Propagate sampled flag in-process and improve docs

CHANGELOG.md

@@ -6,7 +6,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## v0.16.0
 ### Added
-- The tracer now supports B3 context propagation. Propagation can be set by using the `propagator` keyword argument to `Tracer#configure`. Valid values are `:lightstep` (default), and `:b3`.
+- The tracer now supports B3 context propagation. Propagation can be set by using the `propagator` keyword argument to `LightStep.configure`. Valid values are `:lightstep` (default), and `:b3`.
 
 ## v0.15.0
 ### Added

README.md

@@ -27,6 +27,9 @@ Or install it yourself as:
     # Initialize the singleton tracer
     LightStep.configure(component_name: 'lightstep/ruby/example', access_token: 'your_access_token')
 
+    # Specify a propagation format (options are :lightstep (default) and :b3)
+    LightStep.configure(component_name: 'lightstep/ruby/example', access_token: 'your_access_token', :propagator :b3)
+
     # Create a basic span and attach a log to the span
     span = LightStep.start_span('my_span')
     span.log(event: 'hello world', count: 42)

lib/lightstep/span.rb

@@ -56,7 +56,7 @@ def initialize(
       ref = ref.context if (Span === ref)
 
       if SpanContext === ref
-        @context = SpanContext.new(id: LightStep.guid, trace_id: ref.trace_id)
+        @context = SpanContext.new(id: LightStep.guid, trace_id: ref.trace_id, sampled: ref.sampled?)
         set_baggage(ref.baggage)
         set_tag(:parent_span_guid, ref.id)
       else
@@ -83,6 +83,7 @@ def set_baggage_item(key, value)
       @context = SpanContext.new(
         id: context.id,
         trace_id: context.trace_id,
+        sampled: context.sampled?,
         baggage: context.baggage.merge({key => value})
       )
       self
@@ -94,6 +95,7 @@ def set_baggage(baggage = {})
       @context = SpanContext.new(
         id: context.id,
         trace_id: context.trace_id,
+        sampled: context.sampled?,
         baggage: baggage
       )
     end

spec/lightstep_spec.rb

@@ -72,6 +72,20 @@ def init_callback_tracer(callback)
     expect(child_span.span_context.baggage).to eq(parent_span.span_context.baggage)
   end
 
+  it 'should inherit true sampled flag from parent span' do
+    tracer = init_test_tracer
+    parent_ctx = LightStep::SpanContext.new(id: LightStep.guid, trace_id: LightStep.guid, sampled: true)
+    child_span = tracer.start_span('child_span', child_of: parent_ctx)
+    expect(child_span.span_context).to be_sampled
+  end
+
+  it 'should inherit false sampled flag from parent span' do
+    tracer = init_test_tracer
+    parent_ctx = LightStep::SpanContext.new(id: LightStep.guid, trace_id: LightStep.guid, sampled: false)
+    child_span = tracer.start_span('child_span', child_of: parent_ctx)
+    expect(child_span.span_context).not_to be_sampled
+  end
+
   it 'should allow operation_name updates' do
     tracer = init_test_tracer
     span = tracer.start_span('original')