Questions tagged [oracles]

Oracle is a way of implementing a Smart Contract. Instead of running the contract code directly on the blockchain, the code is executed on some special off-chain entities called oracles which then send the result of the code to the blockchain network with a signature.

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Does Chainlink store Oracle response for a transaction somewhere on blockchain?

Lets consider an example of transaction lifecycle where a smart contract uses Oracle to get external data ETH/USD price feed that is changed in real-time. Transaction is executed during mining, so it ...
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Are oracles too slow for DEFI arbitrage?

It seems that a lot of platforms that make you money via 'arbitrage' rely on Oracles to find a profitable spread opportunity. I assume users are competing against other users (on the same platform) ...
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Unable to get response back from chainlink node using truffle console

I am trying to fetch close prices of a property deployed on a server running on a chainlink node. Here's what a snippet from my contract (RealEstateAPIConsumer.sol) looks like : function ...
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Could there be multiple asset pools In a DAMM liquidity pool?

In a DAMM (dynamic automated market making) DEX (decentralized exchange) the ration between two assets, e.g. DAI/ETH does not have to be 50/50 anymore, like it used to be in a AMM, (automated market ...
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Is Chainlink's price reference data free to consume?

I was looking at feeds.chain.link and it's not immediately obvious if anyone can tap into all these price feeds without incurring a cost: For instance, I did find the ETH/USD aggregator contract, ...
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Rationale for using ETH as the unit of account for oracle pricing data

These are Compound Finance's former oracle contracts: PriceOracle PriceOracleProxy I say "former" because Compound switched to the Open Price Feed UniwapAnchoredView.sol oracle on Aug 17, ...
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Should I use an average or median price for my oracle?

Excerpt from Compound's The Open Price Feed: This is accomplished through a View Contract, which reads, parses, aggregates, transforms, etc from the storage contract. The determination of ...
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Rock, paper, scissors and Secrether.io

I have thought of a RPS game using secrether.io: playerA hashes keccak256(move+11charsRandomData) as hash and sends it to RPS smart contract. RPS creates a transaction to Secrether Smart Contract - ...
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Does Ethereum 2.0 still have use cases for oracles, why?

It seems to me Ethereum 2.0 would only require that one node creates blocks at a time, does that make unnecessary oracles.
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Is first call to oraclize query free in mainnet, as in testnet?

We were trying to include oraclize query to get price feed in one our contracts, as of now we have observed that the first oraclize is free in kovan. Does same applies for mainnet or else we has to ...
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What is a blockchain oracle?

What is a blockchain oracle for smart contracts? And why is it needed? I've seen a lot of posts about "how do oracles work", and "what is the oracle problem" but I don't understand ...
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How can the contract move funds from a user wallet to a contract address

We are creating a system where every month some ethers shall be transferred from user wallet to a contract wallet. We are focusing on creating a dapp too, so a user will initiate this request and once ...
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How is Chainlink decentralized? [closed]

I believe one of the main criticisms of chainlink is that it is not decentralized enough, adding more nodes would be a big step in a positive direction. When I pull data through a node, that node ...
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Explicit type conversion not allowed from “string memory” to “uint256”

I'm using an oracle to get results from a custom api. The result is in string by default. I want to convert it to uint256, so that I can perform basic arithmetic functions. Here's my code: function ...
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1answer
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How is the volume for the currency pair accounted for on chainlink's reference data feed?

https://feeds.chain.link/ - link for reference. Let's take the LINK/USD feed for example: From my understanding, the aggregation contract fetches the price of LINK in USD from the node operators who ...
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How does chainlink solve the oracle problem? [closed]

I've heard a lot about Chainlink recently -- how Synthetix, Aave and other top Defipulse projects are using them. How exactly does Chainlink solve the oracle problem from a technical perspective?
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Why do I need decentralized oracles?

I've been reading a lot about how smart contracts work, and I'm a little new to the area, but why do we need decentralized oracles? It feels like I can just make an API call from wherever and it's OK?
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How does Oraclize work? [duplicate]

We know that an Oraclize based contract can communicate with the internet sites. We know than Oraclize source is built by Solidity language. We know that there is no command in solidity that can ...
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blockchain oracles to communicate with external api via smart contracts?

Is there is any other oracles other than provable or oraclize to communicate with external api via smart contract.
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Calling a Solidity function automatically in realtime

I have an oracle with a 'getPrice' function that returns the latest ETH/USD price. Let's say, I am implementing a stablecoin contract which requires over-collateralization with ETH. How will I ...
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Provable store an array

I'm trying to understand some basis of Solidity, I get how to get multiple values from one query, but don't really understand how to store them, could anyone explain me how to do it? pragma solidity ^...
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Can't call coinFlip() function the second time

The first time when i run this it runs fine but the second time when i call the coinFlip() function it shows gas estimation failed can someone tell me why it is happening. pragma solidity ^0.6.0; ...
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1answer
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Chainlink node error: BumpGasUntilSafe FindTxBy Attempt: record not found

I am currently testing sending requests to my Chainlink node on Ropsten. I am following the documentation for running a Chainlink node and all went well until. 40 BumpGasUntilSafe FindTxByAttempt: ...
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Is using oraclize to schedule using execution of a function asynchronous?

I am looking for ways to automatically execute a function call every 24 hours in my smart contract and came across this answer. Is the solution here asynchronous, i.e. can the contract execute other ...
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How to send the RFID card no read using Raspberry Pi to smart contract so the details can be stored on Ethereum blockchain? [closed]

Raspberry Pi reads an RFID card and has to send the RFID number to the smart contract to check further details related to the RFID number. Based on the details the payment is done and stored on the ...
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Orcalize Query not working

function getRandomNumber() public payable { require(msg.value >= 0.000175 ether); // 175,000 gas * 1 Gwei = 0.000175 ETH bytes32 queryId = oraclize_query("URL", "json(https://...
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Chainlink services are not supporting the privateFor transactions in Quorum/Kaleido

We are exploring Kaleido and Chainlink for one of our use cases. What we have done: We have created a network of Quorum/Raft nodes. We had setup the chainlink service for the network. We have setup ...
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Town Crier Relay

I'm reading the paper Town Crier: An Authenticated Data Feed for Smart Contracts and i'm failing to understand this bit The Relay is an ordinary user-space application. It does not benefit from ...
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onlyOwner / onlyProvable with oracle functions using Provable

Is it possible to make a function onyOwner, since one of them must obviously be called by Provable's server? Or is there an equivalent modifier to it, such as onlyProvable? If not, would there be a ...
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1answer
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Are arguments from Provable callback's function mandatory?

Since I am only using Provable (formerly Oraclize) in order to make a cron job, and calling only a function from inside my smart contract (like here), I was wondering if the parameters myid and result ...
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address recovery from signature

Sorry for the long question, I tried to keep it as standalone as possible. For my master thesis I'm analyzing historical data coming from price oracles contract events. In particular, the MakerDAO ...
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Oraclizer does not respond periodically

Contract that use oraclizer work just fine from moment of deploy. But three days ago oraclizer start to ignore requests of my contract(not allways). In this trx oracle dont return callback, but when ...
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Smart contract and oracles

I'm having trouble understanding the flow: Contract <==observes/injects== Oracle <==requestdata==> API I read several articles like this and I'm aware of the theory of the flow. But what ...
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Oracle used by a Smart Contract no longer available

Ethereum relies on Oracles to provide information about the outside world used by SmartContracts. Also, when a node syncs (in slow mode) it has to go over all transactions (including SmartContract ...
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1answer
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Oraclize ( provable) updates the value only one time

I'm trying to write a smart contract that gives me the current timestamp. The very important part is that i want this to happen locally, not on test networks. After some research, i installed ethereum-...
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1answer
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Multiple callbacks with provable random oracle

I'm making a simple lottery game where there are hourly, daily and weekly prizes. My contract has functions to pick winners for each of these game types. Each game types will have different number of ...
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155 views

Call an existing python code inside a solidity smart contract

I want to call some existing code (written in Python) inside my Ethereum smart contract (written in solidity). Is it possible to do that? if so, how can we do it?
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1answer
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Provable/Oraclalize: How to get msg.sender in __callback

How do I get the msg.sender of the user who called randomNumber() in the __callback? pragma solidity ^0.5.11; import "github.com/provable-things/ethereum-api/provableAPI_0.4.25.sol"; contract ...
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1answer
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How to setup an oracle in Vyper?

I need an ETH-USD price oracle for my vyper contract. So far, the oracle services I've found, like chainlink, are written in solidity. Is it possible to use a solidity oracle in a vyper contract? How ...
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How does oraclize deal with chain reorg?

As title, does oraclize deal with the case where the query transaction and callback transaction are executed in different side chains? I mean in this situation: A-B \ B'->C->D->....' ...
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Fetch ETH USD Rate from past using Oracle

Is it possible to fetch the USD rate of ETH at a specific time in the past to a smart contract from an external API using an oracle? i.e. I have a function which tracks whether now > start + 10 ...
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How to fix gas estimation failed error while getting random number from Provable Random DS?

I'm using Provable for getting a random number and I am using following code snippet from their github: https://github.com/provable-things/ethereum-examples/blob/master/solidity/random-datasource/...
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153 views

How to build the seamless bridge between two blockchain platform?

How to build the bridge between two different consensus blockchain platform? use case: 1.we need to ensure visibility of the transaction in both platforms to assure its integrity When a smart ...
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1answer
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__callback was called after the specified delay

My smart contract should return the ETH rate from Coinbase api .. So i'm using Provable engine and i'm testing my smart contract locally using ganache and ethereum-bridge . It's expected that result ...
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1answer
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Why Oraclize / Provable can call URLs, although it's forbidden in Ethereum?

So the library Oraclize if I understand correctly, allows you on solidity to get a result from a URL inside a callback. But I also read that you can't communicate with the external world in Ethereum ...
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Oraclize : Calling more than one API independently [duplicate]

There are 2 API 's which has to be called in different time delays recursively. For example : API_1 = 20 mins delay and API_2 = 24 hr delay. How can we call the above 2 API's independently based on ...
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Oraclize ethereum bridge : Notifying __callback tx error to frontend

I have called API dynamically using Oraclize with the delay of 10 minutes. The code is shown below and it works well. uint256 constant DELAY = 60*10; event Log(string result); function ...
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2answers
191 views

Random number generation in certain range

I need to add a random number function in my smart contract. Is it best to use Oraclize and e.g. random.org? It's not a lottery which means the random number generation does not require heavy security....
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Set the price by calling another contract and getting result from it

I want to set the price in Token every time the contract is deployed by calling ETHUSD in constructor and getting result from it. pragma solidity ^0.5.0; import "./ETHUSD.sol"; contract Token { ...
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Accessing private variables using assembly

I would like program an oracle service which I would like to charge a fee for. Therefore, I would store the data of interest as a private variable in my oracle contract. This private variable should ...

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