Uniswap 900K gas estimation fixing solution

[k06a]

Related issues: vyperlang/vyper#1091, Uniswap/v1-contracts#39

We suggest to move _emit call before tokenFallback to resolve Uniswap 900K gas estimation. Solidity passes 63/64 of gas in subcalls and now estimator increases gas until 1/64 of gas left is enough for _emit call.

Currently gas estimator is feeding Uniswap proxy until 1/64 of gasleft would be enough for _emit call.

Moving _emit before tokenFallback would decrease gas estimation to 100K instead of 900K

[k06a]

Also limiting tokenFallback gas is a good idea. For example provide Math.min(gasleft(), 200000) of gas.

[k06a]

Same valid for all synth tokens. See for example sETH+ETH Uniswap pool transactions: https://etherscan.io/address/0xe9cf7887b93150d4f2da7dfc6d502b216438f244

[k06a]

It seems having some synths minted from user wallet, increases gas limit to 10M: https://www.reddit.com/r/synthetix_io/comments/djd6ca/uniswap_synthetix_gas_required_exceeds_allowance/

[k06a]

It is not possible to swap SNX to DAI or any other token because of this bug.

[marc0olo]

@hav-noms why is this closed? I am not able to swap sETH to ETH on uniswap due to this bug

[ihlec]

@hav-noms the problem seams to still exists.

For certain transactions it would be useful to send the transaction with a default user defined gas limit after the gas estimation failed.

Currently the users are facing unresponsive dApps.

e.g. Uniswap:
inpage.js:1 MetaMask - RPC Error: gas required exceeds allowance (12426210) or always failing transaction Object (anonymous) @ inpage.js:1 index.tsx:283 estimateGas failed removeLiquidityETHWithPermit Array(10) Object (anonymous) @ index.tsx:283 inpage.js:1 MetaMask - RPC Error: gas required exceeds allowance (12426210) or always failing transaction Object (anonymous) @ inpage.js:1 index.tsx:283 estimateGas failed removeLiquidityETHWithPermitSupportingFeeOnTransferTokens Array(10) Object (anonymous) @ index.tsx:283 index.tsx:295 This transaction would fail. Please contact support.