Smart contracts have the ability to "emit" events during execution. Events are also known as "logs" in Ethereum. The output of the events are stored in transaction receipts under a logs section. Events have become pretty widely used in Ethereum smart contracts to log when a significant action has occured, particularly in token contracts (i.e. ERC-20) to indicate that a token transfer has occured. These sections will walk you through the process of reading events from the blockchain as well as subscribing to events so that you get notified in real time as the transaction gets mined.
FAQs
What is the difference between logs and events in Ethereum? ›
What are Logs or Events? Logs and events are used synonymously—smart contracts generate logs by firing off events, so logs provide insights into events that occur within the smart contract. Logs can be found on transaction receipts.
Where are the events stored in Ethereum? ›Events are also known as "logs" in Ethereum. The output of the events are stored in transaction receipts under a logs section.
How to decode Ethereum data? ›2 Answers
- You need the smart contract ABI files to decode the transaction.
- You need a framework and library that can take ABI files and your Data payload and decode it for you.
- One library, for example, is Web.py and its decode_function_input function but there are others.
Sep 22, 2023
Event logs are used to track and troubleshoot system issues, monitor for security threats, and comply with regulatory requirements. One of the primary uses of event logs is to use them to troubleshoot system issues.
What are event logs and its example? ›These store information based on the Windows system's audit policies. Typical events logs stored include login attempts and resource access. For example the Windows security log stores a record when the computer attempts to verify account credentials when a user tries to log on to a machine.
How to query Ethereum events? ›Querying Events
- Step 1: Install Node and NPM.
- Step 2: Create an Alchemy app.
- Step 3: Create a node project.
- Step 4: Get the event logs.
Understanding event logs
Events are declared using the event keyword, and they allow smart contracts to send asynchronous notifications to clients. Events can be used to notify users of changes in the contract state, and they can be filtered, searched, and archived for future reference.
Topics in Ethereum Log Records
The first part of a log record consists of an array of topics. These topics are used to describe the event. The first topic usually consists of the signature (a keccak256 hash) of the name of the event that occurred, including the types (uint256, string, etc.) of its parameters.
One common method is to use a blockchain explorer, which is a tool that allows you to search the Ethereum blockchain for transactions and addresses. By entering the address you want to trace, you can see all the transactions associated with that address, as well as any other addresses that have interacted with it.
How do you debug a transaction code? ›Entering the "/h" command into the command field (upper left corner of screen) is the normal way of starting debugging. However, if you do not have a command field available (e.g. on popups) simple create a shortcut with system-command = "/H" (instead of a transaction code).
How do you trace Ethereum? ›
Yes, it is possible to trace an Ethereum transaction after it has been confirmed. There are various blockchain explorers, such as Etherscan, that can be used to track and view all Ethereum transactions.
What code is Ethereum written in? ›Solidity is the primary language used to develop smart contracts for Ethereum as well as other private blockchains, such as the enterprise-oriented Hyperledger Fabric blockchain.
What data is stored on Ethereum? ›Data is stored on the Ethereum blockchain in blocks. Each block is made up of a series of transactions, and each transaction contains data that can be stored on the Ethereum blockchain. The data stored in these transactions can be anything from financial transactions, to the results of a smart contract execution.
What is Ethereum codes? ›The Ethereum Code system is an automated trading platform designed using artificial intelligence technology. This Ethereum Code review will investigate this trading bot in detail to find out if it helps simplify the whole trading process.
What is the difference between logs and events? ›Unlike logs, events describe a unit of work, meaning they contain all of the information about what it took for a service to perform a certain job. And, not every log is an event in its entirety. Logs are usually only portions of events. A group of logs can compose a single event.
What is the difference between log and event in solidity? ›Logs are written by the smart contract when the contract emits events, but these logs cannot be ready by the smart contract. The inaccessability of the logs allows developers to store data on-chain that is more searchable and gas efficient than saving data to the smart contract's storage variables.
What is the difference between event viewer and log? ›The (Windows) Event Viewer shows the event of the system. The "Windows Logs" section contains (of note) the Application, Security and System logs - which have existed since Windows NT 3.1. Event Tracing for Windows (ETW) providers are displayed in the "Applications and Services Log" tree.
What is the difference between event sourcing and logging? ›Event logging just means recording the events that occur in a system. Event sourcing means recording extra information about those events, so that you can recreate the state of the system at any point in time by reconstructing the chain of events that occurred up until that point in time.