Firebase push key - allowed characters

Question

I am wondering what kind of characters are allowed in the push key. Does it generate also a symbol underscore(_)? I always get a push key with letters with -.

Answer 1

Push keys use a modified Base64 alphabet:

-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz

They are comprised of a timestamp and a random value. The algorithm is described here.

With Firebase keys in general, there is a small set of illegal characters and they are listed in this answer:

Character Set Limitations

Note that URLs used to construct Firebase references may contain any unicode characters except:

• . (period)
• $ (dollar sign)
• [ (left square bracket)
• ] (right square bracket)
• # (hash or pound sign)
• / (forward slash)