Add tracing and relevant tests (#21)

* Add tracing and relevant tests.

* fixup! Add tracing and relevant tests.

* gofmt the code 🤷

* fixup! gofmt the code 🤷

tracing/tracing.go

@@ -0,0 +1,113 @@
+package tracing
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/sdk/resource"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	semconv "go.opentelemetry.io/otel/semconv/v1.21.0"
+	"go.opentelemetry.io/otel/trace"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+type TracingSetup struct {
+	tracerProvider *sdktrace.TracerProvider
+	tracer         trace.Tracer
+}
+
+type TraceSpanInfo struct {
+	TraceParent string `json:"traceparent"`
+}
+
+// NewTracing creates a new tracing setup with OTLP exporter
+func NewTracing(ctx context.Context, endpoint string) (*TracingSetup, error) {
+	if ctx == nil {
+		return nil, fmt.Errorf("context cannot be nil")
+	}
+	if endpoint == "" {
+		return nil, fmt.Errorf("endpoint cannot be empty")
+	}
+
+	conn, err := grpc.DialContext(ctx, endpoint,
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+		grpc.WithBlock(),
+		grpc.WithReturnConnectionError(),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create gRPC connection to collector: %w", err)
+	}
+
+	exporter, err := otlptracegrpc.New(ctx, otlptracegrpc.WithGRPCConn(conn))
+	if err != nil {
+		return nil, fmt.Errorf("failed to create trace exporter: %w", err)
+	}
+
+	res, err := resource.New(ctx,
+		resource.WithAttributes(
+			semconv.ServiceName("graphql-monitoring-proxy"),
+		),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create resource: %w", err)
+	}
+
+	tracerProvider := sdktrace.NewTracerProvider(
+		sdktrace.WithBatcher(exporter),
+		sdktrace.WithResource(res),
+	)
+	otel.SetTracerProvider(tracerProvider)
+	otel.SetTextMapPropagator(propagation.TraceContext{})
+
+	tracer := tracerProvider.Tracer("graphql-monitoring-proxy")
+
+	return &TracingSetup{
+		tracerProvider: tracerProvider,
+		tracer:         tracer,
+	}, nil
+}
+
+// ExtractSpanContext extracts span context from TraceSpanInfo
+func (ts *TracingSetup) ExtractSpanContext(spanInfo *TraceSpanInfo) (trace.SpanContext, error) {
+	carrier := propagation.MapCarrier{
+		"traceparent": spanInfo.TraceParent,
+	}
+	ctx := context.Background()
+	ctx = otel.GetTextMapPropagator().Extract(ctx, carrier)
+	spanCtx := trace.SpanContextFromContext(ctx)
+	if !spanCtx.IsValid() {
+		return trace.SpanContext{}, fmt.Errorf("invalid span context")
+	}
+	return spanCtx, nil
+}
+
+// ParseTraceHeader parses X-Trace-Span header content
+func ParseTraceHeader(headerContent string) (*TraceSpanInfo, error) {
+	var spanInfo TraceSpanInfo
+	if err := json.Unmarshal([]byte(headerContent), &spanInfo); err != nil {
+		return nil, fmt.Errorf("failed to parse trace header: %w", err)
+	}
+	return &spanInfo, nil
+}
+
+// Shutdown cleanly shuts down the tracer provider
+func (ts *TracingSetup) Shutdown(ctx context.Context) error {
+	if ts.tracerProvider == nil {
+		return nil
+	}
+	return ts.tracerProvider.Shutdown(ctx)
+}
+
+// StartSpan starts a new span with the given name and parent context
+func (ts *TracingSetup) StartSpan(ctx context.Context, name string) (trace.Span, context.Context) {
+	if ts.tracer == nil {
+		return trace.SpanFromContext(ctx), ctx
+	}
+	ctx, span := ts.tracer.Start(ctx, name)
+	return span, ctx
+}