package tracing import ( "context" "fmt" "net/http" "github.com/caddyserver/caddy/v2" "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/v1.17.0" "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, } version, _ := caddy.Version() res, err := ot.newResource(webEngineName, version) 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), otelhttp.WithSpanNameFormatter(ot.spanNameFormatter), ) 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.WebEngineName(webEngineName), semconv.WebEngineVersion(webEngineVersion), )) } // spanNameFormatter performs the replacement of placeholders in the span name func (ot *openTelemetryWrapper) spanNameFormatter(operation string, r *http.Request) string { return r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer).ReplaceAll(operation, "") }