Meta transaction with web3

Question

iam just wondering. Are meta transactions not the same like raw transactions, which are signed by the user in frontend and send to a backend, where the transaction gets deployed?

Answer 1

Meta-transactions are different because if a user signs a transaction and forwards it to a meta-tx relay which broadcasts it to the network (sendRawTransaction()), the signer account would still be charged for gas computation, not the meta-tx relay.

The purpose of meta-transactions is to lower barrier adoption by enabling ether-less account to interact with smart contract. Basically another account acts as a relay to forward the transaction and bear the cost of the transaction fees (gas).

Example: An ether-less account account_x wants to send a transaction to a contract account_y (MyContract.myMethod()) via the meta-tx relay owner of a funded account_z.

i. account_x extracts the bytes-code from the smart contract transaction he wants to perform

var txdata = MyContract.myMethod().encodeABI();

ii. account_x signs with his private key the message sha3(txdata)

var signature = await web3.eth.personal.sign(message, account_x);

iii. account_x sends the following information to the relay

POST https://metatx-relay.net/sendtx
{
   "txdata": txdata,
   "from": account_x,
   "to": account_y,
   "msg": message,
   "signature": signature
}

iv. The relay backend gets the message and checks the signature

var accountRecovered = web3.eth.accounts.recover(req.body.message,req.body.signature)
if(accountRecovered == req.body.from) { // good to go }

v. The relay backend sends the transaction to MyContract (account_y) using it funded account account_z

web3.eth.sendTransaction({
    from: account_z,
    to: req.body.to,
    data: req.body.txdata
}).then(function(receipt){
    ...
});

Caveats: This is a very simplified flow !!!

• No msg.sender possible

The transaction is sent and paid by the relay, so it's not possible to use the alias msg.sender in the smart contract to identify the original sender account_x.

• The meta-tx relay is centralized and transaction requests could be censored

Building a network of relays with reward mechanism would be the way to go I believe where transaction request are randomly assigned to a relay.

See BouncerProxy contract

• Whitelisted accounts.

Reference:

• Thanks to Austin Griffith for his work: a working prototype of a meta-tx relay network with reward mechanism (economic incentive) and whitelisted addresses.

Answer 2

I suggest you this article. There is a detailed explanation of how meta transactions work, a link to a GitHub repository, and a demo online: https://medium.com/coinmonks/gas-free-transactions-meta-transactions-explained-f829509a462d