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Merge pull request #359 from matrix-org/rav/mxid_grammar

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Define MXID grammar
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Richard van der Hoff 8 years ago committed by GitHub
parent e5f5d0c55e 72449294bc
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specification/intro.rst
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@ -94,11 +94,8 @@ instant messages, VoIP call setups, or any other objects that need to be
reliably and persistently pushed from A to B in an inter-operable and federated
manner.
Overview
--------
Architecture
~~~~~~~~~~~~
------------
Matrix defines APIs for synchronising extensible JSON objects known as
"events" between compatible clients, servers and services. Clients are
@ -142,7 +139,7 @@ a long-lived GET request.
| V | V
+------------------+ +------------------+
| |---------( HTTPS )--------->| |
| homeserver | | homeserver |
| homeserver | | homeserver |
| |<--------( HTTPS )----------| |
+------------------+ Server-Server API +------------------+
History Synchronisation
@ -150,22 +147,19 @@ a long-lived GET request.
Users
+++++
~~~~~
Each client is associated with a user account, which is identified in Matrix
using a unique "User ID". This ID is namespaced to the homeserver which
using a unique "user ID". This ID is namespaced to the homeserver which
allocated the account and has the form::
@localpart:domain
The ``localpart`` of a user ID may be a user name, or an opaque ID identifying
this user. The ``domain`` of a user ID is the domain of the homeserver.
.. TODO-spec
- Need to specify precise grammar for Matrix IDs
See the `Identifier Grammar`_ section for full details of the structure of
user IDs.
Events
++++++
~~~~~~
All data exchanged over Matrix is expressed as an "event". Typically each client
action (e.g. sending a message) correlates with exactly one event. Each event
@ -180,7 +174,7 @@ of a "Room".
.. _package naming conventions: https://en.wikipedia.org/wiki/Java_package#Package_naming_conventions
Event Graphs
++++++++++++
~~~~~~~~~~~~
.. _sect:event-graph:
@ -204,7 +198,7 @@ of its parents. The root event should have a depth of 1. Thus if one event is
before another, then it must have a strictly smaller depth.
Room structure
++++++++++++++
~~~~~~~~~~~~~~
A room is a conceptual place where users can send and receive events. Events are
sent to a room, and all participants in that room with sufficient access will
@ -215,8 +209,12 @@ which have the form::
There is exactly one room ID for each room. Whilst the room ID does contain a
domain, it is simply for globally namespacing room IDs. The room does NOT
reside on the domain specified. Room IDs are not meant to be human readable.
They are case-sensitive. The following conceptual diagram shows an
reside on the domain specified.
See the `Identifier Grammar`_ section for full details of the structure of
a room ID.
The following conceptual diagram shows an
``m.room.message`` event being sent to the room ``!qporfwt:matrix.org``::
{ @alice:matrix.org } { @bob:domain.com }
@ -229,7 +227,7 @@ They are case-sensitive. The following conceptual diagram shows an
| |
V |
+------------------+ +------------------+
| homeserver | | homeserver |
| homeserver | | homeserver |
| matrix.org | | domain.com |
+------------------+ +------------------+
| ^
@ -283,23 +281,21 @@ from the other servers participating in a room.
Room Aliases
^^^^^^^^^^^^
++++++++++++
Each room can also have multiple "Room Aliases", which look like::
#room_alias:domain
.. TODO
- Need to specify precise grammar for Room Aliases
See the `Identifier Grammar`_ section for full details of the structure of
a room alias.
A room alias "points" to a room ID and is the human-readable label by which
rooms are publicised and discovered. The room ID the alias is pointing to can
be obtained by visiting the domain specified. Note that the mapping from a room
alias to a room ID is not fixed, and may change over time to point to a
different room ID. For this reason, Clients SHOULD resolve the room alias to a
room ID once and then use that ID on subsequent requests. Room aliases MUST NOT
exceed 255 bytes (including the domain).
room ID once and then use that ID on subsequent requests.
When resolving a room alias the server will also respond with a list of servers
that are in the room that can be used to join via.
@ -319,16 +315,16 @@ that are in the room that can be used to join via.
|________________________________|
Identity
++++++++
~~~~~~~~
Users in Matrix are identified via their matrix user ID (MXID). However,
Users in Matrix are identified via their Matrix user ID. However,
existing 3rd party ID namespaces can also be used in order to identify Matrix
users. A Matrix "Identity" describes both the user ID and any other existing IDs
from third party namespaces *linked* to their account.
Matrix users can *link* third-party IDs (3PIDs) such as email addresses, social
network accounts and phone numbers to their user ID. Linking 3PIDs creates a
mapping from a 3PID to a user ID. This mapping can then be used by Matrix
users in order to discover the MXIDs of their contacts.
users in order to discover the user IDs of their contacts.
In order to ensure that the mapping from 3PID to user ID is genuine, a globally
federated cluster of trusted "Identity Servers" (IS) are used to verify the 3PID
and persist and replicate the mappings.
@ -339,7 +335,7 @@ user IDs using 3PIDs.
Profiles
++++++++
~~~~~~~~
Users may publish arbitrary key/value data associated with their account - such
as a human readable display name, a profile photo URL, contact information
@ -350,7 +346,7 @@ as a human readable display name, a profile photo URL, contact information
names allowed to be?
Private User Data
+++++++++++++++++
~~~~~~~~~~~~~~~~~
Users may also store arbitrary private key/value data in their account - such as
client preferences, or server configuration settings which lack any other
@ -361,6 +357,220 @@ dedicated API. The API is symmetrical to managing Profile data.
private user data, but with different ACLs?
Identifier Grammar
------------------
Server Name
~~~~~~~~~~~
A homeserver is uniquely identified by its server name. This value is used in a
number of identifiers, as described below.
The server name represents the address at which the homeserver in question can
be reached by other homeservers. The complete grammar is::
server_name = dns_name [ ":" port]
dns_name = host
port = *DIGIT
where ``host`` is as defined by `RFC3986, section 3.2.2
<https://tools.ietf.org/html/rfc3986#section-3.2.2>`_.
Examples of valid server names are:
* ``matrix.org``
* ``matrix.org:8888``
* ``1.2.3.4`` (IPv4 literal)
* ``1.2.3.4:1234`` (IPv4 literal with explicit port)
* ``[1234:5678::abcd]`` (IPv6 literal)
* ``[1234:5678::abcd]:5678`` (IPv6 literal with explicit port)
Common Identifier Format
~~~~~~~~~~~~~~~~~~~~~~~~
The Matrix protocol uses a common format to assign unique identifiers to a
number of entities, including users, events and rooms. Each identifier takes
the form::
&localpart:domain
where ``&`` represents a 'sigil' character; ``domain`` is the `server name`_ of
the homeserver which allocated the identifier, and ``localpart`` is an
identifier allocated by that homeserver.
The sigil characters are as follows:
* ``@``: User ID
* ``!``: Room ID
* ``$``: Event ID
* ``#``: Room alias
The precise grammar defining the allowable format of an identifier depends on
the type of identifier.
User Identifiers
++++++++++++++++
Users within Matrix are uniquely identified by their Matrix user ID. The user
ID is namespaced to the homeserver which allocated the account and has the
form::
@localpart:domain
The ``localpart`` of a user ID is an opaque identifier for that user. It MUST
NOT be empty, and MUST contain only the characters ``a-z``, ``0-9``, ``.``,
``_``, ``=``, and ``-``.
The ``domain`` of a user ID is the `server name`_ of the homeserver which
allocated the account.
The length of a user ID, including the ``@`` sigil and the domain, MUST NOT
exceed 255 characters.
The complete grammar for a legal user ID is::
user_id = "@" user_id_localpart ":" server_name
user_id_localpart = 1*user_id_char
user_id_char = DIGIT
/ %x61-7A ; a-z
/ "-" / "." / "=" / "_"
.. admonition:: Rationale
A number of factors were considered when defining the allowable characters
for a user ID.
Firstly, we chose to exclude characters outside the basic US-ASCII character
set. User IDs are primarily intended for use as an identifier at the protocol
level, and their use as a human-readable handle is of secondary
benefit. Furthermore, they are useful as a last-resort differentiator between
users with similar display names. Allowing the full unicode character set
would make very difficult for a human to distinguish two similar user IDs. The
limited character set used has the advantage that even a user unfamiliar with
the Latin alphabet should be able to distinguish similar user IDs manually, if
somewhat laboriously.
We chose to disallow upper-case characters because we do not consider it
valid to have two user IDs which differ only in case: indeed it should be
possible to reach ``@user:matrix.org`` as ``@USER:matrix.org``. However,
user IDs are necessarily used in a number of situations which are inherently
case-sensitive (notably in the ``state_key`` of ``m.room.member``
events). Forbidding upper-case characters (and requiring homeservers to
downcase usernames when creating user IDs for new users) is a relatively simple
way to ensure that ``@USER:matrix.org`` cannot refer to a different user to
``@user:matrix.org``.
Finally, we decided to restrict the allowable punctuation to a very basic set
to ensure that the identifier can be used as-is in as wide a number of
situations as possible, without requiring escaping. For instance, allowing
"%" or "/" would make it harder to use a user ID in a URI. "*" is used as a
wildcard in some APIs (notably the filter API), so it also cannot be a legal
user ID character.
The length restriction is derived from the limit on the length of the
``sender`` key on events; since the user ID appears in every event sent by the
user, it is limited to ensure that the user ID does not dominate over the actual
content of the events.
Matrix user IDs are sometimes informally referred to as MXIDs.
Historical User IDs
<<<<<<<<<<<<<<<<<<<
Older versions of this specification were more tolerant of the characters
permitted in user ID localparts. There are currently active users whose user
IDs do not conform to the permitted character set, and a number of rooms whose
history includes events with a ``sender`` which does not conform. In order to
handle these rooms successfully, clients and servers MUST accept user IDs with
localparts from the expanded character set::
extended_user_id_char = %x21-7E
Mapping from other character sets
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
In certain circumstances it will be desirable to map from a wider character set
onto the limited character set allowed in a user ID localpart. Examples include
a homeserver creating a user ID for a new user based on the username passed to
``/register``, or a bridge mapping user ids from another protocol.
.. TODO-spec
We need to better define the mechanism by which homeservers can allow users
to have non-Latin login credentials. The general idea is for clients to pass
the non-Latin in the ``username`` field to ``/register`` and ``/login``, and
the HS then maps it onto the MXID space when turning it into the
fully-qualified ``user_id`` which is returned to the client and used in
events.
Implementations are free to do this mapping however they choose. Since the user
ID is opaque except to the implementation which created it, the only
requirement is that the implemention can perform the mapping
consistently. However, we suggest the following algorithm:
1. Encode character strings as UTF-8.
2. Convert the bytes ``A-Z`` to lower-case.
* In the case where a bridge must be able to distinguish two different users
with ids which differ only by case, escape upper-case characters by
prefixing with ``_`` before downcasing. For example, ``A`` becomes
``_a``. Escape a real ``_`` with a second ``_``.
3. Encode any remaining bytes outside the allowed character set, as well as
``=``, as their hexadecimal value, prefixed with ``=``. For example, ``#``
becomes ``=23``; ``á`` becomes ``=c3=a1``.
.. admonition:: Rationale
The suggested mapping is an attempt to preserve human-readability of simple
ASCII identifiers (unlike, for example, base-32), whilst still allowing
representation of *any* character (unlike punycode, which provides no way to
encode ASCII punctuation).
Room IDs and Event IDs
++++++++++++++++++++++
A room has exactly one room ID. A room ID has the format::
!opaque_id:domain
An event has exactly one event ID. An event ID has the format::
$opaque_id:domain
The ``domain`` of a room/event ID is the `server name`_ of the homeserver which
created the room/event. The domain is used only for namespacing to avoid the
risk of clashes of identifiers between different homeservers. There is no
implication that the room or event in question is still available at the
corresponding homeserver.
Event IDs and Room IDs are case-sensitive. They are not meant to be human
readable.
.. TODO-spec
What is the grammar for the opaque part? https://matrix.org/jira/browse/SPEC-389
Room Aliases
++++++++++++
A room may have zero or more aliases. A room alias has the format::
#room_alias:domain
The ``domain`` of a room alias is the `server name`_ of the homeserver which
created the alias. Other servers may contact this homeserver to look up the
alias.
Room aliases MUST NOT exceed 255 bytes (including the ``#`` sigil and the
domain).
.. TODO-spec
- Need to specify precise grammar for Room Aliases. https://matrix.org/jira/browse/SPEC-391
License
-------

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