func decodeJSONBody()

in server/cmd/harp-server/internal/dispatchers/vault/routes/helpers.go [108:158]
38 lines of code
9 McCabe index (conditional complexity)

func decodeJSONBody(w http.ResponseWriter, r *http.Request, dst interface{}) error {
	// Limit body size to 1Mb
	r.Body = http.MaxBytesReader(w, r.Body, 1048576)

	// Disallow unknown fields deserialization
	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()

	err := dec.Decode(&dst)
	if err != nil {
		var syntaxError *json.SyntaxError
		var unmarshalTypeError *json.UnmarshalTypeError

		switch {
		case errors.As(err, &syntaxError):
			msg := fmt.Sprintf("Request body contains badly-formed JSON (at position %d)", syntaxError.Offset)
			return &malformedRequest{status: http.StatusBadRequest, msg: msg}

		case errors.Is(err, io.ErrUnexpectedEOF):
			msg := "Request body contains badly-formed JSON"
			return &malformedRequest{status: http.StatusBadRequest, msg: msg}

		case errors.As(err, &unmarshalTypeError):
			msg := fmt.Sprintf("Request body contains an invalid value for the %q field (at position %d)", unmarshalTypeError.Field, unmarshalTypeError.Offset)
			return &malformedRequest{status: http.StatusBadRequest, msg: msg}

		case strings.HasPrefix(err.Error(), "json: unknown field "):
			fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
			msg := fmt.Sprintf("Request body contains unknown field %s", fieldName)
			return &malformedRequest{status: http.StatusBadRequest, msg: msg}

		case errors.Is(err, io.EOF):
			msg := "Request body must not be empty"
			return &malformedRequest{status: http.StatusBadRequest, msg: msg}

		case err.Error() == "http: request body too large":
			msg := "Request body must not be larger than 1MB"
			return &malformedRequest{status: http.StatusRequestEntityTooLarge, msg: msg}

		default:
			return fmt.Errorf("json decode error: %w", err)
		}
	}

	if dec.More() {
		msg := "Request body must only contain a single JSON object"
		return &malformedRequest{status: http.StatusBadRequest, msg: msg}
	}

	return nil
}