Questions tagged [blockchain]

The Ethereum blockchain is a distributed database based on the Ethereum whitepaper specification and stores both the full transaction list and the most recent state.

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Should I convert Centeralised web app to Multichain because it is free to use and more secure compare to webapp?

I am Web app developer and exploring the blockchain technology from few months. I want to convert the live centralized WebApp to Decentralized Blockchain application. I know there is a high cost ...
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1answer
39 views

Implementing ERC721 Marketplace

I'm working on a project where I need to implement an ERC721 marketplace. It doesn't work for some reason and wanted to know if I'm doing everything correctly. The way I approached this was: The ...
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do users should be aware of smart contract of the dApp they are using?

So dApps are frontend + contract. Users interact with smart contracts via frontend. Do users i.e. people should be aware of how the contract is designed while using any dApp? are their any risks of ...
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1answer
25 views

Does it align with the base concept of blockchain, if one stores the hash value generated from IPFS network in a database?

A friend of mine utilized IPFS to store data files regarding some user info.But for an android application of the same, he retrieved all hash values(same user but different files) and stored it in a ...
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0answers
7 views

console.log(App.ticTacToeInstance.events); in createNewgame function getting undefined

import Web3 from "web3"; import { default as contract } from 'truffle-contract' import ticTacToeArtifact from "../../build/contracts/TicTacToe.json"; import $ from "jquery"; let TicTacToe = ...
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23 views

what will happen to transactions on smaller length chain when peered with longer length chain in private ethereum

what will happen to transactions on smaller length chain when peered with longer length chain in private ethereum? Below is the scenario Step 1: I have started Ethreum private chain in 2 different ...
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1answer
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html:82 Uncaught ReferenceError: App is not defined at HTMLButtonElement.onclick (html:82)

It's showing me uncaught reference error in my index.html file <div id="candidate-box"></div> <button class="btn btn-primary" onclick="App.vote()">Vote</button> ...
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How I can use blockchain in my current Mobile wallet application?

I want to apply the blockchain concept for my Fiat currency wallet. I have android app and use the nodejs in backend(API). I want to apply the blockchain in payment module to secure the payments. ...
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Head of blockchain fall back to 0 after unsafe shutdown, how to reset it to the latest?

System information Geth version: 1.8.27 OS & Version: Linux Docker version: 18.09.0 Background gcmode is full, syncmode is fast. Single node in private network. datadir mount to docker volume. ...
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Sending ethereum smart contract transactions to miners

We are building a decentralized document issuance application using the ethereum blockchain. For every transaction, some gas costs deduced in the form of ether. Is it possible to host ethereum miner ...
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I can see my ethereum but its not going to my wallet

My ethereum has been confirmed delivered but not in my wallet,fairly new but I have made successful transactions before,I can see my ethereum in etherscan.io 0x2ecc74c6e9c42eea14863fbc1e1d9656b339a6ec ...
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How can i make payment application using the blockchain? [closed]

i want to make payment based application by scratch using blockchain, so where can i learn from scratch and what are the different component that i should learn to make an application or a website ...
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Interaction smart contract and third-party app : How to make sure the request comes from the original contract?

I'm working on a blockchain project where I need to access data stored outside the smart contract. The smart contract own a RSA keypair (one public and one private key). We want the private key to ...
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20 views

Block-chain data retrieval

I'm using a testrpc to test my sensor contract, where many account get to submit data to the block-chain whether using an html client side application or using the smart contract is self. How can I ...
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1answer
19 views

Etherescan Unique Address Growth Chart - How is it computed?

how does Etherscan get this information from the blockchain? Is it possible via using a web3 module? Any insight? https://etherscan.io/chart/address
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Getting TxnHash but not recipt web3j android

I dont know if question is asked before but I did not find any. I am facing this issue since yesterday. I am able to get balance and txnHash but it never shows on etherScan.io , nor it gives me txn. ...
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1answer
13 views

What would web3.js respond with in this case?

I have a mapping to a struct in my contract mapping (uint=> Student) students; struct Student { bool passed; } Now I want to call a particular student with a particular ID to see if he has ...
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Can anybody help me with protocol development?

I have seen a lot of resources for dApp development but I don't know how to start learning more about protocol development. I have read whitepapers, some articles and started reading go-ethereum's ...
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1answer
34 views

Create multiple tokens for a unique property

here is the idea: we assign a set of unique tokens to a company and then we allow people to buy some tokens and get partial ownership of that company. How can I achieve this? I was thinking of ...
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28 views

Geth Sync failed

I started to sync Ethereum using command geth --syncmode "fast" on my windows system. It was taking so much time so i have stopped sync and used the following command. geth --syncmode "fast" --cache=...
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1answer
45 views

totalSupply doesn't pass test

I'm starting programming. I wanted to do my first contract and I assigned totalSupply to 1000000. pragma solidity ^0.5.8; /** * The DappToken contract Constructor Set the total number of tokens ...
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36 views

Hosting pet-shop DApp on IPFS - JSON Files problem

I am trying to host DApp "pet-shop" which one of the truffle boxes on IPFS. rsyncing of src, build/contracts and ipfs add files went very well and there are plenty of peers as seeders on the network ...
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1answer
18 views

can't get struct in return

I am trying to execute unit tests for a solidity smart contract: I have: mapping (bytes16=>Device) public Device_Table struct Device { bytes16 UUID; bytes16 hardware_UUID; string ...
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2answers
25 views

Does it align to the base concept of blockchain, if one stores the hash value generated from IPFS network in a database?

A friend of mine utilized IPFS to store data files regarding some user info.But for an android application of the same, he retrieved all hash values(same user but different files) and stored it in a ...
0
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1answer
32 views

Hash functions in solidity

I'am trying to hash two bytes16 variables to produce bytes32 or bytes16 variable : bytes16 T=hash(bytes16 t1, bytes16 t2) I looked in documentation but I didn't find anything
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2answers
72 views

How to concatenate two bytes16 to bytes32

I'am trying to concatenate tow bytes16 to form a bytes32 func concat(bytes16 t1, bytes16 t2) public returns (bytes32) I'am not finding anything in solidity documentation! Is anyone have an idea ...
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1answer
33 views

Are transactions with zero data included within a block guaranteed to be successful?

I know there are transaction receipts to verify that a transaction included in a block was executed successfully and funds were actually transferred. But can receipt verification be skipped if I'm ...
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33 views

Cannot read property 'deployed' of undefined

Hello i try with web3 to run frontend with remix. The chrome shows the error from title for this line> App.contracts.Creation.deployed().then(function(instance) { I would love to help me!
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50 views

Unhandled Rejection (TypeError): Election.methods.addCandidate is not a function

//solidity code function addCandidate(string memory _name) public { candidatesCount++; candidates[candidatesCount] = Candidate(candidatesCount, _name, 0); } //App....
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1answer
83 views

Deploy dapp on private blockchain network

i have create a private network with 2 nodes. I have connect an account with metamask from my private network and i have created a full dapp ( contract,front-end). Now i want to deploy the whole dapp ...
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57 views

Error while importing Libp2p package in blockchain

I have installed some js-libp2p's packages on my Ethereum Blockchain-ipfs project and I wrote some codes like below. const TCP = require('libp2p-tcp'); const MulticastDNS = require('libp2p-mdns'); ...
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23 views

Time in blockchain and HTML

I'm trying to get time once data is submitted off-chain, since only way to get on-chain is via now to get the block time. Off-chain I'm using "document.getElementById("demo").innerHTML = Date()" to ...
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1answer
123 views

No web3.min.js while download Zip file from Github

I am following a youtube tutorial to make a simple dApp. In this tutorial he is telling to get Web3 from GitHub. I downloaded the Zip of Web3 from the GitHub and i get following folders and file after ...
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61 views

How to compile solidity code in Kali Linux

I have tried to install the remix IDE for compile my codes in solidity, since for some reason the remix IDE don't open online. I executed the codes bellow and give that errors. Sorry anything ...
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Can't call contract function in Remix in Web3 provider mode, but it works in Javascript VM

A simple contract for addition, an error is reported when calling the function add in Web3 provider mode: "Gas estimation errored with the following message (see below). The transaction execution ...
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44 views

Why this error occurring when i running my dapp?

I create a dapp using Solidity,Web3Js,Javascript and Html with metamask i always getting this error when i am trying to submit my transition i am getting this error at c (inpage.js:1) at ...
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1answer
118 views

Solidity Error Address / Address Payable

I'm currently learning solidity programming to create a basic smart contract based on a 2018 tutorial where solidity was using version 4. I'm currently using truffle v5.0.21. I understand that there ...
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0answers
113 views

Problem connecting web3 via websocket to node with nginx

we are trying to connect to a geth node via WebSockets to be able to subscribe to contract events. This node is created with docker and this docker uses nginx as a proxy. We can connect easily with ...
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0answers
43 views

Solidity: TypeError: Member “unbond” not unique after argument-dependent lookup in contract super EthGatedMarket

I'm getting this error: TypeError: Member "unbond" not unique after argument-dependent lookup in contract super EthGatedMarket. super.unbond(msg.sender, gatewaySpecifier, quantity); ^----------...
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2answers
293 views

Offchain vs Sidechain vs StateChannel

What are the main differences between off-chain, sidechain and state channel? And what are the use-cases of all of these?
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1answer
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Three questions

I have recently become interested in crypto and after much reading on Ethereum I still have three burning questions that perhaps some of you can help with. Apologies in advance as some of these might ...
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148 views

Error: The data field must be HEX encoded data

I am trying to make a simple dApp by using a tutorial. I am using the following command ; npm install ganache-cli web3 so that we can use web3 to get fake ethereum nodes/accounts by connecting it ...
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1answer
104 views

Can't connect to localhost:8545 while using ethereumjs-testrpc web3?

I am developing a simple Voting dApp by following a tutorial. In this tutorial we are using npm install ethereumjs-testrpc web3 so that we can get the fake nodes of Ethereum. For that i first ...
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13 views

How can I combine Quorum and Zero Knowledge Range Proofs

How can I combine Quorum and Zero Knowledge Range Proofs I have 20 years of experience at java JEE coding, and 10 years in devops as well, but no experience with blockchains, or the Go language. I ...
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12 views

What repo in loom do I fork to create my own sidechain?

I am trying to create a sidechain. I believe I need the code for the node that supports the sidechain. How many repos will I need to collect to properly start my own sidechain? Ideally a proof of ...
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Could the parity-ethereum client incorporate doing range proofs in the ethereum blockchain?

I want to be able to prove that I have stored a number that is in the range of a minimum and maximum value, (a range proof) without revealing the number, and put the value into the ethereum blockchain,...
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How to get the value from the frontend form and save value to the blockchain using +web3 1.0.0-beta.37 + reactjs

I am writing my first Dapp and want to save the value of the form to the blockchain. I am Using React and web3 js 1.0.0-beta.37 on the frontend. Also I am new to react. Following is my App.js ...
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2answers
48 views

How blocks in a blockchain are identified that store concerned policy?

I am working on blockchain. My project is to store Role based access control policies(user-role assignment and role-permission assignment) in blockchain. Policies are written in 2 dimensional array (...
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1answer
21 views

What does it mean that Solidity can encode arbitrary state transition functions?

From Ethereum White Paper: "What Ethereum intends to provide is a blockchain with a built-in fully fledged Turing-complete programming language that can be used to create "contracts" that can ...
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1answer
41 views

plug our own consensus in any one of ethereum client? [duplicate]

Actually i try to add new consensus and will through modifying some consensus to see its effect on transaction throughput. so what platform should i use that provide me this facility or should i use ...