pervaje28megh/library-entry--blockchain

functionality for storing and checking the existence of entries based on their hashed values.

Library-Entry--Blockchain

The code you provided is a simple Solidity smart contract written for the Ethereum blockchain. Let's go through the code and understand its functionality.

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;

contract Library {

The contract is named "Library" and is specified to follow the GPLv3 license. It is written using Solidity version 0.8.0.

    mapping (bytes32 => bool) private entryExists;

The contract declares a private mapping called entryExists. It maps a bytes32 hash value to a boolean indicating whether an entry exists or not.

    event NewEntry(bytes32 indexed entryHash);

The contract defines an event called "NewEntry", which is emitted when a new entry is added. It includes the indexed parameter entryHash, which is of type bytes32.

    function addEntry(string memory entry) public {
        bytes32 hash = keccak256(bytes(entry));
        require(!entryExists[hash], "Entry already exists");
        entryExists[hash] = true;
        emit NewEntry(hash);
    }

The addEntry function takes a string parameter called entry and adds it as a new entry to the library. First, it calculates the keccak256 hash of the entry string using keccak256(bytes(entry)). It then checks if an entry with the calculated hash already exists in the entryExists mapping. If it does, the function reverts with the error message "Entry already exists." If the entry doesn't exist, the function sets the corresponding mapping value to true and emits the "NewEntry" event with the calculated hash.

    function checkEntry(string memory entry) public view returns (bool) {
        bytes32 hash = keccak256(bytes(entry));
        return entryExists[hash];
    }
}

The checkEntry function takes a string parameter called entry and returns a boolean indicating whether the entry exists in the library. It calculates the hash of the entry string and retrieves the corresponding boolean value from the entryExists mapping.

Overall, this contract provides a simple library-like functionality for storing and checking the existence of entries based on their hashed values.