many improvements with options and noop stuff

* add many options helpers
* fix noop client to allow publish messages to topic in broker
* fix noop server to allow registering in registry
* fix noop server to allow subscribe to topic in broker
* fix new service initialization

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tracer/context.go

@@ -0,0 +1,36 @@
+// Package trace provides an interface for distributed tracing
+package tracer
+
+import (
+	"context"
+
+	"github.com/unistack-org/micro/v3/metadata"
+)
+
+const (
+	traceIDKey = "Micro-Trace-Id"
+	spanIDKey  = "Micro-Span-Id"
+)
+
+// FromContext returns a span from context
+func FromContext(ctx context.Context) (traceID string, parentSpanID string, isFound bool) {
+	traceID, traceOk := metadata.Get(ctx, traceIDKey)
+	microID, microOk := metadata.Get(ctx, "Micro-Id")
+	if !traceOk && !microOk {
+		isFound = false
+		return
+	}
+	if !traceOk {
+		traceID = microID
+	}
+	parentSpanID, ok := metadata.Get(ctx, spanIDKey)
+	return traceID, parentSpanID, ok
+}
+
+// NewContext saves the trace and span ids in the context
+func NewContext(ctx context.Context, traceID, parentSpanID string) context.Context {
+	return metadata.MergeContext(ctx, map[string]string{
+		traceIDKey: traceID,
+		spanIDKey:  parentSpanID,
+	}, true)
+}