From 22379d3f318b2cd3a4c995ff1c45bda33d935a46 Mon Sep 17 00:00:00 2001
From: Ivan Topolnjak <ivantopo@gmail.com>
Date: Tue, 23 May 2017 19:06:32 +0200
Subject: get some basic sampling going

---
 .../main/scala/kamon/trace/SpanContextCodec.scala  | 87 ++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 kamon-core/src/main/scala/kamon/trace/SpanContextCodec.scala

(limited to 'kamon-core/src/main/scala/kamon/trace/SpanContextCodec.scala')

diff --git a/kamon-core/src/main/scala/kamon/trace/SpanContextCodec.scala b/kamon-core/src/main/scala/kamon/trace/SpanContextCodec.scala
new file mode 100644
index 00000000..6e687d66
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/trace/SpanContextCodec.scala
@@ -0,0 +1,87 @@
+package kamon.trace
+
+import java.net.{URLDecoder, URLEncoder}
+import java.util.concurrent.ThreadLocalRandom
+
+import io.opentracing.propagation.TextMap
+import kamon.util.HexCodec
+
+trait SpanContextCodec[T] {
+  def inject(spanContext: SpanContext, carrier: T): Unit
+  def extract(carrier: T, sampler: Sampler): SpanContext
+}
+
+object SpanContextCodec {
+
+  val TextMap: SpanContextCodec[TextMap] = new TextMapSpanCodec(
+    traceIDKey  = "TRACE_ID",
+    parentIDKey = "PARENT_ID",
+    spanIDKey   = "SPAN_ID",
+    sampledKey  =  "SAMPLED",
+    baggagePrefix = "BAGGAGE_",
+    baggageValueEncoder = identity,
+    baggageValueDecoder = identity
+  )
+
+  val ZipkinB3: SpanContextCodec[TextMap] = new TextMapSpanCodec(
+    traceIDKey  = "X─B3─TraceId",
+    parentIDKey = "X─B3─ParentSpanId",
+    spanIDKey   = "X─B3─SpanId",
+    sampledKey  =  "X─B3─Sampled",
+    baggagePrefix = "X─B3─Baggage-",
+    baggageValueEncoder = urlEncode,
+    baggageValueDecoder = urlDecode
+  )
+
+  private def urlEncode(s: String): String = URLEncoder.encode(s, "UTF-8")
+  private def urlDecode(s: String): String = URLDecoder.decode(s, "UTF-8")
+
+  private class TextMapSpanCodec(traceIDKey: String, parentIDKey: String, spanIDKey: String, sampledKey: String, baggagePrefix: String,
+    baggageValueEncoder: String => String, baggageValueDecoder: String => String) extends SpanContextCodec[TextMap] {
+
+    override def inject(spanContext: SpanContext, carrier: TextMap): Unit = {
+      carrier.put(traceIDKey, encodeLong(spanContext.traceID))
+      carrier.put(parentIDKey, encodeLong(spanContext.parentID))
+      carrier.put(spanIDKey, encodeLong(spanContext.spanID))
+
+      spanContext.baggageItems().forEach { entry =>
+        carrier.put(baggagePrefix + entry.getKey, baggageValueEncoder(entry.getValue))
+      }
+    }
+
+    override def extract(carrier: TextMap, sampler: Sampler): SpanContext = {
+      var traceID: String = null
+      var parentID: String = null
+      var spanID: String = null
+      var sampled: String = null
+      var baggage: Map[String, String] = Map.empty
+
+      carrier.forEach { entry =>
+        if(entry.getKey.equals(traceIDKey))
+          traceID = baggageValueDecoder(entry.getValue)
+        else if(entry.getKey.equals(parentIDKey))
+          parentID = baggageValueDecoder(entry.getValue)
+        else if(entry.getKey.equals(spanIDKey))
+          spanID = baggageValueDecoder(entry.getValue)
+        else if(entry.getKey.equals(sampledKey))
+          sampled = entry.getValue
+        else if(entry.getKey.startsWith(baggagePrefix))
+          baggage = baggage + (entry.getKey.substring(baggagePrefix.length) -> baggageValueDecoder(entry.getValue))
+      }
+
+      if(traceID != null && spanID != null) {
+        val actualParent = if(parentID == null) 0L else decodeLong(parentID)
+        val isSampled = if(sampled == null) sampler.decide(ThreadLocalRandom.current().nextLong()) else sampled.equals("1")
+
+        new SpanContext(decodeLong(traceID), decodeLong(spanID), actualParent, isSampled, baggage)
+      } else null
+    }
+
+    private def decodeLong(input: String): Long =
+      HexCodec.lowerHexToUnsignedLong(input)
+
+    private def encodeLong(input: Long): String =
+      HexCodec.toLowerHex(input)
+
+  }
+}
-- 
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