Getting the transaction hash on function call

Question

I am new to Solidity, Web3, and Ethereum. I am trying to build a web application through which users can upload a file to IPFS, then store the IPFS hash in the blockchain. I am using the React truffle box and the value is being stored via the SimpleStorage contract that's included with the box.

So essentially, the ideal scenario would be: User A uploads the file to IPFS and its hash is stored in the blockchain. User B can then access the file by typing the transaction hash and getting its storage value to check whether it's authentic or not.

The problem is that in order for User B to be able to check the file's authenticity, they need to have the transaction hash. Is there a way for a function to return the hash on function call? I can get it manually through Ganache, but that's just impractical.

The blockchain is very nice because it gives you the ability to permanently store data within it, but is there a way to check that data?

Thank you.

Answer 1

with that simpleStorage contract, you are storing a value in a smart contract on the blockchain. So User B need only the address of that deployed smart contract and then he could call the method get() from that contract to get the stored value.

contract SimpleStorage {
  uint storedData;

  function set(uint x) public {
    storedData = x;
  }

  function get() public view returns (uint) {
    return storedData;
  }
}

with web3js you can deploy a contract and get its address with this code

// When the data is already set as an option to the contract itself

myContract.options.data = '0x12345...';

myContract.deploy({
    arguments: [<not needed in your contract>]
})
.send({
    from: '0x1234567890123456789012345678901234567891',
    gas: 1500000,
    gasPrice: '30000000000000'
})
.then((newContractInstance) => {
    console.log(newContractInstance.options.address) // instance with the new contract address
});

https://web3js.readthedocs.io/en/1.0/web3-eth-contract.html

more infos: truffle save the address of the deployed contract, the abi, meta data and bytecode.... in the build Folder