Token transfer notification via Smart Contract example
Here is an example of a contract that uses EPNS communicator to send notification whenever the contract receives fund.

Prerequisites

What's going to happen

  • We create a channel and copy it's address
  • We import interface and function call to trigger notification
  • We deploy the contract and add the contract address as delegate
  • Watch in 😲 as each transfer now notifies the wallet address about tokens received

Tutorial time

PUSH protocol also supports sending notifications to user wallets directly from your smart contract and that too by only adding 2 lines of extra code to your smart contract
πŸŽ‰
.
The best way to do it is by creating your channel first > tweaking your smart contract with notification logic and finally adding the deployed contract address as delegate to your channel.
To learn more about how to import interface and the function call of send notification, please see Using Smart Contract​

Code

pragma solidity ^0.6.2;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v3.0.0/contracts/token/ERC20/ERC20.sol";
​
// PUSH Comm Contract Interface
interface IPUSHCommInterface {
function sendNotification(address _channel, address _recipient, bytes calldata _identity) external;
}
​
contract Push is ERC20 {
// EPNS COMM ADDRESS ON ETHEREUM KOVAN, CHECK THIS: https://docs.epns.io/developers/developer-tooling/epns-smart-contracts/epns-contract-addresses
address public EPNS_COMM_ADDRESS = 0x87da9Af1899ad477C67FeA31ce89c1d2435c77DC;
​
constructor ()
ERC20("Push Token", "PUSH")
public {
_mint(msg.sender, 1000 * 10 ** uint(decimals()));
}
​
function transfer(address to, uint amount) override public returns (bool success) {
address owner = _msgSender();
_transfer(owner, to, amount);
​
//"0+3+Hooray! ", msg.sender, " sent ", token amount, " PUSH to you!"
IPUSHCommInterface(EPNS_COMM_ADDRESS).sendNotification(
0x050Ca75E3957c37dDF26D58046d8F9967B88190c, // from channel
to, // to recipient, put address(this) in case you want Broadcast or Subset. For Targetted put the address to which you want to send
bytes(
string(
// We are passing identity here: https://docs.epns.io/developers/developer-guides/sending-notifications/advanced/notification-payload-types/identity/payload-identity-implementations
abi.encodePacked(
"0", // this is notification identity: https://docs.epns.io/developers/developer-guides/sending-notifications/advanced/notification-payload-types/identity/payload-identity-implementations
"+", // segregator
"3", // this is payload type: https://docs.epns.io/developers/developer-guides/sending-notifications/advanced/notification-payload-types/payload (1, 3 or 4) = (Broadcast, targetted or subset)
"+", // segregator
"Tranfer Alert", // this is notificaiton title
"+", // segregator
"Hooray! ", // notification body
addressToString(msg.sender), // notification body
" sent ", // notification body
uint2str(amount.div(10 ** uint(decimals()))), // notification body
" PUSH to you!" // notification body
)
)
)
);
return true;
}
​
// Helper function to convert address to string
function addressToString(address _address) internal pure returns(string memory) {
bytes32 _bytes = bytes32(uint256(uint160(_address)));
bytes memory HEX = "0123456789abcdef";
bytes memory _string = new bytes(42);
_string[0] = '0';
_string[1] = 'x';
for(uint i = 0; i < 20; i++) {
_string[2+i*2] = HEX[uint8(_bytes[i + 12] >> 4)];
_string[3+i*2] = HEX[uint8(_bytes[i + 12] & 0x0f)];
}
return string(_string);
}
​
// Helper function to convert uint to string
function uint2str(uint _i) internal pure returns (string memory _uintAsString) {
if (_i == 0) {
return "0";
}
uint j = _i;
uint len;
while (j != 0) {
len++;
j /= 10;
}
bytes memory bstr = new bytes(len);
uint k = len - 1;
while (_i != 0) {
bstr[k--] = byte(uint8(48 + _i % 10));
_i /= 10;
}
return string(bstr);
}
}
​
Copy link
On this page
Prerequisites
What's going to happen
Tutorial time
Code