182 lines
7.1 KiB
ReStructuredText
182 lines
7.1 KiB
ReStructuredText
============================
|
|
Synapse Server-to-Server API
|
|
============================
|
|
|
|
A description of the protocol used to communicate between Synapse home servers;
|
|
also known as Federation.
|
|
|
|
|
|
Overview
|
|
========
|
|
|
|
The server-server API is a mechanism by which two home servers can exchange
|
|
Synapse 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.
|
|
|
|
|
|
{ Synapse entities } { Synapse entities }
|
|
^ | ^ |
|
|
| events | | events |
|
|
| V | V
|
|
+------------------+ +------------------+
|
|
| |---------( HTTP )---------->| |
|
|
| Home Server | | Home Server |
|
|
| |<--------( HTTP )-----------| |
|
|
+------------------+ +------------------+
|
|
|
|
|
|
Transactions and PDUs
|
|
=====================
|
|
|
|
The communication between home servers is performed by a bidirectional exchange
|
|
of messages. These messages are called Transactions, and are encoded as JSON
|
|
objects with a dict as the top-level element, passed over HTTP. 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 miliseconds)
|
|
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":[...]}
|
|
|
|
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.
|
|
|
|
(* 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 Synapse 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.]]
|
|
|
|
|
|
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 paginate events on a given context:
|
|
|
|
GET .../paginate/: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.]]
|