I am working on an appengine app in Go and when I tried to get an appengine User's ID and convert it to a 64-bit int with this code:
id, err := strconv.ParseInt(user.ID, 10, 64)
I got this error:
ERROR: error executing inner: strconv.ParseInt: parsing "185804764220139124118": value out of range
Does this error occur on appengine IDs in deployed code as well?
The ID field of the User type is defined with type string. Just because it contains digits, there is no guarantee that it fits into an int64.
The Go AppengineSDK uses values that fit into int64, but this is not true in production environment. They are usually longer than the max value of int64. They are handed to you as strings, so treat them like that: strings. Nothing forces you to convert them to a number. I don't know where you got the idea to convert them to numbers, but don't do that. They are strings.
Note: User.ID is not to be mistaken with Key.IntID() which is defined to be of type int64.
Most probably yes. Reading app engine documentation, it is written that:
The default policy generates a random sequence of unused IDs that are approximately uniformly distributed. Each ID can be up to 16 decimal digits long.
From Go specs int32 is -2147483648 through 2147483647. which is not enough for 16 decimals, but int64 is enough.