@callback handle_event(
  event_type :: event_name(),
  data :: event_data(),
  user_state :: any()
) ::
  {:ok, user_state :: any()}
  | {:stop, returning :: any()}
  | {:halt, returning :: any()}

Callback for event handling.

This callback takes an event type, an event data and user_state as the input.

The initial user_state is the third argument in Saxy.parse_string/3 and Saxy.parse_stream/3. It can be accumulated and passed around during the parsing time by returning it as the result of the callback implementation, which can be used to keep track of data when parsing is happening.

Returning {:ok, new_state} continues the parsing process with the new state.

Returning {:stop, anything} stops the prosing process immediately, and anything will be returned. This is usually handy when we want to get the desired return without parsing the whole file.

Returning {:halt, anything} stops the prosing process immediately, anything will be returned, together with the rest of buffer being parsed. This is usually handy when we want to get the desired return without parsing the whole file.

SAX Events

There are a couple of events that need to be handled in the handler.

• :start_document.
• :start_element.
• :characters – the binary that matches CharData* and Reference. Note that it is not trimmed and includes ALL whitespace characters that match CharData.
• :cdata – the binary that matches CData*.
• :end_document.
• :end_element.

Check out event_data() type for more information of what are emitted for each event type.

Examples

defmodule MyEventHandler do
  @behaviour Saxy.Handler

  def handle_event(:start_document, prolog, state) do
    {:ok, [{:start_document, prolog} | state]}
  end

  def handle_event(:end_document, _data, state) do
    {:ok, [{:end_document} | state]}
  end

  def handle_event(:start_element, {name, attributes}, state) do
    {:ok, [{:start_element, name, attributes} | state]}
  end

  def handle_event(:end_element, name, state) do
    {:ok, [{:end_element, name} | state]}
  end

  def handle_event(:characters, chars, state) do
    {:ok, [{:chacters, chars} | state]}
  end
end