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1. philicious

   added

   feature-request

   on Oct 31, 2019
2. philicious commented on Dec 10, 2019

   

   philicious

   on Dec 10, 2019

   Author

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   as we needed this feature, my dear colleague @martinheld implemented the class directly in our service to save time. ( inspired by https://github.com/census-instrumentation/opencensus-node/blob/master/packages/opencensus-propagation-stackdriver/src/stackdriver-format.ts )

   unfortunately we didnt find the time afterwards to make a proper PR here. reasons:

   • it was coded in Kotlin and not Java as the opencensus lib
   • inject fun is still missing (we didnt need it)
   • trace-options from header ( ;o=TRACE_TRUE (0 or 1) ) is not respected and hardcoded as true

   however wanted to share the code as it might help people. anyone is invited to take it and maybe someone makes a proper PR for this !

   its used simply like

   val tracer = Tracing.getTracer()
   val spanContext = OpencensusStackdriverPropagation.extract(call.request)
   val rootSpan = tracer.spanBuilderWithRemoteParent("my-span-name", spanContext).startScopedSpan()
   ...

   import io.ktor.request.ApplicationRequest
   import io.ktor.request.header
   import io.opencensus.trace.SpanContext
   import io.opencensus.trace.TraceId
   import io.opencensus.trace.SpanId
   import io.opencensus.trace.TraceOptions
   import io.opencensus.trace.Tracestate
   
   object OpencensusStackdriverPropagation {
   
       val TRACE_CONTEXT_HEADER_NAME = "x-cloud-trace-context"
       val TRACE_TRUE = 0x1
   
       fun extract(request: ApplicationRequest): SpanContext? {
           val traceContextHeader = request.header(TRACE_CONTEXT_HEADER_NAME)
   
           logger.debug("$TRACE_CONTEXT_HEADER_NAME: $traceContextHeader")
   
           if (traceContextHeader == null) return null
   
           lateinit var traceParams: Triple<String?, String?, Int?>
   
           try {
               traceParams = getTraceParams(traceContextHeader)
           } catch (e: Exception) {
               logger.error(e.message)
               return null
           }
   
           return getSpanContext(traceParams)
       }
   
       private fun getSpanContext(traceParams: Triple<String?, String?, Int?>): SpanContext? {
           val (traceId, spanId, options) = traceParams
   
           if (traceId != null && spanId != null && options != null) {
               val traceIdObj  = TraceId.fromLowerBase16(traceId)
               val spanIdObj  = SpanId.fromLowerBase16(spanId)
               val optionsObj = TraceOptions.fromByte(options.toByte())
   
               val spanContext = SpanContext.create(traceIdObj, spanIdObj, optionsObj, Tracestate.builder().build())
               logger.debug("returning SpanContext: $spanContext")
               return spanContext
           }
   
           return null
       }
   
       private fun getTraceParams(traceContextHeader: String): Triple<String?, String?, Int?> {
   
           val regex = """([0-9a-fA-F]+)(?:\/([0-9]+))""".toRegex()
           val matchResult = regex.find(traceContextHeader)
   
           if (matchResult == null || matchResult.groups.size <3) {
               logger.debug("Parsing tracing context header failed")
               return Triple(null, null, null)
           }
   
           val(traceId, parsedSpanId) = matchResult.destructured
   
           val spanIdHex = parsedSpanId.toULong().toString(16)
           val spanId = "0000000000000000$spanIdHex".takeLast(16)
   
           val options = TRACE_TRUE
   
           return Triple(traceId, spanId, options)
       }
   }

   👍React with 👍3Reacted by Richard Johnson, jgladun and Daniel Compton
3. danielcompton commented on Mar 11, 2020

   

   danielcompton

   on Mar 11, 2020

   Last edited by danielcompton

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   Thanks for the tips here @philicious. I was working on this yesterday, and I found the algorithm Zipkin uses for parsing the X-Cloud-Trace-Context header:

   https://github.com/openzipkin/zipkin-gcp/blob/14b59d13ac5126e3fa677952a86ce1fcb96e9e3a/propagation-stackdriver/src/main/java/zipkin2/propagation/stackdriver/XCloudTraceContextExtractor.java#L44-L95