Room Version 1

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

Client considerations

Clients which implement the redaction algorithm locally should refer to the redactions section below.

Redactions

Upon receipt of a redaction event, the server must strip off any keys not in the following list:

• event_id
• type
• room_id
• sender
• state_key
• content
• hashes
• signatures
• depth
• prev_events
• prev_state
• auth_events
• origin
• origin_server_ts
• membership

The content object must also be stripped of all keys, unless it is one of the following event types:

• m.room.member allows key membership.
• m.room.create allows key creator.
• m.room.join_rules allows key join_rule.
• m.room.power_levels allows keys ban, events, events_default, kick, redact, state_default, users, users_default.
• m.room.aliases allows key aliases.
• m.room.history_visibility allows key history_visibility.

Server implementation components

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.

Redactions

See above.

Event IDs

An event has exactly one event ID. Event IDs in this room version have the format:

$opaque_id:domain

where domain is the server name of the homeserver which created the room, and opaque_id is a locally-unique string.

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 format

Events in version 1 rooms have the following structure:

{
  "auth_events": [
    "$af232176:example.org",
    {
      "sha256": "abase64encodedsha256hashshouldbe43byteslong"
    }
  ],
  "content": {
    "key": "value"
  },
  "depth": 12,
  "event_id": "$a4ecee13e2accdadf56c1025:example.com",
  "hashes": {
    "sha256": "thishashcoversallfieldsincasethisisredacted"
  },
  "origin": "example.com",
  "origin_server_ts": 1404838188000,
  "prev_events": [
    "$af232176:example.org",
    {
      "sha256": "abase64encodedsha256hashshouldbe43byteslong"
    }
  ],
  "room_id": "!UcYsUzyxTGDxLBEvLy:example.org",
  "sender": "@alice:example.com",
  "signatures": {
    "example.com": {
      "ed25519:key_version:": "these86bytesofbase64signaturecoveressentialfieldsincludinghashessocancheckredactedpdus"
    }
  },
  "type": "m.room.message",
  "unsigned": {
    "age": 4612
  }
}

Deprecated event content schemas

Events sent into rooms of this version can have formats which are different from their normal schema. Those cases are documented here.

m.room.power_levels events accept values as strings

In order to maintain backwards compatibility with early implementations, each of the integer-valued properties within m.room.power_levels events can be encoded as strings instead of integers. This includes the nested values within the events, notifications and users properties. For example, the following is a valid m.room.power_levels event in this room version:

{
  "content": {
    "ban": "50",
    "events": {
      "m.room.power_levels": "100"
    },
    "events_default": "0",
    "state_default": "50",
    "users": {
      "@example:localhost": "100"
    },
    "users_default": "0"
  },
  "origin_server_ts": 1432735824653,
  "room_id": "!jEsUZKDJdhlrceRyVU:example.org",
  "sender": "@example:example.org",
  "state_key": "",
  "type": "m.room.power_levels"
}

When the value is representative of an integer, they must be the following format:

• a single base 10 integer, no float values or decimal points, optionally with any number of leading zeroes ("100", "000100");
• optionally prefixed with a single - or + character before the integer ("+100", "-100").
• optionally with any number of leading or trailing whitespace characters (" 100 ", " 00100 ", " +100 ", " -100 ");

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 prev_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 property, reject.
   5. Otherwise, allow.
2. Considering the event’s auth_events:
   1. If there are duplicate entries for a given type and state_key pair, reject.
   2. If there are entries whose type and state_key don’t match those specified by the auth events selection algorithm described in the server specification, reject.
   3. If there are entries which were themselves rejected under the checks performed on receipt of a PDU, reject.
   4. If there is no m.room.create event among the entries, reject.
3. If the content of the m.room.create event in the room state has the property m.federate set to false, and the sender domain of the event does not match the sender domain of the create event, 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 there is no state_key property, or no membership property 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 a third_party_invite property:
         1. If target user is banned, reject.
         2. If content.third_party_invite does not have a signed property, reject.
         3. If signed does not have mxid and token properties, 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 property.
            2. A list of public keys in the public_keys property.
         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 the users property in content is not an object 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 the properties users_default, events_default, state_default, ban, redact, kick, invite check if they were added, changed or removed. For each found alteration:
       1. If the current value is greater than the sender’s current power level, reject.
       2. If the new value is greater than the sender’s current power level, reject.
    4. For each entry being changed in, or removed from, the events property:
       1. If the current value is greater than the sender’s current power level, reject.
    5. For each entry being added to, or changed in, the events property:
       1. If the new value is greater than the sender’s current power level, reject.
    6. For each entry being changed in, or removed from, the users property, other than the sender’s own entry:
       1. If the current value is greater than or equal to the sender’s current power level, reject.
    7. For each entry being added to, or changed in, the users property:
       1. If the new value is greater than the sender’s current power level, reject.
    8. 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.

State resolution

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 the event_type and state_key of E is replaced by the event_id of E.

The room state S(E) before E is the resolution of the set of states {S′(E′), S′(E″), …} after the prev_events {E′, E″, …}. of 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 (event_type, state_key). The events thus affected are said to be conflicting events.

Canonical JSON

Servers MUST NOT strictly enforce the JSON format specified in the appendices for the reasons described there.