Message Call Transaction

A message call transaction is a type of transaction in Ethereum that is used to interact with a smart contract or another EOA. It is initiated by an external account (i.e., an Externally Owned Account or EOA) and sends a message to the contract, triggering a function call within the contract.
A message call transaction contains several fields:
  • Nonce: A unique value used to prevent replay attacks.
  • Gas price: The amount of ether (ETH) paid per unit of gas consumed by the transaction.
  • Gas limit: The maximum amount of gas that the transaction is allowed to consume.
  • To: The address of the contract that the message is being sent to.
  • Value: The amount of ether (ETH) being sent with the message.
  • Data: The input data for the function call being triggered in the contract.
When a message call transaction is executed, the EVM (Ethereum Virtual Machine) creates a new execution context, loads the code of the contract specified in the "To" field, and executes the function specified in the "Data" field using the input parameters provided in the same field.
The contract function can modify the state of the contract, emit events, or even call other contracts or external functions using message call transactions. Once the function has completed execution, the state changes made by the function are saved to the blockchain.
If the transaction runs out of gas before it completes, all changes to the state are reverted, and any ether sent with the transaction is refunded to the sender.
+----------------------+
| Smart Contract |
| |
| Contract Code and |
| Data Variables |
+----------------------+
|
| Execution
| Context
|
v
+----------------------+ +----------------------+ +----------------------+
| External Account | | External Account | | External Account |
| | | | | |
| Nonce | | Nonce | | Nonce |
| Balance | | Balance | | Balance |
| Contract Code | | Contract Code | | Contract Code |
| Storage Data | | Storage Data | | Storage Data |
| | | | | |
+----------------------+ +----------------------+ +----------------------+
| | |
| | |
| | |
| Message Call | Message Call |
+-------------------------> |
+------------------------->
In this representation, there are three external accounts, each with a nonce, balance, contract code, and storage data. The smart contract is represented as a separate entity with its own contract code and data variables. The message call transaction is depicted as an arrow from the external account to the smart contract, passing along the execution context.
During a message call transaction, an external account sends a message to a smart contract, which triggers the execution of the contract code. The message contains input data, which can be used by the smart contract to perform specific actions or modify its state. The smart contract can also return output data as a result of its execution.
The state of the external account and the smart contract can be updated during the execution of the message call transaction, such as changes in the nonce, balance, contract code, or storage data.