Trait-based initialization and other utilities

Adds the concept of a 'platform', a centralized place in which
environment-specific information will be managed, and provides common
initialization logic for most "standard" apps.

As part of the common initialization, other parts of core have also
been reworked:

- HTTP-related unmarshallers and path matchers have been factored out
  from core.json to a new core.rest.directives package (core.json
  extends those unmarshallers and matchers for backwards
  compatibility)

- CORS handling has also been moved to a dedicated utility trait

- Some custom headers have been moved from raw headers to typed ones
  in core.rest.headers

- The concept of a "reporter" has been introduced. A reporter is a
  context-aware combination of tracing and logging. It is intended to
  issue diagnostic messages that can be traced across service
  boundaries.

Closes #192
Closes #195

1 files changed, 33 insertions, 0 deletions

diff --git a/src/main/scala/xyz/driver/core/rest/headers/Traceparent.scala b/src/main/scala/xyz/driver/core/rest/headers/Traceparent.scala
new file mode 100644
index 0000000..9d470ad
--- /dev/null
+++ b/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 scala.util.Try
+
+/** Encapsulates 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(traceId: String, spanId: String) extends ModeledCustomHeader[Traceparent] {
+  override def renderInRequests            = true
+  override def renderInResponses           = true
+  override val companion: Traceparent.type = Traceparent
+  override def value: String               = f"01-$traceId-$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(
+      traceId,
+      spanId
+    )
+  }
+}