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Redo architecture diagram. Reword parts of federation. Formatting fixes and tweaks.

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Kegan Dougal 2014-08-29 10:30:14 +01:00
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docs/specification.rst
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@ -28,6 +28,9 @@ Architecture
- Client is an end-user (web app, mobile app) which uses C-S APIs to talk to the home server.
A given client is typically responsible for a single user.
- A single user is represented by a User ID, scoped to the home server which allocated the account.
User IDs MUST have @ prefix; looks like @foo:domain - domain indicates the user's home
server.
- Home server provides C-S APIs and has the ability to federate with other HSes.
Typically responsible for N clients.
- Federation's purpose is to share content between interested HSes; no SPOF.
@ -46,10 +49,16 @@ participants in that room will receive the message. Rooms are uniquely
identified via a room ID. There is exactly one room ID for each room. Each
room can also have an alias. Each room can have many aliases.
::
- Room IDs MUST have ! prefix; looks like !foo:domain - domain is simply for namespacing,
the room does NOT reside on any one domain. NOT human readable.
How events flow in rooms
========================
- Room Aliases MUST have # prefix; looks like #foo:domain - domain indicates where this
alias can be mapped to a room ID. Key point: human readable / friendly.
- Aliases can be queried on the domain they specify, which will return a room ID if a
mapping exists. These mappings can change.
::
{ @alice:matrix.org } { @bob:domain.com }
| ^
@ -61,23 +70,22 @@ room can also have an alias. Each room can have many aliases.
V |
+------------------+ +------------------+
| Home Server | | Home Server |
| matrix.org |<-------Federation--------->| domain.com |
| matrix.org |<-------Federation------->| domain.com |
+------------------+ +------------------+
Room ID: !qporfwt:matrix.org Room ID: !qporfwt:matrix.org
Servers: matrix.org, domain.com Servers: matrix.org, domain.com
Members: Members:
- @alice:matrix.org - @alice:matrix.org
- @bob:domain.com - @bob:domain.com
| ................................. |
|______| Shared State |_______|
| Room ID: !qporfwt:matrix.org |
| Servers: matrix.org, domain.com |
| Members: |
| - @alice:matrix.org |
| - @bob:domain.com |
|.................................|
- Federation's goal is to maintain the shared state. Don't need FULL state in order
to be a part of a room.
- Introduce the DAG.
- Events are wrapped in PDUs.
- Room IDs MUST have ! prefix; looks like !foo:domain - domain is simply for namespacing,
the room does NOT reside on domain. NOT human readable.
- Room Aliases MUST have # prefix; looks like #foo:domain - domain indicates where this
alias can be mapped to a room ID. Key point: human readable / friendly.
- User IDs MUST have @ prefix; looks like @foo:domain - domain indicates the user's home
server.
- Aliases can be queried on the domain they specify, which will return a room ID if a
mapping exists. These mappings can change.
Identity
--------
@ -103,7 +111,7 @@ Receiving live updates on a client
Rooms
=====
- How are they created?
- How are they created? PDU anchor point: "root of the tree".
- Adding / removing aliases.
- Invite/join dance
- State and non-state data (+extensibility)
@ -167,7 +175,7 @@ below:
- ``body`` : "string" - The alt text of the image, or some kind of content
description for accessibility e.g. "image attachment".
ImageInfo:
ImageInfo:
Information about an image::
{
@ -186,8 +194,7 @@ ImageInfo:
- ``body`` : "string" - A description of the audio e.g. "Bee Gees -
Stayin' Alive", or some kind of content description for accessibility e.g.
"audio attachment".
AudioInfo:
AudioInfo:
Information about a piece of audio::
{
@ -205,7 +212,7 @@ AudioInfo:
- ``body`` : "string" - A description of the video e.g. "Gangnam style",
or some kind of content description for accessibility e.g. "video attachment".
VideoInfo:
VideoInfo:
Information about a video::
{
@ -624,61 +631,62 @@ can also be performed.
There are three main kinds of communication that occur between home servers:
- Queries
:Queries:
These are single request/response interactions between a given pair of
servers, initiated by one side sending an HTTP request to obtain some
servers, initiated by one side sending an HTTP GET 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
:Ephemeral Data Units (EDUs):
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
:Persisted Data Units (PDUs):
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.
EDUs and PDUs are further wrapped in an envelope called a Transaction, which is
transferred from the origin to the destination home server using an HTTP PUT request.
Transactions and EDUs/PDUs
--------------------------
Transactions
------------
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.
of Transaction messages, which are encoded as JSON objects, 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.
Each transaction has:
- An opaque transaction ID.
- A timestamp (UNIX epoch time in milliseconds) generated by its origin server.
- An origin and destination server name.
- A list of "previous IDs".
- A list of PDUs and EDUs - the actual message payload that the Transaction carries.
::
{"transaction_id":"916d630ea616342b42e98a3be0b74113",
{
"transaction_id":"916d630ea616342b42e98a3be0b74113",
"ts":1404835423000,
"origin":"red",
"destination":"blue",
"prev_ids":["e1da392e61898be4d2009b9fecce5325"],
"pdus":[...],
"edus":[...]}
"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
The ``prev_ids`` field contains 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
The ``pdus`` field of a transaction is a list, containing zero or more PDUs.[*]
Each PDU is itself a JSON object 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.
@ -687,27 +695,35 @@ 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.
PDUs and EDUs
-------------
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)
[[TODO(paul): Update this structure so that 'pdu_id' is a two-element
[origin,ref] pair like the prev_pdus are]]
::
{"pdu_id":"a4ecee13e2accdadf56c1025af232176",
{
"pdu_id":"a4ecee13e2accdadf56c1025af232176",
"context":"#example.green",
"origin":"green",
"ts":1404838188000,
"pdu_type":"m.text",
"prev_pdus":[["blue","99d16afbc857975916f1d73e49e52b65"]],
"content":...
"is_state":false}
"is_state":false
}
In contrast to the transaction layer, it is important to note that the prev_pdus
In contrast to Transactions, 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
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