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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19 views

Setting a value for ERC20 token on private blockchain?

Background: Currently we have an Dapp running on Ropsten. We've created an ERC20 token on Ropsten. Our employees are awarded these tokens over time. We want to use Dappos to allow our employees to ...
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14 views

How to create blockchain nodes locally

For educational purposes I am implementing a blockchain from scratch without the use of any frameworks. How would I go about testing my blockchain using multiple nodes when I only have access to one ...
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1answer
166 views

Python state channel client

Stumbled upon this piece of Solidity code which is an Ethereum payment channel : https://github.com/mattdf/payment-channel How am I to write a Python client that interacts with it over Web3 ? What ...
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1answer
218 views

Connecting to blockchain on azure using web3.js and websocket

right now, I am trying to write a service using web3 which will 'subscribe' to all 'perndingtransactions' on blockchain to perform further actions. web3 documentation says that 'Httpprovider' cant be ...
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1answer
56 views

Static difficulty in 1.8.27 for local network

I am having trouble getting geth 1.8.27 to have a static difficulty on a private network. I followed the instructions from here. But when I test it, the difficulty still increases. I tried again, ...
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1answer
102 views

How do I deposit an Ether amount to the smart contract function, namely deposit ? (Metamask version 0.20.7)

I have a problem with using the deposit () function on a smart contract. How do you use metamask 0.20.7 ? const contractInstance = web3.eth.contract(contractAbi).at(contractAddress); contractInstance....
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1answer
143 views

Unable to send ether to account

I am trying to send ehter using this code web3.eth.accounts.wallet.add(privateKey); web3.eth.sendTransaction({ to:someAddress, from:onwer, value:amount*1, ...
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1answer
43 views

How to kill a contract in ethereum?

I'm trying to kill this contract /** *Submitted for verification at Etherscan.io on 2016-08-31 */ //sol Wallet // Multi-sig, daily-limited account proxy/wallet. // @authors: // Gav Wood <g@...
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Migrating 2 contracts in one Contract.sol script using 'truffle migrate'

I have 2 contracts in 1 .sol file and when I run 'truffle migrate', it tells me that it has deployed 1 of the contracts and given me an additional error: Blockquote Invalid number of parameters ...
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1answer
38 views

How to match the data in the struct?

If the Set function receives two inputs 1.["0xca35b7d915458ef540ade6068dfe2f44e8fa733c",50,"ROC","park"] 2.["0x14723a09acff6d2a60dcdf7aa4aff308fddc160c",60,"AU","school"] How can I return all the ...
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1answer
188 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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1answer
99 views

testing the hello world application on a different computer when the compute crashes/node not working

I am new to the blockchain technology. I want to test the blockchain functionality of a decentralized ledger. I have created a hello world smart contract(on solidity, geth, mist browser) on computer ...
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3answers
509 views

Can't compile old solidity contracts(version 0.4.17)

I'm new with blockchain development. I'm working on an old project which use solidity 0.4.17 and truffle ^4.0.0-beta.2; These versions were in the package.json file of the project. When I installed ...
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1answer
44 views

Store and Display the Json file in Blockchain

I have stored my data on firebase, and taken as a JSON file, the JSON should be separated and display into the webpage through the Ethereum blockchain, for example: { product: "Shoes", prize: "85"...
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1answer
18 views

Getting error in Deposit function in smart contract : The constructor should be payable if you send value

I am getting the error while deposit the amount in remix. Following is my code pragma solidity ^0.4.19; contract Savings { address owner; uint256 deadline; modifier onlyOwner() { require(...
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2answers
25 views

Token Sale Smart Contract

I am new to Ethereium Block Chain and have been trying some code written in solidity as follows. pragma solidity ^0.5.0; import "./MyERC20Token.sol"; import "./ERC20Burnable.sol"; contract ...
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1answer
96 views

About send Ethereum Classic (ETC) coin

Need guideline for send ETC coin using web3js,As per documented flow I understand we can access all methods same as ETH but I have query regarding set provider for ETC after that I can connect to ETC ...
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2answers
25 views

Etherscan says there is not enough ether, why?

Etherscan says there is not enough ether, why? Arguments, which i enter => requestLoan(3,31,3) and after change account, provideGuarantee(0,3) I have created dApp and how it looks in my code you can ...
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3answers
290 views

Unlocking Ethereum wallet using Geth JSON-RPC

When I use ETH with JSON-RPC I have error "message": "authentication needed: password or unlock» and If I manually unlock I have other error "message": "insufficient funds for gas * price + value" Any ...
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1answer
170 views

Installing Ganache GUI on windows 8.1

How to install Ganache UI on windows 8.1 ? I downloaded from Official website but after downloading i am unable to install it on my machine. I tried to install it through power shell but facing ...
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3answers
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What is Geth's “fast” sync, and why is it faster?

One of the answers to this question suggested using Geth's --fast flag to help quickly synchronise the block data. How does the flag work, and how does using it speed up the synchronisation? Are we ...
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1answer
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Smart contracts, tokens and ether

I am sending some ethers and tokens to my smart contract. So how will the contract differentiate between ethers and tokens? Code will be helpful
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1answer
131 views

Is there an explorer like Etherscan for Remix JS VM sandbox blockchain

I created a contract and did some transactions. I would like to explore the transactions in the sandbox blockchain in my brower (Chrome). But the tx hash is not found in the REMIX VM Debugger http://...
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1answer
262 views

Unable to interact with DApp deployed on quorum

I am unable to interact with contract using Dapp deployed on Quorum blockchain (using metamask). I am following "https://truffleframework.com/tutorials/building-dapps-for-quorum-private-enterprise-...
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0answers
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Are there more important “impossible triangles” aside from CAP theorem, FLP impossibility and Zamfir's triangle?

I have come across CAP theorem, FLP impossibility, and Zamfir's triangle ever since I began to study blockchain. As I interpret CAP theorem as the tradeoff between consistency, Availability, and ...
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1answer
504 views

Error occurred when trying to send rpc requests(s)

I am using the nethereum package in .Net and trying to invoke a smart contract with web3. Initially it was working fine, but suddenly I am getting an error while trying to get the transaction count. ...
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2answers
45 views

Is Ethereum a common blockchain for all type of smart contracts (several thousands)

I have read that full nodes run all the contracts(several thousands) to verify them so aren't they using too much energy (and also thus spending money) to verify each and every contract that is ...
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3answers
29k views

How can I store data in ethereum blockchain

I want to store pdf hash in blockchain I already read this post What are some proposed ways of storing data in Ethereum? But I'm beginner in this domain and I don't understand... Is it possible to ...
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19 views

Where's a contract storage stored exactly and how does it interact with the blockchain? [duplicate]

From what I've understood a contract is a special account that gets initialized with a 256 bit array and this array is stored as the root hash of a merkle tree, is that correct? But where is this ...
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1answer
124 views

Testing Smart Contract

We all know a smart contract is a normal piece of code which can have intended and unintended bugs. DAO attack is such an example where a bug has led to a heavy loss. Suppose I want to check what all ...
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1answer
127 views

iOS node not syncing with private BKC

I use the Geth framework and Swift 4 to boot a node inside an iOS 11.0 app. This node connects to my local BKC (to 4 nodes to be precise). Here are some tests I made : if I start 3 computer nodes ...
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1answer
650 views

web3 not connecting to Infura / Rinkeby Testnet

I've successfully deployed my Smart-Contract to the Rinkeby TestNet via Remix. Everything works perfectly from within Remix. But when I try to get my web DApp to fire methods in my Smart-Contract - ...
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2answers
480 views

Safe to share geths chaindata folder?

As many people have quite a hard time syncing their wallets to even get started with Ethereum I offer my chaindata folder as a regular dump (.tar.gz). Downloading a dump is in most cases way faster ...
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36 views

how transaction in block-chain is validated

Please explain complete procedure/journey how transaction in block-chain get validated by miners, From broadcast of transaction to become part of new block.
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1answer
127 views

How my Cryptocurrency Exchange supports Fiat Currency?

Which mechanism is used in Cryptocurrency for converting Fiat currency into Cryptocurrency? Do they maintain stock for particular Cryptocurrency? or they have tie-ups with organisations like (ethereum....
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1answer
75 views

Contract address is not shown in rinkeby testnet etherscan

I am using Getch with truffle framework and i created an account. I have Migrations and Election.sol. After i can migrate, i couldnt see it in etherscan website. Although truffle migrate --reset --...
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1answer
26 views

What happens in a 50% Attack

I thik it is kind of clear to me that of 50%+1 attack, but now i am thinking about something that occurred when i was testing a DAPP in a two node network. Each node had a blockchain (the same ...
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3answers
55 views

Restricting payment from one account only

I am a beginner in ethereum DApp development and I am testing my Contracts in Remix IDE. My question is that can I restrict only one account to pay for all the transactions happening on my application ...
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3answers
528 views

IPFS. Add a directory recursively with an HTTP api

Is there an HTTP api equivalent of doing: ipfs add -r resources/public where resources/public is a directory with a static website (index.html in the root, css, js etc). Doing: curl -F file=...
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1answer
395 views

How to increase gas limit ethereum

I am facing this error : Error: exceeds block gas limit When i run below command it returns 5000. web3.eth.getBlock("latest").gasLimit so as per someone's suggestion 21000 gasLimit is needed to ...
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1answer
16 views

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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1answer
626 views

geth - admin,addPeer() and static-nodes.json don't work

I'm trying to connect two nodes (both miners) on my private network. They are based on the same VM in different data directories. They have different ports and are based on the same genesis file and ...
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1answer
241 views

Transfer data using solidity transfer function

Can we use transfer function in solidity to transfer the data? My code _dest.transfer(txn.value)(txn.data); and it is showing the error that this type is not callable.
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1answer
330 views

Posting data from raspberry pi on blockchain and retrieving it back

I am new to blockchain technology. I just want to know if it is possible to post the data from raspberry pi on blockchain (ethereum) and retrieve the posted data for viewing. My question is if its ...
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1answer
213 views

Resource allocation and smart contracts

I'm wondering if the following scenario could work with smart contracts. I'm very new to Blockchain so what I'm saying might sound too silly. I have 10 users who are sharing a common resource. There ...
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1answer
332 views

oraclize calling a REST API

I am trying to call a third party REST API that I developed using spring boot, and I want to call a function(param1,param2) in the API from the oracle using the oraclize_query() (POST request), but I ...
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1answer
5k views

What Ethereum blockchain explorers exist?

What blockchain explorers exist and What special features do they have? Are they open-source? How reliable are they (approximate uptime in %)? Is there a testnet version?
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1answer
607 views

How to make API calls from a .NET Application to an Ethereum Private Network

I'm starting on blockchain development and I have a question: I was wondering if it is possible to make RPC calls to a private ethereum network (handling user private keys is not a problem in our ...
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2answers
349 views

Smart Contract - Update implementation using a Relay with delegateCall

I know that smart contracts are supposed to be immutable and that's the whole point, but to expect someone to implement a logic that never changes (no upgrade or no bugs) from day 1 is also ...
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3answers
235 views

How do i add to a nested array within a struct

I am unable to add elements to a array within the struct struct D { string name; address key; } struct Aone { string aid; B[] blist; D[] dlist; } ...

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