func errorHandler()

in images/custom-error-pages/rootfs/main.go [100:184]
75 lines of code
12 McCabe index (conditional complexity)

func errorHandler(path, defaultFormat string) func(http.ResponseWriter, *http.Request) {
	defaultExts, err := mime.ExtensionsByType(defaultFormat)
	if err != nil || len(defaultExts) == 0 {
		panic("couldn't get file extension for default format")
	}
	defaultExt := defaultExts[0]

	return func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		ext := defaultExt

		if os.Getenv("DEBUG") != "" {
			w.Header().Set(FormatHeader, r.Header.Get(FormatHeader))
			w.Header().Set(CodeHeader, r.Header.Get(CodeHeader))
			w.Header().Set(ContentType, r.Header.Get(ContentType))
			w.Header().Set(OriginalURI, r.Header.Get(OriginalURI))
			w.Header().Set(Namespace, r.Header.Get(Namespace))
			w.Header().Set(IngressName, r.Header.Get(IngressName))
			w.Header().Set(ServiceName, r.Header.Get(ServiceName))
			w.Header().Set(ServicePort, r.Header.Get(ServicePort))
			w.Header().Set(RequestId, r.Header.Get(RequestId))
		}

		format := r.Header.Get(FormatHeader)
		if format == "" {
			format = defaultFormat
			log.Printf("format not specified. Using %v", format)
		}

		cext, err := mime.ExtensionsByType(format)
		if err != nil {
			log.Printf("unexpected error reading media type extension: %v. Using %v", err, ext)
			format = defaultFormat
		} else if len(cext) == 0 {
			log.Printf("couldn't get media type extension. Using %v", ext)
		} else {
			ext = cext[0]
		}
		w.Header().Set(ContentType, format)

		errCode := r.Header.Get(CodeHeader)
		code, err := strconv.Atoi(errCode)
		if err != nil {
			code = 404
			log.Printf("unexpected error reading return code: %v. Using %v", err, code)
		}
		w.WriteHeader(code)

		if !strings.HasPrefix(ext, ".") {
			ext = "." + ext
		}
		// special case for compatibility
		if ext == ".htm" {
			ext = ".html"
		}
		file := fmt.Sprintf("%v/%v%v", path, code, ext)
		f, err := os.Open(file)
		if err != nil {
			log.Printf("unexpected error opening file: %v", err)
			scode := strconv.Itoa(code)
			file := fmt.Sprintf("%v/%cxx%v", path, scode[0], ext)
			f, err := os.Open(file)
			if err != nil {
				log.Printf("unexpected error opening file: %v", err)
				http.NotFound(w, r)
				return
			}
			defer f.Close()
			log.Printf("serving custom error response for code %v and format %v from file %v", code, format, file)
			io.Copy(w, f)
			return
		}
		defer f.Close()
		log.Printf("serving custom error response for code %v and format %v from file %v", code, format, file)
		io.Copy(w, f)

		duration := time.Now().Sub(start).Seconds()

		proto := strconv.Itoa(r.ProtoMajor)
		proto = fmt.Sprintf("%s.%s", proto, strconv.Itoa(r.ProtoMinor))

		requestCount.WithLabelValues(proto).Inc()
		requestDuration.WithLabelValues(proto).Observe(duration)
	}
}