flatc-build-cmd.sh

# To build the flatbuffer binary
flatc -c -b member.fbs m.room.member_example.json
# see member_generated.h for the code that gets generated that's capable of reading the binary message

# The .h is for C. To generate other language bindings:
flatc --js -c -b member.fbs m.room.member_example.json
flatc --go -c -b member.fbs m.room.member_example.json
flatc --python -c -b member.fbs m.room.member_example.json
flatc --csharp -c -b member.fbs m.room.member_example.json
# etc...

# To parse json back out from the flatbuffer (just for debugging, kind of defeats the purpose to use this in practice):
flatc --strict-json --raw-binary -o json_out -t member.fbs -- m.room.member_example.bin
# (see contents of json_out folder)

m.room.member_example.json

{
  "age": 242352,
  "content": {
    "membership": "join",
    "avatar_url": "mxc://localhost/SEsfnsuifSDFSSEF#auto",
    "displayname": "Alice Margatroid"
  },
  "invite_room_state": [
    {
      "type": "m.room.name",
      "state_key": "",
      "content": {
        "name": "Forest of Magic"
      }
    },
    {
      "type": "m.room.join_rules",
      "state_key": "",
      "content": {
        "join_rules": "invite"
      }
    }
  ],
  "state_key": "@alice:localhost",
  "origin_server_ts": 1431961217939,
  "event_id": "$WLGTSEFSEF:localhost",
  "type": "m.room.member",
  "room_id": "!Cuyf34gef24t:localhost",
  "sender": "@example:localhost"
}

member.fbs

table MemberContent {
  membership:string;
  avatar_url:string;
  displayname:string;
}

table RoomStateContent {
  name:string;
  join_rules:string;
}

table RoomState {
  type:string;
  state_key:string;
  content:RoomStateContent;
}

table Member {
  age:int;
  content:MemberContent;
  state_key:string;
  origin_server_ts:ulong;
  event_id:string;
  type:string;
  room_id:string;
  sender:string;
  invite_room_state:[RoomState];
}

root_type Member;