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diff --git a/docs/server-server/specification.rst b/docs/server-server/specification.rst deleted file mode 100644 index 17cffafdd4..0000000000 --- a/docs/server-server/specification.rst +++ /dev/null @@ -1,231 +0,0 @@ -=========================== -Matrix Server-to-Server API -=========================== - -A description of the protocol used to communicate between Matrix home servers; -also known as Federation. - - -Overview -======== - -The server-server API is a mechanism by which two home servers can exchange -Matrix event messages, both as a real-time push of current events, and as a -historic fetching mechanism to synchronise past history for clients to view. It -uses HTTP connections between each pair of servers involved as the underlying -transport. Messages are exchanged between servers in real-time by active pushing -from each server's HTTP client into the server of the other. Queries to fetch -historic data for the purpose of back-filling scrollback buffers and the like -can also be performed. - - - { Matrix clients } { Matrix clients } - ^ | ^ | - | events | | events | - | V | V - +------------------+ +------------------+ - | |---------( HTTP )---------->| | - | Home Server | | Home Server | - | |<--------( HTTP )-----------| | - +------------------+ +------------------+ - -There are three main kinds of communication that occur between home servers: - - * Queries - These are single request/response interactions between a given pair of - servers, initiated by one side sending an HTTP request to obtain some - information, and responded by the other. They are not persisted and contain - no long-term significant history. They simply request a snapshot state at the - instant the query is made. - - * EDUs - Ephemeral Data Units - These are notifications of events that are pushed from one home server to - another. They are not persisted and contain no long-term significant history, - nor does the receiving home server have to reply to them. - - * PDUs - Persisted Data Units - These are notifications of events that are broadcast from one home server to - any others that are interested in the same "context" (namely, a Room ID). - They are persisted to long-term storage and form the record of history for - that context. - -Where Queries are presented directly across the HTTP connection as GET requests -to specific URLs, EDUs and PDUs are further wrapped in an envelope called a -Transaction, which is transferred from the origin to the destination home server -using a PUT request. - - -Transactions and EDUs/PDUs -========================== - -The transfer of EDUs and PDUs between home servers is performed by an exchange -of Transaction messages, which are encoded as JSON objects with a dict as the -top-level element, passed over an HTTP PUT request. A Transaction is meaningful -only to the pair of home servers that exchanged it; they are not globally- -meaningful. - -Each transaction has an opaque ID and timestamp (UNIX epoch time in -milliseconds) generated by its origin server, an origin and destination server -name, a list of "previous IDs", and a list of PDUs - the actual message payload -that the Transaction carries. - - {"transaction_id":"916d630ea616342b42e98a3be0b74113", - "ts":1404835423000, - "origin":"red", - "destination":"blue", - "prev_ids":["e1da392e61898be4d2009b9fecce5325"], - "pdus":[...], - "edus":[...]} - -The "previous IDs" field will contain a list of previous transaction IDs that -the origin server has sent to this destination. Its purpose is to act as a -sequence checking mechanism - the destination server can check whether it has -successfully received that Transaction, or ask for a retransmission if not. - -The "pdus" field of a transaction is a list, containing zero or more PDUs.[*] -Each PDU is itself a dict containing a number of keys, the exact details of -which will vary depending on the type of PDU. Similarly, the "edus" field is -another list containing the EDUs. This key may be entirely absent if there are -no EDUs to transfer. - -(* Normally the PDU list will be non-empty, but the server should cope with -receiving an "empty" transaction, as this is useful for informing peers of other -transaction IDs they should be aware of. This effectively acts as a push -mechanism to encourage peers to continue to replicate content.) - -All PDUs have an ID, a context, a declaration of their type, a list of other PDU -IDs that have been seen recently on that context (regardless of which origin -sent them), and a nested content field containing the actual event content. - -[[TODO(paul): Update this structure so that 'pdu_id' is a two-element -[origin,ref] pair like the prev_pdus are]] - - {"pdu_id":"a4ecee13e2accdadf56c1025af232176", - "context":"#example.green", - "origin":"green", - "ts":1404838188000, - "pdu_type":"m.text", - "prev_pdus":[["blue","99d16afbc857975916f1d73e49e52b65"]], - "content":... - "is_state":false} - -In contrast to the transaction layer, it is important to note that the prev_pdus -field of a PDU refers to PDUs that any origin server has sent, rather than -previous IDs that this origin has sent. This list may refer to other PDUs sent -by the same origin as the current one, or other origins. - -Because of the distributed nature of participants in a Matrix conversation, it -is impossible to establish a globally-consistent total ordering on the events. -However, by annotating each outbound PDU at its origin with IDs of other PDUs it -has received, a partial ordering can be constructed allowing causallity -relationships to be preserved. A client can then display these messages to the -end-user in some order consistent with their content and ensure that no message -that is semantically in reply of an earlier one is ever displayed before it. - -PDUs fall into two main categories: those that deliver Events, and those that -synchronise State. For PDUs that relate to State synchronisation, additional -keys exist to support this: - - {..., - "is_state":true, - "state_key":TODO - "power_level":TODO - "prev_state_id":TODO - "prev_state_origin":TODO} - -[[TODO(paul): At this point we should probably have a long description of how -State management works, with descriptions of clobbering rules, power levels, etc -etc... But some of that detail is rather up-in-the-air, on the whiteboard, and -so on. This part needs refining. And writing in its own document as the details -relate to the server/system as a whole, not specifically to server-server -federation.]] - -EDUs, by comparison to PDUs, do not have an ID, a context, or a list of -"previous" IDs. The only mandatory fields for these are the type, origin and -destination home server names, and the actual nested content. - - {"edu_type":"m.presence", - "origin":"blue", - "destination":"orange", - "content":...} - - -Protocol URLs -============= - -All these URLs are namespaced within a prefix of - - /_matrix/federation/v1/... - -For active pushing of messages representing live activity "as it happens": - - PUT .../send/:transaction_id/ - Body: JSON encoding of a single Transaction - - Response: [[TODO(paul): I don't actually understand what - ReplicationLayer.on_transaction() is doing here, so I'm not sure what the - response ought to be]] - - The transaction_id path argument will override any ID given in the JSON body. - The destination name will be set to that of the receiving server itself. Each - embedded PDU in the transaction body will be processed. - - -To fetch a particular PDU: - - GET .../pdu/:origin/:pdu_id/ - - Response: JSON encoding of a single Transaction containing one PDU - - Retrieves a given PDU from the server. The response will contain a single new - Transaction, inside which will be the requested PDU. - - -To fetch all the state of a given context: - - GET .../state/:context/ - - Response: JSON encoding of a single Transaction containing multiple PDUs - - Retrieves a snapshot of the entire current state of the given context. The - response will contain a single Transaction, inside which will be a list of - PDUs that encode the state. - - -To backfill events on a given context: - - GET .../backfill/:context/ - Query args: v, limit - - Response: JSON encoding of a single Transaction containing multiple PDUs - - Retrieves a sliding-window history of previous PDUs that occurred on the - given context. Starting from the PDU ID(s) given in the "v" argument, the - PDUs that preceeded it are retrieved, up to a total number given by the - "limit" argument. These are then returned in a new Transaction containing all - off the PDUs. - - -To stream events all the events: - - GET .../pull/ - Query args: origin, v - - Response: JSON encoding of a single Transaction consisting of multiple PDUs - - Retrieves all of the transactions later than any version given by the "v" - arguments. [[TODO(paul): I'm not sure what the "origin" argument does because - I think at some point in the code it's got swapped around.]] - - -To make a query: - - GET .../query/:query_type - Query args: as specified by the individual query types - - Response: JSON encoding of a response object - - Performs a single query request on the receiving home server. The Query Type - part of the path specifies the kind of query being made, and its query - arguments have a meaning specific to that kind of query. The response is a - JSON-encoded object whose meaning also depends on the kind of query. |