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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187 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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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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554 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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52 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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10 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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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
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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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1answer
79 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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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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1answer
43 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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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
57 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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173 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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27 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
26 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
58 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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2answers
273 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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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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1answer
77 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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1answer
58 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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100 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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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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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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2answers
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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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1answer
115 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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98 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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1answer
155 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
95 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
416 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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173 views

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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112 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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1answer
158 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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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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2answers
112 views

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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1answer
361 views

oraclize calling a REST API

I am trying to call a third party REST API that I developed using spring boot, and I want to call a function(param1,param2) in the API from the oracle using the oraclize_query() (POST request), but I ...
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1answer
63 views

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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86 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
131 views

How do Ethereum smart contracts work with external outcomes?

Since every node has to execute a smart contract and receive the same result, Ethereum smart contracts can't go out to the Internet to verify data. So, how do these sites that bet on the outcomes of ...
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29k 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?
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301 views

How to include headers in oraclize GET request

I need to be able to include an API key as a header within my GET request to an api using oraclize in solidity. The oraclize documentation states that you can define arguments to send however, you ...
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1answer
56 views

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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1answer
42 views

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
28 views

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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4answers
2k views

Issues getting a simple oraclize example to work, callback never executed

I have been trying to deploy and test the basic "SimpleDice" smart contract provided as an example from Oraclize. I have had to adjust it to work with solidity 0.4.2 a bit, but maybe I am missing ...
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47 views

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 use oraclize fee from contract balance instead of sender's wallet? [duplicate]

I am using oraclize query. I have a function that user's invoke but I dont want users to pay the gas fee for oraclize query, I want that fee to be paid by my contract balance, and if my balance is not ...
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2answers
131 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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37 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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135 views

__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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382 views

Non Deterministic External Service Call

As per the basic rules of blockchains believe it is mentioned that no service call from the smart contract should be made where the result is non deterministic. What I understand is if the result is ...

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