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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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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16 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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Oraclize random datasource, what is trusted by using it?

I'm currently looking into ways of accessing randomness in a smartcontract. I found oraclize random datasource https://github.com/oraclize/ethereum-examples/tree/master/solidity/random-datasource and ...
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15 views

An oracle for real currency values

I would like to get an oracle for values of countries' based currencies. Are there such free oracles?
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1answer
73 views

What is the verification process of nodes on chainLink?

chainLink is a decentralized system similar to Ethereum, which can help smart contracts execute get requests and return the results. The result of chainLink execution also needs to be verified by ...
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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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156 views

Call several endpoints in an Oraclize nested query and return an array

I am trying to get an average of ETH/USD conversion rate through Oraclize. My query works well when calling one single HTTP endpoint but I would like to call several endpoints within the same query ...
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0answers
77 views

How does a relying party learn a PageSigner server's public key?

Hoping for some insight Into to page signing... I understand that: https://tlsnotary.org/pagesigner.html can provide proofs that a specific web page was returned from a third-party TLS-protected ...
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0answers
235 views

Error in dapp developed using 'Truffle' framework -Smart contract function call won't get executed

I am developing a dapp using 'testrpc' and 'truffle'.I have also used ethereum-bridge for Oraclize.I have written a smart contract function which calls a url using 'OraclizeQuery'. The following is ...
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259 views

Connection between two blockchains

I am looking for an approach to creating a connection between two blockchain-networks. I found out that I can use oracles to get data from extern systems (= second blockchain-network). But how can I ...
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19 views

What is best approach for generating random NFTs?

I am thinking of developing small DApp where user would collect cards (NFT). Each card would have some image and value associated with it. User collects cards by purchasing Pack of Five Cards which ...
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1answer
14 views

Price feed of multiple coins in a single GET request

I have used Chainlink oracle to get the price feed of a single coin. But I want to fetch the latest price of 100s of coins from the smart contract using oracle. Is it possible to get the price of ...
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51 views

Chainlink - on-chain contract functioning

The on-chain aggregation smart contract for ETH/USD on the mainnet (https://data.chain.link/eth-usd) is at this address https://etherscan.io/address/0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419#code. If ...
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17 views

Oraclize external rest api call failure handling

Using https://oraclize.it, I can perform something like this oraclize_query("URL","json(https://api.postcodes.io/postcodes).status", '{"postcodes" : ["...
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48 views

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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38 views

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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53 views

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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59 views

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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60 views

How to handle Oraclize if it's failed?

I'm using the Oraclize to get the random number for bets. When the function bet() is called and if the oraclize is failed it should call the pingOracle() again. Below is example function bet() public ...
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1answer
85 views

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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2answers
320 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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2answers
197 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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37 views

Tutorial for ZAP inegration with Oracle

Oracle is a trusted third party API from which smart contract will fetch the data. Zap is a way to monetize the data which smart contract is getting using a token called zap token. Is there any ...
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141 views

“Augur” vs. “Oraclize” : What is the main difference?

Can we say that "Augur" is a decentralized Oracle against "Oraclize" as a centralized model? I mean can we consider Augur as a decentralized Oracle and on the other hand, Oraclize as a centralized ...
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37 views

How to know the price of the day of ETH in USD by Oracles?

Consider in a contract the payer intends to pay recipient ETH based on USD (ex. the salary is 1 USD but paid by ETH). So, if today contract needs to know equivalent value of 1 ETH in USD exactly at ...
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63 views

How do we deploy a smart contract with Oraclize to Rinkeby Network?

I have created a smart contract with Oraclize logic which I tested locally using Truffle. Now I want to test it on Rinkeby network along with my front end, what it the process to do so ? How do we ...
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1answer
169 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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102 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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160 views

Oraclize: oraclize_newRandomDSQuery always reverted

I'm using oraclize for generating random number for my smart contract. I have tested successfully with 2 methods: Using WolframAlpha Using random.org service But when I try oraclize_newRandomDSQuery....
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1answer
194 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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52 views

Back of the envelope Oraclize callback cost calculations for

How does one do a back of the envelope calculation about how much the Oraclize callback will cost? Does it cost more if a query is returning a large amount versus a small amount of data? Does it cost ...
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2answers
222 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
97 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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1answer
103 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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1answer
66 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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183 views

Oraclize Queries Not Working On Rinkeby

I have the following contract (https://gist.github.com/postables/365f418b85c9d93503001682d6cc779e) which works when using Oraclize's web IDE version of remix. However when testing the contract out on ...
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158 views

Convert an hexadecimal string to bytes in pure Solidity

I am using Oraclize to recover a signature from a website. When I have it, I have to check if the address who signed it is correct. To do that, I would use ECRecovery from Zeppelin. The signature ...
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36 views

How to ensure users send just enough for Oraclize query?

In my contract, users send along ETH to cover the costs of their Oraclize query. Right now, they must send a fixed sum set by the contract owner. Whatever remains stays with the contract. How can ...
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35 views

What happens when an Oracle becomes unavailable?

If all contracts in the chain must be verifiable by all nodes at all the time, what happens when an Oracle service goes down, e.g. because the company supporting it goes bankrupt?
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400 views

Flow of an oracle

This is a code example from Solidity documentation: pragma solidity ^0.4.11; contract Oracle { struct Request { bytes data; function(bytes memory) external callback; } Request[] ...
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415 views

Avoiding out of gas errors when making Oraclize queries that have callbacks which trigger more queries

I have a contract that I want to automatically check the price of ethereum everyday. right now I have a method called startContract which calls a function setConversion which makes a query set for 1 ...
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266 views

How can I automatically send token in exchange for Ether

I want to send tokens in exchange for Ether. And I want to send tokens in terms of 1 JPY / 1 token. So I have to get ETH/JPY rate on smartcontract. I tried to use oraclize to get its rate. But because ...
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15 views

JIT events on etherum

I would like to write a contract, that fetches a data from oracle in a specific point of time (or later) Is there any option to pop up an event in some point in the future in Ethereum contract? The ...
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1answer
19 views

Chainlink Price Feed - function fails when price not hard-coded but correctly displays in console

I'm experiencing a challenge and hoping for some guidance/help/assist... I've been working on implementing price feed. Testing locally with hardcoded return price works like a charm, no issues. When ...
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1answer
85 views

Make a GET Request over the Binance Smart Chain with a Chainlink Oracle

I am trying to call to an BSC Oracle to make an HTTP request according this ChainLink example. In my example I am goin to use the BSC mainnet 56 and a other JobID obviously: My steps: I created the ...
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2answers
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Smart Contracts and API Calls: How to check API repeatedly without paying a fee?

I'm new to this entire space, so please bear with me. I'm trying to create a betting app. I want people to sign the contract and say they'll put up some money that they'll either win or lose depending ...
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1answer
28 views

Send ETH Transaction based on price

I'd like to be able to execute an ETH transaction on chain based on a change in price of an asset. This seems like a job for an Oracle, but aside from an app that's not on chain that watches for ...
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9 views

How I can check request status with provable.xyz?

Simple question but I failed to find the answer. Before Oraclize became provable, there was an api endpoint for checking the status of a specific request id. This for example helped to determine if an ...
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20 views

Oracle service and oracle smart contract

I read this article https://medium.com/@robinagist/building-an-ethereum-oracle-with-web3-js-1-0-1272b59cfc31 but there are some things I didn't understand. Does the oracle need a node (like geth or ...
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2answers
37 views

Is an Oracle a Smart Contract or an EOA?

As provided in the Title, I am not clear about the concept connected to Oracles. I'm wondering if it is a Smart Contract or an EOA? Can somebody bring more clarity to the concept?