add utility function for retrieving a trace id

NEXT_CHANGELOG.md

@@ -48,6 +48,17 @@ The router will now return a response with the status code `406 Not Acceptable`
 By [@Geal](https://github.com/Geal) in https://github.com/apollographql/router/pull/1652
 
 ## 🚀 Features
+
+### router now provides TraceId ([PR #1663](https://github.com/apollographql/router/issues/1536))
+
+If you need a reliable way to link together the various stages of pipeline processing, you can now use
+
+```
+apollo_router::tracer::TraceId
+```
+
+By [@garypen](https://github.com/garypen) in https://github.com/apollographql/router/pull/1663
+
 ## 🐛 Fixes
 
 ### Update our helm documentation to illustrate how to use our registry ([#1643](https://github.com/apollographql/router/issues/1643))

apollo-router/src/lib.rs

@@ -69,6 +69,7 @@ pub mod services;
 mod spec;
 mod state_machine;
 mod test_harness;
+pub mod tracer;
 
 pub use crate::configuration::Configuration;
 pub use crate::configuration::ListenAddr;

apollo-router/src/tracer.rs

@@ -0,0 +1,90 @@
+//! Trace Ids for the router.
+
+#![warn(unreachable_pub)]
+#![warn(missing_docs)]
+use std::fmt;
+
+use opentelemetry::trace::TraceContextExt;
+use tracing::Span;
+use tracing_opentelemetry::OpenTelemetrySpanExt;
+
+/// Trace ID
+#[derive(Debug, PartialEq, Eq)]
+pub struct TraceId([u8; 16]);
+
+impl TraceId {
+    /// Invalid Trace ID
+    pub const INVALID: TraceId = TraceId([0; 16]);
+
+    /// Create a TraceId. If called from an invalid context
+    /// (e.g.: not in a span, or in a disabled span), then
+    /// the value of the TraceId is [`TraceId::INVALID`].
+    pub fn new() -> Self {
+        TraceId(
+            Span::current()
+                .context()
+                .span()
+                .span_context()
+                .trace_id()
+                .to_bytes(),
+        )
+    }
+
+    /// Convert the TraceId to bytes.
+    pub fn as_bytes(&self) -> &[u8; 16] {
+        &self.0
+    }
+
+    /// Convert the TraceId to u128.
+    pub fn to_u128(&self) -> u128 {
+        u128::from_be_bytes(self.0)
+    }
+}
+
+impl Default for TraceId {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl fmt::Display for TraceId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.to_u128())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use opentelemetry::sdk::export::trace::stdout;
+    use tracing::span;
+    use tracing_subscriber::layer::SubscriberExt;
+    use tracing_subscriber::Registry;
+
+    use super::TraceId;
+
+    #[test]
+    fn it_returns_invalid_trace_id() {
+        let my_id = TraceId::new();
+        assert_eq!(my_id, TraceId::INVALID);
+        assert_eq!(my_id.as_bytes(), &[0; 16])
+    }
+
+    #[test]
+    fn it_returns_valid_trace_id() {
+        // Create a new OpenTelemetry pipeline
+        let tracer = stdout::new_pipeline().install_simple();
+        // Create a tracing layer with the configured tracer
+        let telemetry = tracing_opentelemetry::layer().with_tracer(tracer);
+        // Use the tracing subscriber `Registry`, or any other subscriber
+        // that impls `LookupSpan`
+        let subscriber = Registry::default().with(telemetry);
+        // Trace executed code
+        tracing::subscriber::with_default(subscriber, || {
+            // Spans will be sent to the configured OpenTelemetry exporter
+            let root = span!(tracing::Level::TRACE, "trace test");
+            let _enter = root.enter();
+
+            assert!(TraceId::new() != TraceId::INVALID);
+        });
+    }
+}