Smart Contract Occurrences

Smart contract events transmit new data emanating from a contract.

Why are Smart Contract Events Important?

Listening to smart contract events notifies applications and users in real time when something new occurs within a smart contract.

Where are Events Used in Smart Contract Applications?

Frontend

If you swap tokens on a website using a AMM DEX smart contract, the token balances will know when to be updated on the frontend almost instantly using events.

Backend

Trading bots have the capability to monitor events related to AMM DEX swap contracts, enabling them to identify potential arbitrage opportunities. In the physical world, IoT robotics applications connected to a smart contract can be managed through events. Chainlink oracle nodes also rely on smart contract events to determine when to facilitate communication between the real world and blockchains.

How to Listen to Smart Contract Events on Shardeum?

Websockets

We are planning to include WebSocket RPC URL support in the future, allowing users to subscribe to smart contract events. This will enable users to reduce the need for making API calls to check for new data after each new block, bundle, or cycle.

Polling

You can also read smart contract events using Shardeum cycles (we monitor blocks/bundles to accomplish this).

Reading events with Shardeum Cycles:

To obtain the current cycle: retrieve the most recent block, then divide the result by 10, and round down.
Create the JSON URL using:

Example with:
```
 startCycle = endCycle = 49
 address = 0x23FF65f07cAbAd1643440a0114d71260F2Bb6352
```
https://explorer-dapps.shardeum.org/api/transaction?startCycle=19020&endCycle=19045&address=0x245E2395712F888CeD1033C924115105dC32e388

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 zero 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 latest cycle

Listening for the latest cycle, which might contain 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;
    }   

}

What are Polling Cycles in Shardeum?

Table of contents

Smart Contract Occurrences

Why are Smart Contract Events Important?

Where are Events Used in Smart Contract Applications?

Frontend

Backend

How to Listen to Smart Contract Events on Shardeum?

Websockets

Polling

Reading events with Shardeum Cycles:

JSON URL Filter Variables

Event Listening With Polling Examples:

Javascript

Rust

Listening for the latest cycle

Javascript

Python

Go

Rust

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Dhiraj Yadav

Dhiraj Yadav