[OpenTracing] Context propagation implementation (#495)

* Added: Propagators to OpenTracer.

* Added: Specs for OpenTracer::Propagators.

* Fixed: OpenTracer::Tracer#start_span not using provided SpanContext.

* Added: OpenTracer context propagation integration specs.

lib/ddtrace/opentracer.rb

@@ -20,6 +20,11 @@ def load_opentracer
       require 'ddtrace/opentracer/scope_manager'
       require 'ddtrace/opentracer/thread_local_scope'
       require 'ddtrace/opentracer/thread_local_scope_manager'
+      require 'ddtrace/opentracer/distributed_headers'
+      require 'ddtrace/opentracer/propagator'
+      require 'ddtrace/opentracer/text_map_propagator'
+      require 'ddtrace/opentracer/binary_propagator'
+      require 'ddtrace/opentracer/rack_propagator'
       require 'ddtrace/opentracer/global_tracer'
 
       # Modify the OpenTracing module functions

lib/ddtrace/opentracer/binary_propagator.rb

@@ -0,0 +1,24 @@
+module Datadog
+  module OpenTracer
+    # OpenTracing propagator for Datadog::OpenTracer::Tracer
+    module BinaryPropagator
+      extend Propagator
+
+      # Inject a SpanContext into the given carrier
+      #
+      # @param span_context [SpanContext]
+      # @param carrier [Carrier] A carrier object of Binary type
+      def self.inject(span_context, carrier)
+        nil
+      end
+
+      # Extract a SpanContext in Binary format from the given carrier.
+      #
+      # @param carrier [Carrier] A carrier object of Binary type
+      # @return [SpanContext, nil] the extracted SpanContext or nil if none could be found
+      def self.extract(carrier)
+        SpanContext::NOOP_INSTANCE
+      end
+    end
+  end
+end

lib/ddtrace/opentracer/distributed_headers.rb

@@ -0,0 +1,42 @@
+require 'ddtrace/span'
+require 'ddtrace/ext/distributed'
+
+module Datadog
+  module OpenTracer
+    # DistributedHeaders provides easy access and validation to headers
+    class DistributedHeaders
+      include Datadog::Ext::DistributedTracing
+
+      def initialize(carrier)
+        @carrier = carrier
+      end
+
+      def valid?
+        # Sampling priority is optional.
+        !trace_id.nil? && !parent_id.nil?
+      end
+
+      def trace_id
+        value = @carrier[HTTP_HEADER_TRACE_ID].to_i
+        return if value <= 0 || value >= Datadog::Span::MAX_ID
+        value
+      end
+
+      def parent_id
+        value = @carrier[HTTP_HEADER_PARENT_ID].to_i
+        return if value <= 0 || value >= Datadog::Span::MAX_ID
+        value
+      end
+
+      def sampling_priority
+        hdr = @carrier[HTTP_HEADER_SAMPLING_PRIORITY]
+        # It's important to make a difference between no header,
+        # and a header defined to zero.
+        return unless hdr
+        value = hdr.to_i
+        return if value < 0
+        value
+      end
+    end
+  end
+end

lib/ddtrace/opentracer/propagator.rb

@@ -0,0 +1,22 @@
+module Datadog
+  module OpenTracer
+    # OpenTracing propagator for Datadog::OpenTracer::Tracer
+    module Propagator
+      # Inject a SpanContext into the given carrier
+      #
+      # @param span_context [SpanContext]
+      # @param carrier [Carrier] A carrier object of the type dictated by the specified `format`
+      def inject(span_context, carrier)
+        raise NotImplementedError
+      end
+
+      # Extract a SpanContext in the given format from the given carrier.
+      #
+      # @param carrier [Carrier] A carrier object of the type dictated by the specified `format`
+      # @return [SpanContext, nil] the extracted SpanContext or nil if none could be found
+      def extract(carrier)
+        raise NotImplementedError
+      end
+    end
+  end
+end

lib/ddtrace/opentracer/rack_propagator.rb

@@ -0,0 +1,60 @@
+require 'ddtrace/propagation/http_propagator'
+
+module Datadog
+  module OpenTracer
+    # OpenTracing propagator for Datadog::OpenTracer::Tracer
+    module RackPropagator
+      extend Propagator
+      extend Datadog::Ext::DistributedTracing
+      include Datadog::Ext::DistributedTracing
+
+      BAGGAGE_PREFIX = 'ot-baggage-'.freeze
+      BAGGAGE_PREFIX_FORMATTED = 'HTTP_OT_BAGGAGE_'.freeze
+
+      class << self
+        # Inject a SpanContext into the given carrier
+        #
+        # @param span_context [SpanContext]
+        # @param carrier [Carrier] A carrier object of Rack type
+        def inject(span_context, carrier)
+          # Inject Datadog trace properties
+          Datadog::HTTPPropagator.inject!(span_context.datadog_context, carrier)
+
+          # Inject baggage
+          span_context.baggage.each do |key, value|
+            carrier[BAGGAGE_PREFIX + key] = value
+          end
+
+          nil
+        end
+
+        # Extract a SpanContext in Rack format from the given carrier.
+        #
+        # @param carrier [Carrier] A carrier object of Rack type
+        # @return [SpanContext, nil] the extracted SpanContext or nil if none could be found
+        def extract(carrier)
+          # First extract & build a Datadog context
+          datadog_context = Datadog::HTTPPropagator.extract(carrier)
+
+          # Then extract any other baggage
+          baggage = {}
+          carrier.each do |key, value|
+            baggage[header_to_baggage(key)] = value if baggage_header?(key)
+          end
+
+          SpanContextFactory.build(datadog_context: datadog_context, baggage: baggage)
+        end
+
+        private
+
+        def baggage_header?(header)
+          header.start_with?(BAGGAGE_PREFIX_FORMATTED)
+        end
+
+        def header_to_baggage(key)
+          key[BAGGAGE_PREFIX_FORMATTED.length, key.length].downcase
+        end
+      end
+    end
+  end
+end

lib/ddtrace/opentracer/text_map_propagator.rb

@@ -0,0 +1,73 @@
+require 'ddtrace/ext/distributed'
+
+module Datadog
+  module OpenTracer
+    # OpenTracing propagator for Datadog::OpenTracer::Tracer
+    module TextMapPropagator
+      extend Propagator
+      extend Datadog::Ext::DistributedTracing
+      include Datadog::Ext::DistributedTracing
+
+      BAGGAGE_PREFIX = 'ot-baggage-'.freeze
+
+      class << self
+        # Inject a SpanContext into the given carrier
+        #
+        # @param span_context [SpanContext]
+        # @param carrier [Carrier] A carrier object of Rack type
+        def inject(span_context, carrier)
+          # Inject Datadog trace properties
+          span_context.datadog_context.tap do |datadog_context|
+            carrier[HTTP_HEADER_TRACE_ID] = datadog_context.trace_id
+            carrier[HTTP_HEADER_PARENT_ID] = datadog_context.span_id
+            carrier[HTTP_HEADER_SAMPLING_PRIORITY] = datadog_context.sampling_priority
+          end
+
+          # Inject baggage
+          span_context.baggage.each do |key, value|
+            carrier[BAGGAGE_PREFIX + key] = value
+          end
+
+          nil
+        end
+
+        # Extract a SpanContext in TextMap format from the given carrier.
+        #
+        # @param carrier [Carrier] A carrier object of TextMap type
+        # @return [SpanContext, nil] the extracted SpanContext or nil if none could be found
+        def extract(carrier)
+          # First extract & build a Datadog context
+          headers = DistributedHeaders.new(carrier)
+
+          datadog_context = if headers.valid?
+                              Datadog::Context.new(
+                                trace_id: headers.trace_id,
+                                span_id: headers.parent_id,
+                                sampling_priority: headers.sampling_priority
+                              )
+                            else
+                              Datadog::Context.new
+                            end
+
+          # Then extract any other baggage
+          baggage = {}
+          carrier.each do |key, value|
+            baggage[item_to_baggage(key)] = value if baggage_item?(key)
+          end
+
+          SpanContextFactory.build(datadog_context: datadog_context, baggage: baggage)
+        end
+
+        private
+
+        def baggage_item?(item)
+          item.start_with?(BAGGAGE_PREFIX)
+        end
+
+        def item_to_baggage(key)
+          key[BAGGAGE_PREFIX.length, key.length]
+        end
+      end
+    end
+  end
+end

lib/ddtrace/opentracer/tracer.rb

@@ -100,21 +100,6 @@ def start_span(operation_name,
                      start_time: Time.now,
                      tags: nil,
                      ignore_active_scope: false)
-        # Get the parent Datadog span
-        parent_datadog_span = case child_of
-                              when Span
-                                child_of.datadog_span
-                              else
-                                ignore_active_scope ? nil : scope_manager.active && scope_manager.active.span.datadog_span
-                              end
-
-        # Build the new Datadog span
-        datadog_span = datadog_tracer.start_span(
-          operation_name,
-          child_of: parent_datadog_span,
-          start_time: start_time,
-          tags: tags || {}
-        )
 
         # Derive the OpenTracer::SpanContext to inherit from
         parent_span_context = case child_of
@@ -126,6 +111,14 @@ def start_span(operation_name,
                                 ignore_active_scope ? nil : scope_manager.active && scope_manager.active.span.context
                               end
 
+        # Build the new Datadog span
+        datadog_span = datadog_tracer.start_span(
+          operation_name,
+          child_of: parent_span_context && parent_span_context.datadog_context,
+          start_time: start_time,
+          tags: tags || {}
+        )
+
         # Build or extend the OpenTracer::SpanContext
         span_context = if parent_span_context
                          SpanContextFactory.clone(span_context: parent_span_context)
@@ -144,8 +137,12 @@ def start_span(operation_name,
       # @param carrier [Carrier] A carrier object of the type dictated by the specified `format`
       def inject(span_context, format, carrier)
         case format
-        when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK
-          return nil
+        when OpenTracing::FORMAT_TEXT_MAP
+          TextMapPropagator.inject(span_context, carrier)
+        when OpenTracing::FORMAT_BINARY
+          BinaryPropagator.inject(span_context, carrier)
+        when OpenTracing::FORMAT_RACK
+          RackPropagator.inject(span_context, carrier)
         else
           warn 'Unknown inject format'
         end
@@ -158,8 +155,12 @@ def inject(span_context, format, carrier)
       # @return [SpanContext, nil] the extracted SpanContext or nil if none could be found
       def extract(format, carrier)
         case format
-        when OpenTracing::FORMAT_TEXT_MAP, OpenTracing::FORMAT_BINARY, OpenTracing::FORMAT_RACK
-          return SpanContext::NOOP_INSTANCE
+        when OpenTracing::FORMAT_TEXT_MAP
+          TextMapPropagator.extract(carrier)
+        when OpenTracing::FORMAT_BINARY
+          BinaryPropagator.extract(carrier)
+        when OpenTracing::FORMAT_RACK
+          RackPropagator.extract(carrier)
         else
           warn 'Unknown extract format'
           nil

spec/ddtrace/opentracer/binary_propagator_spec.rb

@@ -0,0 +1,23 @@
+require 'spec_helper'
+
+require 'ddtrace/opentracer'
+require 'ddtrace/opentracer/helper'
+
+if Datadog::OpenTracer.supported?
+  RSpec.describe Datadog::OpenTracer::BinaryPropagator do
+    include_context 'OpenTracing helpers'
+
+    describe '#inject' do
+      subject { described_class.inject(span_context, carrier) }
+      let(:span_context) { instance_double(Datadog::OpenTracer::SpanContext) }
+      let(:carrier) { instance_double(Datadog::OpenTracer::Carrier) }
+      it { is_expected.to be nil }
+    end
+
+    describe '#extract' do
+      subject(:span_context) { described_class.extract(carrier) }
+      let(:carrier) { instance_double(Datadog::OpenTracer::Carrier) }
+      it { is_expected.to be(Datadog::OpenTracer::SpanContext::NOOP_INSTANCE) }
+    end
+  end
+end