cmd/noxy: respond with appropriate status 5xx on context errors

cmd/noxy/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"flag"
@@ -197,6 +198,8 @@ func writeError(w http.ResponseWriter, err error) {
 		w.WriteHeader(http.StatusBadRequest)
 	case errors.Is(err, noxy.ErrNotFound):
 		w.WriteHeader(http.StatusNotFound)
+	case errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled):
+		w.WriteHeader(http.StatusServiceUnavailable)
 	}
 	fmt.Fprint(w, err.Error())
 }