Solana/SPL Token/Instruction Deep Dive (Part 2)

In the previous lesson, we learned how to use spl_create() to create an SPL token with metadata. In this lesson, we'll dive into another essential operation: how does spl_mint() mint tokens and distribute them to a target address (or to yourself)?

Source Code

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

def spl_mint(self, mint: pxsol.core.PubKey, recv: pxsol.core.PubKey, amount: int) -> None:
    # Mint a specified number of tokens and distribute them to self. 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.
    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(mint, 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.mint_to(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_mint() method assembles a transaction consisting of 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_account_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 automatically creates an associated token account for the recipient. The use of create_idempotent() ensures that the transaction won't fail even if the account already exists. This is the key difference between AssociatedTokenAccount.create_idempotent() and AssociatedTokenAccount.create(). You can think of this instruction as:

• If the target associated token account already exists, exit normally.
• If it doesn't exist, create it and exit normally.

As the name suggests, create_idempotent() is idempotent. In math and computer science, idempotency means that performing the same operation multiple times yields the same result, no side effects from repeated execution.

Instruction 2: Mint Tokens

r1 = pxsol.core.Requisition(pxsol.program.Token.pubkey, [], bytearray())
r1.account.append(pxsol.core.AccountMeta(mint, 1))
r1.account.append(pxsol.core.AccountMeta(recv_account_pubkey, 1))
r1.account.append(pxsol.core.AccountMeta(self.pubkey, 2))
r1.data = pxsol.program.Token.mint_to(amount)

This code mints a specified amount of tokens to the recipient's account. Minting requires mint authority, and in the pxsol.wallet.Wallet design, the token's mint authority is, by default, the token creator.

Minting increases the total supply of the token.