How to perform swap from token to ETH?

[blnkoff]

Hello. I want to write code that interacts with the Uniswap universal router. I have written a code for swapping from ETH to a token. (But I haven't checked it yet). How I can write the same code for swapping from token to ETH? I think code will be almost the same as swapEth, but with little changes. What I need to change?

@change_network(CONTRACTS_PATH)
async def swapToEth(self, input_token: Token, amount_out: TokenAmount) -> HexBytes:
    pass

@validate_call()
@change_network(CONTRACTS_PATH)
async def swapEth(
        self,
        output_token: Token,
        amount_in: TokenAmount,
        gas: TokenAmount = Wei(500_000)
) -> HexBytes:
    codec = RouterCodec()
    wallet = self.wallet

    chained = codec.encode.chain()
    weth_address = await self._weth()
    path = [weth_address, output_token.address]

    min_amount_out = await self._min_amount_out(amount_in, weth_address, output_token.address)
    print(min_amount_out)
    wrapped_eth = chained.wrap_eth(FunctionRecipient.ROUTER, min_amount_out)

    swapped = wrapped_eth.v2_swap_exact_in(
        FunctionRecipient.SENDER,
        min_amount_out,
        min_amount_out,
        path,
        payer_is_sender=False
    )

    encoded = swapped.build(codec.get_default_deadline())
    params = await wallet.build_tx_params(
        recipient=self._universal_router.address,
        value=amount_in,
        raw_data=encoded,
        gas=gas
    )

    gas = await wallet.estimate_gas(params)

    params['gas'] = gas

    return await wallet.transact(params)

[Elnaril]

Hello @blnkoff !

Check this tutorial, it explains how to swap 2 tokens. Just replace the bought token (usdt in the tuto) with weth and add an unwrap command at the end of the chain.

Also make sure to adapt the web3.py methods if you use a recent version.

[Elnaril]

At the same time, code swapping from eth to token works

yes, approval is needed for token to eth ...

[blnkoff]

At the same time, code swapping from eth to token works

yes, approval is needed for token to eth ...

Transaction: 0x9a1947c190582c8d779fde55329be8caf50458876f56063f06f9e006d0cd6589
Gas usage: 23199
Block number: 17365010
Block time: Fri Dec 27 2024 21:37:53 GMT+0300 (Moscow Standard Time)
Runtime error: revert
Revert reason: Uni::approve: amount exceeds 96 bits

Here was an error. I've reduced number for approval, but it still doesn't work. Here an error after sending swapping transaction

Transaction: 0xddfcbf609bb7b0cd6b1e96db58ff4ef85285c08de2ba4d609e9ad7370037756f
Gas usage: 73836
Block number: 17365017
Block time: Fri Dec 27 2024 21:40:07 GMT+0300 (Moscow Standard Time)
Runtime error: revert

I'm using ganache with infura like you in your guide/

[Elnaril]

The Uni contract approval uses an uint256, so not sure why you get this error ...

Happy to look into an issue which is actually in the lib or in this tutorial but yours is not.
I'm closing this discussion as unrelated but feel free to reopen one if you pinpoint such issue.

[blnkoff]

maybe you have some another code example? I tried to use this code in main net. It doesn't work

[Elnaril]

Yes, have a look into the integration tests