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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34 views

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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0answers
15 views

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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0answers
154 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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1answer
52 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
69 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
223 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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248 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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1answer
53 views

Oraclize can't compile Remix “undeclared identifier”

I was following this, I assume, very simple tutorial for generating a random number using oraclize: https://www.youtube.com/watch?v=J05DBPdkeAo But I end up getting this error and I dont understant ...
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0answers
49 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
61 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
135 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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36 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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117 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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0answers
33 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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58 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
311 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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0answers
93 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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0answers
144 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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51 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
169 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
94 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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0answers
178 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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0answers
146 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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0answers
34 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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0answers
32 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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371 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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400 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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0answers
264 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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29 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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21 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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2answers
64 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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48 views

Oraclize: Truffle migrate failed

I'm trying to migrate a contract into a ganache chain. It needs to use Oraclize - in the end, the plan is to have a private chain using Oraclize via ethereum-bridge. However, truffle migrate fails ...
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0answers
63 views

HTTP query create request error for oraclize

I have tried to deploy a sample contract having oraclizer query using truffle+ethereum bridge+solidity. First ethereum bridge made up and got OAR address which is used in sample contract in ...
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2answers
226 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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39 views

Dapp design to handle delay in callback response from Oraclize

In my dapp design I am receiving few user inputs via a form and passing them to a smart contract. Inside the smart contract I am using Oraclize service to timestamp the user inputs. Its a known fact ...
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1answer
143 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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2answers
156 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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59 views

Oraclize + CBOR Bug?

I'm making a computation query to Oraclize: import "https://github.com/oraclize/ethereum-api/blob/master/oraclizeAPI_0.4.sol" bytes scriptMultihash = "QmVJyXAmxdfuVgazi2PtnwXJdSiYPpkcvv6EydccQKkiZW";...
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1answer
148 views

Concatenating a variable value to a bytes32

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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1answer
48 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
92 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
147 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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110 views

Using Oraclize for ICO smart contract

What is the advantages of using Oraclize for the development of an ICO Smart contract? doesn't it just add unnecessary complexity?
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1answer
519 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
65 views

Using oraclize function into fallback function

I have an issue with my oraclize. I need to call oraclaze 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
53 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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1answer
96 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
55 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
39 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 ...