MARIONETTE

  Marionette is the remote protocol that lets OOP programs communicate
  with, instrument, and control Gecko.

DESCRIPTION

  Marionette is an automation driver for Mozilla’s Gecko engine.
  It can remotely control either the UI or the internal JavaScript of
  the Gecko platform, such as Firefox.  It can control both the chrome
  and the content document, giving a high level of control and ability to
  replicate user interaction.  In addition to performing actions on the
  browser, Marionette can also read properties and attributes of the DOM.

USAGE

  It is included in Firefox, but not enabled by default unless the
  --marionette flag is passed or the marionette.enabled preference is
  set to true.

  To start Firefox with the remote protocol turned on:

  	% firefox --marionette
  	…
  	1491228343089	Marionette	INFO	Listening on port 2828

  This binds to a TCP socket, over which CLIENTS can communicate with
  Marionette using the PROTOCOL.

PROTOCOL

  Marionette provides an asynchronous, parallel pipelining user-facing
  interface.  Message sequencing limits chances of payload race conditions
  and provides a uniform way in which payloads are serialised.

  Clients that deliver a blocking WebDriver interface are still expected
  to not send further command requests before the response from the last
  command has come back, but if they still happen to do so because of
  programming error, no harm will be done.  This guards against bugs
  such as https://bugzil.la/1207125.

  Schematic flow of messages:

  	             client      server
  	               |            |
  	    msgid=1    |----------->|
  	               |  command   |
  	               |            |
  	    msgid=2    |<-----------|
  	               |  command   |
  	               |            |
  	    msgid=2    |----------->|
  	               |  response  |
  	               |            |
  	    msgid=1    |<-----------|
  	               |  response  |
  	               |            |

  The protocol consists of a COMMAND message and the corresponding
  RESPONSE message.  A RESPONSE message must always be sent in reply to
  a COMMAND message.

  This means that the server implementation does not need to send the
  reply precisely in the order of the received commands: if it receives
  multiple messages, the server may even reply in random order.  It is
  therefore strongly adviced that clients take this into account when
  implementing the client end of this wire protocol.

  This is required for pipelining messages.  On the server side, some
  functions are fast, and some less so.  If the server must reply in
  order, the slow functions delay the other replies even if its execution
  is already completed.

COMMAND

  The request, or command message, is a four element JSON array as shown
  below, that may originate from either the client- or server remote ends:

  	[type, message ID, command, parameters]

  type
	Must be 0 (integer).  This indicates that the message is the
	COMMAND message.

  message ID
    A 32-bit unsigned integer.  This number is used as sequencing number
    that uniquely identifies a pair of COMMAND and RESPONSE messages.
    The other remote part will reply with a corresponding RESPONSE with
    the same message ID.

  command
    A string identifying the RPC method or command to execute.

  parameters
    An arbitrary JSON serialisable object.

RESPONSE

  The response message is also a four element array as shown below,
  and must always be sent after receiving a COMMAND:

  	[type, message ID, error, result]

  type
    Must be 1 (integer).  This indicates that the message is the RESPONSE
    message.

  message ID
    A 32-bit unsigned integer.  This corresponds to the COMMAND
    message’s message ID.

  error
    If the command executed correctly, this field is null.  If the error
    occurre on the server-side, then this field is an ERROR object.

  result
    The result object associated with the COMMAND, if it executed
    correctly.  If an error occurred on the server-side, this field
    is null.

  The structure of the result entry can vary, but is documented
  individually for each command in ./driver.js.

ERROR OBJECTS

  An ERROR object is a serialisation of JavaScript error types, and is
  structured like this:

  	{
  		"error": "invalid session id",
  		"message": "No active session with ID 1234",
  		"stacktrace": ""
  	}

  All the fields of the error object are required, so the stacktrace and
  message fields may be empty strings.  The error field is on the other
  hand guaranteed to be one of the JSON error codes as laid out by the
  WebDriver standard:

  	https://w3c.github.io/webdriver/webdriver-spec.html#handling-errors

CLIENTS

  Clients may be implemented in any language that is capable of writing
  and receiving data over TCP socket.  A reference client is provided in
  tree (under ./client).  Clients may be implemented both synchronously
  and asynchronously, although the latter is impossible in protocol
  levels 2 and earlier due to the lack of message indexing.

DOCUMENTATION

  General introduction:

  	https://developer.mozilla.org/en-US/docs/Mozilla/QA/Marionette

  Protocol definition:

	https://developer.mozilla.org/en-US/docs/Mozilla/QA/Marionette/Protocol

  Generated Python client API documentation:

  	https://marionette-client.readthedocs.org/

BUGS

  Server and Python client bugs are tracked in the Testing :: Marionette
  component in Bugzilla:

  	https://bugzilla.mozilla.org/buglist.cgi?product=Testing&component=Marionette

  geckodriver (found in ../geckodriver), the HTTP proxy for using W3C
  WebDriver-compatible clients with Marionette, tracks its bugs on GitHub:

  	https://github.com/mozilla/geckodriver/issues
