Trackers

A tracker is a process that gets data from an HTTP API or a Blockchain smart contract.

The structure of this api.json file is as follow:

{
    "ALGO/USD": [
        {
            "URL": "https://api.binance.com/api/v1/klines?symbol=ALGOUSDT&interval=1d&limit=1",
            "param": "$[0][4]",
            "interval": 7200,
        }
    ],
    ...
    "AMPL/ETH": [
        {
          "URL": "Mainnet:0xc5be99a02c6857f9eac67bbce58df5572498f40c,Rinkeby:0x7e62a502232f1feB77Adf8b8ca023cc9fB133418",
          "type": "ethereum",
          "parser": "Uniswap"
        }
    ],
    ...
}

There is three types of index trackers: http, ethereum, file.

HTTP trackers

If not set the default type of an index tracker is http type. also, the default parser for an index tracker is a jsonpath parser that parses data from a JSON payload. also, param is an additional parameter for the parser. for the jsonpath parser, it is the jsonpath param on how to parse the output. see here for more info

On-chain trackers

If the index tracker type was set to ethereum then it's an on-chain tracker that fetches data using on-chain calls on an Ethereum blockchain network.

Currently supported on-chain parsers are Uniswap and Balancer parsers.

Balancer parser

Balancer is a parser that fetches tracker info from a Balancer pool. Balancer pools are liquidity pools for pair of ERC20 tokens. a Balancer pool could exist on both Ethereum mainnet and testnets. for Balancer smart contract addresses see here.

There is an on-chain registry smart contract for Balancer that could be queried to get the best pools for an input pair of ERC20 tokens:

getBestPools(address fromToken, address destToken)

This method will retrieve an array of pool addresses for a token pair that is ordered by liquidity value.

Sometimes there is no deployed testnet Balancer pool to use in the On-chain index tracker. Here are some steps to deploy a Balancer pool on the Rinkeby testnet and add some liquidity to it based on this Balancer doc.

1- Deploy ERC20 tokens as required

​Here is a simple JavaScript project that could be used to deploy an ERC20 token on the Rinkeby testnet.

2- Install and configure the seth client

Install and configure seth client using this Github repository guides.

3- Pool creation

Set address variables:

export BFACTORY=0x9C84391B443ea3a48788079a5f98e2EaD55c9309
export TOKEN1=<token#1-address-from-the-first-step>
export TOKEN2=<token#2-address-from-the-first-step>

Create a new pool:

seth send --gas 5000000 $BFACTORY "newBPool()"

Set BPOOL variable:

export BPOOL=0x... (address returned from the previous command)

Approve ERC20 tokens on the BPool smart contract:

amount=$(seth --to-uint256 $(seth --to-wei 1000000 ether))
seth send $TOKEN1 "approve(address,uint256)" $BPOOL $amount
seth send $TOKEN2 "approve(address,uint256)" $BPOOL $amount

Wait for confirmations. after that bind tokens using the bind method. for example:

# Bind 1000000 TOKEN1 with a denormalized weight of 5
amount=$(seth --to-uint256 $(seth --to-wei 1000000 ether))
weight=$(seth --to-uint256 $(seth --to-wei 5 ether))
seth send $BPOOL "bind(address, uint256, uint256)" $TOKEN1 $amount $weight

Let's confirm that all the tokens were added by using some query method:

seth call $BPOOL "getNumTokens()"

Set a swap fee and finalize:

fee=$(seth --to-uint256 $(seth --to-wei 0.003 ether))
seth send $BPOOL "setSwapFee(uint256)" $fee
seth send $BPOOL "finalize()"

All done. Let's confirm that we received BPTs by calling balanceOf directly on the pool address (since the pools themselves are ERC20 tokens):

seth --from-wei $(seth --to-dec $(seth call $BPOOL "balanceOf(address)" $ETH_FROM))

Uniswap parser

Uniswap is a parser that fetches tracker info from a UniswapV2 pair. the easiest way to add UniswapV2 testnet pair is to call the addLiquidity contract method on Uniswap RouterV2 smart contract on different Ethereum networks. see addresses. the method is as follow:

function addLiquidity(
  address tokenA,
  address tokenB,
  uint amountADesired,
  uint amountBDesired,
  uint amountAMin,
  uint amountBMin,
  address to,
  uint deadline
) external returns (uint amountA, uint amountB, uint liquidity);

This required to deploy some ERC20 token beforehand and will create a Uniswap V2 pair if already not exists for the provided pair. there is a factory method that could be used to get the pair address here.