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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Blockchain overhead - general question

I was reviewing the blockchain technology the other day, Maybe this is not the right place or maybe I should rephrase my question but.. Blockchain is peer to peer, every peer stores the data Data is ...
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Retrieving the first and latest transaction date of a contract

Etherscan offers a time series of ethereum transaction of a contract address. Is there a way to retrieve this data? For example the duration mentioned here https://etherscan.io/address/...
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How to store data on ethereum blockchain WITHOUT IPFS

Hi guys ^^ i want to store PDF file on ethereum blockchain without use of IPFS. I want to do it because i have my own private network where this data will be only stored. That's why i want to store it ...
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How ETH is generated?

I still do not get the concept of Ethereum. How does the ETH money/coin/value is generated? Who generate that? Are the miners who process a transaction get ETH from the other user (fee) or the system ...
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Smart Contract deployment failed

I am making my project of BlockChain subject. I am having a problem with deploying smart contracts. Can anyone help me with this error I have tried everything I could but still failed to resolve this ...
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If you need a server to store HTML and java script code, then what is the use of the block chain?

I have been studying block chain for a while, and I came to know that decentralisation of data is its greatest pros. From my understanding, if block chain is massively adopted in the future, we will ...
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Api to get total transfer count of an ERC-721 Token

I want to retrieve the total number of an erc 721 token's transfers/ transactions. I couldn't scrape the transfers value from etherscan as well e.g. given here https://etherscan.io/token/...
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Do testnets ever merge with mainnets?

Does a testnet ever merge with the mainnet? In other words, if I have ETH on a testnet, will I ever have actual ETH or do testnets remain for testing forever? I Googled in multiple ways but could ...
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How can fix in smart contract written in solidity?

TypeError: Invalid type for argument in function call. Invalid implicit conversion from address to address payable requested. selfdestruct(admin); pragma solidity >=0.4.21 <0.6.0; ...
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How can Ethereum sustain short block creation times if the uncle transactions are not counted?

Lower block times are clearly desirable. Why does not Bitcoin reduce block creation times to 15 seconds just like Ethereum in this case? Because it would lead to too many forks. The main problem with ...
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Unable to Unlock Account Even After specifying allow-insecure-unlock

Software: Ubuntu on VirtualBox Update, tried putting two dashes, on allow-insecure-unlock, doesn't work solidity@solidity:~$ geth attach http://127.0.0.1:8545 --allow-insecure-unlock Incorrect Usage:...
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How does the reentrancy attack work?

Consider the following contracts contract Victim{ //... function donate() public payable { credit[msg.sender] += msg.value; } function withdraw(uint amount) public { if (credit[...
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blockchain solidity tracking system

I am trying to make a code in solidity to add items to a blockchain which contains items and their tracking history (like when trace your order online for an item) (which at first are located in "...
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Blockchain Performance Metrics

How can I measure blockchain execution time, latency and throughput? Which API do I use to measure? Anyone suggest any article or book for me to read about the blockchain performance metrics?
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Contract is failing on approve function in Ethereum with Solidity [closed]

My contract file is this http://prntscr.com/pvvkme. My Test file are these http://prntscr.com/pvvkme & http://prntscr.com/pvvlmg My migration file is this http://prntscr.com/pvvm5b My errors are ...
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error in remix IDE

I am facing this type of Error in 'remix IDE' while connecting it to 'web3.js@0.20.2' Error: Failed to decode output: Error: insufficient data for uint256 type (arg="", coderType="uint256", value="...
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web3.eth.contract not working

I have web3@0.20.2 installed using npm . when I call web3.eth.contract() it says that it is not a function and when I use new web3.eth.contract it says it is neither a constructor. This is my code &...
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IPFS file uploading issue [closed]

I just installed IPFS version 0.4.22 on my Mac. When I try to upload/add a file in TERMINAL - using the following command: ipfs add myLogo.jpg I get this error: Error: ipfs repo needs migration ...
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1answer
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How to substitute attributes instead of roles in access control coding for solidity?

Say, the role-based access control consists of two roles. But if I want to replace the roles to maybe location and time, how to go about it?
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Does Geth provide a private or public network?

I'm new to the Blockchain world, lacking experience and I'm looking for some assistance. I'm just syncing with ethereum network by using Geth and rinkeby network. by using this command: geth --...
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Ethereum development environment for Windows 10

I am new to Ethereum and Solidity. Currently learning it from youtube videos and some blogs. So far I have been doing stuff in the remix IDE on a browser. Now I want to perform the same things on my ...
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1answer
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How to write smart contract to check deployed owner is intitiating the contract or not, everytime?

I want to write a smart contract where it would check it is owner of the deployed contract is trying to instantiate the contract or not. And by doing to i want to allow only the owner to call smart ...
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How often Geth/Parity access the archive chain files? Can I store remote?

I'm running a full archive node to receive and send funds (ETH & other tokens also). The size of the blockchain is very large, so I'm thinking about storing it remotely and mount as an sshfs ...
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Consortium vs. Permissioned Blockchains

I hear these two terms interchangeably Consortium Blockchain and Permissioned Blockchain. Are they the same? If not, can you please show the difference between them. P.S. Since there exists no ...
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CI/CD principles for creating an ethereum network on Cloud

I am setting up an ethereum network on the public cloud. Are there any specific CI/CD principles specific to Ethereum which could be implemented while setting up Ethereum Network on Cloud? Also, are ...
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getPastEvents on localhost is not a function error

Now, I'm working on an Ethereum Blockchain project to transfer the ownership of stored devices by using local web3 provider at the truffle environment. Truffle v5.0.27 (core: 5.0.27) Solidity v0.5....
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Could this work? Proof of Consistency?

So, I have been doing some research on Blockchain , for my dissertation, recently and had spent a lot of time researching consensus protocols. This had led me to wondering if there is any other ways ...
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Does transaction hash in Ropsten ( testnet) deprecate ever?

I want to know whether transaction hash created in testnet stay forever or after sometime it gets deleted? Like in IPFS garbage collector deletes unpinned files after two weeks. IPFS is also ...
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Why use nodepools or backends?

I have a fundamental question about eth/blockchain infrastructure. I see several posts talking about the need for backend node infrastructure when launching a dapp/ smart contract. This infrastructure ...
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1answer
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Invalid sender address, failed to deploy a transaction to the blockchain network

Description I'm trying to deploy a contract to rinkeby network, but everytime I like to deploy the contract it throwing error as invalid sender. Compile code const path = require('path'); const fs =...
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How to change push() method to simple code?

I have this code but it's static and I wanna change it dynamically. function addCandidates(){ if( own == 1 ){ candidate[0].candidate_ID[0] = 1; candidate[0].candidate_ID[1] = 2; ...
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Quorum-maker-node not starting

I have created a node in quorum-maker using my ip address but that node is not starting.If i create a node using local ip(127.0.0.1), node starts.why?
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Are there any virtual IoT simulators that facilitate the connection with Ethereum Blockchain?

I already built a smart contract for Ethereum Blockchain by using truffle; Now, I'm looking to connect my smart contract with the IoT environment. So are there any IoT simulators (platform, framework,...
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Can we connect custom Ethereum currency through java's web3j library ? If yes then how?

Im trying to create my own new currency using solidity and ethereum platform and also i want to create an Ewallet of my currency using java so that my ewallet could communicate through api .If u ...
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1answer
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Why do I always get “Returned values are not valid, did it run Out of Gas”?

I'm new on Ethereum blockchain and I'm working on deploy and using smart contract using truffle on my private blockchain. I have followed exactly this guide https://www.trufflesuite.com/docs/...
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Linked contracts not running on go-ethereum

A very simple linked contracts example where A contract has a variable and B contract queries the A contract's variable is running ok on Ropsten+myetherwallet and Remix sandbox, but it fails when ...
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1answer
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Why my smart contract's function always return 0?

I'm new on Ethereum. I'm trying to deploy my first smart contract in my private blockchain but my function always returns 0. I wrote the simple Smart Contract: pragma solidity^0.5.0; contract ...
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1answer
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Is QTUM is a coin or a Token?

According to Etherscan Qtum is a Token, holding supply with verified smart contract. But its official site contains its own protocol and integration mechanism. Is it still a token under ETH or it has ...
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How to find out in blockchain ledger the current ownership of asset being transacted

I am new to blockchain and smart contract as well. In smart contract we can only save the current state of any transaction but if we need to know the previously expunged transactional data ie, the ...
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How simulate blockchain and smart contract in VANET?

I am a beginner in the blokchain, I am blocked how I start simulate a blockchain and smart contract in vanet. Can you help me and inform me how I have to simulate blockchain and smart contract in the ...
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2answers
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validation of data integrity in block

I am learning ethreum dapps development and have developed some dapps. I was thinking about supply chain dapp which i think , is very good application of blockchain as it ensures all the history of a ...
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How Merkle Patricia Trie updates the account balance?

This is my understanding of the Merkle Patricia Trees in Ethereum so far: There are three kinds of merkle trees storing diff info - state, transaction and receipt. When a new block is added it ...
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How to transfer ERC20 token from one account to another account but paying the transaction fee from third account?

I want to transfer token from account A to account B by paying transaction fee from account C.I have tried the following logic but token transfer from contract to contract mean contract transfer token ...
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2answers
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Failed to read genesis file: open genesis.json: permission denied

First of all I have to say that all this things will work on my windows machine. Today I started to do the same things on a ubuntu machine (with ssh and private key authentication). I've created a ...
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How to build an ethereum based wallet with custom UI?

I have been interested in ethereum for quite some time now and have always wanted to learn ethereum development. I decided to create my custom erc20 tokens i was able to create 2,00,000 tokens. Now i ...
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1answer
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How to download the blockchain of a single ethereum contract’s address?

The blockchain required to run ethereum is several Terabytes large. This means more than 9 years would be required to download it with my connection speed. In my case, I just want to know if the ...
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Why is PoW needed to confirm transactions and add new blocks [closed]

I have read and I vaguely understand about how Proof of Work works and what does it do. But why PoW? Or more bluntly, why do we need any algorithm at all to add new blocks. What would happen if ...
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Exchange ERC20 token with other ERC20 token

I have 2 ERC20 tokens. The contract are designed as standard ERC20. Here are the 2 tokens to take as an example - AUDC --> Contract Address: (0xContractAUDC) Wallet Address: (...
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Blockchain Development [closed]

I want to build a blockchain network such that if one node updates, all the other linked nodes gets update too. Think of it as Centralized Hospital record in multiple cities, if any of the city pushes ...
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web3.exceptions.BadFunctionCallOutput: Could not decode contract function call getEvidence return data b'' for output_types ['string']

Solidity Code: function getEvidence(string memory _evidenceID) view public returns (string memory) { require(evidenceOwner[_evidenceID] == msg.sender); string memory evidenceHash = ...