Integrating NEAR and Chainlink

This repository serves to demonstrate how a smart contract on NEAR can access off-chain data using an incentivized oracle solution with fungible tokens as payments. This repository is in continual development and tracking issues here.

There are a number of subdirectories in the project that represent the moving pieces of a simple oracle system.

• Client Contract (The contract that wants a token price from an off-chain API)
• Oracle Contract (An on-chain smart contract that accepts a fungible token payment and stores a request to be processed off-chain)
• Oracle Node (An off-chain machine continuously polling the Oracle Contract on NEAR, and fulfilling requests)
  • Note: code for the Oracle Node is not included in this repository, but one can use an oracle protocol like Chainlink
• Fungible Token (The token paid by the Client Contract to the Oracle Contract in exchange for getting an answer to the Client's request)

Get NEAR-CLI, Rust, and set up testnet accounts

We'll be using NEAR CLI, a command line tool that makes things simpler. Please have NodeJS version 12 or greater. Then install globally with:

npm install -g near-cli

These smart contracts are written in Rust. Please follow these directions to get Rust going on your local machine.

Install Rustup:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

(Official documentation)

Follow the directions which includes running:

source $HOME/.cargo/env

Add wasm target to your toolchain:

rustup target add wasm32-unknown-unknown

(Info on wasm32-unknown-unknown)

Rust is now ready on your machine.

Next, create a NEAR testnet account with Wallet.

Set an environment variable to use in these examples. For instance, if your test account is oracle.testnet set it like so in your terminal:

export NEAR_ACCT=oracle.testnet

(Windows users: please look into using set instead of export, surrounding the environment variable in % instead of beginning with $, and using escaped double-quotes \" where necessary instead of the single-quotes provided in these instructions.)

Create sub-accounts::

near create-account oracle.$NEAR_ACCT --masterAccount $NEAR_ACCT
near create-account client.$NEAR_ACCT --masterAccount $NEAR_ACCT
near create-account oracle-node.$NEAR_ACCT --masterAccount $NEAR_ACCT
near create-account near-link.$NEAR_ACCT --masterAccount $NEAR_ACCT

We've gone over the different roles earlier, but let's focus on what will happen to get a request fulfilled.

Client Contract will call the Oracle Contract to make a request for external data. Client Contract gives the Oracle Contract an allowance to take NEAR LINK from it. Before officially adding the request, it will transfer_from to capture the payment, keeping track of this amount in the withdrawable_token state variable. The Oracle Node will be continuously polling the state of its Oracle Contract using the paginated get_requests function. The Oracle Node will get the API results needed, and send back the answer to the Oracle Contract. The Oracle Contract makes a cross-contract call to the callback address (NEAR account) at the callback method provided. It has now fulfilled the request and removes it from state.

Build, deploy, and initialize

Let's begin!

Build the oracle, client, and NEAR LINK contracts with:

./build

Run all tests:

./test

Then deploy and instantiate like so…

NEAR LINK

near deploy --accountId near-link.$NEAR_ACCT --wasmFile near-link-token/res/near_link_token.wasm --initFunction new --initArgs '{"owner_id": "near-link.'$NEAR_ACCT'", "total_supply": "1000000"}'

Oracle contract

near deploy --accountId oracle.$NEAR_ACCT --wasmFile oracle/res/oracle.wasm --initFunction new --initArgs '{"link_id": "near-link.'$NEAR_ACCT'", "owner_id": "oracle.'$NEAR_ACCT'"}'

Client contract

near deploy --accountId client.$NEAR_ACCT --wasmFile client/res/client.wasm --initFunction new --initArgs '{"oracle_account": "oracle.'$NEAR_ACCT'"}'

Minor housekeeping

Before the oracle node can fulfill the request, they must be authorized. We might as well do this from the get-go.

near call oracle.$NEAR_ACCT add_authorization '{"node": "oracle-node.'$NEAR_ACCT'"}' --accountId oracle.$NEAR_ACCT

(Optional) Check authorization to confirm:

near view oracle.$NEAR_ACCT is_authorized '{"node": "oracle-node.'$NEAR_ACCT'"}'

Give fungible tokens and set allowances

Give 50 NEAR LINK to client:

near call near-link.$NEAR_ACCT transfer '{"new_owner_id": "client.'$NEAR_ACCT'", "amount": "50"}' --accountId near-link.$NEAR_ACCT --amount .0365

Note: above, we use the amount flag in order to pay for the state required. (See more about state staking here)

(Optional) Check balance to confirm:

near view near-link.$NEAR_ACCT get_balance '{"owner_id": "client.'$NEAR_ACCT'"}'

client contract gives oracle contract allowance to spend 20 NEAR LINK on their behalf:

near call near-link.$NEAR_ACCT inc_allowance '{"escrow_account_id": "oracle.'$NEAR_ACCT'", "amount": "20"}' --accountId client.$NEAR_ACCT --amount .0696

(Optional) Check allowance to confirm:

near view near-link.$NEAR_ACCT get_allowance '{"owner_id": "client.'$NEAR_ACCT'", "escrow_account_id": "oracle.'$NEAR_ACCT'"}'

Make a request

Let's make a request to a Chainlink node and request an ETH-USD price:

• Packed JSON arguments: {"get":"https://min-api.cryptocompare.com/data/price?fsym=ETH&tsyms=USD","path":"USD","times":100}
• Base64 encoded arguments: eyJnZXQiOiJodHRwczovL21pbi1hcGkuY3J5cHRvY29tcGFyZS5jb20vZGF0YS9wcmljZT9mc3ltPUVUSCZ0c3ltcz1VU0QiLCJwYXRoIjoiVVNEIiwidGltZXMiOjEwMH0=

We'll show two ways to have the client contract send the oracle contract a request. First, we'll directly call the oracle contract using the key pair (i.e. keys) from the client contract.

1. Client contract makes a direct request to oracle contract with payment of 10 NEAR LINK. We can do this because we have the key pair for the client contract.

near call oracle.$NEAR_ACCT request '{"payment": "10", "spec_id": "dW5pcXVlIHNwZWMgaWQ=", "callback_address": "client.'$NEAR_ACCT'", "callback_method": "token_price_callback", "nonce": "1", "data_version": "1", "data": "eyJnZXQiOiJodHRwczovL21pbi1hcGkuY3J5cHRvY29tcGFyZS5jb20vZGF0YS9wcmljZT9mc3ltPUVUSCZ0c3ltcz1VU0QiLCJwYXRoIjoiVVNEIiwidGltZXMiOjEwMH0="}' --accountId client.$NEAR_ACCT --gas 300000000000000

2. Any NEAR account calls the client contract, providing request arguments. Upon receiving this, the client contract sends a cross-contract call to the oracle contract to store the request. (Payment and other values are hardcoded here, the nonce is automatically incremented. This assumes that the client contract contract only wants to use one oracle contract.)

near call client.$NEAR_ACCT get_token_price '{"symbol": "eyJnZXQiOiJodHRwczovL21pbi1hcGkuY3J5cHRvY29tcGFyZS5jb20vZGF0YS9wcmljZT9mc3ltPUVUSCZ0c3ltcz1VU0QiLCJwYXRoIjoiVVNEIiwidGltZXMiOjEwMH0=", "spec_id": "dW5pcXVlIHNwZWMgaWQ="}' --accountId client.$NEAR_ACCT --gas 300000000000000

View pending requests

The oracle node is continually polling the state of the oracle contract to see the paginated request summary. This shows which accounts have requests pending and the total amount of pending requests:

near view oracle.$NEAR_ACCT get_requests_summary '{"max_num_accounts": "10"}'

Note: aside from get_requests_summary there is also get_requests_summary_from. Since the TreeMap data structure is ordered, the former will list the first N (max_num_accounts). Usage of get_requests_summary_from is for paging, providing a window of results to return. Please see function details for parameters and usage.

For folks who prefer to see a more low-level approach to hitting the RPC, here's the curl command performing the same query:

curl -d '{"jsonrpc": "2.0", "method": "query", "id": "chainlink", "params": {"request_type": "call_function", "finality": "final", "account_id": "oracle.'$NEAR_ACCT'", "method_name": "get_requests_summary", "args_base64": "eyJtYXhfbnVtX2FjY291bnRzIjogIjEwIn0="}}' -H 'Content-Type: application/json' https://rpc.testnet.near.org

The above will return something like:

{
  "jsonrpc": "2.0",
  "result": {
    "result": [
      91,
      123,
      34,
      97,
      99,
      99,
      111,
      117,
      110,
      116,
      34,
      58,
      34,
      99,
      108,
      105,
      101,
      110,
      116,
      46,
      100,
      101,
      109,
      111,
      46,
      116,
      101,
      115,
      116,
      110,
      101,
      116,
      34,
      44,
      34,
      116,
      111,
      116,
      97,
      108,
      95,
      114,
      101,
      113,
      117,
      101,
      115,
      116,
      115,
      34,
      58,
      49,
      125,
      93
    ],
    "logs": [],
    "block_height": 10551293,
    "block_hash": "Ljh67tYk5bGXPu9TamJNG4vHp18cEBDxebKHpEUeZEo"
  },
  "id": "chainlink"
}

We'll outline a quick way to see the results if the machine has Python installed. Copy the value of the innermost result key, which is an array of unsigned 8-bit integers.

Open the Python REPL with the command python and see the prompt with >>>.

Enter the below replacing BYTE_ARRAY with the the innermost result value (including the square brackets):

res = BYTE_ARRAY

then:

''.join(chr(x) for x in res)

and python will print something like:

'[{"account":"client.demo.testnet","total_requests":1}]'

The previous command (calling the method get_requests_summary) is useful if there has been significant scaling from many client accounts/contracts. To see the individual requests for a particular user, use the following command:

near view oracle.$NEAR_ACCT get_requests '{"account": "client.'$NEAR_ACCT'", "max_requests": "10"}'

The oracle node uses the passed request arguments to fetch the price of (for example) Basic Attention Token (BAT) and finds it is at $0.19 per token. The data 0.19 as a Vec<u8> is MTkuMQ==

There's a third method to get all the requests, ordered by account name and nonce, where a specified maximum number of results is provided.

near view oracle.$NEAR_ACCT get_all_requests '{"max_num_accounts": "100", "max_requests": "100"}'

Fulfill the request

Oracle Node uses its NEAR account keys to fulfill the request:

near call oracle.$NEAR_ACCT fulfill_request '{"account": "client.'$NEAR_ACCT'", "nonce": "0", "data": "MTkuMQ=="}' --accountId oracle-node.$NEAR_ACCT --gas 300000000000000

(Optional) Check the client contract for the values it has saved:

near view client.$NEAR_ACCT get_received_vals '{"max": "100"}'

Check final balance/allowance

(Optional) Check the balance of client contract:

near view near-link.$NEAR_ACCT get_balance '{"owner_id": "client.'$NEAR_ACCT'"}'

Expect 40

(Optional) Check the allowance of oracle contract:

near view near-link.$NEAR_ACCT get_allowance '{"owner_id": "client.'$NEAR_ACCT'", "escrow_account_id": "oracle.'$NEAR_ACCT'"}'

Expect 10

The oracle node and oracle contract are assumed to be owned by the same person/entity. The oracle contract has "withdrawable tokens" that can be taken when it's most convenient. Some oracles may choose to transfer these tokens immediately after fulfillment. Here we are using the withdrawable pattern, where gas is conserved by not transferring after each request fulfillment.

Also, when the feature of cancelling requests is implemented, the withdrawable tokens is used to ensure the correct amount of fungible tokens can be withdrawn without interfering with possible cancellations within a given period.

Withdraw tokens

(Optional) Check the withdrawable tokens on the oracle contract with this command:

near view oracle.$NEAR_ACCT get_withdrawable_tokens

(Optional) Check the fungible token balance of the client and the base account we'll be extracting to it. (This is the original account we set the NEAR_ACCT environment variable to, for demonstration purposes)

near view near-link.$NEAR_ACCT get_balance '{"owner_id": "oracle.'$NEAR_ACCT'"}'
near view near-link.$NEAR_ACCT get_balance '{"owner_id": "'$NEAR_ACCT'"}'

Finally, withdraw the fungible tokens from the oracle contract into the oracle node, the base account, who presumably owns both the oracle node and oracle contract.

near call oracle.$NEAR_ACCT withdraw '{"recipient": "oracle-node.'$NEAR_ACCT'", "amount": "10"}' --accountId oracle.$NEAR_ACCT --gas 300000000000000

You may use the previous two get_balance view methods to confirm that the fungible tokens have indeed been withdrawn.

Notes

The client is responsible for making sure there is enough allowance for fungible token transfers. It may be advised to add a cushion in addition to expected fungible token transfers as duplicate requests will also decrease allowance.

Scenario: a client accidentally sends the same request or a request with the same nonce. The fungible token transfer occurs, decrementing the allowance on the fungible token contract. Then it is found that it's a duplicate, and the fungible tokens are returned. In this case, the allowance will not be increased as this can only be done by the client itself.

One way to handle this is for the client to have logic to increase the allowance if it receives the response indicating a duplicate request has been sent. Another way might be to increase the allowance before each request. Again, this decision is up to the owner of the client contract.

Outstanding work

There are various issues opened in this repository. As mentioned early in this document, this is an ever-growing repository. Soon we'll implement using the expiration to allow the client contract to cancel their request and receive the tokens back if it's within the window. There's also work in terms of setting up the PreCoordinator and whatnot.

Contributors are welcome to get involved!