ODF integration¶

This documents layout the changes required to support rich-text collaborative editing.

It is unclear at this stage, the mechanics of WebODF. Important items to analyse are:

• Is a web server component required or not
• How to identify/mix multiple editing flows part of the same session
• How multi-party works as opposed to P2P

Possible SDK changes¶

Signaling¶

There is no need to alter anything related to SIP signalling. The SIP call id, which is unique for each session can be used as an identifier to group data related to same session inside the media streams.

Media¶

Media requires reliable transport which in SIP can only be MSRP. This provides reliable end-to-end transmission, TLS encryption and NAT traversal. Optional, OTR end-to-end encryption can be used.

Variant 1¶

This is by far the simplest way. Establish a standard MSRP chat stream and add 'application/odf+xml' to the list of supported payloads by subclassing the standard Chat stream from the SDK.

class ODFChatStream(ChatStream):
    accept_types = ['message/cpim', 'text/*', 'application/im-iscomposing+xml', 'application/odf+xml']

Then, during the session, send the data over the stream using:

stream.send_message(data, content_type='application/odf+xml', timestamp=ISOTimestamp.now())

On the receiving end, in the notification handler for message received:

def _NH_ChatStreamGotMessage(self, stream, data):
    message = data.message
    if message.content_type == 'application/odf+xml',:
        # do something in the web view handling the editor
        return

Optionally, one can add an attribute to the MSRP stream to signal the support for this feature inside the media stream:

class ODFChatStream(ChatStream):
    accept_types = ['message/cpim', 'text/*', 'application/im-iscomposing+xml', 'application/odf+xml']
    def _create_local_media(self, uri_path):
        local_media = super(BlinkChatStream, self)._create_local_media(uri_path)
        local_media.attributes.append(SDPAttribute('features', 'odf-editor'))
        return local_media

After session negotiation, the clients can invoke their corespondent GUI elements related to the collaborative editing when detecting odf-editor feature in the remote stream. This approach will work with any MSRP chat implementation, the data will piggy-back on top of an existent chat stream in a non-disruptive way, which makes development of other end-points easy as no internal mechanisms of SIP session session initiation must be done.

Variant 2¶

Create a complete new media type based on MSRP protocol similar to file-transfer or screen sharing. See SIP SIMPLE Client SDK MSRP streams definition:

sipsimple/streams/msrp.py

Example of a new type of stream

class ODFStream(MSRPStreamBase):
    type = 'odf'

    media_type = 'odf'
    accept_types = ['application/odf+xml']
    accept_wrapped_types = ['*']

Once established, the MSRP stream can cary back and forth payloads of the types specified in the stream definition. Is up to the end-points to handle the actual payloads and match various files shared through this mechanism over the same session. The SIP session id can be used to group together various flows within the same stream.

This mechanism will require similar changes in other clients that wish to implement this feature, it is more complex but have the advantage that it can be negotiated by the use of a SIP Invite where the remote party can accept or reject the session request.

Presence¶

Optionally, SIP end-points supporting this feature can advertise this capability by publishing it using the SIP SIMPLE Presence payload. For this, the end-point capabilities must be extended to support odf as a different media type.

sipsimple/payloads/caps.py

GUI changes¶

The GUI must handle sessions for incoming and outgoing media stream defined above by creating its own controller that it is invoked either when negotiating the session, when a proper payload arrives over the chat channel or when user clicks in the GUI to start editing.

As the code is written and maintained by a third-party, the best approach is to have a separate window. Reusing Blink chat main window for ODF may conflict with future changes made by Blink developers.

Multi-party editing¶

SylkServer is the ideal candidate for mixing media, it has built-in web server and MSRP switch capabilities.