[Prototype] propagation: add EnvCarrier

propagation/env.go

@@ -0,0 +1,43 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package propagation // import "go.opentelemetry.io/otel/propagation"
+
+import (
+	"os"
+	"strings"
+)
+
+// EnvCarrier is a TextMapCarrier that uses the environment variables as a
+// storage medium for propagated key-value pairs. The keys are uppercased
+// before being used to access the environment variables.
+// This is useful for propagating values that are set in the environment
+// and need to be accessed by different processes or services.
+// The keys are uppercased to avoid case sensitivity issues across different
+// operating systems and environments.
+type EnvCarrier struct{}
+
+var _ TextMapCarrier = EnvCarrier{}
+
+// Get returns the value associated with the passed key.
+// The key is uppercased before being used to access the environment variable.
+func (EnvCarrier) Get(key string) string {
+	k := strings.ToUpper(key)
+	return os.Getenv(k)
+}
+
+// Set stores the key-value pair in the environment variable.
+// The key is uppercased before being used to set the environment variable.
+func (EnvCarrier) Set(key, value string) {
+	k := strings.ToUpper(key)
+	_ = os.Setenv(k, value)
+}
+
+// Keys lists the keys stored in this carrier.
+// This method is not implemented for EnvCarrier as it is not possible to
+// list all environment variables in a portable way.
+func (EnvCarrier) Keys() []string {
+	// I don't know why TextMapCarrier even has a Keys method.
+	// It looks like it was some mistake in the original design.
+	return nil
+}

propagation/env_test.go

@@ -0,0 +1,64 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package propagation_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/trace"
+)
+
+func TestExtractValidTraceContextFromEnv(t *testing.T) {
+	stateStr := "key1=value1,key2=value2"
+	state, err := trace.ParseTraceState(stateStr)
+	require.NoError(t, err)
+
+	tests := []struct {
+		name string
+		envs map[string]string
+		want trace.SpanContext
+	}{
+		{
+			name: "sampled",
+			envs: map[string]string{
+				"TRACEPARENT": "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01",
+			},
+			want: trace.NewSpanContext(trace.SpanContextConfig{
+				TraceID:    traceID,
+				SpanID:     spanID,
+				TraceFlags: trace.FlagsSampled,
+				Remote:     true,
+			}),
+		},
+		{
+			name: "valid tracestate",
+			envs: map[string]string{
+				"TRACEPARENT": "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-00",
+				"TRACESTATE":  stateStr,
+			},
+			want: trace.NewSpanContext(trace.SpanContextConfig{
+				TraceID:    traceID,
+				SpanID:     spanID,
+				TraceState: state,
+				Remote:     true,
+			}),
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			ctx := context.Background()
+			for k, v := range tc.envs {
+				t.Setenv(k, v)
+			}
+			ctx = prop.Extract(ctx, propagation.EnvCarrier{})
+			assert.Equal(t, tc.want, trace.SpanContextFromContext(ctx))
+		})
+	}
+}