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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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1answer
9 views

How will i start transaction in new ethereum network

I just installed a new ethereum network & created two accounts. In that case who will verify my transactions?? How will that miner get there ethereum? My account's balance is zero ,So how will i ...
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1answer
11 views

Is there any transaction fee like gas in ethereum in bitcoin?

I am new in blockchain & wondering how an ethereum is free if there is a gas fee which user has to pay & Is there any transaction fee like gas in ethereum in bitcoin ??
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ethereum blockchain elements are added by the user through html form [on hold]

I am trying to build my own app. I use this site as guide. https://www.dappuniversity.com/articles/the-ultimate-ethereum-dapp-tutorial I am trying to make my app, for this example, a user will add ...
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1answer
51 views

Do we have to compile and deploy our contract to ethereum each time we start a test rpc?

I'm trying to develop a voting application, I have successfully compiled the app and also deployed it to ethereum blockchain. Now I've closed the test rpc and node console, and when I restarted node ...
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1answer
20 views

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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2answers
130 views

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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2answers
49 views

Ethereum Enterprise Blockchain

I am starting a project that I need to build a solution to track products (ex: from farm until it gets to the supermarket) Basically, I need to set up a blockchain structure for my company(private) ...
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1answer
187 views

Performance Analysis of Ethereum Clients Geth and Parity

I want to do performance analysis of Geth and Parity. I want to run 1000 transactions serially on each client and want to get transaction processing time for each transaction. How can i get these ...
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1answer
79 views

How can I execute transferFrom function in node js

There is solidity erc865 code function transferFromPreSigned( bytes _signature, address _from, address _to, uint256 _value, uint256 _fee, uint256 _nonce ) public ...
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1answer
36 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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0answers
31 views

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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1answer
46 views

Where, or how, can I programmatically get a complete history of the major cryptocurrencies?

I would like to programmatically get a complete list of the historical: Number of transactions Average Transaction Fee Hashrate Mining Profitability Difficulty Block Time Block Size related to the ...
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12 views

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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2answers
140 views

Retrieve CHAIN_ID of the executing chain from a Solidity contract

Is there a way to directly be able to retrieve CHAIN_ID information about the executing chain from a smart contract? I know that for any chain that has EIP-155 implemented, CHAIN_IDs are retrievable ...
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1answer
45 views

Calling a function from another contract is not working. But calling the function from deployed contract is working

I have a problem with calling a function from another contract. I don't know why it is not working. Contract DateTime(https://github.com/pipermerriam/ethereum-datetime) is a util for converting ...
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2answers
304 views

Quorum 7nodes example unable to attach to geth node 1,2,4,5,6,7 but node 3 is working

Quorum 7nodes example all of sudden gave fatal error unable to attach to remote geth. Problem: can't attach to geth node Every time I import metamask account to geth node (using personal.importRawKey(...
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1answer
49 views

Are state changes reversed if the contract “crashes” during execution?

Are state changes reversed if the contract "crashes" during execution? I know that state changes are reversed, if the contract runs out of gas during execution. However, are state changes also ...
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1answer
17 views

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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1answer
23 views

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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1answer
36 views

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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5answers
229 views

Mist / Ethereum Wallet question

I bought a very small amount of ETH on coinbase just to try it, and I wanted to create my own wallet to get it out. However, I've been trying to get Mist working for 3 days and it is always stuck on ...
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3answers
29 views

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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0answers
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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
18 views

When is chain data (length) compared between nodes? Is there any way to control this?

I am trying to use an ethereum blockchain in a multiagent network. I would like to control when information is exchanged between nodes to keep the network synchronous, so I am trying to figure out how ...
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1answer
59 views

How does Ethereum know who called a function first?

Scenerio 1 Say I have a function f(). Whoever calls the function first gets a reward. Persons A, B, and C all call the function at roughly the same time. Who will receive the reward? Scenerio 2 ...
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1answer
51 views

How to automate blockchain transactions of users without having to ask them to enter wallet addresses?

I am working on a game with an in-game currency. The goal would be that when a player buys something, he only have to click on buy, without having to enter the public address and so on. Are smart ...
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1answer
14 views

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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1answer
27 views

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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1answer
62 views

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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1answer
73 views

Deploying fails with different compile version

I'm trying to implement a simple card game. Actually, everything is working fine. Until I tried to move from 0.4.0 to 0.4.22. Any idea what is going wrong? Thanks a lot. And here the code: pragma ...
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1answer
80 views

In what way does Sharding allocate transactions for each shard? state? or node selection?

In what way does Sharding allocate transactions for each shard? I know that accounts are assigned to each shard based on prefix in the account's address and each shard processes the transactions ...
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2answers
63 views

Who are the miners?

In blockchain there are some miners who calculate hash and get reward but my question is who are the miners or how can I be a miner (assume). If there are then I can be connected to a miner? I am ...
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2answers
122 views

Is Merkle tree applicable at block level also?

As per my understanding, Merkle tree is applied in case of transactions. Through Merkle tree we generate root hash transaction from all the transaction present in a block. So does it work the same way ...
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1answer
140 views

Synchronous call of external contract function in Solidity

I have two Solidity contracts, where contract Caller depends on a second contract Callee. Contract Callee provides a public view function which checks the validity of a string (e.g. an password), ...
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2answers
68 views

Massive Download [ETH] smart contracts

This question have just been published in StackOverflow as well, but you might be able to guide me on a better direction: I'm looking for the most valid path to download and keep downloading every ...
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1answer
280 views

Why my geth system daemon not sync?

I've a machine with Ubuntu Server 16.04.4 LTS, the purpose of this machine is run a Geth process reachable by a web services. This is my "unit service": [Unit] Description=Ethereum go client [...
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1answer
58 views

The value of my variable change

I have two contracts (A and B) in the same smart contract. When I access from B to a A's variable the value is different that I can see from A. For instance, when I access from A to that variable ...
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1answer
25 views

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 ...
0
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1answer
141 views

How to connect with Metamask and Smart contract?

I am ready with my frontend design. I have only 3 files HTML, CSS, and JAVASCRIPT. So, I didn't create any project or DAPP to have other files. Now next step is to connect with metamask and smart ...
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5answers
17k views

How to find contract's address?

I successfully setup a private blockchain and created the "hello world" contract according to tutorial from etherium web site. One thing that I can't figure out is how to find the contract later. I ...
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2answers
21 views

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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1answer
79 views

Error using web3.js from OpenZeppelin

Please, i need help. I am using truffle to test a smart contract. I run "truffle develop", then "migrate". The contract has been stored in the network. Then I run the command "test". An error occurred:...
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1answer
32 views

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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1answer
63 views

liaison entre web3 et nodejs [using web3js and nodjs]

Bonjour, j'ai développé une app avec nodejs et je voulais la transférer vers une dapp en intégrant le web3 librairie. En effet j'ai crée les smart contract il le me reste juste la façon de faire la ...
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1answer
79 views

What would an Etheruem-like blockchain look like if each block were just an IPFS hash?

I see a lot of people tout the enormous benefits of using IPFS as a store of data. Meanwhile, the Ethereum blockchain is over 1TB in size, with quesitonable need to keep the earlier blocks. In ...
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6answers
12k views

Best way to test a smart contract

I just want to deploy and call a simple sample smart contract only for testing purpose. Do I need to download the entire ethereum blockchain? Its too huge and takes too long to download. Can someone ...
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1answer
31 views

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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1answer
118 views

GETH Error on personal_sendTransaction/eth_sendTransaction

Been trying to use personal_sendTransaction / eth_sendTransaction for days but I cannot get pass this error. I have tried different combination of gas/gasprice/value but I cannot make it work. PS. ...
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1answer
114 views

Query Ethereum Blockchain for functions return value of a Specified Smart Contract

I want to get smart contract functions return value sent by a specified smart contract within a range of blocks. I found a [manual] working method to achieve this: async function getTxsByAccount(...
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1answer
39 views

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 ...