +311,10 @@ impl<S, N, E, W> Layer<S, N, E, W> {
     /// By default, `fmt::Layer` will write any `FormatEvent`-internal errors to
     /// the writer. These errors are unlikely and will only occur if there is a
     /// bug in the `FormatEvent` implementation or its dependencies.
-    /// 
+    ///
     /// If writing to the writer fails, the error message is printed to stderr
     /// as a fallback.
-    /// 
+    ///
     /// [`FormatEvent`]: crate::fmt::FormatEvent
     pub fn log_internal_errors(self, log_internal_errors: bool) -> Self {
         Self {
@@ -623,6 +623,16 @@ impl<S, T, W> Layer<S, format::JsonFields, format::Format<format::Json, T>, W> {
             ..self
         }
     }
+
+    /// Set the function to optionally make an OTel `TraceId`.
+    #[cfg(feature = "otel")]
+    pub fn with_make_trace_id(self, make_trace_id: Box<dyn format::MakeTraceId>) -> Self {
+        Layer {
+            fmt_event: self.fmt_event.with_make_trace_id(make_trace_id),
+            ..self
+        }
+    }
+
 }
 
 impl<S, N, E, W> Layer<S, N, E, W> {

tracing-subscriber/src/fmt/format/json.rs

@@ -321,6 +321,13 @@ where
                     .serialize_entry("threadId", &format!("{:?}", std::thread::current().id()))?;
             }
 
+            #[cfg(feature = "otel")]
+            if let Some((make_trace_id, current_span)) = self.make_trace_id.as_ref().zip(current_span) {
+                if let Some(trace_id) = make_trace_id(current_span.extensions()) {
+                    serializer.serialize_entry("trace_id", &trace_id.to_string())?;
+                }
+            }
+
             serializer.end()
         };
 

tracing-subscriber/src/fmt/format/mod.rs

@@ -60,6 +60,11 @@ mod pretty;
 #[cfg_attr(docsrs, doc(cfg(feature = "ansi")))]
 pub use pretty::*;
 
+#[cfg(feature = "otel")]
+use crate::registry::Extensions;
+#[cfg(feature = "otel")]
+use opentelemetry::trace::TraceId;
+
 /// A type that can format a tracing [`Event`] to a [`Writer`].
 ///
 /// `FormatEvent` is primarily used in the context of [`fmt::Subscriber`] or
@@ -407,6 +412,43 @@ pub struct Format<F = Full, T = SystemTime> {
     pub(crate) display_thread_name: bool,
     pub(crate) display_filename: bool,
     pub(crate) display_line_number: bool,
+    #[cfg(feature = "otel")]
+    pub(crate) make_trace_id: Option<Box<dyn MakeTraceId>>
+}
+
+/// Optionally make an OTel `TraceId`.
+#[cfg(feature = "otel")]
+pub trait MakeTraceId: Fn(Extensions<'_>) -> Option<TraceId> + Send + Sync {
+    /// Clone self into a boxed [MakeTraceId].
+    fn clone_box<'a>(&self) -> Box<dyn 'a + MakeTraceId>
+    where
+        Self: 'a;
+}
+
+#[cfg(feature = "otel")]
+impl Debug for Box<dyn MakeTraceId> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "MakeTraceId")
+    }
+}
+
+#[cfg(feature = "otel")]
+impl<F> MakeTraceId for F
+    where
+        F: Fn(Extensions<'_>) -> Option<TraceId> + Clone + Send + Sync {
+    fn clone_box<'a>(&self) -> Box<dyn 'a + MakeTraceId>
+    where
+        Self: 'a,
+    {
+        Box::new(self.clone())
+    }
+}
+
+#[cfg(feature = "otel")]
+impl<'a> Clone for Box<dyn 'a + MakeTraceId> {
+    fn clone(&self) -> Self {
+        self.clone_box()
+    }
 }
 
 // === impl Writer ===
@@ -585,6 +627,8 @@ impl Default for Format<Full, SystemTime> {
             display_thread_name: false,
             display_filename: false,
             display_line_number: false,
+            #[cfg(feature = "otel")]
+            make_trace_id: None,
         }
     }
 }
@@ -605,6 +649,8 @@ impl<F, T> Format<F, T> {
             display_thread_name: self.display_thread_name,
             display_filename: self.display_filename,
             display_line_number: self.display_line_number,
+            #[cfg(feature = "otel")]
+            make_trace_id: None,
         }
     }
 
@@ -644,6 +690,8 @@ impl<F, T> Format<F, T> {
             display_thread_name: self.display_thread_name,
             display_filename: true,
             display_line_number: true,
+            #[cfg(feature = "otel")]
+            make_trace_id: None,
         }
     }
 
@@ -675,6 +723,8 @@ impl<F, T> Format<F, T> {
             display_thread_name: self.display_thread_name,
             display_filename: self.display_filename,
             display_line_number: self.display_line_number,
+            #[cfg(feature = "otel")]
+            make_trace_id: None,
         }
     }
 
@@ -704,6 +754,8 @@ impl<F, T> Format<F, T> {
             display_thread_name: self.display_thread_name,
             display_filename: self.display_filename,
             display_line_number: self.display_line_number,
+            #[cfg(feature = "otel")]
+            make_trace_id: None,
         }
     }
 
@@ -720,6 +772,8 @@ impl<F, T> Format<F, T> {
             display_thread_name: self.display_thread_name,
             display_filename: self.display_filename,
             display_line_number: self.display_line_number,
+            #[cfg(feature = "otel")]
+            make_trace_id: None,
         }
     }
 
@@ -801,6 +855,15 @@ impl<F, T> Format<F, T> {
             .with_file(display_location)
     }
 
+    /// Set the function to optionally make an OTel `TraceId`.
+    #[cfg(feature = "otel")]
+    pub fn with_make_trace_id(self, make_trace_id: Box<dyn MakeTraceId>) -> Self {
+        Format {
+            make_trace_id: Some(make_trace_id),
+            ..self
+        }
+    }
+
     #[inline]
     fn format_timestamp(&self, writer: &mut Writer<'_>) -> fmt::Result
     where