inner_transactions.md

Inner transactions

Example use

Algo faucet

from pyteal import *
from pytealext import MakeInnerPaymentTxn

# smart contract
faucet_program = Seq(
    MakeInnerPaymentTxn(
        receiver=Txn.sender(),
        amount=Int(1000),
        fee=Int(2000),
    )
)

Opt-in contract to ASA

from pyteal import *
from pytealext import MakeInnerAssetTransferTxn

AMAZING_COIN_ID = 123456

# smart contract
faucet_program = Seq(
    MakeInnerAssetTransferTxn(
        asset_receiver=Global.current_application_address(),
        asset_amount=Int(0),
        xfer_asset=Int(AMAZING_COIN_ID),  # Txn.assets must contain this ID!
        # fee=Int(0),  # uncomment to specify that the fee must be pooled
    )
)

Combining with subroutines

If you're using a certain template for transfers in your app or making a lot of transfers, you may consider wrapping MakeInner*Txn into a Subroutine

from pyteal import *
from pytealext import MakeInnerAssetTransferTxn

ASSET_ID = 1234
PARASITE_ADDRESS = "SomeAddress..."

@Subroutine(TealType.none)
def SimpleAssetTransfer(receiver: Expr, amount: Expr):
    return MakeInnerAssetTransferTxn(
        asset_receiver=receiver,
        asset_amount=amount,
        xfer_asset=Int(ASSET_ID),  # this ID must be present in Txn.assets!
        fee=Int(0),  # The fee must be pooled, we don't want our contract to pay for the inner Txn
    )

# a piece of program which sends the creator 10000 units of an asset but also sends a small amount to another address
program_piece = Seq(
    Assert(Txn.sender() == Global.creator_address()),
    SimpleAssetTransfer(Txn.sender(), Int(10000)),
    SimpleAssetTransfer(Addr(PARASITE_ADDRESS), Int(10))
)

Transaction groups

With TEAL v6 it's possible to create inner transactions in groups. Below example presents how to use pytealext to accomplish that.

from pyteal import *
from pytealext import MakeInnerGroupTxn, InnerNoOpTxn, InnerAssetTransferTxn

app_to_call = Int(12345)
amount_to_deposit = Int(100)
asset_id = Int(222)
app_address = AppParam.address(app_to_call)
method = MethodSignature("deposit(string,axfer)void")

# In the parent transaction the following must be set:
# - Txn.accounts must contain the app_address
# - Txn.assets must contain the asset_id
# - Txn.applications must contain app_to_call
# otherwise the inner txn will fail
# Should the fee be set to 0 like below, the parent transaction group should pay the fees
deposit_and_call = Seq(
    app_address,
    MakeInnerGroupTxn(
        InnerAssetTransferTxn(
            asset_receiver=app_address.value(),
            asset_amount=amount_to_deposit,
            xfer_asset=asset_id,
            fee=Int(0), # must be pooled
        ),
        InnerNoOpTxn(
            application_id=app_to_call,
            application_args=[method, Bytes("Hello")],
            fee=Int(0), # must be pooled
        )
    ),
)