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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46 views

Oraclize parity error

I have a contract in Remix which runs perfectly on the Ethereum Ropsten Test net. I now want to deploy the contractin the main ethereum net using parity. When I click to deploy the contract in parity ...
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1answer
181 views

Private Ethereum Smart Contract API call to notify (without needing the external api response to update the state) without using Oraclize

In a Private Ethereum Smart Contract, can we do an external API call just to notify (without needing the external api response to update the state) without using Oraclize? Understand Oraclize is ...
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63 views

Oraclize usage on blockchain

Is it possible to use oraclize for the purpose of communicating between ethereum private and public blockchains? For example, if i triggered an event in private blockchain, that event should be ...
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4answers
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How do oracle services work under the hood?

I have read many questions about oracle services, but I do not understand how they work. Often I read answers like this: https://ethereum.stackexchange.com/a/9825/5892 Smart contract can not ...
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7answers
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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?
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1answer
57 views

What is an oracle?

What is an oracle? 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 what they are?
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1answer
35 views

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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1answer
21 views

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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1answer
13 views

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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1answer
34 views

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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2answers
284 views

Retrieve and store data into a local database using smart contract

For my information oraclize can be use to retrieve data from several data source but what if i need to get from a local database such as oracle,sql, etc. Is there any way of doing it? PS: I am ...
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1answer
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Truffle fails to migrate an Oraclize contract into Ganache

I have a contract that is using Oraclize. When deploying the contract from the Remix IDE into Ganache/Ethereum-bridge via MetaMask, the contract is fully functional. However, when trying to migrate ...
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1answer
26 views

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
64 views

How can I assign the value that I'm fetching using Oraclize to a member in a structure

I have the following code: contract CheckBet is usingOraclize { struct Weather { uint curr_temperature; uint high_temperature; uint low_temperature; } Weather ...
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1answer
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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
106 views

Unable to return string using Oraclize

I'm trying to do a simple coin flip using WolframAlpha and Oraclize, this is my smart contract pragma solidity ^0.4.18; import './usingOraclize.sol'; contract CoinFlipOracle is usingOraclize { ...
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1answer
117 views

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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0answers
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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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3answers
894 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" ...
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2answers
147 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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3answers
686 views

ERP systems and Ethereum

I wanted to know the integration state of ERP system (like SAP) and Ethereum. Is there an API that allow a smart contract to fetch information from a ERP to store that data? Thanks in advance Best!
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2answers
157 views

How to use fiat exchange rate oracle in DAPP?

my team is trying to develop a DAPP about fiat exchange rate. How to get the latest fiat exchange rate (USD/EURO etc.) accurately from external Oracles(Or are there better ways doing this)?
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2answers
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Does running a Geth RPC server locally also require having a full Ethereum node?

I've been trying to learn about smart contracts and attempting to work through a few examples. Specifically, I found this one about creating an Oracle -- https://github.com/axic/tinyoracle. The ...
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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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1answer
41 views

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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1answer
165 views

Solidity Oraclize error

I am learning to use oracles in solidity and I have taken this code to see how it works. But I get the following error: "VM error: revert. revert The transaction has been reverted to the initial state....
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1answer
107 views

Orcalize query multi value callback

So I know JSONPATH can be used to select multiple values from a json response with an orcalize query like in the below example http://app.oraclize.it/home/test_query#VVJMKEdFVCk=:...
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2answers
36 views

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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1answer
98 views

Cannot get Oracalize to work on Ropsten

I have tried to run Oracalize as 1:1 of the example provided on their site. During the creation of the contract, I am also sending 1 ether to it (so it is not empty). Still even 30 minutes after this, ...
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2answers
439 views

Capturing an event fired from a contract that was called from another contract

I'm trying calculate tax on arbitrary items/values. To do this I have a single contract is used as an 'Oracle' to get the tax from an external system. This contract defines functions to be called from ...
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2answers
137 views

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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2answers
195 views

How secure is an Oracle?

I am working on oracles. I saw this link - https://kndrck.co/posts/ethereum_oracles_a_simple_guide/ The code works, I tested it. But what is the issue to me, is the code actually secure? Can someone ...
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1answer
35 views

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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1answer
562 views

Time Specified calls in Solidity using Oraclize

I have started learning coding in Solidity and I have written the below contract using the official Oraclize guidelines. My aim is to: Make the update() function be called on its own on the ...
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1answer
54 views

Unable to mine smart contract using Oraclize - Invalid JSON RPC response,error code : -32603

I am trying to use Oraclize to make a REST call. Please find below my contract code - pragma solidity ^0.4.16; import "./usingOraclize.sol"; //Importing Oraclize(verion 0.4) contract ...
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1answer
21 views

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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1answer
20 views

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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1answer
22 views

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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1answer
86 views

Using oraclize function into fallback function

I have an issue with my oraclize. I need to call oraclize for update exchange rate. If I call function updatePrice() manually - it's ok, global variable dollarCost is updating. But if I call ...
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0answers
38 views

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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0answers
16 views

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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1answer
33 views

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
35 views

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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1answer
61 views

Why does Ethereum need exchanges?

As I understand, currently the preferred way to acquire ETH (for investment purpuses) is through a third-party exchange service. Isn't ethereum all about executing smart contracts when a specific ...
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0answers
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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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0answers
15 views

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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0answers
100 views

Confirm Oraclize is not working on Ropsten? (No callback returned)

I have a contract on Ropsten testnet that was working fine up until 2 hours and 30 minutes ago. I don't believe it is an error on my side because the code hasn't been changed or redeployed. You can ...
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1answer
153 views

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
166 views

Concatenating a variable value to a bytes32 [duplicate]

I am using Oraclize for randomness. The range of random numbers I want depends on a variable maxNumber, and will be 0 - maxNumber. If you scroll to the right of my code snippet below, you'll see ...
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2answers
28 views

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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