How to build a transaction without signatures in Rust SDK?

mpoplavkov · December 13, 2023, 6:34pm

I want to build a transaction without signing it. This might be useful for:

estimating transaction fees;
simulating the transaction.

I don’t want to sign the transaction and send it to simulation, because, in that case, the http request might be intercepted and the signed transaction might be used by a fraud.

The easiest example of a transaction to build is transfer. Here is how transfer transaction is constructed in fuels-rs:

github.com

FuelLabs/fuels-rs/blob/d809a24597af277de503abbc1afc7ca25ce31c95/packages/fuels-accounts/src/account.rs#L200-L219


      
          async fn transfer(
              &self,
              to: &Bech32Address,
              amount: u64,
              asset_id: AssetId,
              tx_policies: TxPolicies,
          ) -> Result<(TxId, Vec<Receipt>)> {
              let provider = self.try_provider()?;
              let network_info = provider.network_info().await?;
          
              let inputs = self.get_asset_inputs_for_amount(asset_id, amount).await?;
              let outputs = self.get_asset_outputs_for_amount(to, asset_id, amount);
          
              let mut tx_builder =
                  ScriptTransactionBuilder::prepare_transfer(inputs, outputs, tx_policies, network_info);
          
              self.add_witnessses(&mut tx_builder);
              self.adjust_for_fee(&mut tx_builder, amount).await?;
          
              let tx = tx_builder.build(provider).await?;

There is a line responsible for adding a signature:

self.add_witnessses(&mut tx_builder);

I’ve tried to duplicate this code for building the transaction and removed the line with add_witnessses. But it turns out that ScriptTransactionBuilder.build function expects all signatures to be present. I get the following error:

InvalidData("signature missing for coin with owner...")

Is there a way to construct a transaction without signatures?

PS: in fuels-ts it is possible

In the transfer implementation the signing is done inside sendTransaction method. But the construction of the transaction request without signing it is totally valid:
fuels-ts/packages/wallet/src/account.ts at 166a48bb45b35fa5295ddce20d1f6e256b133a67 · FuelLabs/fuels-ts · GitHub

calldelegation · December 23, 2023, 5:39pm

This should be resolved here How to sign a transaction in Rust SDK? - #2 by calldelegation

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How to build a transaction without signatures in Rust SDK?

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