[#12] tracing: Add tracing package

Add tracing config, implementation and setup

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/tracing/propagator.go

@@ -0,0 +1,96 @@
+package tracing
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/trace"
+)
+
+const (
+	traceIDHeader = "x-frostfs-trace-id"
+	spanIDHeader  = "x-frostfs-span-id"
+	flagsHeader   = "x-frostfs-trace-flags"
+)
+
+const (
+	flagsSampled = 1 << iota
+)
+
+// propagator serializes SpanContext to/from headers.
+// x-frostfs-trace-id - TraceID, 16 bytes, hex-string (32 bytes).
+// x-frostfs-span-id - SpanID, 8 bytes, hexstring (16 bytes).
+// x-frostfs-trace-flags - trace flags (now sampled only).
+type propagator struct{}
+
+// Propagator is propagation.TextMapPropagator instance, used to extract/inject trace info from/to remote context.
+var Propagator propagation.TextMapPropagator = &propagator{}
+
+// Inject injects tracing info to carrier.
+func (p *propagator) Inject(ctx context.Context, carrier propagation.TextMapCarrier) {
+	sc := trace.SpanFromContext(ctx).SpanContext()
+	if !sc.TraceID().IsValid() || !sc.SpanID().IsValid() {
+		return
+	}
+
+	var flags int
+	if sc.IsSampled() {
+		flags = flags | flagsSampled
+	}
+
+	carrier.Set(traceIDHeader, sc.TraceID().String())
+	carrier.Set(spanIDHeader, sc.SpanID().String())
+	carrier.Set(flagsHeader, fmt.Sprintf("%x", flags))
+}
+
+// Extract extracts tracing info from carrier and returns context with tracing info.
+// In case of error returns ctx.
+func (p *propagator) Extract(ctx context.Context, carrier propagation.TextMapCarrier) context.Context {
+	spanConfig := trace.SpanContextConfig{}
+	var err error
+
+	traceIDStr := carrier.Get(traceIDHeader)
+	traceIDDefined := false
+	if traceIDStr != "" {
+		traceIDDefined = true
+		spanConfig.TraceID, err = trace.TraceIDFromHex(traceIDStr)
+		if err != nil {
+			return ctx
+		}
+	}
+
+	spanIDstr := carrier.Get(spanIDHeader)
+	spanIDDefined := false
+	if spanIDstr != "" {
+		spanIDDefined = true
+		spanConfig.SpanID, err = trace.SpanIDFromHex(spanIDstr)
+		if err != nil {
+			return ctx
+		}
+	}
+
+	if traceIDDefined != spanIDDefined {
+		return ctx //traceID + spanID must be defined OR no traceID and no spanID
+	}
+
+	flagsStr := carrier.Get(flagsHeader)
+	if flagsStr != "" {
+		var v int64
+		v, err = strconv.ParseInt(flagsStr, 16, 32)
+		if err != nil {
+			return ctx
+		}
+		if v&flagsSampled == flagsSampled {
+			spanConfig.TraceFlags = trace.FlagsSampled
+		}
+	}
+
+	return trace.ContextWithRemoteSpanContext(ctx, trace.NewSpanContext(spanConfig))
+}
+
+// Fields returns the keys whose values are set with Inject.
+func (p *propagator) Fields() []string {
+	return []string{traceIDHeader, spanIDHeader, flagsHeader}
+}