D31_chainlink

Chainlink Service

Chainlink is a decentralized oracle network designed to securely connect smart contracts on blockchain platforms with external data and services. It acts as a bridge between blockchains and real-world data, such as financial market prices, weather information, and other off-chain data sources. By providing reliable data feeds to smart contracts, Chainlink enhances the functionality and applicability of blockchain applications across various industries, enabling them to execute transactions based on real-time information.

The Chainlink service in the emulator consists of two types of nodes (called servers in the emulator):

• ChainlinkServer: Operates the Chainlink software starting with a pre-configured setup. It funds a Chainlink node and an Ethereum account using faucet, deploys an oracle contract with the LINK token contract address and node address as an authorized user, and establishes a one-to-one relationship between the node and the contract. Pre-configured jobs are created with the oracle contract address on the server.

• ChainlinkUserServer: To demonstrate how to use the Chainlink service.

Interact with Chainlink using CLI

You can interact with the Chainlink nodes using the Chainlink CLI. The Chainlink CLI is a command-line tool that allows you to interact with the Chainlink node. You can use the CLI to create and manage Chainlink jobs, check the status of the Chainlink node, and more. The Chainlink CLI can be accessed by running the following command on Chainlink nodes:

# chainlink admin login

Default username: seed@example.com
Default password: blockchainemulator

Instructions on how to use the Chainlink CLI can be found here.

Interacting with Chainlink using GUI

Login

Each Chainlink node comes with a web UI that can be used to interact with the node. You can access the UI by navigating to http://<host_ip>:6688. It allows you to create and manage Chainlink jobs.

Dashboard

After the login, we will enter the dashboard. From here, we can create and manage Chainlink jobs, check the status of the Chainlink node, and more. It will show the address of the account created during chainlink start command which should be funded with 5 ETH tokens.

Account Balance
Address  0xC485bC418643777f98A0C0eF31244Ea766028088
Native Token Balance 5.000000000000000000
LINK Balance         0.00000000

Instructions on how to use the dashboard to manage jobs can be found here

Chainlink User Server

The Chainlink User Server is an example to demonstrate how to use the Chainlink service to request external data. To do that, a user contract needs to be deployed to the blockchain. Users will interact with this contract, which will interact with the Chainlink service to get the data from the outside.

Set up the user contract

Setting up the user contract takes several steps. When the user node start, these steps will be automatically carried out.

1. Get LINK token contract address and oracle contract addresses from the Ethereum Utility server
2. Create an Ethereum account and fund the account using the faucet server
3. Deploy the user contract
4. Invoke the setLinkToken function of the user contract to set the LINK token contract address
5. Invoke the addOracles function of the user contract to add oracle contract addresses in the user contract
6. Send 1 ETH to the LINK token contract to fund the user account with LINK tokens
7. Invoke the transfer function of the LINK contract to transfer 100 LINK tokens from the user account to the user contract account.

How the process works

Once everything is set up, a user can request ETH price by invoking the requestETHPriceData(api, path) function in the user contract. This will trigger a series of actions:

• Upon receiving a request, the user contract invokes the LINK contract, which invokes the Chainlink oracle contracts. The involvement of the LINK contract ensures that the oracle gets paid (with LINK tokens)

  • Each oracle gets x number of LINK tokens for each job
  • The LINK contract will deduct k*x number of LINK tokens from the user contract account (k is the number of oracles invoked)

• Each oracle contract emits a message to notify its outside counterpart, i.e., a Chainlink node, which is always monitoring the blockchain for such messages

• Each Chainlink node does the following:

  • Fetch the outside data from the specified api
  • Process the data it using the specified path
  • Give the result to the oracle contract, which invokes the callback function provided by the user contract

• The user contract processes and save the response; for example, it may calculate the average from the data sent back from all the oracles

• The user eventually uses a local call to get the response

Check the logs of the Chainlink user server

You can check the logs on the Chainlink User Server to see the entire progress.

# Find the container ID of the Chainlink User Service
$ docker ps | grep Chainlink-User

$ docker logs -f <container ID>

In the logs, you will see the contract address of the user contract deployed by the Chainlink User Service. At the end of the logs, you will see the latest ETH price.

...
INFO - Successfully set Link token contract address in user contract.
INFO - Successfully add oracles to user contract.
INFO - Sent 1 ETH to LINK token contract successfully.
INFO - Transferred LINK tokens to user contract successfully.
INFO - User contract balance: 100000000000000000000
INFO - Requested ETH price data successfully.
INFO - Awaiting responses... Current responses count: 0
INFO - Awaiting responses... Current responses count: 0
INFO - Awaiting responses... Current responses count: 3
INFO - Response count: 3
INFO - Average ETH price: 381753
INFO - Chainlink user example service completed.

Interact with the user contract using Remix

You can interact the user contract using Remix or other Ethereum development tool. To get the User contract address, you can check the logs of the Chainlink User Server or use the following method

# Get the container ID 
$ docker ps | grep Chainlink-User

# Get the user contract address from the Chainlink-User container
$ docker exec -it <container ID> cat /chainlink_user/info/user_contract.json
{"contract_address": "0x313bF07a4Ba9275AfEaB59c19c922a0e027e9c89"}

With this address, you can invoke the requestETHPriceData(api, path) function of the user contract. The api is the external API where we want to get the data from, and the path is the json path that leads to the specific data item in the response (the response from the external API contains a lot of data items; if we replace PRICE with OPENDAY, we can select a different item):

api = "https://min-api.cryptocompare.com/data/pricemultifull?fsyms=ETH&tsyms=USD"
path = "RAW,ETH,USD,PRICE"

Interact with the user contract using Python

You can also use a python program to interact with the user contract. A sample program test_user.py can be found in the current folder. We need to change the IP addresses and the user contract address in the program, as they are emulator specific. The ethereum nodes have "Ethereum" included in their container names, while the faucet server has "Faucet" included in the names.

eth_url    = "http://10.160.0.72:8545"      # one of the ethereum nodes
faucet_url = "http://10.163.0.72:80/fundme" # the faucet server
user_contract_address = "0x313bF07a4Ba9275AfEaB59c19c922a0e027e9c89"

The script will interact with the user contract and display the latest price of the asset. Here is the output:

2024-06-05 09:24:48,048 - INFO - Sending a fund request to the Faucet server
2024-06-05 09:25:05,119 - INFO - Successfully requested funds from faucet: { ... }
INFO - Checking current ETH price in user contract
INFO - Current ETH price in user contract: 381384
INFO - Initiating a new request for ETH price data
INFO - API for ETH price: https://min-api.cryptocompare.com/data/pricemultifull?fsyms=ETH&tsyms=USD
INFO - Path for extracting price: RAW,ETH,USD,PRICE
INFO - Sent transaction for ETH price data request. 
       Hash: 0xc28ae96432d8214e99070ee65ec7a0076c9599f6b9b75df273eb57cfc5d5334c
INFO - Status of Transaction receipt for ETH price data request: 1
INFO - Request for ETH price data successful
INFO - Sleeping for 60 seconds to allow oracles to respond
INFO - Checking ETH price
INFO - Responses received from oracles
INFO - Responses count: 3
INFO - Updated ETH price: 381405