What are Polling Cycles in Shardeum?

What are Smart Contract Events?

Smart contract events announce new data originating from a contract.

Why are Smart Contract Events Significant?

Listening to smart contract events notifies applications and users in real-time that something new has occurred within a smart contract.

Where are Events Utilised in Smart Contract Applications?

Frontend

If you exchange tokens on a website using an AMM DEX smart contract, the token balances will be updated on the frontend almost immediately using events.

Backend

Trading bots can monitor AMM DEX swap contract events and identify potential arbitrage opportunities. IoT robotics applications in the physical world, linked to a smart contract, can be managed using events. Chainlink oracle nodes also rely on smart contract events to determine when to facilitate communication between the real world and blockchains.

How to Observe Smart Contract Events on Shardeum?

Websockets

We have plans to introduce WebSocket RPC URL support in the future for subscribing to smart contract events. This will allow users to conserve API calls, as opposed to polling for new data with each new block/bundle/cycle.

Polling

Reading smart contract events can also be accomplished using Shardeum cycles (we monitor blocks/bundles for this purpose).

Reading events using Shardeum Cycles:

1. To obtain the current cycle: retrieve the most recent block, then divide it by 10 and round down.

2. Construct the JSON URL with:

An example with:

startCycle = endCycle = 49
address = 0x23FF65f07cAbAd1643440a0114d71260F2Bb6352

https://explorer-dapps.shardeum.org/api/transaction?startCycle=19020&endCycle=19045&address=0x245E2395712F888CeD1033C924115105dC32e388

1. Filter for transactions per page [please note, 10 transactions per page]:

https://explorer-dapps.shardeum.org/api/transaction?startCycle=19020&endCycle=19045&address=0x245E2395712F888CeD1033C924115105dC32e388&page=1

JSON URL Filter Variables

?startCycle=lastestCycle
&endCycle=lastestCycle
&address=addressToListenTo
&page=1

Event Listening With Polling Examples:

Reading transaction events from the null address (address(0)) from cycle 0 to 1000:

Javascript

const axios = require('axios');

let baseUrl = "https://explorer-dapps.shardeum.org/api/transaction?startCycle=19020&endCycle=19045&address=0x245E2395712F888CeD1033C924115105dC32e388"

getTransactionsToAddressCycleRange(baseUrl)

async function readJSONLoop(totalTransactions) {

    let total = totalTransactions;
    let pageIndex = 1

    while ( total > 0 ) {

        let filterUrl = baseUrl + "&page=" + pageIndex
        console.log(filterUrl)

        let responseRawJSON = await axios.get(filterUrl);
        responseRawJSON = responseRawJSON.data;
        console.log(responseRawJSON);

        total -= 10;
        pageIndex++;
    }

}

async function getTransactionsToAddressCycleRange(baseUrl) {

    let responseRawJSON = await axios.get(baseUrl);
    let responseDataJSON = responseRawJSON.data;
    let totalTransactions = responseDataJSON.totalTransactions
    console.log(totalTransactions);

    readJSONLoop(totalTransactions)

}

Python

from urllib.request import urlopen
import json

transactionsInCycleRangeUrlString = "https://explorer-dapps.shardeum.org/api/transaction?startCycle=19020&endCycle=19045&address=0x245E2395712F888CeD1033C924115105dC32e388"
transactionsInCycleRangeUrlOpened = urlopen(transactionsInCycleRangeUrlString)
transactionsInCycleRangeUrlJSON = json.loads(transactionsInCycleRangeUrlOpened.read())
totalTransactions = transactionsInCycleRangeUrlJSON["totalTransactions"]
print(totalTransactions)
pageIndex = 1

while totalTransactions > 0:
    print(pageIndex)
    print(totalTransactions)
    pageIndexIncrementUrlString = transactionsInCycleRangeUrlString + "&page=" + str(pageIndex)
    pageIndexIncrementUrlOpened = urlopen(pageIndexIncrementUrlString)
    rawTransactionDataPage = json.loads(pageIndexIncrementUrlOpened.read())
    print(rawTransactionDataPage)
    totalTransactions -= 10
    pageIndex += 1

Go

package main

import (
   "io/ioutil"
   "log"
   "net/http"
   "encoding/json"
   "strconv"
)

func main() {

   baseUrl := "https://explorer-dapps.shardeum.org/api/transaction?startCycle=";
   transactionCount := getTransactionCount(6928, baseUrl)
   log.Println(transactionCount)

   readJsonLoop(transactionCount, baseUrl)

}

type transactionCountJson struct {
    Success bool `json:"success"`
   TotalTransactions int `json:"totalTransactions"`
}

func getTransactionCount(cycleNumber int, baseUrl string) (x int) {

   getRequestUrl := 
      baseUrl +
      strconv.Itoa(cycleNumber)+
      "&endCycle="+
      strconv.Itoa(cycleNumber);
   log.Println(getRequestUrl)

   resp, err := http.Get(getRequestUrl)
   if err != nil {
      log.Fatalln(err)
   }

   rawBodyBytes, err := ioutil.ReadAll(resp.Body)
   if err != nil {
      log.Fatalln(err)
   }

   var transactionCountJsonInstance transactionCountJson

   err = json.Unmarshal(rawBodyBytes, &transactionCountJsonInstance)
   if err != nil {
      log.Fatalln(err)
   }

   return transactionCountJsonInstance.TotalTransactions;
}

func readJsonLoop(totalTransactions int, baseUrl string) {

   total := totalTransactions;
   pageIndex := 1;

   for total > 0 {

      getRequestUrl := 
         baseUrl+
         strconv.Itoa(6928)+
         "&endCycle="+
         strconv.Itoa(6928)+
         "&page=" + 
         strconv.Itoa(pageIndex)
      log.Println(getRequestUrl)

      resp, err := http.Get(getRequestUrl)
      if err != nil {
         log.Fatalln(err)
      }

      rawBodyBytes, err := ioutil.ReadAll(resp.Body)
      if err != nil {
         log.Fatalln(err)
      }

      log.Printf(string(rawBodyBytes))

      total -= 10;
      pageIndex++;
   }

}

Rust

use serde_json;

#[tokio::main]
async fn main() -> Result<(), reqwest::Error> {

    let base_url = String::from("https://explorer-dapps.shardeum.org/api/transaction?startCycle=");
    let cycle_number = 6928;

    let transaction_count : u64 = get_transaction_count(cycle_number.clone(), base_url.clone()).await;    
    println!("transaction_count: {:#?}", transaction_count);

    read_json_loop(cycle_number.clone(), base_url.clone(), transaction_count).await;

    Ok(())
}

async fn get_transaction_count(cycle_number: u64, base_url: String) -> u64   {

    let get_request_url = 
        base_url +
        &cycle_number.to_string() +
        "&endCycle=" +
        &cycle_number.to_string();
    println!("getRequestUrl: {:#?}", get_request_url);

    let new_todo: serde_json::Value = reqwest::Client::new()
        .get(get_request_url)
        .send()
        .await.unwrap()
        .json()
        .await.unwrap();

    println!("JSON raw response: {:#?}", new_todo);
    println!("{:#?}", new_todo["success"]);
    println!("{:#?}", new_todo["totalTransactions"]);
    println!("{:#?}", new_todo["totalTransactions"].as_u64().unwrap());

    return new_todo["totalTransactions"].as_u64().unwrap();

}

async fn read_json_loop(cycle_number: u64, base_url: String, total_transactions: u64) {

   let mut total : i64 = total_transactions as i64; //Convert value to be signed so we do not have an underflow error when the value become negative.
   let mut page_index = 1;

   while total > 0 {

        let get_request_url = 
            base_url.clone() +
            &cycle_number.to_string() +
            "&endCycle=" +
            &cycle_number.to_string() +
            "&page=" + 
            &page_index.to_string();
        println!("getRequestUrl: {:#?}", get_request_url);

        let new_todo: serde_json::Value = reqwest::Client::new()
            .get(get_request_url)
            .send()
            .await.unwrap()
            .json()
            .await.unwrap();

        println!("JSON raw response: {:#?}", new_todo);

        total -= 10;
        page_index += 1;
    }   

}

Listening for the most recent cycle

Listening for the most recent cycle, which may include transaction events from an address:

Javascript

const axios = require('axios');
const ethers = require('ethers')

const rpcURL = "https://dapps.shardeum.org/"

const provider = new ethers.providers.JsonRpcProvider(rpcURL)

const timeMilliSec = 1000;

listenForCycle()

function timeout(ms) {
    return new Promise(resolve => setTimeout(resolve,ms));
}

async function listenForCycle() {
  while (true){

    console.log("Current cycle (1 cycle = 10 blocks [bundles]) ")
    let cycle = await provider.getBlockNumber();
    console.log(Math.floor(cycle/10))

    let baseUrlCycleAddress = "https://explorer-dapps.shardeum.org/api/transaction?startCycle=" + cycle + "&endCycle=" + cycle + "&address=0x0000000000000000000000000000000000000000" 
    console.log(baseUrlCycleAddress)

    let responseRawJSON = await axios.get(baseUrlCycleAddress);
    let responseDataJSON = responseRawJSON.data;
    let totalTransactions = responseDataJSON.totalTransactions
    console.log(totalTransactions);

    readJSONLoopLatestCycle(totalTransactions,baseUrlCycleAddress)

    await timeout(60*timeMilliSec)

  }
}

async function readJSONLoopLatestCycle(totalTransactions,baseUrl) {

    let total = totalTransactions;
    let pageIndex = 1

    while ( total > 0 ) {

        let filterUrl = baseUrl + "&page=" + pageIndex
        console.log(filterUrl)

        let responseRawJSON = await axios.get(filterUrl);
        responseRawJSON = responseRawJSON.data;
        console.log(responseRawJSON);

    total -= 10;
        pageIndex++;
    }

}

Python

from web3 import Web3
import time
import math
from urllib.request import urlopen
import json

ShardeumConnectionHTTPS = "https://dapps.shardeum.org/";
web3 = Web3(Web3.HTTPProvider(ShardeumConnectionHTTPS))

print("Connected to Web3? ")
print(web3.isConnected())

print("Chain ID? ")
print(web3.eth.chain_id)

addressToSubscribeTo = "0x0000000000000000000000000000000000000000"

while True:
print("Current cycle (1 cycle = 10 blocks [bundles]) ")
cycle =  (math.floor(web3.eth.blockNumber/10))  #Divide current bundle [block] by 10, then round down to get cycle.
print(cycle)

transactionsInCycleRangeUrlString = "https://explorer-dapps.shardeum.org/api/transaction?startCycle=" + str(cycle) + "&endCycle=" + str(cycle) + "&address=" + addressToSubscribeTo
print(transactionsInCycleRangeUrlString)
transactionsInCycleRangeUrlOpened = urlopen(transactionsInCycleRangeUrlString)
transactionsInCycleRangeUrlJSON = json.loads(transactionsInCycleRangeUrlOpened.read())
totalTransactions = transactionsInCycleRangeUrlJSON["totalTransactions"]
print(totalTransactions)
pageIndex = 1

while totalTransactions > 0:
    print(pageIndex)
    print(totalTransactions)
    pageIndexIncrementUrlString = transactionsInCycleRangeUrlString + "&page=" + str(pageIndex)
    pageIndexIncrementUrlOpened = urlopen(pageIndexIncrementUrlString)
    rawTransactionDataPage = json.loads(pageIndexIncrementUrlOpened.read())
    print(rawTransactionDataPage)
    totalTransactions -= 10
    pageIndex += 1

time.sleep(60)

Go

package main

import (
   "io/ioutil"
   "log"
   "net/http"
   "encoding/json"
   "context"
   "math/big"
   "strconv"
   "time"

   "github.com/ethereum/go-ethereum/ethclient"
)

func main() {

   client, chainID := clientSetup("https://dapps.shardeum.org/")

   log.Println("chainID: ", chainID)


   for {

      header, err := client.HeaderByNumber(context.Background(), nil)
      if err != nil {
         log.Fatal(err)
      }

      blockNumber := header.Number
      bigNumberTenBundlesPerCycle, _ := new(big.Int).SetString("10", 10)  //Value 10, decimal units also 10. 
      cycleNumber := new(big.Int).Div(blockNumber, bigNumberTenBundlesPerCycle)
      bigNumberOne, _ := new(big.Int).SetString("1", 10)  //Value 1, decimal units 10. 
      cycleNumberMinusOne := new(big.Int).Sub(cycleNumber, bigNumberOne)
      log.Println(cycleNumberMinusOne)

      baseUrl := "https://explorer-dapps.shardeum.org/api/transaction?startCycle=";
      transactionCount := getTransactionCount(cycleNumberMinusOne, baseUrl)
      log.Println(transactionCount)

      readJsonLoop(cycleNumberMinusOne,baseUrl,transactionCount)

      time.Sleep(60 * time.Second)

   }

}

type transactionCountJson struct {
    Success bool `json:"success"`
   TotalTransactions int `json:"totalTransactions"`
}

func getTransactionCount(cycleNumber *big.Int, baseUrl string) (x int) {

   getRequestUrl := 
      baseUrl +
      cycleNumber.String()+
      "&endCycle="+
      cycleNumber.String();
   log.Println(getRequestUrl)

   resp, err := http.Get(getRequestUrl)
   if err != nil {
      log.Fatalln(err)
   }

   rawBodyBytes, err := ioutil.ReadAll(resp.Body)
   if err != nil {
      log.Fatalln(err)
   }

   var transactionCountJsonInstance transactionCountJson

   err = json.Unmarshal(rawBodyBytes, &transactionCountJsonInstance)
   if err != nil {
      log.Fatalln(err)
   }

   return transactionCountJsonInstance.TotalTransactions;
}

func readJsonLoop(cycleNumber *big.Int, baseUrl string, totalTransactions int) {

   total := totalTransactions;
   pageIndex := 1;

   for total > 0 {

      getRequestUrl := 
         baseUrl+
         cycleNumber.String()+
         "&endCycle="+
         cycleNumber.String()+
         "&page=" + 
         strconv.Itoa(pageIndex)
      log.Println(getRequestUrl)

      resp, err := http.Get(getRequestUrl)
      if err != nil {
         log.Fatalln(err)
      }

      rawBodyBytes, err := ioutil.ReadAll(resp.Body)
      if err != nil {
         log.Fatalln(err)
      }

      log.Printf(string(rawBodyBytes))

      total -= 10;
      pageIndex++;
   }

}

func clientSetup(wssConnectionURL string) (client *ethclient.Client, chainID *big.Int) {

   client, err := ethclient.Dial(wssConnectionURL) //Also works with HTTPS connections. 
   if err != nil {
       log.Fatal(err)
   }

   chainID, err = client.NetworkID(context.Background())
   if err != nil {
      log.Fatal(err)
   }
   return
}

Rust

use serde_json;
use ethers_providers::{Middleware, Provider, Http};
use std::thread::{sleep};
use std::time::{Duration};

#[tokio::main]
async fn main() {

    let rpc_shardeum_https = "https://dapps.shardeum.org/";

    let provider = Provider::<Http>::try_from(rpc_shardeum_https).expect("could not instantiate HTTP Provider");

    let chainid = provider.get_chainid().await.unwrap();
    println!("Got chainid: {}", chainid);

    loop{

        let current_block_number = provider.get_block_number().await.unwrap();
        println!("current_block_number: {:?}", current_block_number);

        let current_cycle_number = current_block_number/10;
        println!("current_cycle_number: {:?}", current_cycle_number);

        let current_cycle_number_minus_one = current_cycle_number-1;
        println!("current_cycle_number: {:?}", current_cycle_number_minus_one);

        let base_url = String::from("https://explorer-dapps.shardeum.org/api/transaction?startCycle=");

        let transaction_count : u64 = get_transaction_count(current_cycle_number_minus_one.as_u64().clone(), base_url.clone()).await;    
        println!("transaction_count: {:#?}", transaction_count);

        read_json_loop(current_cycle_number_minus_one.as_u64().clone(), base_url.clone(), transaction_count).await;

        sleep(Duration::from_millis(60000)); // Sleep for 60 seconds.

    }

}

async fn get_transaction_count(cycle_number: u64, base_url: String) -> u64   {

    let get_request_url = 
        base_url +
        &cycle_number.to_string() +
        "&endCycle=" +
        &cycle_number.to_string();
    println!("getRequestUrl: {:#?}", get_request_url);

    let new_todo: serde_json::Value = reqwest::Client::new()
        .get(get_request_url)
        .send()
        .await.unwrap()
        .json()
        .await.unwrap();

    println!("JSON raw response: {:#?}", new_todo);
    println!("{:#?}", new_todo["success"]);
    println!("{:#?}", new_todo["totalTransactions"]);
    println!("{:#?}", new_todo["totalTransactions"].as_u64().unwrap());

    return new_todo["totalTransactions"].as_u64().unwrap();

}

async fn read_json_loop(cycle_number: u64, base_url: String, total_transactions: u64) {

   let mut total : i64 = total_transactions as i64; //Convert value to be signed so we do not have an underflow error when the value become negative.
   let mut page_index = 1;

   while total > 0 {

        let get_request_url = 
            base_url.clone() +
            &cycle_number.to_string() +
            "&endCycle=" +
            &cycle_number.to_string() +
            "&page=" + 
            &page_index.to_string();
        println!("getRequestUrl: {:#?}", get_request_url);

        let new_todo: serde_json::Value = reqwest::Client::new()
            .get(get_request_url)
            .send()
            .await.unwrap()
            .json()
            .await.unwrap();

        println!("JSON raw response: {:#?}", new_todo);

        total -= 10;
        page_index += 1;
    }