[samplers/jaegerremote] Change parser to support enums as both string…

…s and numbers (#3183)

* squash

* delint

* undo .gitignore

* Move changelog entry to unreleased

---------

Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>
Co-authored-by: Tyler Yahn <codingalias@gmail.com>

CHANGELOG.md

@@ -12,12 +12,17 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Add the new `go.opentelemetry.io/contrib/instrgen` package to provide auto-generated source code instrumentation. (#3068)
 
+### Changed
+
+- `samplers/jaegerremote`: change to use protobuf parser instead of encoding/json to accept enums as strings. (#3183)
+
 ## [1.14.0/0.39.0/0.8.0] - 2023-02-07
 
 ### Changed
 
 - Change `runtime.uptime` instrument in `go.opentelemetry.io/contrib/instrumentation/runtime` from `Int64ObservableUpDownCounter` to `Int64ObservableCounter`,
  since the value is monotonic. (#3347)
+- `samplers/jaegerremote`: change to use protobuf parser instead of encoding/json to accept enums as strings. (#3183)
 
 ### Fixed
 

samplers/jaegerremote/README.md

@@ -1,6 +1,6 @@
 # Jaeger Remote Sampler
 
-This package implements [Jaeger remote sampler](https://www.jaegertracing.io/docs/latest/sampling/#collector-sampling-configuration).
+This package implements [Jaeger remote sampler](https://www.jaegertracing.io/docs/latest/sampling/#remote-sampling).
 Remote sampler allows defining sampling configuration for services at the backend, at the granularity of service + endpoint.
 When using the Jaeger backend, the sampling configuration can come from two sources:
 

samplers/jaegerremote/sampler_remote.go

@@ -17,7 +17,7 @@
 package jaegerremote // import "go.opentelemetry.io/contrib/samplers/jaegerremote"
 
 import (
-	"encoding/json"
+	"bytes"
 	"fmt"
 	"io"
 	"net/http"
@@ -26,6 +26,8 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/gogo/protobuf/jsonpb"
+
 	jaeger_api_v2 "go.opentelemetry.io/contrib/samplers/jaegerremote/internal/proto-gen/jaeger-idl/proto/api_v2"
 	"go.opentelemetry.io/otel/sdk/trace"
 )
@@ -311,7 +313,11 @@ type samplingStrategyParserImpl struct{}
 
 func (p *samplingStrategyParserImpl) Parse(response []byte) (interface{}, error) {
 	strategy := new(jaeger_api_v2.SamplingStrategyResponse)
-	if err := json.Unmarshal(response, strategy); err != nil {
+	// Official Jaeger Remote Sampling protocol contains enums encoded as strings.
+	// Legacy protocol contains enums as numbers.
+	// Gogo's jsonpb module can parse either format.
+	// Cf. https://github.com/open-telemetry/opentelemetry-go-contrib/issues/3184
+	if err := jsonpb.Unmarshal(bytes.NewReader(response), strategy); err != nil {
 		return nil, err
 	}
 	return strategy, nil

samplers/jaegerremote/sampler_remote_test.go

@@ -535,3 +535,55 @@ func getSamplingStrategyResponse(strategyType jaeger_api_v2.SamplingStrategyType
 	}
 	return nil
 }
+
+func TestSamplingStrategyParserImpl(t *testing.T) {
+	assertProbabilistic := func(t *testing.T, s *jaeger_api_v2.SamplingStrategyResponse) {
+		require.NotNil(t, s.GetProbabilisticSampling(), "output: %+v", s)
+		require.EqualValues(t, 0.42, s.GetProbabilisticSampling().GetSamplingRate(), "output: %+v", s)
+	}
+	assertRateLimiting := func(t *testing.T, s *jaeger_api_v2.SamplingStrategyResponse) {
+		require.NotNil(t, s.GetRateLimitingSampling(), "output: %+v", s)
+		require.EqualValues(t, 42, s.GetRateLimitingSampling().GetMaxTracesPerSecond(), "output: %+v", s)
+	}
+	tests := []struct {
+		name   string
+		json   string
+		assert func(t *testing.T, s *jaeger_api_v2.SamplingStrategyResponse)
+	}{
+		{
+			name:   "official JSON probabilistic",
+			json:   `{"strategyType":"PROBABILISTIC","probabilisticSampling":{"samplingRate":0.42}}`,
+			assert: assertProbabilistic,
+		},
+		{
+			name:   "official JSON rate limiting",
+			json:   `{"strategyType":"RATE_LIMITING","rateLimitingSampling":{"maxTracesPerSecond":42}}`,
+			assert: assertRateLimiting,
+		},
+		{
+			name:   "legacy JSON probabilistic",
+			json:   `{"strategyType":0,"probabilisticSampling":{"samplingRate":0.42}}`,
+			assert: assertProbabilistic,
+		},
+		{
+			name:   "legacy JSON rate limiting",
+			json:   `{"strategyType":1,"rateLimitingSampling":{"maxTracesPerSecond":42}}`,
+			assert: assertRateLimiting,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			val, err := new(samplingStrategyParserImpl).Parse([]byte(test.json))
+			require.NoError(t, err)
+			s := val.(*jaeger_api_v2.SamplingStrategyResponse)
+			test.assert(t, s)
+		})
+	}
+}
+
+func TestSamplingStrategyParserImpl_Error(t *testing.T) {
+	json := `{"strategyType":"foo_bar","probabilisticSampling":{"samplingRate":0.42}}`
+	val, err := new(samplingStrategyParserImpl).Parse([]byte(json))
+	require.Error(t, err, "output: %+v", val)
+	require.Contains(t, err.Error(), `unknown value "foo_bar"`)
+}