Questions tagged [events]

Solidity events and logging problems. Events allow the convenient usage of the EVM logging facilities, which in turn can be used to “call” JavaScript callbacks in the user interface of a dapp, which listen for these events.

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34 views

Accessing the network through light node

I've been trying, unsuccessfully, to make a web3.py app that needs to catch events, with the use of filters. After hours and hours of testing it appeared the problem was that Infura, which is the ...
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2answers
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Do logs/events last forever?

https://thegraph.com/ seems to rely on the assumption that events will last forever. But this post: https://www.reddit.com/r/ethereum/comments/a2ocy6/full_notes_from_fridays_eth_1x_sync_call/ seems ...
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1answer
29 views

Who Receives An Event?

I have a smart contract that emits an event, and I've set-up a listener in my client-side app that can register this event. But I'm curious, who receives this event? If say 20 different people from ...
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How to Listen to Contract Events in Drizzle

Let's take the example of the SimpleStorage contract that comes with the truffle box drizzle-box How can we listen to the event StorageSet and console.log it to the JS console? drizzleOptions.js ...
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1answer
583 views

watching for events in web3 v1.x.x

I deployed a contract and would like to watch for events on that contract. var access_manager_erc20_abi = require('./AccessManagerERC20_abi.js'); //To read the abi. //In this js file i export abi ...
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Get the entries of an event by an event filter in web3.py

here is my Solidity Contract: # Solidity source code contract_source_code = ''' pragma solidity ^0.4.1; contract Identities { event ExistProduction(bool); address private owner; mapping(address =&...
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Truffle test to verify events can be queried by the address of the signing user?

I'm trying to write a test which verifies I can query a given type of events by the user/address which sign them. I would like to apply TDD (relevant to say I haven't made the implementation for this ...
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1answer
103 views

How to interact with events from a smart contract?

can we get access to watch the event and get logged data from them and use it for processing in a smart contract? Like matching an state variable with the data logged by an event .
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1answer
370 views

List holders and tokens for an ERC-721 contract

Given a contract, I want to map the holders to their token ids. For example, the contract 0xFBeef911Dc5821886e1dda71586d90eD28174B7d is an ERC-721 contract for KnownOriginDigitalAsset. Etherscan ...
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1answer
294 views

How to read “allevents” using Python web3 (there's capability in web3.js)?

Is there a mechanism to create a listener for all events being emitted from a smart contract for the python web3 library. There is a way to do it in web3.js: myContract.events.allEvents([options][, ...
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Indexed event parameter only returns 1st character in address

pragma solidity ^0.4.13; contract OwnedI { /** * Event emitted when a new owner has been set. * @param previousOwner The previous owner, who happened to effect the change. * @param ...
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Truffle Test Sell Event Assertion Error

When I test my selling event in truffle.So, the following error comes:- The solidity code is :- event Sell(address _buyer, uint256 _amount); // Buy token function buyTokens(uint256 _numberOfTokens) ...
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2answers
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My contract is not emitting events

This is my contract: pragma solidity ^0.4.22; contract Test { event Deposit( address indexed from, uint amt ); event Withdrawal( address indexed to, uint amt ); address owner; constructor()...
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1answer
373 views

Web3 event listener not reacting to emitter

I'm writing a program in JS/Node that, amongst other things, subscribes to a smart contract event waiting for it to happen. There's a lot going on on the code, so I've got it separated. The main ...
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2answers
872 views

How to get only latest log from my event?

I currently am using Oraclize in my contract and I make a call to a contract function from my front-end and don't want to continue onto the next call until the Oraclize function has returned. So I ...
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2answers
3k views

Web3j listening to events

I'm tinkering with web3j and most of the things that I want to do succeed, however I seem to not be able to listen to events. I've extended the ballot.sol contract you get with remix by adding an ...
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1answer
319 views

Web3j how to get event args when parsing logs?

I'm trying to get an event args in web3j version 4.0.1. I use the simple syntax which is explained in the docs. I'm getting the log object but there is no args property or such thing in it. Here is my ...
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1answer
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Output order changes after the event triggered

I'm new to solidity so for educational purpose I'm developing EVoting application. I've written a smart contract for candidate registration and also developed UI for getting the registered candidate ...
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1answer
77 views

Different outputs on event log subscription

These are the two ways I found to track events on the Ethereum blockchain. One of them doesn't contain the data I need. Why not? Way 1 does NOT contain the data I need Result: subscription = web3wss....
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1answer
205 views

solidity-coverage adds extra events which make unit-test fail

It seems that when using the latest solidity-coverage (0.5.11), truffle (5.0.0-next.25) ganache-cli (6.2.4-beta.1) and solc (0.5.0) additional events / logs are emitted during tests which make the ...
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1answer
29 views

Reading Ledger from etherscan API vs Emitting Events

Consider the following function from a solidity Contract: function createProduct(uint _price, string memory _desc) public payable{ emit UserLedgerUpdated(_desc, -1*int(msg.value)); } I want my ...
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1answer
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How to get the timestamp from the latest event on the etherscan.io apis

How to get the timestamp from the latest event on a contract using the etherscan.io api ? I'm using the getLogs call this way: https://api.etherscan.io/api?module=logs&action=getLogs&...
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2answers
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Can a contract listen to events of another contract?

I read that to listen to events you need to use web3.js. Are there other ways of doing it? Can a contract even somehow listen to events of another contract? Thanks!
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2answers
119 views

Can we assume that Ethereum Events (aka Logs) are in-sequence

Lets consider a simple Contract that is to track a variable. A client App needs to access this variable's history to show a graph. I can create an Array inside the Contract, and push() the value ...
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2answers
552 views

Truffle Tests Events via JavaScript

I am testing my contract via the chai and truffle-assertions libraries from a JavaScript file and am testing if events return the correct values. I have an event called Message. In my function, the ...
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5answers
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web3: How do I get past events of myContract.myEvent?

I use the following JS code to get notified of Solidity events and it works well for incoming new events: myContract.myEvent().watch((error, result) => { if (error) console.log('Error in ...
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3answers
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How to properly catch events using MochaJs

Good day, I'm using mochajs to test my Solidity code using truffle and testrpc. In my contract I got the following event and function: contract store{ event MoneyIn (address _from, uint256 ...
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1answer
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Logs and events: How are arguments of “watch” defined?

In order to watch an event we can use: var temp; eventx.watch (function(error, result){ temp = result.args.val.toNumber();}); Question 1: What is the role of: function(error, result){ temp = result....
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1answer
33 views

Event firing before data is actually set [Testnet]

Today I've faced the behavior similiar to this post. Event firing before data is actually set I'm getting events using infura and then checking for the state. I expect to read updated blockchain ...
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1answer
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What is the change in smart contract when the 'chain reorganizations'?

Recently I learned about 'chain reorganization'. What is the change in smart contract when the 'chain reorganizations'? for example, contract Contract{ event LOG_Increase(); uint sum = 0; ...
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1answer
346 views

Emit event while require statement fails

I would like to be able to log a result of a condition: if(time > 5) { emit Result("time is larger than 5"); } else { emit Result("time is less than 5"); } This will work just fine, but ...
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1answer
148 views

What is the difference between writing emit in an event and not using emit? [duplicate]

For example, event CoinTransfer(address sender, address receiver, uint amount); What is the difference between CoinTransfer(msg.sender, receiver, amount); and emit CoinTransfer(msg.sender, receiver, ...
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3answers
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Where do contract event logs get stored in the Ethereum architecture?

Background on Events: https://github.com/ethereum/wiki/wiki/Solidity-Features Events allow the convenient usage of the EVM logging facilities. Events are inheritable members of contracts. When they ...
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1answer
1k views

How can we parse and deal with BigNumber (BN) args in Solidity events?

In the past, web3 events published numeric events like so: BigNumber { s: 1, e: 17, c: [ 1000 ] } } Now with web3.js 1.0, big numbers come down as objects like this: <BN: de0b6b3a7640000> ...
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1answer
73 views

Is there any point in adding msg.sender to an event?

I am asked to provide the value of msg.sender as part of an event emitted in a function. It is something like: contract MyContract { event MyEvent(address indexed sender, uint256 input, uint256 ...
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1answer
2k views

Uncaught Error: Returned values aren't valid, did it run Out of Gas?

I'm listening to events of my deployed contract. Whenever a transaction gets completed and event is fired receiving the response causes following error: Uncaught Error: Returned values aren't valid,...
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1answer
56 views

How can a user be informed of the reason for a revert if there is no event log available?

I presume a typical case of smart contract use is purchasing tokens from a smart contract using Metamask. If the contract is at all complex (such as a tiered pricing sale with various caps) and a ...
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1answer
23 views

Should I maintain an array of all the valid keys in a given mapping?

I have a contract which maintains a map of valid wallets. In this map, the keys are wallet addresses and the values are wallet parameters: struct WalletParams { bool valid; uint x; uint ...
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1answer
1k views

Solidity | Web3 | Subscribing events

I'm finding a way to subscribe the specific event in the Smart Contract and there is a web3.eth.subscribe to subscribe an event. [Web3.js 1.0.0] The web3.eth.subscribe function lets you subscribe ...
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1answer
357 views

How filter event based on a value?

I have this solidity event : event ValidateData( address professorAddr, address studentAddr, bytes32 data ); in Javascript I want watch the event only when the ...
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1answer
73 views

Event to track transactions on the backend

I'm currently developing a betting website built on top of Ethereum and am facing the following doubt. In my contract there is an event at the end of the placeBet function which tracks the summary of ...
0
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1answer
716 views

Subscribing to event using web3j

I'm trying to subscribe to a smart contract event from my java app using web3j. I deployed my contract to truffle, here it is: pragma solidity ^0.4.24; contract MyContract { string message; ...
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1answer
383 views

How to read past events from the blockchain? [duplicate]

I can read events as they happen with: const eventsWatch = myContract.allEvents(); eventsWatch.watch((err, res) => { if (err) return; console.log("Event:", res.event, res.args); ...
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1answer
1k views

Contracts will not compile using truffle with the “emit” keyword included in front of events [duplicate]

I notice there has been changes made to solidity and that the word emit is now to be used in front of event triggers (to distinguish from functions being called). However when I include these in ...
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2answers
766 views

Watch multiple contracts/events?

Is there a way to watch events from multiple contracts with just one watch-statement (something like [contract1.event, contract2.event, ...].watchAll() ) in Javascript? Code is just for illustration ...
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1answer
102 views

Using the same event name in different contracts

Suppose I have two different contracts, and I implement an event in each one of them. If I use the same event name in both contracts, will it make it more difficult (or even impossible) to filter the ...
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1answer
61 views

Web3js 1.0 events: closing the contract.events “socket”

My code is the following: contract.events.Deposit({}, function (err, event) { if (err) { console.error; } else { console.log(event.blockNumber); } }) .on('data', ...
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2answers
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Indexed Variables On Event Not Being Decoded

I'm currently returning back all events with no filter and all the indexed variables are being returned but they are encoded. The other none indexed variables are visible and being retrieved fine and ...
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0answers
143 views

Unable to catch contract event using parity websockets

I have a contract deployed on ropsten which emits event when ether amount is deposited in it. I can see the event appearing in etherscan. this.web3Socket = new Web3(new Web3.providers....
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1answer
140 views

Scalability of using getPastLogs

In order to have a list of the instances of the same contracts created, one method used is to emit an event for each instance created. To query the events(or called logs), we can use web3.eth....