move opentelemetry into trace package, and refactoring (#996)

* move opentelemetry into trace package, and refactoring

* rename rewritten package names

core/trace/opentelemetry/agent.go

@@ -0,0 +1,68 @@
+package opentelemetry
+
+import (
+	"sync"
+
+	"github.com/tal-tech/go-zero/core/logx"
+	"github.com/tal-tech/go-zero/core/syncx"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/jaeger"
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/sdk/resource"
+	tracesdk "go.opentelemetry.io/otel/sdk/trace"
+	semconv "go.opentelemetry.io/otel/semconv/v1.4.0"
+)
+
+var (
+	once    sync.Once
+	enabled syncx.AtomicBool
+)
+
+// Enabled returns if prometheus is enabled.
+func Enabled() bool {
+	return enabled.True()
+}
+
+// StartAgent starts a prometheus agent.
+func StartAgent(c Config) {
+	once.Do(func() {
+		if len(c.Endpoint) == 0 {
+			return
+		}
+
+		// Just support jaeger now
+		if c.Batcher != "jaeger" {
+			return
+		}
+
+		exp, err := jaeger.New(jaeger.WithCollectorEndpoint(jaeger.WithEndpoint(c.Endpoint)))
+		if err != nil {
+			logx.Error(err)
+			return
+		}
+
+		tp := tracesdk.NewTracerProvider(
+			// Set the sampling rate based on the parent span to 100%
+			tracesdk.WithSampler(tracesdk.ParentBased(tracesdk.TraceIDRatioBased(c.Sampler))),
+			// Always be sure to batch in production.
+			tracesdk.WithBatcher(exp),
+			// Record information about this application in an Resource.
+			tracesdk.WithResource(resource.NewSchemaless(semconv.ServiceNameKey.String(c.Name))),
+		)
+
+		otel.SetTracerProvider(tp)
+		otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))
+		otel.SetErrorHandler(otelErrHandler{})
+
+		enabled.Set(true)
+	})
+}
+
+// errHandler handing otel errors.
+type otelErrHandler struct{}
+
+var _ otel.ErrorHandler = otelErrHandler{}
+
+func (o otelErrHandler) Handle(err error) {
+	logx.Errorf("[otel] error: %v", err)
+}