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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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Solidity Getter and Setter Error

I started my first code in solidity . when i was implemented getter and setter i have face some error . The Following code, pragma solidity ^0.5.0; contract MyFirstContract{ string private name;...
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How Ethereum consensus validates same transaction from different miners?

In an Ethereum node, my brief understanding regarding transaction flow is below. When a client initiates a transaction, all mining nodes receives this request. Based on gas price, miner choose to ...
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is there any method convert mutiple params to one bytes in web3js ,and then get these original data from bytes in solidity?

eg: the params in js code below,how to convert to one bytes var min=100; var max=100000000000; var price=1000000000000000000000000000; var name="john"; in solidity code below,how to get original ...
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how to convert params to bytes in javascript and parse uint256 from bytes in solidity

for example: user call this function from javascript. function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) How can I put these three uint value to bytes and ...
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Will Eth 2.0 be implemented in geth (go-ethereum) or will it run on a new client?

Geth is the official implementation of Ethereum based on the coding language Go. Currently, there are 8 teams that are building Eth 2.0 https://www.coindesk.com/next-gen-buidlers-the-8-teams-working-...
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Data availability in Ethereum/Hyperledger-fabric (Blockchain)

I have a use-case like there is an admin who creates application and invites several user to use that application. Now, i need to audit trail over the activities done by the user. Users no need to ...
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Event not visible on Etherscan transaction list

I have a BuyToken event when user send ether to smart contract they will receive tokens based on ether amount. For ex: 1 ETH = 1000 Token. /// This notifies clients about the Buy Token event BuyToken(...
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Convert a string received from oraclize like {54, 41, 42, 76, 10, 58, 27, 83,} to an array of uints in Solidity [duplicate]

Maybe if a lib like solidity-stringutils used to slice "," and then use parseInt to pass each number as uint to an array. Can you explain or help me with that?
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Inspecting IPFS files

Is it possible to store / catalogue every file which is being published over IPFS ? Is only encryption the viable way to securely publish files over the internet ?
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How many Times I can Bid on Same domain name and Is There any way to increase bidding amount during auction

Is it Possible to increase my bidding during ENS auction period ?How can see highest bidding before reveling period. How many times i can bid for the same doamin in 3 days aution period
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Connection of web3 with Ropsten

How do I connect my web3 to ropsten network. I know how to pass the url of ropsten netwrok in web3 instance in my script tag but when i try to to console.log(web3.eth.defaultaccount) it gives me ...
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Transaction not getting confirmed because of transfer function even after making the address payable

The finaliseRequest transaction is not getting confirmed no matter what I do. I am sure it is failing at the transfer function. I had made the address to address payable also and changed the function ...
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Unknown Ethereum folder on my C drive

I have an Ethereum folder which weights 2.5GB in this path: C:\Users\xxx\AppData\Roaming which has two folders in it: geth keystore Do i need 'em ? It's not going to broke my ...
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errored: Error encoding arguments: Error: invalid address (arg=“”, type=“string”, value=“”)

The contract code is getting compiler properly in remix but only when trying to deploy this error is coming creation of InsuranceClaim errored: Error encoding arguments: Error: invalid address (arg=""...
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Can I turn any ethreum address to an account on the node?

I am planning to create an account in my client app using web3,I want to have the privateKey on the app too. is there anyway to propagate this address as an account on an Ethereum node?
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How to get live mempool transactions whitout full blokchain

I just want to analyse all mempool txs in realtime. I cant use an api because after several requests my ip gets blocked for some minutes, so I dont get the txs in this time. Thank you for help.
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How storing data on blockchain works? [closed]

I would like a simple explanation about how data is stored in a blockchain. When I was searching for a definition of a blockchain i says that it is a shared ledger and database that keeps records of ...
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24 views

How the hashing of the block data ensures the data integrity?

In ethereum, as a node controller I can able to access the leveldb. If I try to modify some value directly into the db, the value of the new hash and the next block's parent hash doesn't match right ?...
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How long you can consider a pending transaction as invalid?

I saw here that the time that a transaction can be at pending status changed, but didn't say how much Due to overwhelming amounts of pending transactions during ICOs, many public nodes (etherscan, ...
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32 views

Peering over a direct L2 link without IP addresses

As part of a big solution incorporating blockchain and data networking, I'd like to know how would 2 nodes establish a blockchain peering on their direct L2 Ethernet Link that has no IP addresses ...
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TypeError: Type contract InsuranceClaim is not implicitly convertible to expected type address

I am confused why the following code is not working. Any help would be greatly appreciated. pragma solidity >=0.4.22 <0.6.0 contract InsuranceClaimFactory{ address public claimer; ...
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Error in setup blockchain template in AWS

I Tried to setup aws blockchain template for ethereum as mentioned here i followed all required steps but i got errors. i'm attaching error with this question.
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How do you get the UTXOs a transaction is spending using web3.js?

I'm unsure how to get the UTXOs that a transaction is spending. Here's what I have so far. I get transaction details from txhash web3.eth.getTransaction("...
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Can I use the blockchain as a web server?

Is it possible to use the blockchain as "web server"? Even if a web app stores all data per smart contracts on the blockchain I still need a central server to get the web app initially. Is there an ...
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Can i get the same output from geth that is shown in Etherscan (VM Trace Transaction)

Etherscan have a section to show VM trace (example: https://etherscan.io/vmtrace?txhash=0xce26e9f59d895a63ce38b0a7d0b1649a58909a7ae24029f7fee39cb4b94980df&type=parity#raw). How do i get this ...
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1answer
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How to calculate token buy and sell prices?

I have a ERC20 token string public name = "Token ZIZ"; string public symbol = "ZIZ"; uint8 public decimals = 18; uint256 public totalSupply = 1000000 * 10 ** uint256(decimals); //...
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27 views

TypeError: ajtokenSaleInstance.tokensSold is not a function

I am following this tutorial on youtube "Code Your Own Cryptocurrency on Ethereum (Full)" i stuck at one of the part where i am trying to return the value of TokensSold but i keep on getting error as ...
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Understanding what happens between transaction creation and block creation in Proof of Authority

I am currently writing my thesis where I'm investigating the potential of blockchain technology to become the underlying technology in a system that is create and record qualifications. I'm at the ...
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How to access txpool pending transactions using Netherum?

I want to get list of transactions which are in pending state & queued state in txpool. I can see these transactions in pool using txpool.inspect command. I tried code given in nethereum sample ...
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How can I run smart contract locally on my computer?

We all know that Ethereum nodes can run smart contract. But I'm wondering whether can I setup contract run-time environment from Ethereum source code locally so I can run smart contract without ...
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1answer
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Run testnet in a cluster

I have launched a blockchain testnet in a cluster with different nodes and I have some questions about how it works. If I run more than one geth client(a node in the blockchain) in one node of the ...
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IPFS versioning - How to get all files from the IPFS key?

Based on the below code, im able to add a file**(dataobj.txt --QmUUHKjR5ZdrrYmxpXyPrYP3eMyhv9FnRKo1Duv9stzmmw)** and publish a file and then assign to the key "myIPFSKey". Step 1: ipfs add -r ipfs/...
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Library to get a graphic representation of the blockchain

I'm trying to find a library to make a graphic representation of the blockchain. Something similar to Gource but instead with git versions, with ethereum Any idea if something like that exists?
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How PoS Blockchains prevent miner from sending different block?

I'm quite new to the world of crypto and have been wondering, how different blockchains prevent miners/forgers from breaking it. As far as I know, (in PoS, for instance) a forger get's selected to ...
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how percent of stake calculated, what is the base value for that [duplicate]

A person can validate only the percent of transaction that is equal to the percent of their stake, what does that exactly mean, and who is validating the rest of the transaction
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Decentralizing DNS using Blockchain

I intend to do a project on Decentralizing DNS using Blockchain. As I was researching this topic, Namecoin was a name that popped up a lot. On searching further, I got to know that Namecoin hosts ....
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Identify the block which contains a tx

I am deploying a Smart Contract to a private blockchain. Is it possible to get when your node receives the smart contract? Is it possible to identify the block which contains the smart contract? how?
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Incorrect Usage. flag needs an argument: -rpcaddr = Ethereum private blockchain

I'm trying to make Ethereum private blockchain. But facing a error while running this "geth --nodiscover --networkid 42 --datadir .ethereum/ --unlock 0x526d8a6baa472da27215f748236af96bc9f256d7--mine ...
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Is there any period of custody for block rewards in Ethereum?

In Bitcoin, some block heights are required for spending coinbase transaction. But in Ethereum, there's no input/output. Then, is there any maturity time for using block rewards in Ethereum? If yes, ...
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What is meant by locking of ether in proof of stake?

In PoS, forgers stake their ether on a block. These ether are locked and can't be used. What does it mean by locking of ether and how does it work?
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Invalid sender when sending Raw Transaction, signed w/ ethereum-tx on PHP

I am using PHP and ethereum-tx library https://github.com/web3p/ethereum-tx to sign transactions but when trying to send them to the node I got an "invalid sender" error. Besides, exactly the same ...
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Connection error connecting raspberry to my local ganache blockchain

I am following this https://medium.com/@darthrevan344/blockchain-ethereum-iot-poc-machine-maintenance-part-ii-b1eb9293f799 series, but i am stuck at last step where i am not able to run the python ...
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Ethereum Blocksci parser tool

I need a blocksci parser for ethereum. I am using https://github.com/citp/BlockSci for bitcoin . Is any similar blocksci parsing tool for ethereum?.
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When locate a block with both the hash and block number?

In the go-ethereum code, I see functions use both the number and block hash to locate a block. Why is that? Isn't block hash enough? An example function: https://github.com/ethereum/go-ethereum/blob/...
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3answers
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Blockchain flow in food industry [closed]

I am trying to learn blockchain by doing small projects. I was able to complete a small project in blockchain for cryptocurrency using c#. Now, I am trying to understand the flow of a blockchain in ...
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simulation or performance evaluation with Ethereum testnet

I was if you could help me about simulation. How can I simulate the performance of my following IoT-based Application with Ethereum testnet? In my senario,there are some nodes that store sensor data ...
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Simulation with private Ethereum

I need a simulator or environment to simulate my Internet of things network with following scenario: There are N number nodes as Miners(Roadside Unit in a smart city) that store transactions sent by ...
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How to modify existing geth commands

I am wondering if it is possible to modify existing commands on geth. For example the command $puppeth would produce this +-----------------------------------------------------------+ | Welcome to ...
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1answer
45 views

Cloning geth and adding a POS consensus algorithm? [closed]

I am currently learning how to use geth, so far I was able to create a private POW and POA blockchain using one of its consensus types (Clique). I am wondering how feasible it would be to clone the ...
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ERC 721 card game

The general concept of ERC 721 is clear to me. My question is more about the contract deployment. I want to have 100 unique cards, So I thought of these two implementations: Having an initial supply(...