Book Image

Building Blockchain Projects

By : Narayan Prusty
Book Image

Building Blockchain Projects

By: Narayan Prusty

Overview of this book

Blockchain is a decentralized ledger that maintains a continuously growing list of data records that are secured from tampering and revision. Every user is allowed to connect to the network, send new transactions to it, verify transactions, and create new blocks, making it permission-less. This book will teach you what blockchain is, how it maintains data integrity, and how to create real-world blockchain projects using Ethereum. With interesting real-world projects, you will learn how to write smart contracts which run exactly as programmed without any chance of fraud, censorship, or third-party interference, and build end-to-e applications for blockchain. You will learn about concepts such as cryptography in cryptocurrencies, ether security, mining, smart contracts, solidity, and more. You will also learn about web sockets, various API services for Ethereum, and much more. The blockchain is the main technical innovation of bitcoin, where it serves as the public ledger for bitcoin transactions.
Table of Contents (16 chapters)
Title Page
About the Author
About the Reviewers
Customer Feedback

What are event topics?

Topics are values used for indexing events. You cannot search for events without topics. Whenever an event is invoked, a default topic is generated, which is considered the first topic of the event. There can be up to four topics for an event. Topics are always generated in the same order. You can search for an event using one or more of its topics.

The first topic is the signature of the event. The rest of the three topics are the values of indexed parameters. If the index parameter is string, bytes, or array, then the keccak-256 hash of it is the topic instead.

Let's take an example to understand topics. Suppose there is an event of this form:

event ping(string indexed a, int indexed b, uint256 indexed c, string d, int e); 

//invocation of event 
ping("Random String", 12, 23, "Random String", 45);

Here, these four topics are generated. They are as follows:

  • 0xb62a11697c0f56e93f3957c088d492b505b9edd7fb6e7872a93b41cdb2020644: This is the first topic. It is generated using...