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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/v1.7.0"
"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,
}
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))
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),
))
}
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