Add AlwaysParentSample sampler (#455)

* Add AlwaysParentSample

* Update sampler doc

Co-Authored-By: Krzesimir Nowak <[email protected]>

* Address PR comments

Co-authored-by: Krzesimir Nowak <[email protected]>
Co-authored-by: Rahul Patel <[email protected]>

sdk/trace/sampling.go

@@ -77,3 +77,11 @@ func NeverSample() Sampler {
  return SamplingDecision{Sample: false}
  }
 }
+
+// AlwaysParentSample returns a Sampler that samples a trace only
+// if the parent span is sampled.
+// This Sampler is a passthrough to the ProbabilitySampler with
+// a fraction of value 0.
+func AlwaysParentSample() Sampler {
+ return ProbabilitySampler(0)
+}

sdk/trace/sampling_test.go

@@ -0,0 +1,49 @@
+// Copyright 2020, OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package trace_test
+
+import (
+ "testing"
+
+ "go.opentelemetry.io/otel/api/core"
+ sdktrace "go.opentelemetry.io/otel/sdk/trace"
+)
+
+func TestAlwaysParentSampleWithParentSampled(t *testing.T) {
+ sampler := sdktrace.AlwaysParentSample()
+ traceID, _ := core.TraceIDFromHex("4bf92f3577b34da6a3ce929d0e0e4736")
+ spanID, _ := core.SpanIDFromHex("00f067aa0ba902b7")
+ parentCtx := core.SpanContext{
+ TraceID: traceID,
+ SpanID: spanID,
+ TraceFlags: core.TraceFlagsSampled,
+ }
+ if !sampler(sdktrace.SamplingParameters{ParentContext: parentCtx}).Sample {
+ t.Error("Sampling decision should be true")
+ }
+}
+
+func TestAlwaysParentSampleWithParentNotSampled(t *testing.T) {
+ sampler := sdktrace.AlwaysParentSample()
+ traceID, _ := core.TraceIDFromHex("4bf92f3577b34da6a3ce929d0e0e4736")
+ spanID, _ := core.SpanIDFromHex("00f067aa0ba902b7")
+ parentCtx := core.SpanContext{
+ TraceID: traceID,
+ SpanID: spanID,
+ }
+ if sampler(sdktrace.SamplingParameters{ParentContext: parentCtx}).Sample {
+ t.Error("Sampling decision should be false")
+ }
+}