Unmarshal onto partial membershipContent (#428)

This fixes cases where we e.g. receive valid events, but are unable to
unmarshal onto `MembershipContent` because of an invalid `displayname`
(which we don't care about when authing events):

```
json: cannot unmarshal bool into Go struct field MemberContent.displayname of type string"
```

eventauth.go

@@ -112,6 +112,9 @@ type membershipContent struct {
  // The user that authorised the join, in the case that the restricted join
  // rule is in effect.
  AuthorizedVia string `json:"join_authorised_via_users_server,omitempty"`
+
+ // The MXIDMapping used in pseudo ID rooms
+ MXIDMapping *MXIDMapping `json:"mxid_mapping,omitempty"`
 }
 
 // StateNeededForProtoEvent returns the event types and state_keys needed to authenticate the
@@ -983,7 +986,7 @@ func (m *membershipAllower) membershipAllowed(event PDU) error { // nolint: gocy
  var sender *spec.UserID
  var err error
  if event.Type() == spec.MRoomMember {
- mapping := MemberContent{}
+ mapping := membershipContent{}
  if err := json.Unmarshal(event.Content(), &mapping); err != nil {
  return err
  }

eventauth_test.go

@@ -1539,3 +1539,57 @@ func Test_checkUserLevels(t *testing.T) {
  })
  }
 }
+
+// Test that we allow broken membership content, i.e.
+// displayname is boolean, an object or array
+func TestMembershipAllowed(t *testing.T) {
+ testEventAllowed(t, `{
+ "auth_events": {
+ "create": {
+ "type": "m.room.create",
+ "state_key": "",
+ "sender": "@u1:a",
+ "room_id": "!r1:a",
+ "event_id": "$e1:a",
+ "content": {"creator": "@u1:a"}
+ }
+ },
+ "allowed": [{
+ "type": "m.room.member",
+ "state_key": "@u1:a",
+ "sender": "@u1:a",
+ "room_id": "!r1:a",
+ "event_id": "$e2:a",
+ "prev_events": [["$e1:a", {}]],
+ "content": {"membership": "join", "displayname": false}
+ },
+ {
+ "type": "m.room.member",
+ "state_key": "@u1:a",
+ "sender": "@u1:a",
+ "room_id": "!r1:a",
+ "event_id": "$e2:a",
+ "prev_events": [["$e1:a", {}]],
+ "content": {"membership": "join", "displayname": {}}
+ },
+ {
+ "type": "m.room.member",
+ "state_key": "@u1:a",
+ "sender": "@u1:a",
+ "room_id": "!r1:a",
+ "event_id": "$e2:a",
+ "prev_events": [["$e1:a", {}]],
+ "content": {"membership": "join", "displayname": 0}
+ },
+ {
+ "type": "m.room.member",
+ "state_key": "@u1:a",
+ "sender": "@u1:a",
+ "room_id": "!r1:a",
+ "event_id": "$e2:a",
+ "prev_events": [["$e1:a", {}]],
+ "content": {"membership": "join", "displayname": []}
+ }],
+ "not_allowed": []
+ }`)
+}

eventcontent.go

@@ -213,6 +213,7 @@ func NewMemberContentFromEvent(event PDU) (c MemberContent, err error) {
  c.Membership = partial.Membership
  c.ThirdPartyInvite = partial.ThirdPartyInvite
  c.AuthorisedVia = partial.AuthorizedVia
+ c.MXIDMapping = partial.MXIDMapping
  }
  return
 }