1 files changed, 75 insertions, 0 deletions

diff --git a/vendor/go.opencensus.io/trace/sampling.go b/vendor/go.opencensus.io/trace/sampling.go
new file mode 100644
index 0000000..71c10f9
--- /dev/null
+++ b/vendor/go.opencensus.io/trace/sampling.go
@@ -0,0 +1,75 @@
+// Copyright 2017, OpenCensus 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
+
+import (
+        "encoding/binary"
+)
+
+const defaultSamplingProbability = 1e-4
+
+// Sampler decides whether a trace should be sampled and exported.
+type Sampler func(SamplingParameters) SamplingDecision
+
+// SamplingParameters contains the values passed to a Sampler.
+type SamplingParameters struct {
+        ParentContext   SpanContext
+        TraceID         TraceID
+        SpanID          SpanID
+        Name            string
+        HasRemoteParent bool
+}
+
+// SamplingDecision is the value returned by a Sampler.
+type SamplingDecision struct {
+        Sample bool
+}
+
+// ProbabilitySampler returns a Sampler that samples a given fraction of traces.
+//
+// It also samples spans whose parents are sampled.
+func ProbabilitySampler(fraction float64) Sampler {
+        if !(fraction >= 0) {
+                fraction = 0
+        } else if fraction >= 1 {
+                return AlwaysSample()
+        }
+
+        traceIDUpperBound := uint64(fraction * (1 << 63))
+        return Sampler(func(p SamplingParameters) SamplingDecision {
+                if p.ParentContext.IsSampled() {
+                        return SamplingDecision{Sample: true}
+                }
+                x := binary.BigEndian.Uint64(p.TraceID[0:8]) >> 1
+                return SamplingDecision{Sample: x < traceIDUpperBound}
+        })
+}
+
+// AlwaysSample returns a Sampler that samples every trace.
+// Be careful about using this sampler in a production application with
+// significant traffic: a new trace will be started and exported for every
+// request.
+func AlwaysSample() Sampler {
+        return func(p SamplingParameters) SamplingDecision {
+                return SamplingDecision{Sample: true}
+        }
+}
+
+// NeverSample returns a Sampler that samples no traces.
+func NeverSample() Sampler {
+        return func(p SamplingParameters) SamplingDecision {
+                return SamplingDecision{Sample: false}
+        }
+}