How to allow at most two people to be in a chat room in Firebase rules?

Question

I want to use Firebase to setup a 2 person chat. The users will be able to chat when they 'liked' each other. I'm handling the 'liking' on my own SQL server but I want to use Firebase for the chat.

This is dummy data, it wil look like this eventually.

{
  "admins": {
    "chat1": {
      "user_id_1": {
        "active": true
      },
      "user_id_2": {
        "active": true
      }
    }
  },
  "chats": {
    "chat1": {
      "messages": {
        "random_id": {
          "message": "first message",
          "sender": "user_id_1"
        }
      }
    }
  }
}

These are my rules:

{
  "rules": {      
    "admins": {
      "$chatAdmin": {

      }
    },
    "chats": {
      "$chat": {
        ".read": "root.child('admins').child($chat).hasChild(auth.uid)",
        ".write": "root.child('admins').child($chat).hasChild(auth.uid)"
      }
    }
  }
}

So what I want is that every time two users are a 'match', so they 'liked' each other. I want to create their chat in /chats/{sha1(uid1 + uid2)} and give only those 2 users access to it, read and write.

Answer 1

thank me later, hack >

a long as firebase doesn change uid format

export async function sendMessage(myUid, otherUid, content) {
    const conversationId = createConversationId(myUid, otherUid)
    const data = { content, timestamp: new Date().getTime(), authorUid: myUid }
    await firebase.database().ref(`conversations/${conversationId}`).push(data)
    return
}

export function createConversationId(uid1, uid2) {
    return uid1 > uid2 ? `${uid2}${uid1}` : `${uid1}${uid2}`
}

also see

https://gist.github.com/katowulf/4741111