1 files changed, 33 insertions, 0 deletions
diff --git a/core-rest/src/main/scala/xyz/driver/core/rest/headers/Traceparent.scala b/core-rest/src/main/scala/xyz/driver/core/rest/headers/Traceparent.scala
new file mode 100644
index 0000000..866476d
--- /dev/null
+++ b/core-rest/src/main/scala/xyz/driver/core/rest/headers/Traceparent.scala
@@ -0,0 +1,33 @@
+package xyz.driver.core
+package rest
+package headers
+
+import akka.http.scaladsl.model.headers.{ModeledCustomHeader, ModeledCustomHeaderCompanion}
+import xyz.driver.core.reporting.SpanContext
+
+import scala.util.Try
+
+/** Encapsulates a trace context in an HTTP header for propagation across services.
+  *
+  * This implementation corresponds to the W3C editor's draft specification (as of 2018-08-28)
+  * https://w3c.github.io/distributed-tracing/report-trace-context.html. The 'flags' field is
+  * ignored.
+  */
+final case class Traceparent(spanContext: SpanContext) extends ModeledCustomHeader[Traceparent] {
+  override def renderInRequests            = true
+  override def renderInResponses           = true
+  override val companion: Traceparent.type = Traceparent
+  override def value: String               = f"01-${spanContext.traceId}-${spanContext.spanId}-00"
+}
+object Traceparent extends ModeledCustomHeaderCompanion[Traceparent] {
+  override val name = "traceparent"
+  override def parse(value: String) = Try {
+    val Array(version, traceId, spanId, _) = value.split("-")
+    require(
+      version == "01",
+      s"Found unsupported version '$version' in traceparent header. Only version '01' is supported.")
+    new Traceparent(
+      new SpanContext(traceId, spanId)
+    )
+  }
+}