introduce the SpanCustomizer API

3 files changed, 53 insertions, 3 deletions

diff --git a/kamon-core/src/main/scala/kamon/Kamon.scala b/kamon-core/src/main/scala/kamon/Kamon.scala
index f251b1ec..e83f6a5c 100644
--- a/kamon-core/src/main/scala/kamon/Kamon.scala
+++ b/kamon-core/src/main/scala/kamon/Kamon.scala
@@ -24,7 +24,7 @@ import scala.concurrent.Future
 import java.time.Duration
 import java.util.concurrent.{Executors, ScheduledExecutorService, ScheduledThreadPoolExecutor}
 
-import kamon.context.{Codecs, Context, Storage}
+import kamon.context.{Codecs, Context, Key, Storage}
 import org.slf4j.LoggerFactory
 
 import scala.util.Try
@@ -118,6 +118,9 @@ object Kamon extends MetricLookup with ReporterRegistry with Tracer {
     }
   }
 
+  def withContextKey[T, K](key: Key[K], value: K)(f: => T): T =
+    withContext(currentContext().withKey(key, value))(f)
+
 
   override def loadReportersFromConfig(): Unit =
     _reporterRegistry.loadReportersFromConfig()
diff --git a/kamon-core/src/main/scala/kamon/trace/SpanCustomizer.scala b/kamon-core/src/main/scala/kamon/trace/SpanCustomizer.scala
new file mode 100644
index 00000000..4c6220ce
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/trace/SpanCustomizer.scala
@@ -0,0 +1,35 @@
+package kamon.trace
+
+import kamon.context.Key
+import kamon.trace.Tracer.SpanBuilder
+
+/**
+  * Allows users to customize and add additional information to Spans created by instrumentation. The typical use
+  * case for SpanCustomizer instances is to provide proper operation names in situations where the instrumentation
+  * is unable to generate a reasonable enough operation name, e.g. JDBC and HTTP Client calls, instead of having a
+  * default operation name using the statement type or target host a SpanCustomizer can be provided to assign operation
+  * names like "queryUsers" or "getUserProfile" instead.
+  *
+  * Instrumentation wanting to take advantage of SpanCustomizers should look for an instance in the current context
+  * using SpanCustomizer.ContextKey.
+  *
+  */
+trait SpanCustomizer {
+  def customize(spanBuilder: SpanBuilder): SpanBuilder
+}
+
+object SpanCustomizer {
+
+  val Noop = new SpanCustomizer {
+    override def customize(spanBuilder: SpanBuilder): SpanBuilder = spanBuilder
+  }
+
+  val ContextKey = Key.local[SpanCustomizer]("span-customizer", Noop)
+
+  def forOperationName(operationName: String): SpanCustomizer = new SpanCustomizer {
+    override def customize(spanBuilder: SpanBuilder): SpanBuilder =
+      spanBuilder.withOperationName(operationName)
+  }
+}
+
+
diff --git a/kamon-core/src/main/scala/kamon/trace/Tracer.scala b/kamon-core/src/main/scala/kamon/trace/Tracer.scala
index 5f61f3aa..8fa5df5d 100644
--- a/kamon-core/src/main/scala/kamon/trace/Tracer.scala
+++ b/kamon-core/src/main/scala/kamon/trace/Tracer.scala
@@ -91,6 +91,7 @@ object Tracer {
 
   final class SpanBuilder(operationName: String, tracer: Tracer.Default, spanSink: SpanSink) {
     private var parentSpan: Span = _
+    private var initialOperationName: String = operationName
     private var startTimestamp = 0L
     private var initialSpanTags = Map.empty[String, Span.TagValue]
     private var initialMetricTags = Map.empty[String, String]
@@ -133,6 +134,17 @@ object Tracer {
       this
     }
 
+    def withOperationName(operationName: String): SpanBuilder = {
+      this.initialOperationName = operationName
+      this
+    }
+
+    def spanTags: Map[String, Span.TagValue] =
+      this.initialSpanTags
+
+    def metricTags: Map[String, String] =
+      this.initialMetricTags
+
     def ignoreParentFromContext(): SpanBuilder = {
       this.useParentFromContext = false
       this
@@ -150,7 +162,7 @@ object Tracer {
       val samplingDecision: SamplingDecision = parentSpan
         .map(_.context.samplingDecision)
         .filter(_ != SamplingDecision.Unknown)
-        .getOrElse(tracer.sampler.decide(operationName, initialSpanTags))
+        .getOrElse(tracer.sampler.decide(initialOperationName, initialSpanTags))
 
       val spanContext = parentSpan match {
         case Some(parent) => joinParentContext(parent, samplingDecision)
@@ -158,7 +170,7 @@ object Tracer {
       }
 
       tracer.tracerMetrics.createdSpans.increment()
-      Span.Local(spanContext, nonRemoteParent, operationName, initialSpanTags, initialMetricTags, startTimestampMicros, spanSink, tracer.scopeSpanMetrics)
+      Span.Local(spanContext, nonRemoteParent, initialOperationName, initialSpanTags, initialMetricTags, startTimestampMicros, spanSink, tracer.scopeSpanMetrics)
     }
 
     private def joinParentContext(parent: Span, samplingDecision: SamplingDecision): SpanContext =