Room Version 1

This room version is the first ever version for rooms, and contains the building blocks for other room versions.

1   Server implementation components

Warning

The information contained in this section is strictly for server implementors. Applications which use the Client-Server API are generally unaffected by the details contained here, and can safely ignore their presence.

The algorithms defined here should only apply to version 1 rooms. Other algorithms may be used by other room versions, and as such servers should be aware of which version room they are dealing with prior to executing a given algorithm.

Warning

Although room version 1 is the most popular room version, it is known to have undesirable effects. Servers implementing support for room version 1 should be aware that restrictions should be generally relaxed and that inconsistencies may occur until room version 2 (or later) is ready and adopted.

1.1   State resolution

Warning

This section documents the state resolution algorithm as implemented by Synapse as of December 2017 (and therefore the de-facto Matrix protocol). However, this algorithm is known to have some problems.

The room state S’(E) after an event E is defined in terms of the room state S(E) before E, and depends on whether E is a state event or a message event:

  • If E is a message event, then S’(E) = S(E).
  • If E is a state event, then S’(E) is S(E), except that its entry corresponding to E's event_type and state_key is replaced by E's event_id.

The room state S(E) before E is the resolution of the set of states {S’(E’), S’(E’’), …} consisting of the states after each of E's prev_events {E’, E’’, …}.

The resolution of a set of states is defined as follows. The resolved state is built up in a number of passes; here we use R to refer to the results of the resolution so far.

  • Start by setting R to the union of the states to be resolved, excluding any conflicting events.
  • First we resolve conflicts between m.room.power_levels events. If there is no conflict, this step is skipped, otherwise:
    • Assemble all the m.room.power_levels events from the states to be resolved into a list.
    • Sort the list by ascending depth then descending sha1(event_id).
    • Add the first event in the list to R.
    • For each subsequent event in the list, check that the event would be allowed by the authorization rules for a room in state R. If the event would be allowed, then update R with the event and continue with the next event in the list. If it would not be allowed, stop and continue below with m.room.join_rules events.
  • Repeat the above process for conflicts between m.room.join_rules events.
  • Repeat the above process for conflicts between m.room.member events.
  • No other events affect the authorization rules, so for all other conflicts, just pick the event with the highest depth and lowest sha1(event_id) that passes authentication in R and add it to R.

A conflict occurs between states where those states have different event_ids for the same (state_type, state_key). The events thus affected are said to be conflicting events.

1.2   Authorization rules

The types of state events that affect authorization are:

  • m.room.create
  • m.room.member
  • m.room.join_rules
  • m.room.power_levels
  • m.room.third_party_invite

The rules are as follows:

  1. If type is m.room.create:
    1. If it has any previous events, reject.
    2. If the domain of the room_id does not match the domain of the sender, reject.
    3. If content.room_version is present and is not a recognised version, reject.
    4. If content has no creator field, reject.
    5. Otherwise, allow.
  2. Reject if event has auth_events that:
    1. have duplicate entries for a given type and state_key pair
    2. have entries whose type and state_key don't match those specified by the auth events selection algorithm described in the server specification.
  3. If event does not have a m.room.create in its auth_events, reject.
  4. If type is m.room.aliases:
    1. If event has no state_key, reject.
    2. If sender's domain doesn't matches state_key, reject.
    3. Otherwise, allow.
  5. If type is m.room.member:
    1. If no state_key key or membership key in content, reject.
    2. If membership is join:
      1. If the only previous event is an m.room.create and the state_key is the creator, allow.
      2. If the sender does not match state_key, reject.
      3. If the sender is banned, reject.
      4. If the join_rule is invite then allow if membership state is invite or join.
      5. If the join_rule is public, allow.
      6. Otherwise, reject.
    3. If membership is invite:
      1. If content has third_party_invite key:
        1. If target user is banned, reject.
        2. If content.third_party_invite does not have a signed key, reject.
        3. If signed does not have mxid and token keys, reject.
        4. If mxid does not match state_key, reject.
        5. If there is no m.room.third_party_invite event in the current room state with state_key matching token, reject.
        6. If sender does not match sender of the m.room.third_party_invite, reject.
        7. If any signature in signed matches any public key in the m.room.third_party_invite event, allow. The public keys are in content of m.room.third_party_invite as:
          1. A single public key in the public_key field.
          2. A list of public keys in the public_keys field.
        8. Otherwise, reject.
      2. If the sender's current membership state is not join, reject.
      3. If target user's current membership state is join or ban, reject.
      4. If the sender's power level is greater than or equal to the invite level, allow.
      5. Otherwise, reject.
    4. If membership is leave:
      1. If the sender matches state_key, allow if and only if that user's current membership state is invite or join.
      2. If the sender's current membership state is not join, reject.
      3. If the target user's current membership state is ban, and the sender's power level is less than the ban level, reject.
      4. If the sender's power level is greater than or equal to the kick level, and the target user's power level is less than the sender's power level, allow.
      5. Otherwise, reject.
    5. If membership is ban:
      1. If the sender's current membership state is not join, reject.
      2. If the sender's power level is greater than or equal to the ban level, and the target user's power level is less than the sender's power level, allow.
      3. Otherwise, reject.
    6. Otherwise, the membership is unknown. Reject.
  6. If the sender's current membership state is not join, reject.
  7. If type is m.room.third_party_invite:
    1. Allow if and only if sender's current power level is greater than or equal to the invite level.
  8. If the event type's required power level is greater than the sender's power level, reject.
  9. If the event has a state_key that starts with an @ and does not match the sender, reject.
  10. If type is m.room.power_levels:
    1. If users key in content is not a dictionary with keys that are valid user IDs with values that are integers (or a string that is an integer), reject.
    2. If there is no previous m.room.power_levels event in the room, allow.
    3. For each of the keys users_default, events_default, state_default, ban, redact, kick, invite, as well as each entry being changed under the events or users keys:
      1. If the current value is higher than the sender's current power level, reject.
      2. If the new value is higher than the sender's current power level, reject.
    4. For each entry being changed under the users key, other than the sender's own entry:
      1. If the current value is equal to the sender's current power level, reject.
    5. Otherwise, allow.
  11. If type is m.room.redaction:
    1. If the sender's power level is greater than or equal to the redact level, allow.
    2. If the domain of the event_id of the event being redacted is the same as the domain of the event_id of the m.room.redaction, allow.
    3. Otherwise, reject.
  12. Otherwise, allow.

Note

Some consequences of these rules:

  • Unless you are a member of the room, the only permitted operations (apart from the initial create/join) are: joining a public room; accepting or rejecting an invitation to a room.
  • To unban somebody, you must have power level greater than or equal to both the kick and ban levels, and greater than the target user's power level.

1.3   Event format

Events in version 1 rooms have the following structure:

1.3.1   Persistent Data Unit schema

A persistent data unit (event) for room versions 1 and 2.

Persistent Data Unit

Parameter Type Description
room_id string Required. Room identifier.
sender string Required. The ID of the user sending the event.
origin string Required. The server_name of the homeserver that created this event.
origin_server_ts integer Required. Timestamp in milliseconds on origin homeserver when this event was created.
type string Required. Event type
state_key string If this key is present, the event is a state event, and it will replace previous events with the same type and state_key in the room state.
content object Required. The content of the event.
prev_events [[string, Event Hash]] Required. Event IDs and reference hashes for the most recent events in the room that the homeserver was aware of when it made this event.
depth integer Required. The maximum depth of the prev_events, plus one. Must be less than the maximum value for an integer (2^63 - 1). If the room's depth is already at the limit, the depth must be set to the limit.
auth_events [[string, Event Hash]] Required. Event IDs and reference hashes for the authorization events that would allow this event to be in the room.
redacts string For redaction events, the ID of the event being redacted.
unsigned Example Unsigned Data Additional data added by the origin server but not covered by the signatures. More keys than those defined here may be used.
event_id string Required. The event ID for the PDU.
hashes Event Hash Required. Content hashes of the PDU, following the algorithm specified in Signing Events.
signatures {string: {string: string}} Required. Signatures for the PDU, following the algorithm specified in Signing Events.

Example Unsigned Data

Parameter Type Description
age integer The number of milliseconds that have passed since this message was sent.
replaces_state string The event ID of the state event this event replaces.
prev_sender string The sender of the replaced state event.
prev_content object The content of the replaced state event.
redacted_because string A reason for why the event was redacted.

Event Hash

Parameter Type Description
sha256 string Required. The hash.

Example:

{
    "auth_events": [
        [
            "$abc123:matrix.org",
            {
                "sha256": "Base64EncodedSha256HashesShouldBe43BytesLong"
            }
        ]
    ],
    "content": {
        "key": "value"
    },
    "depth": 12,
    "event_id": "$a4ecee13e2accdadf56c1025:example.com",
    "hashes": {
        "sha256": "ThisHashCoversAllFieldsInCaseThisIsRedacted"
    },
    "origin": "matrix.org",
    "origin_server_ts": 1234567890,
    "prev_events": [
        [
            "$abc123:matrix.org",
            {
                "sha256": "Base64EncodedSha256HashesShouldBe43BytesLong"
            }
        ]
    ],
    "redacts": "$def456:matrix.org",
    "room_id": "!abc123:matrix.org",
    "sender": "@someone:matrix.org",
    "signatures": {
        "example.com": {
            "ed25519:key_version:": "86BytesOfSignatureOfTheRedactedEvent"
        }
    },
    "state_key": "my_key",
    "type": "m.room.message",
    "unsigned": {
        "key": "value"
    }
}