To get interface id, use

type(ITest).interfaceId

Remember interfaceId = xor of all selectors (methods) name, don't care to return type, just name

For example:

• Return zero with empty interface

=> bytes4: 0x00000000// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;interface ITest {
}contract Test is ITest {
    bytes4 public constant IID_ITEST = type(ITest).interfaceId;    
}

• Return same id with difference return type

=> bytes4: 0x0ee2cb10// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;interface ITest {
    function getCreator() external;
}contract Test is ITest {
    bytes4 public constant IID_ITEST = type(ITest).interfaceId;   
    
    function getCreator() external override { } 
}===========
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0…

If you are a smart contract developer, you will need to consider something about the contract:

• Clean: No unused code, nonsense comment,
• Well document: Comment to all functions
• Formatted: Reformat, reformat, reformat
• Unit test all functions
• Migration for testnet and mainnet
• Avoid duplication code, avoid using too many unnecessary modifiers to reduce contract size
• Upgradable

*Reusable, Replaceable, Upgradable, Testable => Easier maintenance*

— — —

About some checklist in contract function

• Consider using nonReentrant modifier in paying function to avoid duplicate calls
• Use safe math to check about substract and div operators. Get revert if you div zero, or assign a negative number to uint.
• About…

I have some exp with this kind of topic “Dividend Token”. Just share some thoughts

What is “Dividend Token”?

You should search for more detail. =]] But you can go with some token like BabyCake, SafeMoon, ThunderCake, … cake family. :3

The token has some tax or fee on each transaction (transfer, buy, sell) for:

• 1. Reflection reward on other coins to all holders
• 2. Buyback to increase token buy volume
• 3. Burn as disinflation policy
• 4. Add LP to make the token is more stable
• …

I just focus on “Reflection reward”, how to make it fair and scalable.

Reflection reward

• If you think you…

Preparing source

• Clone pancake-swap-core

git clone git@github.com:pancakeswap/pancake-swap-core.git
cd pancake-swap-core
git checkout -b factory 3b214306770e86bc3a64e67c2b5bdb566b4e94a7
yarn install
yarn compile

• Clone pancake-swap-periphery

git clone git@github.com:pancakeswap/pancake-swap-periphery.git
cd pancake-swap-periphery
git checkout -b router d769a6d136b74fde82502ec2f9334acc1afc0732
yarn install
yarn add @uniswap/v2-core@"file:../pancake-swap-core"
yarn compile

• Clone pancake-swap-interface-v1

git clone git@github.com:pancakeswap/pancake-swap-interface-v1.git
cd pancake-swap-interface-v1
git checkout -b v1 0257017f2daaae2f67c24ded70b5829f74a01b3c
yarn install

Setup

Install contract merger: https://www.npmjs.com/package/sol-merger

npm install sol-merger -g

Prepare PancakeFactory and PancakeRouter

sol-merger pancake-swap-core/contracts/PancakeFactory.sol ./build
sol-merger pancake-swap-core/contracts/PancakePair.sol ./build
sol-merger pancake-swap-periphery/contracts/PancakeRouter01.sol ./build
sol-merger pancake-swap-periphery/contracts/PancakeRouter.sol ./build…

Config Server

• Install here: https://www.zabbix.com/download?zabbix=5.4&os_distribution=ubuntu&os_version=20.04_focal&db=postgresql&ws=nginx
• Config server:

nano /etc/zabbix/zabbix_server.conf===>Update DB information

• Config frontend web

nano /etc/zabbix/web/zabbix.conf.php
===># Update DB information, must be matched with server config above
....# Integrate with server
ZBX_SERVER = '**your zabbix ip address or name**';
ZBX_SERVER_PORT = '10051';
ZBX_SERVER_NAME = '**your zabbix hostname**';Example
$ZBX_SERVER                     = 'localhost';
$ZBX_SERVER_PORT                = '10051';
$ZBX_SERVER_NAME                = 'zabbix.nhancv.com';

• Restart server

sudo systemctl restart zabbix-server
sudo systemctl status zabbix-server
ps -ef | grep zabbix

Setup Agent

• Access to vps agent -> Install zabbix-agent

wget https://repo.zabbix.com/zabbix/5.4/ubuntu/pool/main/z/zabbix-release/zabbix-release_5.4-1+ubuntu20.04_all.deb
dpkg -i zabbix-release_5.4-1+ubuntu20.04_all.deb
apt update
apt install zabbix-agent# If you enable firewall -> open ufw port…

• A contract has an infinite internal storage
• There are 2 limits to practicality: gas costs and the block gas limit.

Example

Create 5k5 players, read one time

https://testnet.bscscan.com/address/0x721ff9e58831b698efd26b9ac744cf8f0aaecbc2#readContract

Max Gas Limit is 28,500,000 at May 12, 2021 = 0.22BNB ~ $145

• [WRITE] Can add 500 player in 1 tx
• [READ] Can not get all 5600 players (1600 is ok)

call to TestPlayerRead.getPlayers
call to TestPlayerRead.getPlayers errored: Error: Internal JSON-RPC error. { "code": -32000, "message": "out of gas" }

• [READ] To read all data, should use paging approach

Setup MongoDB

* Check linux version: lsb_release -a
sudo apt install wget
wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -

* https://docs.mongodb.com/manual/tutorial/install-mongodb-on-debian/
* Debian 10 "Buster"
echo "deb http://repo.mongodb.org/apt/debian buster/mongodb-org/4.4 main" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

* https://docs.mongodb.com/manual/tutorial/install-mongodb-on-ubuntu/
* Ubuntu 20.04 (Focal)
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list

sudo apt update
sudo apt install -y build-essential
sudo apt install -y mongodb-org
sudo systemctl enable mongod
sudo service mongod start

• Controls

- Start: sudo service mongod start
- Verify status: sudo cat /var/log/mongodb/mongod.log …

Make sure your application is stateless: share database/cache, cronjob

Create ecosystem.config.js at root

// https://pm2.keymetrics.io/docs/usage/application-declaration/
// # Start all applications
// pm2 start ecosystem.config.js
//
// # Stop all
// pm2 stop ecosystem.config.js
//
// # Restart all
// pm2 restart ecosystem.config.js
//
// # Reload all
// pm2 reload ecosystem.config.js
//
// # Delete all
// pm2 delete ecosystem.config.js
module.exports = {
  apps: [{
    name: "nestjs-prod",
    script: "./dist/main.js", …