Linked Questions

97
votes
7answers
32k views

How can an Ethereum contract get data from a website?

What is the process/workflow behind the process where an Ethereum contract gets some data from a website?
59
votes
3answers
14k views

Why can't contracts make API calls?

The model that contracts can only accept and process data, instead of also being able to retrieve data from the Internet, seems limiting (even if not, it's less direct). If a concern is that data or ...
22
votes
2answers
64k views

Gas price in ETH unit

I am wondering if there's a website that provides the price of the standard gas limit (21000 Gas, transaction cost for sending ETH) in ETH unit. I checked Ether.Fund site, but it provides the gas ...
19
votes
1answer
4k views

How to access external knowledge / data in a smart contract

let’s say a contract wants to execute on knowledge contained outside the blockchain (e.g. whats the price of gold, what was the avg windspeed in NYC, how many people moved to portland in the last ...
6
votes
3answers
2k views

What is the Oracle Problem definition exactly and briefly?

What is the Oracle Problem definition exactly and briefly? Does it mean "trusting on a centralized Oracle" ? Or "How to reach a consensus between a group of Oracles" ? Is the matter "centralization" ...
8
votes
4answers
1k views

Flash loan security considerations and attacks

What do developers need to be aware of to make their contracts and systems safe against flash loans? What do they have to think about and protect against?
5
votes
2answers
3k views

Is there a way to get the *current* price of ETH in solidity function?

Is it possible to get the current price of ETH in USD in a buyTokens function of a deployed solidity smart contract? For instance, every time GETH starts up is determines the price of ETH during ...
3
votes
1answer
4k views

How to find out the rate of ETH in USD in the contract?

I have a function which can rate ETH in USD. How can I find out the rate of ETH in USD in automatic mode? Can this be done in Solidty? Or do I have to use a third-party language, for example, ...
7
votes
3answers
1k views

Reading Ethereum contract state variables

Is this assumption correct ? There is absolutely no way an ethereum contract can send data to the external world. It can only modify its state variables (later stored in the new block)and send ...
3
votes
3answers
223 views

Can we use block hash as verifiable randomness for the off-chain lottery?

My team is writing a discord lottery bot, we want to use the block hash of some block in the future as a seed for the random generator. We want to allow lottery participants to independently verify ...
2
votes
3answers
632 views

Decentralized database for ethereum?

I'm looking for a way to store data in a decentralized way such that I can access any record from within the smart contract, probably through oracles I guess? I've been looking into gundb but not ...
1
vote
1answer
474 views

Getting stock market data from API or other means?

I'm trying to make a contract that interacts with a market price or a market out come : e.g APPL drops below X or NFLX > Y ... Is it possible in Solidity to call an external API during this ...
3
votes
1answer
552 views

How to set dynamic buy and sell price for my token?

I have built a simple erc-20 token. I used the code given on ethereum.org code as a reference. There they have talked about setting the price of my token. But how do I set it dynamically, as in ...
1
vote
1answer
202 views

Retrieve Uniswap tx data in my solidity smart contract

As the title says, I have my Solidity smart contract and I am trying to import in ti some public data from the Uniswap contract. In particular I would like to have the tx data stored in my contract (...