tracer.go

package tracer

import (
	"fmt"
	"net/http"
	"strings"

	"github.com/alexfalkowski/go-service/telemetry/tracer"
	ts "github.com/alexfalkowski/go-service/transport/strings"
	snoop "github.com/felixge/httpsnoop"
	"go.opentelemetry.io/otel/attribute"
	semconv "go.opentelemetry.io/otel/semconv/v1.25.0"
	"go.opentelemetry.io/otel/trace"
)

// Handler for tracer.
type Handler struct {
	tracer trace.Tracer
}

// NewHandler for tracer.
func NewHandler(tracer trace.Tracer) *Handler {
	return &Handler{tracer: tracer}
}

// ServeHTTP for tracer.
func (h *Handler) ServeHTTP(resp http.ResponseWriter, req *http.Request, next http.HandlerFunc) {
	path, method := req.URL.Path, strings.ToLower(req.Method)
	if ts.IsHealth(path) {
		next(resp, req)

		return
	}

	ctx := extract(req.Context(), req)
	attrs := []attribute.KeyValue{
		semconv.HTTPRoute(path),
		semconv.HTTPRequestMethodKey.String(method),
	}

	ctx, span := h.tracer.Start(trace.ContextWithRemoteSpanContext(ctx, trace.SpanContextFromContext(ctx)), operationName(fmt.Sprintf("%s %s", method, path)),
		trace.WithSpanKind(trace.SpanKindServer), trace.WithAttributes(attrs...))
	defer span.End()

	ctx = tracer.WithTraceID(ctx, span)

	m := snoop.CaptureMetricsFn(resp, func(res http.ResponseWriter) { next(res, req.WithContext(ctx)) })

	span.SetAttributes(semconv.HTTPResponseStatusCode(m.Code))
	tracer.Meta(ctx, span)
}

// NewRoundTripper for tracer.
func NewRoundTripper(tracer trace.Tracer, hrt http.RoundTripper) *RoundTripper {
	return &RoundTripper{tracer: tracer, RoundTripper: hrt}
}

// RoundTripper for tracer.
type RoundTripper struct {
	tracer trace.Tracer
	http.RoundTripper
}

// RoundTrip for tracer.
func (r *RoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	if ts.IsHealth(req.URL.String()) {
		return r.RoundTripper.RoundTrip(req)
	}

	method := strings.ToLower(req.Method)
	ctx := req.Context()
	attrs := []attribute.KeyValue{
		semconv.HTTPRoute(req.URL.Path),
		semconv.HTTPRequestMethodKey.String(method),
	}

	ctx, span := r.tracer.Start(ctx, operationName(fmt.Sprintf("%s %s", method, req.URL.Redacted())), trace.WithSpanKind(trace.SpanKindClient), trace.WithAttributes(attrs...))
	defer span.End()

	ctx = tracer.WithTraceID(ctx, span)

	inject(ctx, req)

	resp, err := r.RoundTripper.RoundTrip(req.WithContext(ctx))

	tracer.Meta(ctx, span)
	tracer.Error(err, span)

	if resp != nil {
		span.SetAttributes(semconv.HTTPResponseStatusCode(resp.StatusCode))
	}

	return resp, err
}

func operationName(name string) string {
	return tracer.OperationName("http", name)
}