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feat: support local fee payer sponsorship while preserving gas station defaults #17

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f71ac55
feat: add local fee payer sponsorship mode
WGB5445 Apr 21, 2026
a95fd09
fix: address PR review feedback for local fee payer mode
WGB5445 Apr 21, 2026
860b606
test: tighten fee payer forwarding assertions and guards
WGB5445 Apr 21, 2026
4bac874
fix: validate fee payer override semantics in base sdk
WGB5445 Apr 21, 2026
5a91649
fix: avoid mutating fee payer address in submit paths
WGB5445 Apr 21, 2026
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22 changes: 22 additions & 0 deletions README.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,28 @@ async def main():
asyncio.run(main())
```

### Gas Sponsorship Modes

By default, write operations continue to use the existing gas station flow based on
`config.gas_station_api_key` / `config.gas_station_url`. No configuration changes are required.

To use a local fee payer account instead of gas station signing, pass
`fee_payer_account` in `BaseSDKOptions`:

```python
from aptos_sdk.account import Account
from decibel import BaseSDKOptions, DecibelWriteDex, TESTNET_CONFIG

sender = Account.generate()
fee_payer = Account.generate()

write = DecibelWriteDex(
TESTNET_CONFIG,
sender,
opts=BaseSDKOptions(fee_payer_account=fee_payer),
)
```

### WebSocket Streaming

```python
Expand Down
97 changes: 94 additions & 3 deletions src/decibel/_base.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@
from typing import TYPE_CHECKING, Any, cast

import httpx
from aptos_sdk.account_address import AccountAddress
from aptos_sdk.async_client import RestClient
from aptos_sdk.authenticator import (
AccountAuthenticator,
Expand All @@ -31,7 +32,6 @@

if TYPE_CHECKING:
from aptos_sdk.account import Account
from aptos_sdk.account_address import AccountAddress

from ._constants import DecibelConfig
from ._gas_price_manager import GasPriceManager, GasPriceManagerSync
Expand All @@ -49,12 +49,14 @@
DEFAULT_MAX_GAS_AMOUNT = 200_000
DEFAULT_GAS_ESTIMATE = 100
MAX_GAS_UNITS_LIMIT = 2_000_000
FEE_PAYER_PLACEHOLDER_ADDRESS = AccountAddress.from_str("0x0")


@dataclass
class BaseSDKOptions:
skip_simulate: bool = False
no_fee_payer: bool = False
fee_payer_account: Account | None = None
node_api_key: str | None = None
gas_price_manager: GasPriceManager | None = None
time_delta_ms: int = 0
Expand All @@ -64,6 +66,7 @@ class BaseSDKOptions:
class BaseSDKOptionsSync:
skip_simulate: bool = False
no_fee_payer: bool = False
fee_payer_account: Account | None = None
node_api_key: str | None = None
gas_price_manager: GasPriceManagerSync | None = None
time_delta_ms: int = 0
Expand All @@ -86,10 +89,14 @@ def __init__(
opts = opts or BaseSDKOptions()
self._skip_simulate = opts.skip_simulate
self._no_fee_payer = opts.no_fee_payer
self._fee_payer_account = opts.fee_payer_account
self._node_api_key = opts.node_api_key
self._gas_price_manager = opts.gas_price_manager
self._time_delta_ms = opts.time_delta_ms

if self._no_fee_payer and self._fee_payer_account is not None:
raise ValueError("no_fee_payer and fee_payer_account cannot be used together")

if config.chain_id is None:
logger.warning(
"Using default ABI for unknown chain_id, "
Expand Down Expand Up @@ -156,7 +163,7 @@ async def build_tx(
else:
gas_unit_price = await self._fetch_gas_price_estimation()

return build_simple_transaction_sync(
transaction = build_simple_transaction_sync(
sender=sender,
data=data,
chain_id=self._chain_id,
Expand All @@ -167,6 +174,8 @@ async def build_tx(
time_delta_ms=self._time_delta_ms,
max_gas_amount=max_gas_amount or DEFAULT_MAX_GAS_AMOUNT,
)
self._apply_fee_payer_address_override(transaction)
return transaction

async def submit_tx(
self,
Expand All @@ -175,12 +184,16 @@ async def submit_tx(
*,
txn_submit_timeout: float | None = None,
) -> PendingTransactionResponse:
self._validate_fee_payer_address(transaction)

if self._no_fee_payer:
return await self._submit_direct(transaction, sender_authenticator, txn_submit_timeout)
return await submit_fee_paid_transaction(
self._config,
transaction,
sender_authenticator,
fee_payer_account=self._fee_payer_account,
node_api_key=self._node_api_key,
txn_submit_timeout=txn_submit_timeout,
)

Expand Down Expand Up @@ -273,6 +286,40 @@ def _sign_transaction(
else:
return raw_txn.sign(signer.private_key)

def _apply_fee_payer_address_override(self, transaction: SimpleTransaction) -> None:
if self._fee_payer_account is None:
return

expected_fee_payer = self._fee_payer_account.address()
current_fee_payer = transaction.fee_payer_address

if current_fee_payer == expected_fee_payer:
return

if current_fee_payer == FEE_PAYER_PLACEHOLDER_ADDRESS:
transaction.fee_payer_address = expected_fee_payer
return

if current_fee_payer is None:
raise ValueError(
"transaction.fee_payer_address must be set when fee_payer_account is used"
)

raise ValueError("transaction.fee_payer_address does not match fee_payer_account")

def _validate_fee_payer_address(self, transaction: SimpleTransaction) -> None:
if self._fee_payer_account is None:
return

expected_fee_payer = self._fee_payer_account.address()
if transaction.fee_payer_address is None:
raise ValueError(
"transaction.fee_payer_address must be set when fee_payer_account is used"
)

if transaction.fee_payer_address != expected_fee_payer:
raise ValueError("transaction.fee_payer_address does not match fee_payer_account")

Comment thread
WGB5445 marked this conversation as resolved.
async def _fetch_gas_price_estimation(self) -> int:
url = f"{self._config.fullnode_url}/estimate_gas_price"
headers = self._build_node_headers()
Expand Down Expand Up @@ -458,11 +505,15 @@ def __init__(
opts = opts or BaseSDKOptionsSync()
self._skip_simulate = opts.skip_simulate
self._no_fee_payer = opts.no_fee_payer
self._fee_payer_account = opts.fee_payer_account
self._node_api_key = opts.node_api_key
self._gas_price_manager = opts.gas_price_manager
self._time_delta_ms = opts.time_delta_ms
self._http_client = opts.http_client

if self._no_fee_payer and self._fee_payer_account is not None:
raise ValueError("no_fee_payer and fee_payer_account cannot be used together")

if config.chain_id is None:
logger.warning(
"Using default ABI for unknown chain_id, "
Expand Down Expand Up @@ -525,7 +576,7 @@ def build_tx(
else:
gas_unit_price = self._fetch_gas_price_estimation()

return build_simple_transaction_sync(
transaction = build_simple_transaction_sync(
sender=sender,
data=data,
chain_id=self._chain_id,
Expand All @@ -536,6 +587,8 @@ def build_tx(
time_delta_ms=self._time_delta_ms,
max_gas_amount=max_gas_amount or DEFAULT_MAX_GAS_AMOUNT,
)
self._apply_fee_payer_address_override(transaction)
return transaction

def submit_tx(
self,
Expand All @@ -544,12 +597,16 @@ def submit_tx(
*,
txn_submit_timeout: float | None = None,
) -> PendingTransactionResponse:
self._validate_fee_payer_address(transaction)

if self._no_fee_payer:
return self._submit_direct(transaction, sender_authenticator, txn_submit_timeout)
return submit_fee_paid_transaction_sync(
self._config,
transaction,
sender_authenticator,
fee_payer_account=self._fee_payer_account,
node_api_key=self._node_api_key,
txn_submit_timeout=txn_submit_timeout,
)

Expand Down Expand Up @@ -640,6 +697,40 @@ def _sign_transaction(
else:
return raw_txn.sign(signer.private_key)

def _apply_fee_payer_address_override(self, transaction: SimpleTransaction) -> None:
if self._fee_payer_account is None:
return

expected_fee_payer = self._fee_payer_account.address()
current_fee_payer = transaction.fee_payer_address

if current_fee_payer == expected_fee_payer:
return

if current_fee_payer == FEE_PAYER_PLACEHOLDER_ADDRESS:
transaction.fee_payer_address = expected_fee_payer
return

if current_fee_payer is None:
raise ValueError(
"transaction.fee_payer_address must be set when fee_payer_account is used"
)

raise ValueError("transaction.fee_payer_address does not match fee_payer_account")

def _validate_fee_payer_address(self, transaction: SimpleTransaction) -> None:
if self._fee_payer_account is None:
return

expected_fee_payer = self._fee_payer_account.address()
if transaction.fee_payer_address is None:
raise ValueError(
"transaction.fee_payer_address must be set when fee_payer_account is used"
)

if transaction.fee_payer_address != expected_fee_payer:
raise ValueError("transaction.fee_payer_address does not match fee_payer_account")

Comment thread
WGB5445 marked this conversation as resolved.
def _fetch_gas_price_estimation(self) -> int:
url = f"{self._config.fullnode_url}/estimate_gas_price"
headers = self._build_node_headers()
Expand Down
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