include trace identifiers in HTTP responses, fixes #558

2 files changed, 20 insertions, 2 deletions

diff --git a/kamon-core-tests/src/test/resources/reference.conf b/kamon-core-tests/src/test/resources/reference.conf
index c092af08..60852722 100644
--- a/kamon-core-tests/src/test/resources/reference.conf
+++ b/kamon-core-tests/src/test/resources/reference.conf
@@ -21,8 +21,14 @@ kamon {
   instrumentation {
     http-server {
       default {
-        tracing.preferred-trace-id-tag = "correlation-id"
-        tracing.tags.from-context.peer = span
+        tracing {
+          preferred-trace-id-tag = "correlation-id"
+          tags.from-context.peer = span
+          response-headers {
+            trace-id = "x-trace-id"
+            span-id = "x-span-id"
+          }
+        }
       }
 
       no-span-metrics {
diff --git a/kamon-core-tests/src/test/scala/kamon/instrumentation/HttpServerInstrumentationSpec.scala b/kamon-core-tests/src/test/scala/kamon/instrumentation/HttpServerInstrumentationSpec.scala
index c3c5f131..62eae45b 100644
--- a/kamon-core-tests/src/test/scala/kamon/instrumentation/HttpServerInstrumentationSpec.scala
+++ b/kamon-core-tests/src/test/scala/kamon/instrumentation/HttpServerInstrumentationSpec.scala
@@ -220,6 +220,18 @@ class HttpServerInstrumentationSpec extends WordSpec with Matchers with SpanInsp
         val span = inspect(handler.span)
         span.tag("peer").value shouldBe "superservice"
       }
+
+      "write trace identifiers on the responses" in {
+        val handler = httpServer().receive(fakeRequest("http://localhost:8080/", "/", "GET", Map(
+          "x-correlation-id" -> "0011223344556677"
+        )))
+
+        val responseHeaders = mutable.Map.empty[String, String]
+        handler.send(fakeResponse(200, responseHeaders), handler.context)
+
+        responseHeaders.get("x-trace-id").value shouldBe "0011223344556677"
+        responseHeaders.get("x-span-id") shouldBe defined
+      }
     }
 
     "all capabilities are disabled" should {