1 files changed, 108 insertions, 0 deletions
diff --git a/modules/caddyhttp/tracing/tracer.go b/modules/caddyhttp/tracing/tracer.go
new file mode 100644
index 0000000..ce23944
--- /dev/null
+++ b/modules/caddyhttp/tracing/tracer.go
@@ -0,0 +1,108 @@
+package tracing
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"github.com/caddyserver/caddy/v2"
+
+	caddycmd "github.com/caddyserver/caddy/v2/cmd"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+	"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/v1.7.0"
+	"go.uber.org/zap"
+)
+
+const (
+	webEngineName                = "Caddy"
+	defaultSpanName              = "handler"
+	nextCallCtxKey  caddy.CtxKey = "nextCall"
+)
+
+// nextCall store the next handler, and the error value return on calling it (if any)
+type nextCall struct {
+	next caddyhttp.Handler
+	err  error
+}
+
+// openTelemetryWrapper is responsible for the tracing injection, extraction and propagation.
+type openTelemetryWrapper struct {
+	propagators propagation.TextMapPropagator
+
+	handler http.Handler
+
+	spanName string
+}
+
+// newOpenTelemetryWrapper is responsible for the openTelemetryWrapper initialization using provided configuration.
+func newOpenTelemetryWrapper(
+	ctx context.Context,
+	spanName string,
+) (openTelemetryWrapper, error) {
+	if spanName == "" {
+		spanName = defaultSpanName
+	}
+
+	ot := openTelemetryWrapper{
+		spanName: spanName,
+	}
+
+	res, err := ot.newResource(webEngineName, caddycmd.CaddyVersion())
+	if err != nil {
+		return ot, fmt.Errorf("creating resource error: %w", err)
+	}
+
+	traceExporter, err := otlptracegrpc.New(ctx)
+	if err != nil {
+		return ot, fmt.Errorf("creating trace exporter error: %w", err)
+	}
+
+	ot.propagators = propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{})
+
+	tracerProvider := globalTracerProvider.getTracerProvider(
+		sdktrace.WithBatcher(traceExporter),
+		sdktrace.WithResource(res),
+	)
+
+	ot.handler = otelhttp.NewHandler(http.HandlerFunc(ot.serveHTTP), ot.spanName, otelhttp.WithTracerProvider(tracerProvider), otelhttp.WithPropagators(ot.propagators))
+	return ot, nil
+}
+
+// serveHTTP injects a tracing context and call the next handler.
+func (ot *openTelemetryWrapper) serveHTTP(w http.ResponseWriter, r *http.Request) {
+	ot.propagators.Inject(r.Context(), propagation.HeaderCarrier(r.Header))
+	next := r.Context().Value(nextCallCtxKey).(*nextCall)
+	next.err = next.next.ServeHTTP(w, r)
+}
+
+// ServeHTTP propagates call to the by wrapped by `otelhttp` next handler.
+func (ot *openTelemetryWrapper) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
+	n := &nextCall{
+		next: next,
+		err:  nil,
+	}
+	ot.handler.ServeHTTP(w, r.WithContext(context.WithValue(r.Context(), nextCallCtxKey, n)))
+
+	return n.err
+}
+
+// cleanup flush all remaining data and shutdown a tracerProvider
+func (ot *openTelemetryWrapper) cleanup(logger *zap.Logger) error {
+	return globalTracerProvider.cleanupTracerProvider(logger)
+}
+
+// newResource creates a resource that describe current handler instance and merge it with a default attributes value.
+func (ot *openTelemetryWrapper) newResource(
+	webEngineName,
+	webEngineVersion string,
+) (*resource.Resource, error) {
+	return resource.Merge(resource.Default(), resource.NewSchemaless(
+		semconv.WebEngineNameKey.String(webEngineName),
+		semconv.WebEngineVersionKey.String(webEngineVersion),
+	))
+}