What is the difference between TOKEN_PROGRAM_ID and ASSOCIATED_TOKEN_ACCOUNT_PROGRAM_ID?

Question

There are two program ids in the code base of solana-program-library. To be precise:

ASSOCIATED_TOKEN_ACCOUNT_PROGRAM_ID = 'ATokenGPvbdGVxr1b2hvZbsiqW5xWH25efTNsLJA8knL'
TOKEN_PROGRAM_ID = 'TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA'

And I do not get the idea of separating these two programs and the general use of them. I mean, I'm well aware of the idea of tokens. But why there are two programs? I have flicked through the code and have noticed such a thing, that there is no js client to associated-token-account, only program. And it seems that it is used only as a part of the @solana/spl-token js client.

As far as I can get it, ASSOCIATED_TOKEN_ACCOUNT_PROGRAM_ID serves only one purpose, this is creation of new accounts. Plus, there is fn process_recover_nested(...) which usage is obscure for me.

So I would appreciate someone's explanation of this differentiation and usage purposes.

Answer 1

Every token needs to be held in an associated token account. This is mapped to a wallet. When minting or transferring, you interact with both of these programs. And I believe process_recover_nested() helps with closing these out so you can recover the SOL balance after you're done minting or transferring a token.

Here's more info on each one:

Associated Token Accounts - defines the convention and provides the mechanism for mapping the user's wallet address to the associated token accounts they hold.

Token Program - This program defines a common implementation for Fungible and Non Fungible tokens.

Closing Accounts process_recover_nested() I believe exists to transfer back the SOL and close out the accounts so you can recover the rent/storage of unneeded accounts after minting or transferring. Note: You can't recover this if you don't use a candy machine or create/own the ATA. For example, if you airdrop directly to a users wallet, you'd be creating and funding the ATA for each token on their behalf, that you don't own, and can't close.