Receipts ======== .. _module:receipts: This module adds in support for receipts. These receipts are a form of acknowledgement of an event. This module defines a single acknowledgement: ``m.read`` which indicates that the user has read up to a given event. Sending a receipt for each event can result in sending large amounts of traffic to a homeserver. To prevent this from becoming a problem, receipts are implemented using "up to" markers. This marker indicates that the acknowledgement applies to all events "up to and including" the event specified. For example, marking an event as "read" would indicate that the user had read all events *up to* the referenced event. Events ------ Each ``user_id``, ``receipt_type`` pair must be associated with only a single ``event_id``. {{m_receipt_event}} Client behaviour ---------------- In v1 ``/initialSync``, receipts are listed in a separate top level ``receipts`` key. In v2 ``/sync``, receipts are contained in the ``ephemeral`` block for a room. New receipts that come down the event streams are deltas which update existing mappings. Clients should replace older receipt acknowledgements based on ``user_id`` and ``receipt_type`` pairs. For example:: Client receives m.receipt: user = @alice:example.com receipt_type = m.read event_id = $aaa:example.com Client receives another m.receipt: user = @alice:example.com receipt_type = m.read event_id = $bbb:example.com The client should replace the older acknowledgement for $aaa:example.com with this one for $bbb:example.com Clients should send read receipts when there is some certainty that the event in question has been **displayed** to the user. Simply receiving an event does not provide enough certainty that the user has seen the event. The user SHOULD need to *take some action* such as viewing the room that the event was sent to or dismissing a notification in order for the event to count as "read". A client can update the markers for its user by interacting with the following HTTP APIs. {{v2_receipts_http_api}} Server behaviour ---------------- For efficiency, receipts SHOULD be batched into one event per room before delivering them to clients. Receipts are sent across federation as EDUs with type ``m.receipt``. The format of the EDUs are:: { : { : { : { } }, ... }, ... } These are always sent as deltas to previously sent receipts. Currently only a single ```` should be used: ``m.read``. Security considerations ----------------------- As receipts are sent outside the context of the event graph, there are no integrity checks performed on the contents of ``m.receipt`` events.