add exports to tracing-util (#387)

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## Description

We don't want `v3-engine-multitenant` to import any opentelemetry
libraries directly, so we add more functions and re-exports here
instead.

V3_GIT_ORIGIN_REV_ID: 2e38b9b1ba6fda23d1bfe8e20549c3a95bd5a2fa

v3/Cargo.lock

@@ -2155,6 +2155,17 @@ dependencies = [
  "urlencoding",
 ]
 
+[[package]]
+name = "opentelemetry-contrib"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4717e7a7b45ef1c0664715a85a8e91ff966b58ffaaccb4d4cc7ff8f15cffd98a"
+dependencies = [
+ "once_cell",
+ "opentelemetry 0.20.0",
+ "opentelemetry_api",
+]
+
 [[package]]
 name = "opentelemetry-http"
 version = "0.9.0"
@@ -3577,6 +3588,7 @@ dependencies = [
  "derive_more",
  "http",
  "opentelemetry 0.20.0",
+ "opentelemetry-contrib",
  "opentelemetry-http",
  "opentelemetry-otlp",
  "opentelemetry-semantic-conventions",

v3/crates/tracing-util/Cargo.toml

@@ -11,6 +11,7 @@ bench = false
 derive_more = "0.99.17"
 # version > 0.20 of opentelemetry doesn't work well with our tracing-utils
 opentelemetry = "0.20.0"
+opentelemetry-contrib = "0.12.0"
 opentelemetry-http = "0.9.0"
 opentelemetry-otlp = "0.13.0"
 opentelemetry_sdk = { version = "0.20.0", features = ["rt-tokio"] }

v3/crates/tracing-util/src/lib.rs

@@ -8,6 +8,15 @@ pub use crate::http::TraceableHttpResponse;
 pub use setup::{shutdown_tracer, start_tracer};
 pub use traceable::{ErrorVisibility, Traceable, TraceableError};
 pub use tracer::{
-    add_event_on_active_span, global_tracer, set_attribute_on_active_span,
+    add_event_on_active_span, get_trace_context, global_tracer, set_attribute_on_active_span,
     set_status_on_current_span, AttributeVisibility, SpanVisibility,
 };
+
+// re-export things from OpenTelemetry to avoid library users importing their own version and
+// risking mismatches and multiple globals
+pub use opentelemetry::propagation::text_map_propagator::TextMapPropagator;
+pub use opentelemetry::trace::get_active_span;
+pub use opentelemetry::trace::Status;
+pub use opentelemetry::Context;
+pub use opentelemetry_contrib::trace::propagator::trace_context_response::TraceContextResponsePropagator;
+pub use opentelemetry_http::HeaderInjector;

v3/crates/tracing-util/src/tracer.rs

@@ -1,13 +1,12 @@
+use crate::traceable::{ErrorVisibility, Traceable, TraceableError};
 use http::HeaderMap;
 use opentelemetry::{
     global::{self, BoxedTracer},
     trace::{get_active_span, FutureExt, SpanRef, TraceContextExt, Tracer as OtelTracer},
-    Key,
+    Context, Key,
 };
 use opentelemetry_http::HeaderExtractor;
-use std::{future::Future, pin::Pin};
+use std::{collections::HashMap, future::Future, pin::Pin};
-
-use crate::traceable::{ErrorVisibility, Traceable, TraceableError};
 
 #[derive(derive_more::Display)]
 pub enum SpanVisibility {
@@ -181,6 +180,16 @@ impl Tracer {
     }
 }
 
+/// Return the current trace context, useful for including it HTTP requests etc
+pub fn get_trace_context() -> HashMap<String, String> {
+    let ctx = Context::current();
+    let mut trace_headers = HashMap::new();
+    global::get_text_map_propagator(|propagator| {
+        propagator.inject_context(&ctx, &mut trace_headers);
+    });
+    trace_headers
+}
+
 /// Util for accessing the globally installed tracer
 pub fn global_tracer() -> Tracer {
     Tracer::new(opentelemetry::global::tracer("engine-tracing-util"))