(Bad) Weather Oracle
This project by no means can be used as a legitimate example for a decentralized oracle design.
Description
This section describes a slightly more interesting use case of Inherents. Instead of providing a constant value the node will access a weather data provider endpoint which fetches current weather parameters at a provided geographical coordinates. A user submits a transaction were they order a weather report for a specified location. The node fetches the transaction data from the last block via a custom RuntimeAPI and the InherentProvider requests the weather data for the specified location. If no transaction is submitted by the user, InherentProvider obtains geolocation by its local IP provider thus converting the inherent data into node specific. As a result an event is created on chain which can be observed as usual with the blockchain explorer.
Source code
Refers to relevant WeatherOracle sections of the Client and Runtime sides in the same repo https://github.com/Retamogordo/substrate-inherents-tutorial-node
Running
Run Alice and Bob nodes in two separate terminals:
./node-template --base-path /tmp/alice --chain local --alice --validator
./node-template --base-path /tmp/bob --chain local --bob --validator
Head to https://polkadot.js.org/apps/#/extrinsics, locate weatherOracle pallet and submit an orderWeatherData transaction with latitude and longitude parameters in float number-like format.
Then head to https://polkadot.js.org/apps/#/explorer and observe WeatherDataSet event data in the Recent Events section.
Why this isn't a feasible oracle
There are a few reasons why this model of "oracle" is not feasible. As said before Inherents are not validated by the rest of the nodes, rather they assumed to be accepted as is. That said the situation when the block producer node cheats is not detectable by other nodes, so if fake data is submitted there is no way to reject it. One possible solution is to keep history of recent data samples and derive from them statistical metrics for current data feasibility. A possibly better solution would be not to use Inherents feature but rather access outer world using Offchain Workers.
Another aspect of the problem is that a centralized trustful provider is utilized by the oracle to fetch data from the external world. A truly decentralized oracle would connect to a variety of data providers applying specific consensus algorithms, like, for example those this document https://research.chain.link/whitepaper-v1.pdf describes.
