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The SafeSdk & the gateway API is great, but can it support full offchain signing?
From the doc:
User1 signs: safeSdk.signTransaction() is offchain,
User2 signs with: safeSdk.approveTransactionHash() <-- but this is an onchain call and requires gas.
Can user2~n just call safeSdk.signTransaction() as well and have this recorded on the safe-gateway so that its available in the queue (from getTransactionQueue)??
Thanks
Yes, all the signers can sign a transaction off-chain and send the signature to the Safe Transaction Service, so it appears on the queue in the web UI.
The @gnosis.pm/safe-core-sdk package allows to sign a transaction off-chain like this:
...
const safeTxHash = await safeCoreSdk.getTransactionHash(safeTransaction)
const signature = await safeCoreSdk.signTransactionHash(safeTxHash)
The @gnosis.pm/safe-service-client package allows to send that signature to the Transaction Service:
import SafeServiceClient from '@gnosis.pm/safe-service-client'
...
const safeService = new SafeServiceClient({ txServiceUrl, ethAdapter })
await safeService.confirmTransaction(safeTxHash, signature.data)
You will find a more complete answer following this guide: https://github.com/safe-global/safe-core-sdk/blob/main/guides/integrating-the-safe-core-sdk.md#confirm-transaction
