matrix-spec/event-schemas/examples/m.room.message#m.file

{
  "age": 146,
  "content": {
    "body": "something-important.doc",
    "filename": "something-important.doc",
    "info": {
      "mimetype": "application/msword",
      "size": 46144
    },
    "msgtype": "m.file",
    "url": "mxc://localhost/FHyPlCeYUSFFxlgbQYZmoEoe"
  },
  "event_id": "$143273582443PhrSn:localhost",
  "origin_server_ts": 1432735824653,
  "room_id": "!jEsUZKDJdhlrceRyVU:localhost",
  "type": "m.room.message",
  "sender": "@example:localhost"
}