HTTP CloudEvents function always returning 500 (for failure tests, retries, etc.)

create.sh

export KIND_CLUSTER_NAME=knative-0.24
export KO_DOCKER_REPO=kind.local

ko apply -f .

kservice.yaml

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: always-fail
spec:
  template:
    metadata:
      annotations:
        autoscaling.knative.dev/maxScale: "1"
        autoscaling.knative.dev/minScale: "1"
    spec:
      containers:
        - image: ko://knative.dev/eventing-rabbitmq/example

main.go

package main

import (
	"context"
	"errors"
	"net/http"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"knative.dev/pkg/logging"
	"knative.dev/pkg/signals"
)

const (
	addr    = ":8080"
	timeout = 5 * time.Second
)

func main() {
	ctx := signals.NewContext()

	r := chi.NewRouter()
	r.Use(middleware.Logger)
	r.Post("/", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusInternalServerError)
	})

	srv := http.Server{
		Addr:         addr,
		Handler:      r,
		ReadTimeout:  timeout,
		WriteTimeout: timeout,
	}

	go func() {
		<-ctx.Done()
		logging.FromContext(ctx).Info("shutting down")
		if err := srv.Shutdown(context.Background()); err != nil {
			logging.FromContext(ctx).Warnf("could not shutdown: %v", err)
		}
	}()

	logging.FromContext(ctx).Infow("listening", "address", addr)
	if err := srv.ListenAndServe(); !errors.Is(err, http.ErrServerClosed) {
		logging.FromContext(ctx).Fatal(err)
	}
}

trigger.yaml

apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: always-fail
spec:
  broker: rabbit
  filter:
    attributes:
      type: com.vmware.vsphere.VmPoweredOnEvent
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: always-fail
      namespace: default