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transactions.md

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In this section, we'll explore the process of submitting and confirming transactions.

Modifiers

We have new modifiers in this iteration of the contract. Let's examine them one by one.

  1. txExists modifier: (Line 13) ensures that the transaction exists. It does this by checking whether the transaction index is less than the length of the transactions array. We'll go into more about in this modifier later in this section.
  2. notExecuted modifier: (Line 18) ensures that the transaction has not been executed. It does this by checking whether the executed variable of the transaction is false.
  3. notConfirmed modifier: (Line 23) ensures that the transaction has not been confirmed by the caller. It does this by checking whether the isConfirmed mapping of the transaction index and the caller's address is false.

Transaction Struct

On line 28, we have a struct called Transaction. We store the struct members: to, value, data, executed, and numConfirmations in individual variables.

Mapping of Confirmations

On line 37, we have a mapping called isConfirmed. This mapping is used to keep track of the confirmations of each transaction. It maps the transaction's index to a mapping of an owner addresses to a boolean value. The boolean value indicates whether this owner has confirmed the transaction.

Transactions Array

On line 39, we have an array called transactions. The array is used to store all the transactions submitted to the multi-signature wallet.

Events

We have four new events in this iteration of the contract:

  1. SubmitTransaction event: emitted whenever a transaction is submitted to the multi-signature wallet.
  2. ConfirmTransaction event: emitted whenever a transaction is confirmed by an owner.
  3. RevokeConfirmation event: emitted whenever a transaction confirmation is revoked by an owner.
  4. ExecuteTransaction event: emitted whenever a transaction is executed.

submitTransaction Function

The submitTransaction function (Line 78) allows users to submit a transaction to the multi-sig wallet. It takes three parameters: to, value, and data. The to parameter is the address of the recipient of the transaction. The value parameter is the amount of Ether to be sent. The data parameter is the data to be sent to the recipient. Only owners can submit transactions.

On line, 85 we create a new transaction struct and push it to the transactions array and emit the SubmitTransaction event. The txIndex variable is used to keep track of the transaction index.

confirmTransaction Function

The confirmTransaction function (Line 98) allows users to confirm a transaction. It takes one parameter: txIndex. It has three modifiers: onlyOwner, txExists, and notExecuted. The onlyOwner modifier ensures that only owners can confirm transactions. The txExists modifier ensures that the transaction exists. The notExecuted modifier ensures that the transaction has not been executed.

On line 101, we store the transaction in a local variable called transaction. We then increment the numConfirmations variable of the transaction and set the isConfirmed mapping of the transaction index and the caller's address to true. Finally, we emit the ConfirmTransaction event.

executeTransaction Function

The executeTransaction function (Line 108) allows users to execute a transaction. On line 113, we require that the number of confirmations of the transaction is greater than or equal to the required number of confirmations. We then set the executed variable of the transaction to true. Finally, send the funds using the call function. This is the call of the recipient address with the value and data of the transaction. If the transaction is successful, we emit the ExecuteTransaction event.

getTransactionCount Function

The getTransactionCount function (Line 132) allows users to retrieve the number of transactions in the multi-signature wallet. It returns the length of the transactions array.

getTransaction Function

The getTransaction function (Line 136) allows users to retrieve a transaction. It returns the transaction struct members that we explored earlier in this section.

Conclusion

In this section, we explored the process of submitting, confirming, and executing transactions. We examined the submitTransaction, confirmTransaction, and executeTransaction functions and understood how they work together to allow multiple users to submit and confirm transactions.

⭐️ Assignment: Make a Transaction

Submit, confirm, and execute a transaction to send 2 Ether to the first account in the "ACCOUNTS" dropdown menu.

  1. Deploy the Multisig contract as in the previous assignment. Make sure that the required number of confirmations is 2.
  2. Fund the multisig from any address by sending 4 Ether as you did in the previous assignment.
  3. Try sending 2 Ether to the first account in the "ACCOUNTS" dropdown menu. Once you have submitted this transaction (with submitTransaction), click on getTransactionCount and should see one transaction or you can click on getTransaction, insert 0 as the transaction index and see the transaction you just submitted.
  4. Now you can click on confirmTransaction and insert 0 as the transaction index. If you click on getTransaction again, you should see that the transaction has been confirmed once.
  5. Switch to the second owner account and confirm the transaction again. If you click on getTransaction again, you should see that the transaction has been confirmed twice.
  6. The last step is to execute the transaction. Click on executeTransaction and insert 0 as the transaction index. If you click on getTransaction again, you should see that the transaction has been executed. You can also check the balance of the first account in the "ACCOUNTS" dropdown menu. It should now be 2 Ether higher and the balance of the multi-signature wallet should be 2 Ether lower.

Hint: If you submit a transaction make sure that the value is in Wei and that the _data field is correctly filled in. E.g. it could look like this: "0x5B38Da6a701c568545dCfcB03FcB875f56beddC4, 2000000000000000000, 0x" for 2 Ether.