OTel-Go Consistent Probability Sampler and conformance tests

.github/dependabot.yml

@@ -723,3 +723,13 @@ updates:
     schedule:
       interval: "weekly"
       day: "sunday"
+  -
+    package-ecosystem: "gomod"
+    directory: "/samplers/probability/consistent"
+    labels:
+      - dependencies
+      - go
+      - "Skip Changelog"
+    schedule:
+      interval: "weekly"
+      day: "sunday"

instrumentation/github.com/astaxie/beego/otelbeego/example_middleware_test.go

@@ -24,7 +24,7 @@ type ExampleController struct {
 
 func (c *ExampleController) Get() {
 	// name of the template in the views directory
-	c.TplName = "index.tpl"
+	c.Controller.TplName = "index.tpl"
 
 	// explicit call to Render
 	if err := Render(&c.Controller); err != nil {

samplers/probability/consistent/base2.go

@@ -0,0 +1,69 @@
+// Copyright The 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 consistent // import "go.opentelemetry.io/contrib/samplers/probability/consistent"
+
+import "math"
+
+// These are IEEE 754 double-width floating point constants used with
+// math.Float64bits.
+const (
+	offsetExponentMask = 0x7ff0000000000000
+	offsetExponentBias = 1023
+	significandBits    = 52
+)
+
+// expFromFloat64 returns floor(log2(x)).
+func expFromFloat64(x float64) int {
+	return int((math.Float64bits(x)&offsetExponentMask)>>significandBits) - offsetExponentBias
+}
+
+// expToFloat64 returns 2^x.
+func expToFloat64(x int) float64 {
+	return math.Float64frombits(uint64(offsetExponentBias+x) << significandBits)
+}
+
+// splitProb returns the two values of log-adjusted-count nearest to p
+// Example:
+//
+//   splitProb(0.375) => (2, 1, 0.5)
+//
+// indicates to sample with probability (2^-2) 50% of the time
+// and (2^-1) 50% of the time.
+func splitProb(p float64) (uint8, uint8, float64) {
+	if p < 2e-62 {
+		// Note: spec.
+		return pZeroValue, pZeroValue, 1
+	}
+	// Take the exponent and drop the significand to locate the
+	// smaller of two powers of two.
+	exp := expFromFloat64(p)
+
+	// Low is the smaller of two log-adjusted counts, the negative
+	// of the exponent computed above.
+	low := -exp
+	// High is the greater of two log-adjusted counts (i.e., one
+	// less than low, a smaller adjusted count means a larger
+	// probability).
+	high := low - 1
+
+	// Return these to probability values and use linear
+	// interpolation to compute the required probability of
+	// choosing the low-probability Sampler.
+	lowP := expToFloat64(-low)
+	highP := expToFloat64(-high)
+	lowProb := (highP - p) / (highP - lowP)
+
+	return uint8(low), uint8(high), lowProb
+}

samplers/probability/consistent/base2_test.go

@@ -0,0 +1,61 @@
+// Copyright The 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 consistent
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSplitProb(t *testing.T) {
+	require.Equal(t, -1, expFromFloat64(0.6))
+	require.Equal(t, -2, expFromFloat64(0.4))
+	require.Equal(t, 0.5, expToFloat64(-1))
+	require.Equal(t, 0.25, expToFloat64(-2))
+
+	for _, tc := range []struct {
+		in      float64
+		low     uint8
+		lowProb float64
+	}{
+		// Probability 0.75 corresponds with choosing S=1 (the
+		// "low" probability) 50% of the time and S=0 (the
+		// "high" probability) 50% of the time.
+		{0.75, 1, 0.5},
+		{0.6, 1, 0.8},
+		{0.9, 1, 0.2},
+
+		// Powers of 2 exactly
+		{1, 0, 1},
+		{0.5, 1, 1},
+		{0.25, 2, 1},
+
+		// Smaller numbers
+		{0.05, 5, 0.4},
+		{0.1, 4, 0.4}, // 0.1 == 0.4 * 1/16 + 0.6 * 1/8
+		{0.003, 9, 0.464},
+
+		// Special cases:
+		{0, 63, 1},
+	} {
+		low, high, lowProb := splitProb(tc.in)
+		require.Equal(t, tc.low, low, "got %v want %v", low, tc.low)
+		if lowProb != 1 {
+			require.Equal(t, tc.low-1, high, "got %v want %v", high, tc.low-1)
+		}
+		require.InEpsilon(t, tc.lowProb, lowProb, 1e-6, "got %v want %v", lowProb, tc.lowProb)
+	}
+}

samplers/probability/consistent/go.mod

@@ -0,0 +1,10 @@
+module go.opentelemetry.io/contrib/samplers/probability/consistent
+
+go 1.15
+
+require (
+	github.com/stretchr/testify v1.7.0
+	go.opentelemetry.io/otel v1.2.0
+	go.opentelemetry.io/otel/sdk v1.1.0
+	go.opentelemetry.io/otel/trace v1.2.0
+)

samplers/probability/consistent/go.sum

@@ -0,0 +1,25 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/google/go-cmp v0.5.6 h1:BKbKCqvP6I+rmFHt06ZmyQtvB8xAkWdhFyr0ZUNZcxQ=
+github.com/google/go-cmp v0.5.6/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+go.opentelemetry.io/otel v1.1.0/go.mod h1:7cww0OW51jQ8IaZChIEdqLwgh+44+7uiTdWsAL0wQpA=
+go.opentelemetry.io/otel v1.2.0 h1:YOQDvxO1FayUcT9MIhJhgMyNO1WqoduiyvQHzGN0kUQ=
+go.opentelemetry.io/otel v1.2.0/go.mod h1:aT17Fk0Z1Nor9e0uisf98LrntPGMnk4frBO9+dkf69I=
+go.opentelemetry.io/otel/sdk v1.1.0 h1:j/1PngUJIDOddkCILQYTevrTIbWd494djgGkSsMit+U=
+go.opentelemetry.io/otel/sdk v1.1.0/go.mod h1:3aQvM6uLm6C4wJpHtT8Od3vNzeZ34Pqc6bps8MywWzo=
+go.opentelemetry.io/otel/trace v1.1.0/go.mod h1:i47XtdcBQiktu5IsrPqOHe8w+sBmnLwwHt8wiUsWGTI=
+go.opentelemetry.io/otel/trace v1.2.0 h1:Ys3iqbqZhcf28hHzrm5WAquMkDHNZTUkw7KHbuNjej0=
+go.opentelemetry.io/otel/trace v1.2.0/go.mod h1:N5FLswTubnxKxOJHM7XZC074qpeEdLy3CgAVsdMucK0=
+golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7 h1:iGu644GcxtEcrInvDsQRCwJjtCIOlT2V7IRt6ah2Whw=
+golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

samplers/probability/consistent/parent.go

@@ -0,0 +1,68 @@
+// Copyright The 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 consistent // import "go.opentelemetry.io/contrib/samplers/probability/consistent"
+
+import (
+	"strings"
+
+	"go.opentelemetry.io/otel"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/trace"
+)
+
+type (
+	parentProbabilitySampler struct {
+		delegate sdktrace.Sampler
+	}
+)
+
+func ParentProbabilityBased(root sdktrace.Sampler, samplers ...sdktrace.ParentBasedSamplerOption) sdktrace.Sampler {
+	return &parentProbabilitySampler{
+		delegate: sdktrace.ParentBased(root, samplers...),
+	}
+}
+
+func (p *parentProbabilitySampler) ShouldSample(params sdktrace.SamplingParameters) sdktrace.SamplingResult {
+	psc := trace.SpanContextFromContext(params.ParentContext)
+
+	// Note: We do not check psc.IsValid(), i.e., we repair the tracestate
+	// with or without a parent TraceId and SpanId.
+	state := psc.TraceState()
+
+	otts, err := parseOTelTraceState(state.Get(traceStateKey), psc.IsSampled())
+
+	if err != nil {
+		otel.Handle(err)
+		value := otts.serialize()
+		if len(value) > 0 {
+			// Note: see the note in
+			// "go.opentelemetry.io/otel/trace".TraceState.Insert(). The
+			// error below is not a condition we're supposed to handle.
+			state, _ = state.Insert(traceStateKey, value)
+		} else {
+			state = state.Delete(traceStateKey)
+		}
+
+		// Fix the broken tracestate before calling the delegate.
+		params.ParentContext =
+			trace.ContextWithSpanContext(params.ParentContext, psc.WithTraceState(state))
+	}
+
+	return p.delegate.ShouldSample(params)
+}
+
+func (p *parentProbabilitySampler) Description() string {
+	return "ParentProbabilityBased" + strings.TrimPrefix(p.delegate.Description(), "ParentBased")
+}