Share data with friends on Firebase -

i developing app needs server backend sync data between devices , friends. while researching if should make own server (which i'd prefer not to) stumpled upon firebase.

what haven´t figured out how public data is. how understood it, whatever send seen every user of app. saw can define rules "the user needs logged in", can specify child should visible user created it? , then, there way invite other user collaborate on child? creator , invited user can see child?

my app running on ios in beginning, guess thats not relevant question, it?

yes can that, can set security rules allow user specific uid (firebase user id) write or read data example...

"users": {   "$uid": {     ".read": "auth != null && auth.uid == $uid"   } } 

also custom authentication can create custom claims grant different access levels (for example admin, editor..etc)

example...

"frood": {   // towel massively useful thing interstellar   // hitchhiker can have   ".read": "auth.hasemergencytowel === true" } 

and invitation part.. can grant permission using child node reference in example...

".read": "data.child(auth.uid).exists()", 

in last case.. if data path requested has child key equal uid of client trying access information able read data,

all detailed information here:

https://firebase.google.com/docs/database/security/user-security#section-revisiting-advanced-example