Saxy v0.8.0 Saxy.Handler behaviour View Source

This module provides callbacks to implement SAX events handler.

Link to this section Summary

Link to this section Callbacks

Link to this callback handle_event(event_type, data, user_state) View Source
handle_event(event_type :: atom(), data :: any(), user_state :: any()) ::
  {:ok, user_state :: any()} | {:stop, 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 feature 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

The event data will be the XML prolog, which is a keyword list of :version, :encoding and :standalone respectively.

:start_element

The event data is the element, which is a two-element tuple, respectively tag name, attributes.

:characters

The event data is the binary that matches CharData* and Reference.

Note that it is not trimmed and includes all the whitespace characters that match CharData.

:end_document

The event data is an empty tuple.

:end_element

The event data is the tag name of the closing element.

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