feat: support baggage propagation in httpc (#2375)

* feat: support baggage propagation in httpc

* chore: use go 1.16

* chore: use go 1.16

* chore: use go ^1.16

* chore: remove deprecated

core/trace/agent.go

@@ -10,7 +10,6 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/exporters/jaeger"
 	"go.opentelemetry.io/otel/exporters/zipkin"
-	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/sdk/resource"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
 	semconv "go.opentelemetry.io/otel/semconv/v1.4.0"
@@ -66,7 +65,7 @@ func startAgent(c Config) error {
 	opts := []sdktrace.TracerProviderOption{
 		// Set the sampling rate based on the parent span to 100%
 		sdktrace.WithSampler(sdktrace.ParentBased(sdktrace.TraceIDRatioBased(c.Sampler))),
-		// Record information about this application in an Resource.
+		// Record information about this application in a Resource.
 		sdktrace.WithResource(resource.NewSchemaless(semconv.ServiceNameKey.String(c.Name))),
 	}
 
@@ -83,8 +82,6 @@ func startAgent(c Config) error {
 
 	tp = sdktrace.NewTracerProvider(opts...)
 	otel.SetTracerProvider(tp)
-	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(
-		propagation.TraceContext{}, propagation.Baggage{}))
 	otel.SetErrorHandler(otel.ErrorHandlerFunc(func(err error) {
 		logx.Errorf("[otel] error: %v", err)
 	}))

core/trace/propagation.go

@@ -0,0 +1,11 @@
+package trace
+
+import (
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/propagation"
+)
+
+func init() {
+	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(
+		propagation.TraceContext{}, propagation.Baggage{}))
+}