Solana/SPL Token/Instruction Deep Dive (Part 3)

This section takes you deep into the on-chain logic behind SPL token transfers, helping you master the correct way to securely and automatically transfer SPL tokens on Solana. The spl_transfer() method primarily does two things:

• Ensures the recipient's associated token account exists. If it doesn't, it creates one automatically.
• Transfers the specified amount of tokens from the sender's associated token account to the recipient's.

Source Code

To save you from constantly switching pages, here's the full code we'll be analyzing.

def spl_transfer(self, mint: pxsol.core.PubKey, recv: pxsol.core.PubKey, amount: int) -> None:
    # Transfers tokens to the target. Note that amount refers to the smallest unit of count, For example, when the
    # decimals of token is 2, you should use 100 to represent 1 token. If the token account does not exist, it will
    # be created automatically.
    self_ata_pubkey = self.spl_account(mint)
    recv_ata_pubkey = Wallet.view_only(recv).spl_account(mint)
    r0 = pxsol.core.Requisition(pxsol.program.AssociatedTokenAccount.pubkey, [], bytearray())
    r0.account.append(pxsol.core.AccountMeta(self.pubkey, 3))
    r0.account.append(pxsol.core.AccountMeta(recv_ata_pubkey, 1))
    r0.account.append(pxsol.core.AccountMeta(recv, 0))
    r0.account.append(pxsol.core.AccountMeta(mint, 0))
    r0.account.append(pxsol.core.AccountMeta(pxsol.program.System.pubkey, 0))
    r0.account.append(pxsol.core.AccountMeta(pxsol.program.Token.pubkey, 0))
    r0.data = pxsol.program.AssociatedTokenAccount.create_idempotent()
    r1 = pxsol.core.Requisition(pxsol.program.Token.pubkey, [], bytearray())
    r1.account.append(pxsol.core.AccountMeta(self_ata_pubkey, 1))
    r1.account.append(pxsol.core.AccountMeta(recv_ata_pubkey, 1))
    r1.account.append(pxsol.core.AccountMeta(self.pubkey, 2))
    r1.data = pxsol.program.Token.transfer(amount)
    tx = pxsol.core.Transaction.requisition_decode(self.pubkey, [r0, r1])
    tx.message.recent_blockhash = pxsol.base58.decode(pxsol.rpc.get_latest_blockhash({})['blockhash'])
    tx.sign([self.prikey])
    txid = pxsol.rpc.send_transaction(base64.b64encode(tx.serialize()).decode(), {})
    pxsol.rpc.wait([txid])

Breakdown of Implementation

The spl_transfer() method assembles and sends a transaction that contains two on-chain instructions.

Instruction 1: Create Associated Token Account

r0 = pxsol.core.Requisition(pxsol.program.AssociatedTokenAccount.pubkey, [], bytearray())
r0.account.append(pxsol.core.AccountMeta(self.pubkey, 3))
r0.account.append(pxsol.core.AccountMeta(recv_ata_pubkey, 1))
r0.account.append(pxsol.core.AccountMeta(recv, 0))
r0.account.append(pxsol.core.AccountMeta(mint, 0))
r0.account.append(pxsol.core.AccountMeta(pxsol.program.System.pubkey, 0))
r0.account.append(pxsol.core.AccountMeta(pxsol.program.Token.pubkey, 0))
r0.data = pxsol.program.AssociatedTokenAccount.create_idempotent()

This code serves the same purpose and function as the first instruction in spl_mint(), ensuring the recipient's associated token account exists.

Instruction 2: Transfer Tokens

r1 = pxsol.core.Requisition(pxsol.program.Token.pubkey, [], bytearray())
r1.account.append(pxsol.core.AccountMeta(self_ata_pubkey, 1))
r1.account.append(pxsol.core.AccountMeta(recv_ata_pubkey, 1))
r1.account.append(pxsol.core.AccountMeta(self.pubkey, 2))
r1.data = pxsol.program.Token.transfer(amount)

This code transfers the specified amount of tokens from the sender's account to the recipient's account. The transfer is ultimately verified and accounted for by the Token-2022 program, which updates both parties' balances accordingly.