Merge pull request #13 from mladens/maintenance-1.x

Update Gauge transport format to one resembling histogram

project/build.properties

@@ -1 +1 @@
-sbt.version=0.13.9
+sbt.version=1.2.8

project/plugins.sbt

@@ -1,4 +1,5 @@
-lazy val root: Project = project.in(file(".")).dependsOn(latestSbtUmbrella)
-lazy val latestSbtUmbrella = uri("git://github.com/kamon-io/kamon-sbt-umbrella.git")
+lazy val umbrella: ProjectRef = ProjectRef(uri("git://github.com/kamon-io/kamon-sbt-umbrella.git"), "kamon-sbt-umbrella")
+lazy val root: Project = project.in(file(".")).dependsOn(umbrella)
 
 addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.5")
+

src/main/scala/kamon/apm/package.scala

@@ -69,4 +69,40 @@ package object apm {
     def tracingRoute    = s"$ingestionApi/tracing/ingest"
   }
 
+
+
+  /*
+   *  Internal HDR Histogram state required to convert index to values and get bucket size information. These values
+   *  correspond to a histogram configured to have 2 significant value digits prevision and a smallest discernible value
+   *  of 1.
+   */
+  def countsArrayIndex(value: Long): Int = {
+
+    val SubBucketHalfCountMagnitude = 7
+    val SubBucketHalfCount          = 128
+    val UnitMagnitude               = 0
+    val SubBucketCount              = Math.pow(2, SubBucketHalfCountMagnitude + 1).toInt
+    val LeadingZeroCountBase        = 64 - UnitMagnitude - SubBucketHalfCountMagnitude - 1
+    val SubBucketMask               = (SubBucketCount.toLong - 1) << UnitMagnitude
+
+    def countsArrayIndex(bucketIndex: Int, subBucketIndex: Int): Int = {
+      assert(subBucketIndex < SubBucketCount)
+      assert(bucketIndex == 0 || (subBucketIndex >= SubBucketHalfCount))
+      val bucketBaseIndex = (bucketIndex + 1) << SubBucketHalfCountMagnitude
+      val offsetInBucket = subBucketIndex - SubBucketHalfCount
+      bucketBaseIndex + offsetInBucket
+    }
+
+    def getBucketIndex(value: Long): Int =
+      LeadingZeroCountBase - java.lang.Long.numberOfLeadingZeros(value | SubBucketMask)
+
+    def getSubBucketIndex(value: Long, bucketIndex: Long): Int  =
+      Math.floor(value / Math.pow(2, (bucketIndex + UnitMagnitude))).toInt
+
+    if (value < 0) throw new ArrayIndexOutOfBoundsException("Histogram recorded value cannot be negative.")
+    val bucketIndex = getBucketIndex(value)
+    val subBucketIndex = getSubBucketIndex(value, bucketIndex)
+    countsArrayIndex(bucketIndex, subBucketIndex)
+  }
+
 }

src/main/scala/kamon/apm/reporters/KamonApmMetric.scala

@@ -1,4 +1,5 @@
-package kamon.apm.reporters
+package kamon.apm
+package reporters
 
 import java.nio.ByteBuffer
 import java.time.Duration
@@ -120,7 +121,15 @@ private[apm] class KamonApmMetric(codeProvidedPlan: Option[Plan]) extends Metric
 
   private def toIngestionMetricValue(metricType: InstrumentType)(metric: MetricValue): IngestionV1.Metric = {
     valueBuffer.clear()
-    ZigZag.putLong(valueBuffer, metricScaler.scaleMetricValue(metric).value)
+    metricType match {
+      case COUNTER =>
+        ZigZag.putLong(valueBuffer, metricScaler.scaleMetricValue(metric).value)
+      case GAUGE =>
+        val offset = countsArrayIndex(metricScaler.scaleMetricValue(metric).value)
+        if(offset > 0) ZigZag.putLong(valueBuffer, -offset)
+        ZigZag.putLong(valueBuffer, 1)
+    }
+
     valueBuffer.flip()
 
     IngestionV1.Metric.newBuilder()