Get Started with web3 Development Easily Based on Ethereum Using FMZ (3)

Listening to Contract Events

Since the debugging tool can only test the code for a short time and output the content only after the code execution is completed, it cannot display and output the log in real time. In this section, we use the FMZ Quant Trading Platform to create live trading to test.

Here we use the Ethereum mainnet, and we listen to the Transfer(address,address,uint256) event of the USDT cryptocurrency contract. Based on what we learned in the last lesson, we designed and wrote an example of continuously listening to the events of a certain smart contract:

function toAmount(s, decimals) {
    return Number((BigDecimal(BigInt(s)) / BigDecimal(Math.pow(10, decimals))).toString())
}

function toInnerAmount(n, decimals) {
    return (BigDecimal(n) * BigDecimal(Math.pow(10, decimals))).toFixed(0)
}

function addEventListener(contractAddress, event, callBack) {
    var self = {}
    self.eventHash = "0x" + Encode("keccak256", "string", "hex", event)
    self.contractAddress = contractAddress
    self.latestBlockNumber = 0
    self.fromBlockNumber = 0
    self.firstBlockNumber = 0
    /* TODO: test
    self.isFirst = true 
    */ 

    self.getBlockNumber = function() {
        var maxTry = 10
        for (var i = 0; i < maxTry; i++) {
            var ret = exchange.IO("api", "eth", "eth_blockNumber")
            if (ret) {
                return toAmount(ret, 0)
            }
            Sleep(5000)
        }
        throw "getBlockNumber failed"
    }

    self.run = function() {
        var currBlockNumber = self.getBlockNumber()
        var fromBlock = "0x" + self.fromBlockNumber.toString(16)
        var toBlock = "0x" + currBlockNumber.toString(16)
        var params = {
            "fromBlock" : fromBlock, 
            "toBlock" : toBlock, 
            "address" : self.contractAddress, 
            "topics" : [self.eventHash]
        }
        // Log("fromBlockNumber:", self.fromBlockNumber, ", currBlockNumber:", currBlockNumber, "#FF0000")

        var logs = exchange.IO("api", "eth", "eth_getLogs", params)
        if (!logs) {
            return 
        }

        for (var i = 0; i < logs.length; i++) {
            if (toAmount(logs[i].blockNumber, 0) > self.latestBlockNumber) {
                /* TODO: test
                if (self.isFirst) {
                    self.firstBlockNumber = toAmount(logs[i].blockNumber, 0)
                    Log("firstBlockNumber:", self.firstBlockNumber)
                    self.isFirst = false 
                }
                */

                callBack(logs[i])
            }
        }

        self.latestBlockNumber = currBlockNumber
        self.fromBlockNumber = self.latestBlockNumber - 1
    }

    self.latestBlockNumber = self.getBlockNumber()
    self.fromBlockNumber = self.latestBlockNumber - 1

    return self
}

var listener = null 
function main() {
    var event = "Transfer(address,address,uint256)"
    var contractAddress = "0xdac17f958d2ee523a2206206994597c13d831ec7"
    var decimals = exchange.IO("api", contractAddress, "decimals")
    Log(exchange.IO("api", contractAddress, "name"), " decimals:", decimals)

    listener = addEventListener(contractAddress, event, function(log) {        
        var fromAddress = "0x" + exchange.IO("encodePacked", "address", log.topics[1])
        var toAddress = "0x" + exchange.IO("encodePacked", "address", log.topics[2])
        Log("Transfer:", fromAddress, "->", toAddress, ", value:", toAmount(log.data, decimals), ", blockNumber:", toAmount(log.blockNumber, 0))

        /* TODO: test
        arrLog.push(log)
        */
    })

    while (true) {
        listener.run()
        Sleep(5000)
    }
}

/* TODO: test
var arrLog = []
function onexit() {
    Log("End the run and verify the record")
    var firstBlockNumber = listener.firstBlockNumber
    var endBlockNumber = listener.latestBlockNumber

    Log("getLogs, from:", firstBlockNumber, " -> to:", endBlockNumber)
    var fromBlock = "0x" + (firstBlockNumber).toString(16)
    var toBlock = "0x" + (endBlockNumber).toString(16)
    var params = {
        "fromBlock" : fromBlock,
        "toBlock" : toBlock,
        "topics" : ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"],
        "address" : "0xdac17f958d2ee523a2206206994597c13d831ec7"
    }
    var logs = exchange.IO("api", "eth", "eth_getLogs", params)

    Log("arrLog:", arrLog.length)
    Log("logs:", logs.length)

    if (arrLog.length != logs.length) {
        Log("Length varies!")
        return 
    }

    for (var i = 0; i < arrLog.length; i++) {
        Log("Determine the blockNumber:", logs[i].blockNumber == arrLog[i].blockNumber, ", Determine from:", logs[i].topics[1] == arrLog[i].topics[1], 
            "Determine to:", logs[i].topics[2] == arrLog[i].topics[2])
    }
}
*/

Running on live trading:

For the execution results, a validation section (TODO: test) is also written in the code. After a simple validation it can be seen that the Transfer event of the USDT contract is continuously monitored and data is recorded, and a comparison between this data and the event data obtained at once can be observed that the data is consistent with:

Event Filtering

Based on the previous lesson Listening to contract events, we expand on it by adding filters to the listening process to listen for transfers to and from specified addresses. When a smart contract creates a log (i.e. releases an event), the log data topics contains up to 4 pieces of information. So we design a filter rule with [[A1, A2, ...An], null, [C1], D] as an example.

1. [A1, A2, ...An] corresponds to the data at position topics[0].

2. Null corresponds to the data at position topics[1].

3. [C1] corresponds to data at position topics[2].

4. D corresponds to the data at position topics[3].

• If an element in the condition structure is set null means it is not filtered, e.g. null corresponds to topics[1] and any value matches.

• If the element in the condition structure sets a single value indicating that the position must match, e.g. [C1] corresponds to topics[2] or D corresponds to topics[3], and unmatched logs are filtered.

• If the element in the condition structure is an array, it means that at least one of the elements in the array should match, e.g. [A1, A2, ...An] corresponds to topics[0], [A1, A2, ...An] with any one of them matching topics[0], then the logs will not be filtered.

Listening to USDT transfers from exchanges

Monitoring of USDT transactions transferred from and to the Binance Exchange:

function toAmount(s, decimals) {
    return Number((BigDecimal(BigInt(s)) / BigDecimal(Math.pow(10, decimals))).toString())
}

function toInnerAmount(n, decimals) {
    return (BigDecimal(n) * BigDecimal(Math.pow(10, decimals))).toFixed(0)
}

function addEventListener(contractAddress, event, callBack) {
    var self = {}
    self.eventHash = "0x" + Encode("keccak256", "string", "hex", event)
    self.contractAddress = contractAddress
    self.latestBlockNumber = 0
    self.fromBlockNumber = 0
    self.firstBlockNumber = 0
    self.filters = []

    self.setFilter = function(filterCondition) {
        if (filterCondition.length > 4) {
            throw "filterCondition error"
        }

        self.filters.push(filterCondition)
        Log("Set filter conditions:", filterCondition)
    }

    self.getTokenBalanceOfWallet = function(walletAddress, tokenAddress, tokenDecimals) {
        var balance = exchange.IO("api", tokenAddress, "balanceOf", walletAddress)
        if (balance) {
            return toAmount(balance, tokenDecimals)
        }
        return null
    }

    self.getBlockNumber = function() {
        var maxTry = 10
        for (var i = 0; i < maxTry; i++) {
            var ret = exchange.IO("api", "eth", "eth_blockNumber")
            if (ret) {
                return toAmount(ret, 0)
            }
            Sleep(5000)
        }
        throw "getBlockNumber failed"
    }

    self.run = function() {
        var currBlockNumber = self.getBlockNumber()
        var fromBlock = "0x" + self.fromBlockNumber.toString(16)
        var toBlock = "0x" + currBlockNumber.toString(16)
        var params = {
            "fromBlock" : fromBlock, 
            "toBlock" : toBlock, 
            "address" : self.contractAddress, 
            "topics" : [self.eventHash]
        }

        var logs = exchange.IO("api", "eth", "eth_getLogs", params)
        if (!logs) {
            return 
        }

        for (var i = 0; i < logs.length; i++) {
            if (toAmount(logs[i].blockNumber, 0) > self.latestBlockNumber) {
                // Check the filter condition, and execute the judgment if the filter condition is set
                if (self.filters.length != 0) {
                    // Initial filter marker
                    var isFilter = true 
                    // Traverse filter condition setting
                    for (var j = 0; j < self.filters.length; j++) {
                        // Take a filter setting, e.g: [[A1, A2, ...An], null, [C1], D]
                        var cond = self.filters[j]

                        // Traverse the filter setting
                        var final = true
                        for (var topicsIndex = 0; topicsIndex < cond.length; topicsIndex++) {
                            // Take one of the conditions in the filter setting, if it is the first condition: i.e. the data to be compared with topics[0]
                            var condValue = cond[topicsIndex]

                            // Data in the logs
                            if (topicsIndex > logs[i].topics.length - 1) {
                                continue 
                            }
                            var topicsEleValue = logs[i].topics[topicsIndex]
                            // If it's a Transfer event, you need to handle the from and to
                            if (logs[i].topics[0] == "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef") {
                                if (topicsIndex == 1 || topicsIndex == 2) {
                                    topicsEleValue = "0x" + exchange.IO("encodePacked", "address", topicsEleValue)
                                }
                            }

                            // If the condValue type is an array, it means that there are multiple comparison conditions in this position, and the multiple condition comparison is a logical or relationship
                            if (Array.isArray(condValue) && condValue.length > 1) {
                                // Determine condValue[0] == topicsEleValue || condValue[1] == topicsEleValue
                                final = final && condValue.some(element => element === topicsEleValue)
                            }else if (condValue === null) {
                                final = final && true
                            } else {
                                final = final && (condValue === topicsEleValue)
                            }
                        }

                        if (final) {
                            isFilter = false 
                        }
                    }

                    if (isFilter) {
                        continue
                    }
                }
                callBack(logs[i])
            }
        }

        self.latestBlockNumber = currBlockNumber
        self.fromBlockNumber = self.latestBlockNumber - 1
    }

    self.latestBlockNumber = self.getBlockNumber()
    self.fromBlockNumber = self.latestBlockNumber - 1

    return self
}

var listener = null 
function main() {
    // Initial clean-up log
    LogReset(1)
    LogProfitReset()

    var event = "Transfer(address,address,uint256)"                          // Listening to events
    var contractAddress = "0xdac17f958d2ee523a2206206994597c13d831ec7"       // USDT contract address
    var decimals = exchange.IO("api", contractAddress, "decimals")           // Get the precision information of USDT token
    var accountBinanceAddress = "0x28C6c06298d514Db089934071355E5743bf21d60" // Binance hot wallet address
    accountBinanceAddress = accountBinanceAddress.toLowerCase()              // Addresses are handled in lowercase
    Log(exchange.IO("api", contractAddress, "name"), " decimals:", decimals)

    // Creating a listener object
    listener = addEventListener(contractAddress, event, function(log) {
        var fromAddress = "0x" + exchange.IO("encodePacked", "address", log.topics[1])
        var toAddress = "0x" + exchange.IO("encodePacked", "address", log.topics[2])
        if (fromAddress == accountBinanceAddress) {
            Log("Binance transfer out - ", " Transfer:", fromAddress, "->", toAddress, ", value:", toAmount(log.data, decimals), ", blockNumber:", toAmount(log.blockNumber, 0), "#CD32CD")
        } else if (toAddress == accountBinanceAddress) {
            Log("Binance transfer in - ", " Transfer:", fromAddress, "->", toAddress, ", value:", toAmount(log.data, decimals), ", blockNumber:", toAmount(log.blockNumber, 0), "#FF0000")
        }        
    })

    // Set up event filtering
    listener.setFilter([null, accountBinanceAddress, null])   // Binance -> USDT
    listener.setFilter([null, null, accountBinanceAddress])   // USDT -> Binance

    var preBalance = 0
    while (true) {
        listener.run()
        var balance = listener.getTokenBalanceOfWallet(accountBinanceAddress, contractAddress, decimals)
        if (balance) {
            var direction = ""
            if (preBalance != 0 && preBalance > balance) {
                direction = " ↓ " + (preBalance - balance) + "#CD32CD"
            } else if (preBalance != 0 && preBalance < balance) {
                direction = " ↑ " + (balance - preBalance) + "#FF0000"
            }
            Log("Binance wallet address:", accountBinanceAddress, " balance:", balance, direction)
            LogProfit(balance, "&")   // Drawing only, no log printing
            preBalance = balance
        }
        LogStatus(_D(), "Binance wallet address:", accountBinanceAddress, ", balance:", balance)
        Sleep(5000 * 3)
    }
}

The above code running in live trading:

In this lesson, we introduced how to design an event filter. And used it to listen for USDT transactions associated with the Binance Exchange hot wallet. You can modify and extend this sample program to listen to any event you are interested in, to see what new transactions smart money has made, what new items the NFT Tycoons have rushed, etc.

Unit conversions

Many of the calculations related to Ethereum have values that exceed the maximum safe integer of the JavaScript language. Therefore, some methods are needed on the FMZ Quant Trading Platform to handle large values, which we have used specifically in previous courses and have not covered in detail. This section will discuss this aspect in detail.

Print the maximum safe integer defined in the JavaScript language:

function main() {
    Log("Number.MAX_SAFE_INTEGER:", Number.MAX_SAFE_INTEGER)
}

Running results:

Number.MAX_SAFE_INTEGER: 9007199254740991

BigInt

The smallest unit defined in Ethereum is 1wei, and the definition 1Gwei is equal to 1000000000 wei. 1Gwei is not really a very large number in Ethereum-related calculations, and some data is much larger than it. So these data with very large values can easily exceed Number.MAX_SAFE_INTEGER: 9007199254740991.

At FMZ Quant Trading Platform, we use the platform's BigInt object to represent these very large integer data. Use the constructor BigInt() to construct the BigInt object. You can construct BigInt objects using numeric, hexadecimal numeric strings as parameters. Use the toString() method of BigInt object to output the data represented by the object as a string.

The operations supported by the BigInt object are:

• Addition: +

• Subtraction: -

• Multiplication: *

• Division: /

• Modulo operations: %

• Power operations: *

Refer to the following code examples:

function main() {
    // Decimal representation of 1Gwei
    var oneGwei = 1000000000

    // Decimal to hexadecimal conversion of 1Gwei
    var oneGweiForHex = "0x" + oneGwei.toString(16)

    Log("oneGwei : ", oneGwei)
    Log("oneGweiForHex : ", oneGweiForHex)

    // Constructing BigInt objects
    Log("1Gwei / 1Gwei : ", (BigInt(oneGwei) / BigInt(oneGweiForHex)).toString(10))
    Log("1Gwei * 1Gwei : ", (BigInt(oneGwei) * BigInt(oneGweiForHex)).toString(10))
    Log("1Gwei - 1Gwei : ", (BigInt(oneGwei) - BigInt(oneGweiForHex)).toString(10))
    Log("1Gwei + 1Gwei : ", (BigInt(oneGwei) + BigInt(oneGweiForHex)).toString(10))
    Log("(1Gwei + 1) % 1Gwei : ", (BigInt(oneGwei + 1) % BigInt(oneGweiForHex)).toString(10))
    Log("1Gwei ** 2 : ", (BigInt(oneGwei) ** BigInt(2)).toString(10))
    Log("The square root of 100 : ", (BigInt(100) ** BigFloat(0.5)).toString(10))

    Log("Number.MAX_SAFE_INTEGER : ", BigInt(Number.MAX_SAFE_INTEGER).toString(10))
    Log("Number.MAX_SAFE_INTEGER * 2 : ", (BigInt(Number.MAX_SAFE_INTEGER) * BigInt("2")).toString(10))
}

Debugging tool testing:

run2023-06-08 11:39:50        Info    Number.MAX_SAFE_INTEGER * 2 : 18014398509481982
2023-06-08 11:39:50        Info    Number.MAX_SAFE_INTEGER : 9007199254740991
2023-06-08 11:39:50        Info    The square root of 100 : 10
2023-06-08 11:39:50        Info    1Gwei ** 2 : 1000000000000000000
2023-06-08 11:39:50        Info    (1Gwei + 1) % 1Gwei : 1
2023-06-08 11:39:50        Info    1Gwei + 1Gwei : 2000000000
2023-06-08 11:39:50        Info    1Gwei - 1Gwei : 0
2023-06-08 11:39:50        Info    1Gwei * 1Gwei : 1000000000000000000
2023-06-08 11:39:50        Info    1Gwei / 1Gwei : 1
2023-06-08 11:39:50        Info    oneGweiForHex : 0x3b9aca00
2023-06-08 11:39:50        Info    oneGwei : 1000000000

BigFloat

The BigFloat object is used similarly to the BigInt object to represent floating point numbers with larger values, and it also supports addition, subtraction, multiplication and division.
The BigFloat object supports the toFixed() method.

Refer to the following code example:

function main() {
    var pi = 3.14
    var oneGwei = "1000000000"
    var oneGweiForHex = "0x3b9aca00"

    Log("pi + oneGwei : ", (BigFloat(pi) + BigFloat(oneGwei)).toFixed(2))
    Log("pi - oneGweiForHex : ", (BigFloat(pi) - BigFloat(oneGweiForHex)).toFixed(2))
    Log("pi * 2.0 : ", (BigFloat(pi) * BigFloat(2.0)).toFixed(2))
    Log("pi / 2.0 : ", (BigFloat(pi) / BigFloat(2.0)).toFixed(2))
}

Debugging tool testing:

2023-06-08 13:56:44        Info    pi / 2.0 : 1.57
2023-06-08 13:56:44        Info    pi * 2.0 : 6.28
2023-06-08 13:56:44        Info    pi - oneGweiForHex : -999999996.86
2023-06-08 13:56:44        Info    pi + oneGwei : 1000000003.14

BigDecimal

The BigDecimal object is compatible with integer values and floating point values, and supports initialization with the BigInt object and the BigFloat object, and it also supports addition, subtraction, multiplication and division.

Refer to the following code example:

function main() {
    var pi = 3.1415
    var oneGwei = 1000000000
    var oneGweiForHex = "0x3b9aca00"

    Log("pi : ", BigDecimal(pi).toFixed(2))
    Log("oneGwei : ", BigDecimal(oneGwei).toString())
    Log("oneGweiForHex : ", BigDecimal(BigInt(oneGweiForHex)).toString())

    Log("BigInt(oneGwei) : ", BigDecimal(BigInt(oneGwei)).toString())    
    Log("BigFloat(pi) : ", BigDecimal(BigFloat(pi)).toFixed(4))

    Log("oneGwei + pi : ", (BigDecimal(oneGwei) + BigDecimal(pi)).toString())
    Log("oneGwei - pi : ", (BigDecimal(oneGwei) - BigDecimal(pi)).toString())
    Log("2.0 * pi : ", (BigDecimal(2.0) * BigDecimal(pi)).toString())
    Log("pi / pi : ", (BigDecimal(pi) / BigDecimal(pi)).toString())
}

Running in the debugging tool:

run2023-06-08 14:52:53        Info    pi / pi : 1
2023-06-08 14:52:53        Info    2.0 * pi : 6.283
2023-06-08 14:52:53        Info    oneGwei - pi : 999999996.8585
2023-06-08 14:52:53        Info    oneGwei + pi : 1000000003.1415
2023-06-08 14:52:53        Info    BigFloat(pi) : 3.1415
2023-06-08 14:52:53        Info    BigInt(oneGwei) : 1e+9
2023-06-08 14:52:53        Info    oneGweiForHex : 1e+9
2023-06-08 14:52:53        Info    oneGwei : 1e+9
2023-06-08 14:52:53        Info    pi : 3.14

Unit conversions

The following two functions: toAmount(), toInnerAmount() we have used many times in previous courses, these two functions are mainly used for data precision conversion.

function toAmount(s, decimals) {
    return Number((BigDecimal(BigInt(s)) / BigDecimal(Math.pow(10, decimals))).toString())
}

function toInnerAmount(n, decimals) {
    return (BigDecimal(n) * BigDecimal(Math.pow(10, decimals))).toFixed(0)
}

The toAmount() function converts (reduces) a variable s according to the precision parameter decimals. In web3 practical development, it is often necessary to deal with some chained hexadecimal data.
We have often encountered this in our previous courses, for example, the data field data in the Transfer(address,address,uint256) event of a smart contract:

desc{
    "data": "0x00000000000000000000000000000000000000000000000001c1a55000000000",
    "topics": ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef", "0x0000000000000000000000006b75d8af000000e20b7a7ddf000ba900b4009a80", "0x000000000000000000000000bcb095c1f9c3dc02e834976706c87dee5d0f1fb6"],
    "transactionHash": "0x27f9bf5abe3148169b4b85a83e1de32bd50eb81ecc52e5af006157d93353e4c4",
    "transactionIndex": "0x0",
    "removed": false,
    "address": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
    "blockHash": "0x847be24a7b159c292bda030a011dfec89487b70e71eed486969b032d6ef04bad",
    "blockNumber": "0x109b1cc",
    "logIndex": "0x0"
}

When processing data "data": "0x00000000000000000000000000000000000000000000000001c1a55000000000", we use the toAmount() function. This processing is designed to do a good job of converting data field data to readable values.

function toAmount(s, decimals) {
    return Number((BigDecimal(BigInt(s)) / BigDecimal(Math.pow(10, decimals))).toString())
}

function main() {
    var data = "0x00000000000000000000000000000000000000000000000001c1a55000000000"
    Log(toAmount(data, 18))  // Print out 0.12656402755905127
}

1 ETH token, as we know, is 1e18 wei, if we get a data 126564027559051260 in wei, how to convert it to ETH tokens?
Using the toAmount(, 18) function is a very simple conversion method. The toInnerAmount() function is the reverse operation of the toAmount() function (depending on the precision, zoom in), and it is easy to convert the data using these two functions.

It is important to note the integer value safety range in the JavaScript language, Number.MAX_SAFE_INTEGER, and the following example illustrates a hidden problem when converting data:

function toAmount(s, decimals) {
    return Number((BigDecimal(BigInt(s)) / BigDecimal(Math.pow(10, decimals))).toString())
}
function toInnerAmount(n, decimals) {
    return (BigDecimal(n) * BigDecimal(Math.pow(10, decimals))).toFixed(0)
}
function main() {
    var amount = 0.01
    var innerAmount = Number(toInnerAmount(amount, 18))       

    Log("Number.MAX_SAFE_INTEGER:", Number.MAX_SAFE_INTEGER)  // 9007199254740991
    Log("innerAmount:", innerAmount)                          // 10000000000000000

    Log("typeof(innerAmount):", typeof(innerAmount), ", innerAmount:", innerAmount)

    // Decimal value 10000000000000000 -> Hexadecimal value 0x2386f26fc10000
    Log("Convert", innerAmount, "to hexadecimal:", innerAmount.toString(16))
    Log("Convert", BigInt(10000000000000000).toString(10), "to hexadecimal:", BigInt(10000000000000000).toString(16))

    Log("0x" + BigInt(10000000000000000).toString(16), "Convert to decimal:", toAmount("0x" + BigInt(10000000000000000).toString(16), 0))
}

It is possible to run in the debugging tool:

run2023-06-15 16:21:40        Info    Convert 0x2386f26fc10000 to decimal: 10000000000000000
2023-06-15 16:21:40        Info    Convert 10000000000000000 to hexadecimal: 2386f26fc10000
2023-06-15 16:21:40        Info    Convert 10000000000000000 to hexadecimal: 10000000000000000
2023-06-15 16:21:40        Info    typeof(innerAmount): number , innerAmount: 10000000000000000
2023-06-15 16:21:40        Info    innerAmount: 10000000000000000
2023-06-15 16:21:40        Info    Number.MAX_SAFE_INTEGER: 9007199254740991

Through observation we found that:

Log("Convert", innerAmount, "to hexadecimal:", innerAmount.toString(16))

This line of code corresponds to the log output: Converting 10000000000000000 to hex: 10000000000000000, which is not converted correctly. The reason is naturally that 10000000000000000 is beyond Number.MAX_SAFE_INTEGER.

But when the decimal value is within the safe range, i.e., less than Number.MAX_SAFE_INTEGER, the toString(16) function converts it properly again, for example:

function main() {
    var value = 1000
    Log("Convert value to hexadecimal:", "0x" + value.toString(16))   // 0x3e8
    Log("Convert 0x3e8 to decimal:", Number("0x3e8"))               // 1000
}

In blockchain, even 0.01 ETH converted to a value of 10000000000000000 in wei will exceed Number.MAX_SAFE_INTEGER``, so a safer conversion for such cases is: BigInt(10000000000000000).toString(16)```.

Simulation Calls

Executing transactions and calling the Write method of smart contracts on Ethereum costs a certain amount of gas and sometimes it fails. It is important to know which transactions are likely to fail before sending them and calling them. There are simulated calls on Ethereum for testing.

eth_call

Ethereum's RPC method eth_call: it can simulate a transaction and return the result of a possible transaction, but it does not actually execute the transaction on the blockchain.

The eth_call method has 2 parameters, the first one is a dictionary structure, transactionObject:

// transactionObject
{
    "from" : ...,     // The address from which the transaction is sent
    "to" : ...,       // The address to which the transaction is addressed
    "gas" : ...,      // The integer of gas provided for the transaction execution
    "gasPrice" : ..., // The integer of gasPrice used for each paid gas encoded as hexadecimal
    "value" : ...,    // The integer of value sent with this transaction encoded as hexadecimal
    "data" : ...,     // The hash of the method signature and encoded parameters. For more information, see the Contract ABI description in the Solidity documentation
}

The second parameter is blockNumber: you can pass the label latest/pending/earliest, etc:

/* blockNumber
The block number in hexadecimal format or the string latest, earliest, pending, safe or 
finalized (safe and finalized tags are only supported on Ethereum, Gnosis, Arbitrum, 
Arbitrum Nova and Avalanche C-chain), see the default block parameter description in 
the official Ethereum documentation
*/

Next, we take the smart contract method approve and transfer calls of the token DAI as an example for simulation calls, and the following test environment is the main Ethereum network.

Simulation call approve

We are all familiar with the approve method for ERC20 contracts, and we have practiced it in previous courses. Since the ERC20 contract is already built into the FMZ platform ABI, there is no need to register the ABI of the smart contract to be called by the simulation.

function main() {
    var contractAddressUniswapV3SwapRouterV2 = "0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45"
    var contractAddress_DAI = "0x6b175474e89094c44da98b954eedeac495271d0f"
    var wallet = exchange.IO("address")

    // encode approve
    var data = exchange.IO("encode", contractAddress_DAI, "approve(address,uint256)", 
        contractAddressUniswapV3SwapRouterV2, "0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff")
    Log("ERC20 token DAI approve encode, data:", data)

    var transactionObject = {
        "from" : wallet,
        "to" : contractAddress_DAI,
        // "gasPrice" : "0x" + parseInt("21270894680").toString(16),
        // "gas" : "0x" + parseInt("21000").toString(16),
        "data" : "0x" + data,
    }
    var blockNumber = "latest"

    var ret = exchange.IO("api", "eth", "eth_call", transactionObject, blockNumber)
    Log("ret:", ret)
}

The code in the example first encodes the approve(address,uint256) method and parameters, and the parameter value 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff of the approve method indicates the maximum number of authorizations. Authorization is given to the smart contract at address 0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45 i.e. the router contract for Uniswap V3. Finally the Ethereum RPC method eth_call is called for simulation. You can see that the gasPrice and gas fields in the transactionObject parameters can be omitted.

The debugging tool is run and the simulation calls the approve method to authorize successfully (it does not authorize actually):

run2023-06-09 11:58:39        Info    ret: 0x0000000000000000000000000000000000000000000000000000000000000001
2023-06-09 11:58:39        Info    ERC20 token DAI approve encode, data: 095ea7b300000000000000000000000068b3465833fb72a70ecdf485e0e4c7bd8665fc45ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff

It is also possible to simulate some failure scenarios, when we adjust the gasPrice and gas parameters, if the ETH in the wallet is not enough to pay the gas fee, an error will be reported::

insufficient funds

When the gas cost is set too low, an error will be reported:

intrinsic gas too low: have 21000, want 21944 (supplied gas 21000)

Simulation call transfer

We are familiar with ERC20's transfer method, which allows you to transfer ERC20 tokens to a certain wallet address, so let's try to simulate a transfer of 1000 DAI to Vitalik Buterin.

function toInnerAmount(n, decimals) {
    return (BigDecimal(n) * BigDecimal(Math.pow(10, decimals))).toFixed(0)
}
function main() {
    var walletVitalik = "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
    var contractAddress_DAI = "0x6b175474e89094c44da98b954eedeac495271d0f"
    var wallet = exchange.IO("address")

    // transfer to Vitalik Buterin
    var decimals_DAI = exchange.IO("api", contractAddress_DAI, "decimals")
    var transferAmount = toInnerAmount(1000, decimals_DAI)
    Log("Transfer amount:", 1000, "DAI, use toInnerAmount convert to:", transferAmount)

    // encode transfer
    var data = exchange.IO("encode", contractAddress_DAI, "transfer(address,uint256)",
        walletVitalik, transferAmount)

    var transactionObject = {
        "from" : wallet,
        "to" : contractAddress_DAI,
        "data" : "0x" + data,
    }
    var blockNumber = "latest"

    var ret = exchange.IO("api", "eth", "eth_call", transactionObject, blockNumber)
    return ret 
}

Since I don't have DAI tokens in this test wallet, running it in the debug tool reported the following error unexpectedly:

execution reverted: Dai/insufficient-balance

Check the wallet address of Vitalik Buterin: 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045, it is clear that this wallet has DAI tokens. So let's adjust the transfer direction of the simulation call and simulate the transfer of 1000 DAI from Vitalik Buterin to us.

Modify the code, where the changes I made comments:

function toInnerAmount(n, decimals) {
    return (BigDecimal(n) * BigDecimal(Math.pow(10, decimals))).toFixed(0)
}
function main() {
    var walletVitalik = "0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045"
    var contractAddress_DAI = "0x6b175474e89094c44da98b954eedeac495271d0f"
    var wallet = exchange.IO("address")

    var decimals_DAI = exchange.IO("api", contractAddress_DAI, "decimals")
    var transferAmount = toInnerAmount(1000, decimals_DAI)
    Log("Transfer amount:", 1000, "DAI, use toInnerAmount convert to:", transferAmount)

    // encode transfer
    var data = exchange.IO("encode", contractAddress_DAI, "transfer(address,uint256)",
        wallet, transferAmount)     // Use the wallet variable as a parameter and change the transfer recipient's address to my own

    var transactionObject = {
        "from" : walletVitalik,     // Use the walletVitalik variable as the value of the from field to simulate that the call was made from the Vitalik Buterin's wallet address
        "to" : contractAddress_DAI,
        "data" : "0x" + data,
    }
    var blockNumber = "latest"

    var ret = exchange.IO("api", "eth", "eth_call", transactionObject, blockNumber)
    Log(ret)
}

Debugging tool test:

2023-06-09 13:34:31        Info    0x0000000000000000000000000000000000000000000000000000000000000001
2023-06-09 13:34:31        Info    Transfer amount: 1000 DAI, use toInnerAmount convert to: 1000000000000000000000

Using the FMZ Quant Trading Platform, it is easy to simulate the results of transactions and avoid unnecessary loss of gas fees from sending potentially failed transactions. We used the example code from this chapter of the course to simulate the call to transfer money to Vitalik Buterin's wallet and Vitalik Buterin's wallet to transfer money to us. Of course, there are many more uses for this eth_call method. Use your imagination, what would you use the eth_call method for?

Identify ERC721 Contracts

We know that tokens like ETH and BTC are homogenized tokens, and the token in your wallet is not different from the token in my wallet. But there are many things in the world that are not homogeneous, such as real estate, antiques, virtual artwork, etc. These cannot be represented by homogeneous tokens in abstraction. Therefore, there is the ERC721 standard to abstract non-homogeneous objects, and there is NFT and related concepts.
So among the many smart contracts deployed on Ethereum, how do we identify which smart contracts are ERC721 standard smart contracts?

To identify ERC721, it is important to know the ERC165 standard first.

ERC165

With the ERC165 standard, a smart contract can declare the interfaces it supports for other contracts to check. An ERC165 interface contract has only one function: supportsInterface(bytes4 interfaceId), the parameter interfaceId is the interface Id to be queried. If the contract implements the interfaceId returns a boolean true value, otherwise it returns a false value.

Here we are going to talk about how this interfaceId is calculated and encoded specifically.

ERC165 Standard shows an example:

soliditypragma solidity ^0.4.20;

interface Solidity101 {
    function hello() external pure;
    function world(int) external pure;
}

contract Selector {
    function calculateSelector() public pure returns (bytes4) {
        Solidity101 i;
        return i.hello.selector ^ i.world.selector;
    }
}

For the function signature of the interface (consisting of a function name and a list of parameter types) to perform a dissimilarity operation, for an ERC165 interface contract where the contract has only one function:

soliditypragma solidity ^0.4.20;

interface ERC165 {
    /// @notice Query if a contract implements an interface
    /// @param interfaceID The interface identifier, as specified in ERC-165
    /// @dev Interface identification is specified in ERC-165. This function
    ///  uses less than 30,000 gas.
    /// @return `true` if the contract implements `interfaceID` and
    ///  `interfaceID` is not 0xffffffff, `false` otherwise
    function supportsInterface(bytes4 interfaceID) external view returns (bool);
}

The interface identifier for this interface is 0x01ffc9a7. You can calculate this by running bytes4(keccak256('supportsInterface(bytes4)')); or using the Selector contract above.

Calculate the function signature directly and take its first 4 bytes to arrive at interfaceId.

function main() {
    var ret = Encode("keccak256", "string", "hex", "supportsInterface(bytes4)")
    Log("supportsInterface(bytes4) interfaceId:", "0x" + ret.slice(0, 8))
}

Tests can be run in the debug tool at:

run2023-06-13 14:53:35        Info    supportsInterface(bytes4) interfaceId: 0x01ffc9a7

It can be seen that the calculated results are consistent with the description in the ERC165 Standard document.

ERC721

Next let's look at the interface definition of the ERC721 contract standard:

solidityinterface ERC721 /* is ERC165 */ {
    event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);

    event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);

    event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);

    function balanceOf(address _owner) external view returns (uint256);

    function ownerOf(uint256 _tokenId) external view returns (address);

    function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external payable;

    function safeTransferFrom(address _from, address _to, uint256 _tokenId) external payable;

    function transferFrom(address _from, address _to, uint256 _tokenId) external payable;

    function approve(address _approved, uint256 _tokenId) external payable;

    function setApprovalForAll(address _operator, bool _approved) external;

    function getApproved(uint256 _tokenId) external view returns (address);

    function isApprovedForAll(address _owner, address _operator) external view returns (bool);
}

If we want to determine whether a smart contract is an ERC721 contract, first we need to know the interfaceId of the ERC721 contract before we can try to use the supportsInterface(bytes4 interfaceId) method to determine it. In previous courses, we have familiarized us with some concepts of the ERC165 standard and the algorithm for calculating the interfaceId, and we write code to calculate directly:

function calcSelector(arrSelector) {
    var ret = null
    if (Array.isArray(arrSelector)) {
        if (arrSelector.length == 1) {
            ret = Encode("keccak256", "string", "hex", arrSelector[0])
        } else if (arrSelector.length == 0) {
            throw "Error: the number of elements in the array is 0"
        } else {
            var viewEncodeData = null
            for (var i = 0; i < arrSelector.length; i++) {
                if (i == 0) {
                    ret = new Uint8Array(Encode("keccak256", "string", "raw", arrSelector[i]))
                } else {
                    viewData = new Uint8Array(Encode("keccak256", "string", "raw", arrSelector[i]))

                    if (viewData.length != ret.length) {
                        throw "Error: TypeArray view length is different"
                    }

                    for (var index = 0; index < ret.length; index++) {
                        ret[index] ^= viewData[index]
                    }
                }
            }
            ret = Encode("raw", "raw", "hex", ret.buffer)
        }
    } else {
        throw "Error: The parameter requires an array type."
    }

    return "0x" + ret.slice(0, 8)
}
function main() {
    // supportsInterface(bytes4): 0x01ffc9a7
    // var ret = calcSelector(["supportsInterface(bytes4)"])

    // ERC721Metadata: 0x5b5e139f
    /* 
    var arrSelector = [
        "name()",
        "symbol()",
        "tokenURI(uint256)"
    ]
    var ret = calcSelector(arrSelector)
    */

    // ERC721: 0x80ac58cd
    // /*
    var arrSelector = [
        "balanceOf(address)",
        "ownerOf(uint256)",
        "safeTransferFrom(address,address,uint256,bytes)",
        "safeTransferFrom(address,address,uint256)",
        "transferFrom(address,address,uint256)",
        "approve(address,uint256)",
        "setApprovalForAll(address,bool)",
        "getApproved(uint256)",
        "isApprovedForAll(address,address)",
    ]
    var ret = calcSelector(arrSelector)
    // */

    Log(ret)
}

The code uses the Encode() function for function signature calculation (the keccak256 algorithm), and for the calculation in the code example above, specifying the output parameter of the Encode() function as "raw", the function returns the ArrayBuffer type of JavaScript language.
To perform a ^ (iso-or) operation on two ArrayBuffer objects, you need to create a TypedArray view based on the ArrayBuffer object, then iterate through the data in it and perform the iso-or operation one by one.

Run in the debugging tool:

run2023-06-13 15:04:09        Info    0x80ac58cd

It can be seen that the calculated results are consistent with those described in eip-721.

soliditypragma solidity ^0.4.20;

/// @title ERC-721 Non-Fungible Token Standard/// @dev See https://eips.ethereum.org/EIPS/eip-721///  Note: the ERC-165 identifier for this interface is 0x80ac58cd.interface ERC721 /* is ERC165 */ {
    /// @dev This emits when ownership of any NFT changes by any mechanism.
    ///  This event emits when NFTs are created (`from` == 0) and destroyed
    ///  (`to` == 0). Exception: during contract creation, any number of NFTs
    ///  may be created and assigned without emitting Transfer. At the time of
    ///  any transfer, the approved address for that NFT (if any) is reset to none.
    event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);
...

With the ERC721 interface Id, we can determine if a contract is an ERC721 standard contract or not. We use BAYC to do the test, which is a contract that follows ERC721. First we need to register the ABI, and since we only call the following three methods, we can register these three methods:

• supportsInterface(interfaceId)

• symbol()

• name()

The specific codes are as follows:

function main() {
    // Contract address for ERC721, BAYC is used here
    var testContractAddress = "0xbc4ca0eda7647a8ab7c2061c2e118a18a936f13d"

    var testABI = `[{
        "inputs": [{
            "internalType": "bytes4",
            "name": "interfaceId",
            "type": "bytes4"
        }],
        "name": "supportsInterface",
        "outputs": [{
            "internalType": "bool",
            "name": "",
            "type": "bool"
        }],
        "stateMutability": "view",
        "type": "function"
    }, {
        "inputs": [],
        "name": "symbol",
        "outputs": [{
            "internalType": "string",
            "name": "",
            "type": "string"
        }],
        "stateMutability": "view",
        "type": "function"
    }, {
        "inputs": [],
        "name": "name",
        "outputs": [{
            "internalType": "string",
            "name": "",
            "type": "string"
        }],
        "stateMutability": "view",
        "type": "function"
    }]`

    // ERC721 Interface Id, calculated in the previous course
    var interfaceId = "0x80ac58cd"

    // Register ABI
    exchange.IO("abi", testContractAddress, testABI)

    // Call the supportsInterface method
    var isErc721 = exchange.IO("api", testContractAddress, "supportsInterface", interfaceId)

    // Output Information
    Log("Contract address:", testContractAddress)
    Log("Contract name:", exchange.IO("api", testContractAddress, "name"))
    Log("Contract code:", exchange.IO("api", testContractAddress, "symbol"))
    Log("Whether the contract is ERC721 standard:", isErc721)
}

Tests can be run in the debugging tool:

run2023-06-13 16:32:57        Info    Whether the contract is ERC721 standard: true
2023-06-13 16:32:57        Info    Contract code: BAYC
2023-06-13 16:32:57        Info    Contract name: BoredApeYachtClub
2023-06-13 16:32:57        Info    Contract address: 0xbc4ca0eda7647a8ab7c2061c2e118a18a936f13d

The contract with the address 0xbc4ca0eda7647a8ab7c2061c2e118a18a936f13d is determined to be ERC721 standard.

In this part, we introduced how to determine ERC721 contracts, so contracts like ERC20, which do not support the ERC165 standard, will have to be identified in another way. Do you know how to check if a contract is ERC20 standard?

Encoding calldata

What is calldata? By the author's understanding, a simple layman's description here is:

The "calldata" is the encoding of a function call or parameter in Ethereum, and the "calldata" is encoded according to the ABI (Application Binary Interface) specification of the contract.

For example, we can encode the balanceOf and transfer method calls of the ERC20 contract we studied in the previous course, together with the parameters of the calls, into a calldata. In some application scenarios, such as interaction between contracts, this scenario will use calldata, and of course there are many other application scenarios that are not listed here.

How to code a smart contract function call to get calldata?

In the FMZ Quant Trading Platform, you can use exchange.IO("encode", ...) to encode smart contract function calls, the use of exchange.IO("encode", ...) is very simple. The first parameter of the function is the fixed string "encode"; the second parameter is the address of the smart contract; the third parameter is the name of the smart contract method to be encoded; the rest of the parameters are passed to the specific parameter value of the smart contract method to be encoded.

eth_sendRawTransaction

When we encode a smart contract method call and generate the corresponding calldata data, if this smart contract method is a Write method (i.e.: write operation), we need to use the generated calldata data as the data field of the transaction and then use the Ethereum RPC method eth_ sendRawTransaction to send a request containing the raw data of that transaction to the Ethereum network.

The eth_sendRawTransaction method has only one parameter, data:

data: The signed transaction (typically signed with a library, using your private key)

The data parameter is a transaction data after the signature calculation, and the transaction data structure of Ethereum has the following main fields:

{
    "nonce": "0x1",                         // Number of transactions on the account of the sender of the transaction
    "gasPrice": "0x12a05f200",              // Traded Gas price
    "gasLimit": "0x5208",                   // Gas limit for trading
    "to": "0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2",    // Target contract address or recipient address
    "value": "0x4563918244F40000",          // Number of Ethereum transferred
    "data": "0x0123456789ABCDEF",           // Data to send to the contract
}

How to sign an Ethereum transaction?

In the FMZ Quant Trading Platform, we use the Encode() function to perform the signature calculation, the specific example we write in the subsequent course "Execute Write method calldata".

Execute Read method calldata

For the execution of the calldata of the Read method, we use the previously learned RPC method: eth_call to execute it. We explained the eth_call RPC method of the Ethereum only did a demonstration of the Write method of the smart contract, in this section, we use the calldata method to demonstrate the execution of the smart contract Read method call. Let's use the balanceOf method of the WETH contract to read the current balance of WETH tokens in the wallet.

We use the debugging tool to test on the Ethereum mainnet at:

function toAmount(s, decimals) {
    return Number((BigDecimal(BigInt(s)) / BigDecimal(Math.pow(10, decimals))).toString())
}
function main() {
    // ABI for WETH contracts
    var abiWETH = `[{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"guy","type":"address"},{"name":"wad","type":"uint256"}],"name":"approve","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"src","type":"address"},{"name":"dst","type":"address"},{"name":"wad","type":"uint256"}],"name":"transferFrom","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"wad","type":"uint256"}],"name":"withdraw","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"decimals","outputs":[{"name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"address"}],"name":"balanceOf","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"dst","type":"address"},{"name":"wad","type":"uint256"}],"name":"transfer","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[],"name":"deposit","outputs":[],"payable":true,"stateMutability":"payable","type":"function"},{"constant":true,"inputs":[{"name":"","type":"address"},{"name":"","type":"address"}],"name":"allowance","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"payable":true,"stateMutability":"payable","type":"fallback"},{"anonymous":false,"inputs":[{"indexed":true,"name":"src","type":"address"},{"indexed":true,"name":"guy","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"src","type":"address"},{"indexed":true,"name":"dst","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"dst","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Deposit","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"src","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Withdrawal","type":"event"}]`

    // WETH contract address
    var wethAddress = "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"

    // Register ABI for WETH contracts
    exchange.IO("abi", wethAddress, abiWETH)

    // The wallet address of the currently configured exchange object
    var walletAddress = exchange.IO("address")

    // Coded WETH contract's deposit method call
    var calldataForDeposit = exchange.IO("encode", wethAddress, "balanceOf(address)", walletAddress)
    Log("calldataForDeposit:", "0x" + calldataForDeposit)

    // Construct the transaction as the first parameter of eth_call
    var transaction = {
        "from" : walletAddress,
        "to" : wethAddress,
        "data" : "0x" + calldataForDeposit,
    }

    // The second parameter of eth_call
    var blockNumber = "latest"

    // Call with eth_call
    var ret = exchange.IO("api", "eth", "eth_call", transaction, blockNumber)
    var wethBalance = exchange.IO("decode", "uint256", ret)   // You can use exchange.IO("decode", ...) function to decode
    Log("wethBalance:", toAmount(wethBalance, 18))            // Converted from wei to WETH units
}

Run in the debugging tool:

run2023-06-15 11:51:31        Info    wethBalance: 0.015
2023-06-15 11:51:31        Info    calldataForDeposit: 0x70a082310000000000000000000000006b3f11d807809b0b1e5e3243df04a280d9f94bf4

If the method of a smart contract has a return value, you can use the exchange.IO("decode", ...) function to decode it. You can see that the passing calldata method is the same as calling the smart contract's balanceOf method directly, getting the WETH balance of 0.015 WETH for my test wallet.

Execute Write method calldata

For the execution of the Write method calldata, it is necessary to use the RPC method: eth_sendRawTransaction.

Let's use the debugging tool and test it on the Ethereum mainnet at:

function toAmount(s, decimals) {
    return Number((BigDecimal(BigInt(s)) / BigDecimal(Math.pow(10, decimals))).toString())
}
function toInnerAmount(s, decimals) {
    return (BigDecimal(s)*BigDecimal(Math.pow(10, decimals))).toFixed(0)
}
function main() {
    // ABI for WETH contracts
    var abiWETH = `[{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"guy","type":"address"},{"name":"wad","type":"uint256"}],"name":"approve","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"src","type":"address"},{"name":"dst","type":"address"},{"name":"wad","type":"uint256"}],"name":"transferFrom","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"wad","type":"uint256"}],"name":"withdraw","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"decimals","outputs":[{"name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"address"}],"name":"balanceOf","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"dst","type":"address"},{"name":"wad","type":"uint256"}],"name":"transfer","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[],"name":"deposit","outputs":[],"payable":true,"stateMutability":"payable","type":"function"},{"constant":true,"inputs":[{"name":"","type":"address"},{"name":"","type":"address"}],"name":"allowance","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"payable":true,"stateMutability":"payable","type":"fallback"},{"anonymous":false,"inputs":[{"indexed":true,"name":"src","type":"address"},{"indexed":true,"name":"guy","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"src","type":"address"},{"indexed":true,"name":"dst","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"dst","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Deposit","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"name":"src","type":"address"},{"indexed":false,"name":"wad","type":"uint256"}],"name":"Withdrawal","type":"event"}]`

    // WETH contract address
    var wethAddress = "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"

    // Register ABI for WETH contract
    exchange.IO("abi", wethAddress, abiWETH)

    // The wallet address of the currently configured exchange object
    var walletAddress = exchange.IO("address")

    // Coded WETH contract's deposit method call
    var calldataForDeposit = exchange.IO("encode", wethAddress, "deposit")
    Log("calldataForDeposit:", "0x" + calldataForDeposit)

    // Get nonce
    var nonce = exchange.IO("api", "eth", "eth_getTransactionCount", walletAddress, "pending")

    // Get gasPrice
    var gasPrice = exchange.IO("api", "eth", "eth_gasPrice")

    // Call the deposit method to change ETH to WETH, you need to transfer ETH, here we convert 0.01ETH to a hexadecimal value in wei
    var innerAmount = BigInt(Number(toInnerAmount(0.005, 18))).toString(16)

    // The transaction call object:
    var obj = {
        "from" : walletAddress,
        "to"  : wethAddress,
        "gasPrice" : gasPrice,
        "value" : "0x" + innerAmount,
        "data" : "0x" + calldataForDeposit,
    }

    // Calculate gasLimit
    var gasLimit = exchange.IO("api", "eth", "eth_estimateGas", obj)

    // Construct a transaction
    var transaction = {
        "to": wethAddress,
        "value": toAmount("0x" + innerAmount, 0),   // Convert to decimal
        "data": "0x" + calldataForDeposit,
        "gasLimit": toAmount(gasLimit, 0),   // Convert to decimal
        "gasPrice": toAmount(gasPrice, 0),   // Convert to decimal
        "nonce": toAmount(nonce, 0),         // Convert to decimal
        "chainId": 1,                        // Ethereum mainnet Id
    }
    Log("transaction:", transaction)

    // Signature, your key is replaced with your private key
    var signedTx = Encode("signTx", "string", "hex", JSON.stringify(transaction), "hex", "0x" + "your key")
    Log("signedTx:", "0x" + signedTx)

    // Call eth_sendRawTransaction to send a transaction
    var ret = exchange.IO("api", "eth", "eth_sendRawTransaction", "0x" + signedTx)
    return ret 
}

Run in the debugging tool:

run2023-06-15 09:58:50        Info    signedTx: 0xf86f4f8504202067888...
2023-06-15 09:58:50        Info    transaction: {"to":"0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2","value":5000000000000000,"data":"0xd0e30db0","gasLimit":27938,"gasPrice":17718863752,"nonce":79,"chainId":1}
2023-06-15 09:58:50        Info    calldataForDeposit: 0xd0e30db0

Execute var ret = exchange.IO("api", "eth", "eth_sendRawTransaction", "0x" + signedTx) function and the returned Transaction Hash is: 0x2ff585504b0fe59b0122f696e8808abfe2f3ce263448066533f3bb8a4f55e8e6. The eth_sendRawTransaction call executes the calldata in it, calling the deposit method of the WETH contract to swap the 0.005 ETH sent for WETH.

Listening to mempool

Before a user's transaction is packaged into the Ethereum blockchain by miners, all transactions will be pooled in Mempool (transaction memory pool), where "miners" also look for transactions with high fees to be packaged first, in order to maximize mining benefits. Therefore, usually the higher the transaction's gasPrice setting, the more likely it is to be packaged.

Some transaction scripts will also sniff Mempool in the hope of finding some profitable transactions. For example, if a transaction is set with a high exchange slippage, the transaction could be subject to a "sandwich attack'' by these transactionscripts. So how do these scripts listen for pending (pending, to-be-packaged) transactions in Mempool?

Listening with the REST protocol

Use the RPC method we learned before: eth_getBlockByNumber, but we do not pass the specific blockNumber this time, we use the "pending" tag.

function main() {
    var data = exchange.IO("api", "eth", "eth_getBlockByNumber", "pending", true)
    if (Array.isArray(data.transactions)) {
        for (var i = 0; i < data.transactions.length; i++) {
            Log(data.transactions[i])
        }
    }
}

Run in the debugging tool:

run2023-06-18 19:23:05        Info    {"blockNumber":"0x10b2027","type":"0x2","accessList":[],"blockHash":"0xf833ed36435c53d63bd7109bb1e85383075534410c14573881bf26d912f46a89","from":"0xd50521974d62f1fa34b8e81cb742ccf6147d05ff","gasPrice":"0x32ea2db37","hash":"0xf8f10f8f473c340b021298feb48d0affe529e8737a309c4cc1902e8989ef0914","input":"0xa22cb4650000000000000000000000001e0049783f008a0085193e00003d00cd54003c710000000000000000000000000000000000000000000000000000000000000001","v":"0x0","value":"0x0","maxFeePerGas":"0x48a413364","maxPriorityFeePerGas":"0x5f5e100","nonce":"0x8","r":"0x8c1cc36f43b02c9e9e454153588cc9d38757f1da69ec49d3cfdda74ab69e06a8","s":"0x2f3dd3e5ddf9e5d42c128a8e900026aca7568fa83c68cf332e1328066ee8d03a","transactionIndex":"0x3a","chainId":"0x1","gas":"0x1142d","to":"0x8c3c0274c33f263f0a55d129cfc8eaa3667a9e8b"}
2023-06-18 19:23:05        Info    {"input":"0x646174613a2c7b2270223a226572632d3230222c226f70223a226d696e74222c227469636b223a2265746873222c226964223a223139323732222c22616d74223a2231303030227d","nonce":"0x1d","blockHash":"0xf833ed36435c53d63bd7109bb1e85383075534410c14573881bf26d912f46a89","from":"0xe7fa86855af674837cea1b58f88b5352543ca27b","gas":"0x81cc","gasPrice":"0x32ea2db37","to":"0xe7fa86855af674837cea1b58f88b5352543ca27b","chainId":"0x1","transactionIndex":"0x39","type":"0x2","value":"0x0","accessList":[],"blockNumber":"0x10b2027","hash":"0x55702f5d14736fc9d0c58fdac2d2052a602db171c46b5e1fa9ff6af5c277f9a2","maxFeePerGas":"0x48a413364","maxPriorityFeePerGas":"0x5f5e100","r":"0x5a703d389d23b51adf8ef0f55db8876e7392636797b68a4be6afe73e76d7e1f2","s":"0x4b4bb11257c4434a0acc2672357f8793476e4bfdf98bc30d2389ce335e7de64e","v":"0x1"}
2023-06-18 19:23:05        Info    {"gas":"0x186a0","nonce":"0x46533","r":"0xfeea052a4ac2283ca058a657a806ba0916d8e7d52d2a577f150c40eb1dfbec65","s":"0x5bf0089a3c060ba787b67a205b44e1065a0d11d132b41737ab9adf0f55066811","transactionIndex":"0x38","value":"0x78f0975742c400","blockHash":"0xf833ed36435c53d63bd7109bb1e85383075534410c14573881bf26d912f46a89","chainId":"0x1","hash":"0x56bdf1b38e23db66e8d1c4014d1e9f690a9217d8a0232489210325fc69e25cf9","v":"0x25","input":"0x","type":"0x0","blockNumber":"0x10b2027","gasPrice":"0x4a817c800","from":"0x97b9d2102a9a65a26e1ee82d59e42d1b73b68689","to":"0xcb513e99c020e9d15a6eafef873fef5d9f078221"}
...

Extract one piece of the data:

{
    "blockNumber": "0x10b2027",
    "type": "0x2",
    "accessList": [],
    "blockHash": "0xf833ed36435c53d63bd7109bb1e85383075534410c14573881bf26d912f46a89",
    "from": "0xd50521974d62f1fa34b8e81cb742ccf6147d05ff",
    "gasPrice": "0x32ea2db37",
    "hash": "0xf8f10f8f473c340b021298feb48d0affe529e8737a309c4cc1902e8989ef0914",
    "input": "0xa22cb4650000000000000000000000001e0049783f008a0085193e00003d00cd54003c710000000000000000000000000000000000000000000000000000000000000001",
    "v": "0x0",
    "value": "0x0",
    "maxFeePerGas": "0x48a413364",
    "maxPriorityFeePerGas": "0x5f5e100",
    "nonce": "0x8",
    "r": "0x8c1cc36f43b02c9e9e454153588cc9d38757f1da69ec49d3cfdda74ab69e06a8",
    "s": "0x2f3dd3e5ddf9e5d42c128a8e900026aca7568fa83c68cf332e1328066ee8d03a",
    "transactionIndex": "0x3a",
    "chainId": "0x1",
    "gas": "0x1142d",
    "to": "0x8c3c0274c33f263f0a55d129cfc8eaa3667a9e8b"
}

Listening with the WebSocket protocol

In the FMZ Quant Trading Platform, we use the Dial function to create WebSocket connections, you can check the FMZ API documentation to learn the Dial function.

The test code in this section runs in the Ethereum mainnet environment, and it is easier to use the FMZ Quant to test in live trading due to the use of WebSocket protocol communication. The Websocket protocol subscription messages are:

{"jsonrpc": "2.0", "id": 1, "method": "eth_subscribe", "params": ["newPendingTransactions"]}

In addition to newPendingTransactions, you can also subscribe to newHeads, logs.

Receiving data pushed by WebSocket connections:

{
    "jsonrpc": "2.0",
    "method": "eth_subscription",
    "params": {
        "subscription": "0x2c5c087b4aa188e008f4747828ef4e61",
        "result": "0x69c4251cecb814e17cfe7a5ee41742a616f9a4d1bbf245c49b186b1006fd14d3"
    }
}

Then further query transaction according to which: "result": "0x69c4251cecb814e17cfe7a5ee41742a616f9a4d1bbf245c49b186b1006fd14d3". For a specific transaction, we use the Ethereum RPC method eth_getTransactionByHash to query.

var ws = null 

function main () {    
    // {"jsonrpc": "2.0", "id": 1, "method": "eth_subscribe", "params": ["xxxxx"]}  , "xxxxx" is the specific message to subscribe to
    var payload = {"jsonrpc": "2.0", "id": 1, "method": "eth_subscribe", "params": ["newPendingTransactions"]}

    // wss://mainnet.infura.io/ws/v3/xxxxx , "xxxxx" is your infura key
    var infuraKey = "your key"

    ws = Dial("wss://mainnet.infura.io/ws/v3/" + infuraKey + "|reconnect=true&payload=" + JSON.stringify(payload))
    if (!ws) {
        throw "websocket link infura failed!"
    }

    // eth_getTransactionByHash call count
    var getTransactionCounter = 0

    var beginTS = new Date().getTime()

    // Loop to get messages
    while (true) {
        // Receive push messages
        var data = ws.read()
        if (data) {
            var ts = new Date().getTime()

            if (ts - beginTS >= 1000) {
                getTransactionCounter = 0
                beginTS = ts 
            }

            // Check transaction details based on txHash
            if (ts - beginTS < 1000 && getTransactionCounter >= 100) {
                Sleep(1000)
                getTransactionCounter = 0
                beginTS = ts 
            }

            var obj = JSON.parse(data)
            if (obj["params"] && obj["params"]["result"]) {
                var transcationInfo = exchange.IO("api", "eth", "eth_getTransactionByHash", obj["params"]["result"])
                Log(obj["params"]["result"], "transcationInfo:", transcationInfo)
            }

            getTransactionCounter++
        }

        LogStatus(_D())
    }
}

function onexit() {
    Log("Disconnect WS connection")
    ws.close()
}

Create a live trading to run the above code, you can receive the data pushed by the WebSocket connection, the data is pushed constantly, we extract one of them - transaction:

{
    "maxPriorityFeePerGas": "0x5f5e100",
    "nonce": "0x1a9",
    "accessList": [],
    "blockNumber": "0x10b1c9f",
    "from": "0x5888700be02f52c8adf85890886ef84a6b8a7829",
    "blockHash": "0x92c3d77ea218cdc0967ab74b6005bb393b92355047f206c7e2d59d41828e7fa9",
    "chainId": "0x1",
    "gasPrice": "0x34fdbf43d",
    "s": "0x7d86ae29a786a61b9e74a7a9e2cc4b39b7913aa3d4c3816ccb07528fed82048a",
    "to": "0xfc2068c3d47b575a60f6a4a7bf60dea0ac368e01",
    "type": "0x2",
    "v": "0x1",
    "value": "0x0",
    "gas": "0x1aad3",
    "hash": "0x2c77c0704aefbb26db460cbb71efdb488df968ad53d2c2b3f1e1172056b40b22",
    "input": "0x42842e0e0000000000000000000000005888700be02f52c8adf85890886ef84a6b8a7829000000000000000000000000d2d07e4d1bb0f40ac3e4aa7cc3ad05d348bfd2c3000000000000000000000000000000000000000000000000000000000000180b",
    "maxFeePerGas": "0x4712d1273",
    "r": "0x8ec58f95f6d9729a6eee075e6976658b6c5346cbc90eb68ac361a40af073b10e",
    "transactionIndex": "0xc1"
}

Excerpted (partial omission) log data:

run2023-06-18 16:20:07        Info    Disconnect WS connection
2023-06-18 16:20:07        Info    0xba07ca903f9eafbfa7d494bb26197713034b9ca2dd3c19bc0898af3f35b59343 transcationInfo: {"accessList":[],"from":"0xe2977d60182da068dfd78693f96362ee7a2e9644","nonce":"0xf","value":"0x0","blockHash":"0x92c3d77ea218cdc0967ab74b6005bb393b92355047f206c7e2d59d41828e7fa9","blockNumber":"0x10b1c9f","chainId":"0x1","hash":"0xba07ca903f9eafbfa7d494bb26197713034b9ca2dd3c19bc0898af3f35b59343","maxFeePerGas":"0x530c30b70","r":"0xf28bfdf372a5401a2e00675c6ebe8d5e73f2c955db44b1aa56240b9197d6cbc7","type":"0x2","v":"0x0","gas":"0x21079","gasPrice":"0x367b3783d","input":"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","maxPriorityFeePerGas":"0x1dcd6500","s":"0x71d51246bb60e792f963a3c75c46fd8f557921ce6face7224c944e1768a76ca","to":"0x0b51eb9d0e54c562fedc07ceba453f05b70c4b79","transactionIndex":"0x40"}
2023-06-18 16:20:07        Info    0x2c77c0704aefbb26db460cbb71efdb488df968ad53d2c2b3f1e1172056b40b22 transcationInfo: {"maxPriorityFeePerGas":"0x5f5e100","nonce":"0x1a9","accessList":[],"blockNumber":"0x10b1c9f","from":"0x5888700be02f52c8adf85890886ef84a6b8a7829","blockHash":"0x92c3d77ea218cdc0967ab74b6005bb393b92355047f206c7e2d59d41828e7fa9","chainId":"0x1","gasPrice":"0x34fdbf43d","s":"0x7d86ae29a786a61b9e74a7a9e2cc4b39b7913aa3d4c3816ccb07528fed82048a","to":"0xfc2068c3d47b575a60f6a4a7bf60dea0ac368e01","type":"0x2","v":"0x1","value":"0x0","gas":"0x1aad3","hash":"0x2c77c0704aefbb26db460cbb71efdb488df968ad53d2c2b3f1e1172056b40b22","input":"0x42842e0e0000000000000000000000005888700be02f52c8adf85890886ef84a6b8a7829000000000000000000000000d2d07e4d1bb0f40ac3e4aa7cc3ad05d348bfd2c3000000000000000000000000000000000000000000000000000000000000180b","maxFeePerGas":"0x4712d1273","r":"0x8ec58f95f6d9729a6eee075e6976658b6c5346cbc90eb68ac361a40af073b10e","transactionIndex":"0xc1"}
2023-06-18 16:20:07        Info    0xbc42d5db10e5cb2e888c76005c522cb2474a0c0a7325feb867b618f69ff26f2a transcationInfo: {"accessList":[],"blockNumber":"0x10b1c9f","gas":"0x1cc12b","hash":"0xbc42d5db10e5cb2e888c76005c522cb2474a0c0a7325feb867b618f69ff26f2a","maxFeePerGas":"0x6ab262e5c","value":"0x0","v":"0x1","chainId":"0x1","from":"0xc1b634853cb333d3ad8663715b08f41a3aec47cc","input":"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
2023-06-18 16:20:06        Info    0xff0945c3d682a37e18ee433d56c8bedbb93d9ac368af968ed8d53b655575e8e5 transcationInfo: {"gas":"0x5208","s":"0x63572e1fa060841b939cea0849154e55781fe0efcbdfe5ce6979b44ce0980e4a","transactionIndex":"0xa7","value":"0x113e9d515e400","blockHash":"0x92c3d77ea218cdc0967ab74b6005bb393b92355047f206c7e2d59d41828e7fa9","hash":"0xff0945c3d682a37e18ee433d56c8bedbb93d9ac368af968ed8d53b655575e8e5","nonce":"0x2","r":"0x698fe26331ad39ba89c4d30985b707792ea4ab09b25205727f8fac2a6120b54a","gasPrice":"0x35458af00","from":"0x228d93af92d03184c07aa9e39b3d2d61b666686d","input":"0x","to":"0x0246177b98a5e42835cdcfaac1c274d3e6c39486","v":"0x26","blockNumber":"0x10b1c9f","type":"0x0","chainId":"0x1"}
...

Decoding Transaction Details

In the previous course, we wrote a monitoring program to monitor pending transactions on Ethereum, get the pushed transaction hash via WebSocket protocol, and then query the specific transaction details based on the transaction hash.

Next we want to do further parsing of the input field data in the transaction details data. The input field data looks like a jumble of hexadecimal data, but it actually encodes the content of the transaction: including the functions called, and the parameters entered, etc.

After repeated and extensive testing, we found that the timeliness and quantity of data pushed over by the WebSocket connection has a lot to do with the RPC node currently in use, and the pushed data received by two different RPC node services (e.g., infura, ALCHEMY) when creating a WebSocket connection at the same time is not exactly the same, and since the current scenario generates a large number of requests, we still need to use a more stable and faster RPC service. The WebSocket connection also pushes a lot of transaction hashes that have been Pending for a long time, and when using eth_getTransactionByHash to query, you often get a null value (tested on FMZ, node.js).

We use the alchemy RPC node this time: wss://eth-mainnet.g.alchemy.com/v2/oKmOQKbneVkxgHZfibs-iFhIlIAl6HDN. The node supports both WebSocket and REST protocols.

We monitor the multicall(uint256,bytes[]) method of the router smart contract of the Uniswap decentralized exchange, so we need to calculate the function signature hash of the method first.

// Take the first 8 characters of the complete hash
// multicall: 0x5ae401dc
var sigHash = "0x" + Encode("keccak256", "string", "hex", "multicall(uint256,bytes[])").slice(0, 8)

Based on the example in the previous lesson, we have made some modifications. When receiving messages pushed by the WebSocket connection, the latest data is received using var data = ws.read(-2) method, and the read() function parameter is set to -2 to indicate that the latest data is returned immediately. We only care about the Transaction that contains the multicall call, using if (tx && tx.input.indexOf(sigHash) ! == -1) to determine the filter.

2 custom functions need to be designed:

• calcAllFuncSigHash(): Calculate signature hash for all methods based on ABI.

• decodeCall(): Decoding function.

Next, when the multicall call is detected, the decoding operation can start, and the parameters of the multicall method are decoded for the first time: deadline and data. deadline is a timestamp that is better understood, and data is another encoded calldata, so you still need to continue to use the decodeCall() function to decode it.

Example of a complete implementation:

var ws = null 
var arrLog = []

const ABI_Route = '[{"inputs":[{"internalType":"address","name":"_factoryV2","type":"address"},{"internalType":"address","name":"factoryV3","type":"address"},{"internalType":"address","name":"_positionManager","type":"address"},{"internalType":"address","name":"_WETH9","type":"address"}],"stateMutability":"nonpayable","type":"constructor"},{"inputs":[],"name":"WETH9","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"}],"name":"approveMax","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"}],"name":"approveMaxMinusOne","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"}],"name":"approveZeroThenMax","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"}],"name":"approveZeroThenMaxMinusOne","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"bytes","name":"data","type":"bytes"}],"name":"callPositionManager","outputs":[{"internalType":"bytes","name":"result","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"bytes[]","name":"paths","type":"bytes[]"},{"internalType":"uint128[]","name":"amounts","type":"uint128[]"},{"internalType":"uint24","name":"maximumTickDivergence","type":"uint24"},{"internalType":"uint32","name":"secondsAgo","type":"uint32"}],"name":"checkOracleSlippage","outputs":[],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes","name":"path","type":"bytes"},{"internalType":"uint24","name":"maximumTickDivergence","type":"uint24"},{"internalType":"uint32","name":"secondsAgo","type":"uint32"}],"name":"checkOracleSlippage","outputs":[],"stateMutability":"view","type":"function"},{"inputs":[{"components":[{"internalType":"bytes","name":"path","type":"bytes"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMinimum","type":"uint256"}],"internalType":"struct IV3SwapRouter.ExactInputParams","name":"params","type":"tuple"}],"name":"exactInput","outputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"}],"stateMutability":"payable","type":"function"},{"inputs":[{"components":[{"internalType":"address","name":"tokenIn","type":"address"},{"internalType":"address","name":"tokenOut","type":"address"},{"internalType":"uint24","name":"fee","type":"uint24"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMinimum","type":"uint256"},{"internalType":"uint160","name":"sqrtPriceLimitX96","type":"uint160"}],"internalType":"struct IV3SwapRouter.ExactInputSingleParams","name":"params","type":"tuple"}],"name":"exactInputSingle","outputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"}],"stateMutability":"payable","type":"function"},{"inputs":[{"components":[{"internalType":"bytes","name":"path","type":"bytes"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"uint256","name":"amountInMaximum","type":"uint256"}],"internalType":"struct IV3SwapRouter.ExactOutputParams","name":"params","type":"tuple"}],"name":"exactOutput","outputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"}],"stateMutability":"payable","type":"function"},{"inputs":[{"components":[{"internalType":"address","name":"tokenIn","type":"address"},{"internalType":"address","name":"tokenOut","type":"address"},{"internalType":"uint24","name":"fee","type":"uint24"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"uint256","name":"amountInMaximum","type":"uint256"},{"internalType":"uint160","name":"sqrtPriceLimitX96","type":"uint160"}],"internalType":"struct IV3SwapRouter.ExactOutputSingleParams","name":"params","type":"tuple"}],"name":"exactOutputSingle","outputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"}],"stateMutability":"payable","type":"function"},{"inputs":[],"name":"factory","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"factoryV2","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"getApprovalType","outputs":[{"internalType":"enum IApproveAndCall.ApprovalType","name":"","type":"uint8"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"components":[{"internalType":"address","name":"token0","type":"address"},{"internalType":"address","name":"token1","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"},{"internalType":"uint256","name":"amount0Min","type":"uint256"},{"internalType":"uint256","name":"amount1Min","type":"uint256"}],"internalType":"struct IApproveAndCall.IncreaseLiquidityParams","name":"params","type":"tuple"}],"name":"increaseLiquidity","outputs":[{"internalType":"bytes","name":"result","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"components":[{"internalType":"address","name":"token0","type":"address"},{"internalType":"address","name":"token1","type":"address"},{"internalType":"uint24","name":"fee","type":"uint24"},{"internalType":"int24","name":"tickLower","type":"int24"},{"internalType":"int24","name":"tickUpper","type":"int24"},{"internalType":"uint256","name":"amount0Min","type":"uint256"},{"internalType":"uint256","name":"amount1Min","type":"uint256"},{"internalType":"address","name":"recipient","type":"address"}],"internalType":"struct IApproveAndCall.MintParams","name":"params","type":"tuple"}],"name":"mint","outputs":[{"internalType":"bytes","name":"result","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"bytes32","name":"previousBlockhash","type":"bytes32"},{"internalType":"bytes[]","name":"data","type":"bytes[]"}],"name":"multicall","outputs":[{"internalType":"bytes[]","name":"","type":"bytes[]"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"deadline","type":"uint256"},{"internalType":"bytes[]","name":"data","type":"bytes[]"}],"name":"multicall","outputs":[{"internalType":"bytes[]","name":"","type":"bytes[]"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"bytes[]","name":"data","type":"bytes[]"}],"name":"multicall","outputs":[{"internalType":"bytes[]","name":"results","type":"bytes[]"}],"stateMutability":"payable","type":"function"},{"inputs":[],"name":"positionManager","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"value","type":"uint256"}],"name":"pull","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[],"name":"refundETH","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"value","type":"uint256"},{"internalType":"uint256","name":"deadline","type":"uint256"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"selfPermit","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"nonce","type":"uint256"},{"internalType":"uint256","name":"expiry","type":"uint256"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"selfPermitAllowed","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"nonce","type":"uint256"},{"internalType":"uint256","name":"expiry","type":"uint256"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"selfPermitAllowedIfNecessary","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"value","type":"uint256"},{"internalType":"uint256","name":"deadline","type":"uint256"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"selfPermitIfNecessary","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"}],"name":"swapExactTokensForTokens","outputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"uint256","name":"amountInMax","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"}],"name":"swapTokensForExactTokens","outputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"amountMinimum","type":"uint256"},{"internalType":"address","name":"recipient","type":"address"}],"name":"sweepToken","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"amountMinimum","type":"uint256"}],"name":"sweepToken","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"amountMinimum","type":"uint256"},{"internalType":"uint256","name":"feeBips","type":"uint256"},{"internalType":"address","name":"feeRecipient","type":"address"}],"name":"sweepTokenWithFee","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"amountMinimum","type":"uint256"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"feeBips","type":"uint256"},{"internalType":"address","name":"feeRecipient","type":"address"}],"name":"sweepTokenWithFee","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"int256","name":"amount0Delta","type":"int256"},{"internalType":"int256","name":"amount1Delta","type":"int256"},{"internalType":"bytes","name":"_data","type":"bytes"}],"name":"uniswapV3SwapCallback","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountMinimum","type":"uint256"},{"internalType":"address","name":"recipient","type":"address"}],"name":"unwrapWETH9","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountMinimum","type":"uint256"}],"name":"unwrapWETH9","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountMinimum","type":"uint256"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"feeBips","type":"uint256"},{"internalType":"address","name":"feeRecipient","type":"address"}],"name":"unwrapWETH9WithFee","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountMinimum","type":"uint256"},{"internalType":"uint256","name":"feeBips","type":"uint256"},{"internalType":"address","name":"feeRecipient","type":"address"}],"name":"unwrapWETH9WithFee","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"value","type":"uint256"}],"name":"wrapETH","outputs":[],"stateMutability":"payable","type":"function"},{"stateMutability":"payable","type":"receive"}]'

function calcAllFuncSigHash(jsonABI) {
    var mapSigHash = {}
    for (var i in jsonABI) {
        var ele = jsonABI[i]
        if (typeof(ele["name"]) != "undefined") {
            if (ele["inputs"]) {
                var funcName = ele["name"]
                if (ele["inputs"].length == 0) {
                    var methodId = "0x" + Encode("keccak256", "string", "hex", funcName + "()").slice(0, 8)
                    mapSigHash[methodId] = {"argsTypeList": [], "argsNameList": [], "funcName": funcName}
                } else {
                    var arr = []
                    var arrName = []
                    var argPrototype = []
                    for (var j in ele["inputs"]) {
                        var inputType = ele["inputs"][j]["type"]
                        if (inputType == "tuple") {                            
                            var components = ele["inputs"][j]["components"]
                            var tupleType = []
                            var protoType = []
                            for (var componentsIdx = 0; componentsIdx < components.length; componentsIdx++) {
                                tupleType.push(components[componentsIdx]["type"])
                                protoType.push(components[componentsIdx]["name"] + " " + components[componentsIdx]["type"])
                            }
                            arr.push("(" + tupleType.join() + ")")
                            arrName.push(ele["inputs"][j]["name"])
                            // Prototype
                            argPrototype.push("tuple" + "(" + protoType.join() + ")")
                        } else {
                            arr.push(inputType)
                            arrName.push(ele["inputs"][j]["name"])
                            // Prototype
                            argPrototype.push(inputType)
                        }                        
                    }
                    var functionSignature = funcName + "(" + arr.join() + ")"
                    var methodId = "0x" + Encode("keccak256", "string", "hex", functionSignature).slice(0, 8)
                    mapSigHash[methodId] = {"argsTypeList": arr, "argsNameList": arrName, "funcName": funcName, "argPrototype": argPrototype}
                }
            }
        }
    }
    return mapSigHash
}

function decodeCall(input, abi) {
    var mapSigHash = calcAllFuncSigHash(JSON.parse(abi))
    var methodId = input.slice(0, 10)
    var data = input.slice(10)

    var decodedArgs = {}
    var infoMethod = mapSigHash[methodId]
    if (typeof(infoMethod) == "undefined") {
        return [methodId, mapSigHash]
    }

    var arr = []
    for (var i = 0; i < infoMethod["argsTypeList"].length; i++) {
        if (infoMethod["argsTypeList"][i].startsWith("(")) {
            arr.push(infoMethod["argPrototype"][i])
        } else {
            arr.push(infoMethod["argsTypeList"][i])
        }
    }

    if (arr.length == 0) {
        return {"funcName": infoMethod["funcName"], "args": decodedArgs}
    }

    var args = exchange.IO("decode", arr.join(), data)

    if (!Array.isArray(args)) {
        args = [args]
    }

    if (args.length != infoMethod["argsNameList"].length) {
        Log("args:", args)
        Log("infoMethod:", infoMethod)
        throw "The decoded args are not equal to the argsNameList"
    }

    for (var i = 0; i < infoMethod["argsNameList"].length; i++) {
        var key = infoMethod["argsNameList"][i]
        var value = args[i]
        decodedArgs[key] = value
    }

    return {"funcName": infoMethod["funcName"], "args": decodedArgs}
}

function main () {
    // {"jsonrpc": "2.0", "id": 1, "method": "eth_subscribe", "params": ["xxxxx"]}  , "xxxxx" is the specific message of the subscription
    var payload = {"jsonrpc": "2.0", "id": 1, "method": "eth_subscribe", "params": ["newPendingTransactions"]}

    // Use the alchemy service
    ws = Dial("wss://eth-mainnet.g.alchemy.com/v2/oKmOQKbneVkxgHZfibs-iFhIlIAl6HDN" + "|reconnect=true&payload=" + JSON.stringify(payload))
    if (!ws) {
        throw "websocket link to alchemy failed!"
    }

    // eth_getTransactionByHash call count
    var getTransactionCounter = 0

    // Start Timestamp
    var beginTS = new Date().getTime()

    // Calculate function signature hash
    var sigHash = "0x" + Encode("keccak256", "string", "hex", "multicall(uint256,bytes[])").slice(0, 8)
    Log("sigHash:", sigHash)

    // Loop for messages
    while (true) {
        var msg = ""
        var recv = null
        // Receive pushed messages, use the read parameter -2, and return the latest data immediately
        var data = ws.read(-2)
        if (data && data != "") {
            var ts = new Date().getTime()

            if (ts - beginTS >= 1000) {
                getTransactionCounter = 0
                beginTS = ts 
            }

            // Check transaction details based on txHash
            if (ts - beginTS < 1000 && getTransactionCounter >= 100) {
                Sleep(1000)
                getTransactionCounter = 0
                beginTS = ts 
            }

            var obj = JSON.parse(data)
            if (obj["params"] && obj["params"]["result"]) {
                var txHash = obj["params"]["result"]
                var tx = exchange.IO("api", "eth", "eth_getTransactionByHash", txHash)

                if (tx && tx.input.indexOf(sigHash) !== -1) {
                    // Decode transaction details
                    arrLog = []
                    var decodedInput = decodeCall(tx.input, ABI_Route)

                    // Log("----------------", txHash, "/", decodedInput["funcName"], "----------------", "#FF0000")
                    arrLog.push("----------------" + txHash + "/" + decodedInput["funcName"] + "----------------" + "#FF0000")
                    arrLog.push(tx.from + " -> " + tx.to)

                    for (var i = 0; i < decodedInput["args"]["data"].length; i++) {
                        var calldata = "0x" + decodedInput["args"]["data"][i]
                        var decodedCalldata = decodeCall(calldata, ABI_Route)

                        // Log("----------------", decodedCalldata["funcName"], "----------------", "#FF0000")
                        arrLog.push("----------------" + decodedCalldata["funcName"] + "----------------" + "#FF0000")

                        for (var key in decodedCalldata["args"]) {
                            // Log(key, decodedCalldata["args"][key])
                            arrLog.push(key + ": " + JSON.stringify(decodedCalldata["args"][key]))
                        }
                    }

                    // Output logs
                    for (var logIdx = arrLog.length - 1; logIdx >= 0; logIdx--) {
                        Log(arrLog[logIdx])
                    }
                }

                getTransactionCounter++
            }
            recv = obj
        } else if (data == null) {
            msg = "The buffer queue is empty, time:" + _D()
        }

        LogStatus(_D(), ", msg:", msg, ", recv:", recv)
    }
}

function onexit() {
    Log("Disconnect WS connection")
    ws.close()
}

function onerror() {
    Log("Disconnect WS connection")
    ws.close()

    for (var logIdx = arrLog.length - 1; logIdx >= 0; logIdx--) {        
        Log(arrLog[logIdx])
    }
}

Create a live trading to test:

run2023-06-20 17:01:00        Info    ----------------0x5288a7bd6e0f57162ca763df722de73793e542734d7d2b7af5755664e2e67910/multicall----------------
2023-06-20 17:01:00        Info    0x851b594033d57c98af753bcb3a7d0237a615de32 -> 0x68b3465833fb72a70ecdf485e0e4c7bd8665fc45
2023-06-20 17:01:00        Info    ----------------exactInputSingle----------------
2023-06-20 17:01:00        Info    params: {"tokenOut":"0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2","fee":"10000","recipient":"0x0000000000000000000000000000000000000002","amountIn":"8952087000296027130940868","amountOutMinimum":"41638694112306829","sqrtPriceLimitX96":"0","tokenIn":"0xe1283567345349942acdfad3692924a1b16cf3cc"}
2023-06-20 17:01:00        Info    ----------------unwrapWETH9----------------
2023-06-20 17:01:00        Info    amountMinimum: "41638694112306829"
2023-06-20 17:01:00        Info    recipient: "0x851b594033d57c98af753bcb3a7d0237a615de32"
2023-06-20 16:59:03        Info    ----------------0x55e0c4a38a17d3aa6e8f558a66c77e9defa9f8f6e347536363ac1b921de9aaf3/multicall----------------
2023-06-20 16:59:03        Info    0x27457ada2dd725c7d0f28e1737bdd0bf583c0f0b -> 0x68b3465833fb72a70ecdf485e0e4c7bd8665fc45
2023-06-20 16:59:03        Info    ----------------swapExactTokensForTokens----------------
2023-06-20 16:59:03        Info    amountIn: "816769666850161"
2023-06-20 16:59:03        Info    amountOutMin: "40404501509302321"
2023-06-20 16:59:03        Info    path: ["0x7863e06bca47ded821fcb53ab788eeb371243eda","0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"]
2023-06-20 16:59:03        Info    to: "0x27457ada2dd725c7d0f28e1737bdd0bf583c0f0b"
2023-06-20 16:58:25        Info    sigHash: 0x5ae401dc

Screenshot:

You can see that the Transaction Hash is 0x5288a7bd6e0f57162ca763df722de73793e542734d7d2b7af5755664e2e67910 for this transaction, and the input data data contains the call to a multicall method call. This transaction is sent in the direction: 0x851b594033d57c98af753bcb3a7d0237a615de32 -> 0x68b3465833fb72a70ecdf485e0e4c7bd8665fc45. 0x68b3465833fb72a70ecdf485e0e4c7bd8665fc45 is Uniswap's router contract address.

The multicall package is parsed to call the contract's exactInputSingle and unwrapWETH9 methods and the specific parameters of these methods.

----------------exactInputSingle----------------
params: {
    "tokenOut":"0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
    "fee":"10000",
    "recipient":"0x0000000000000000000000000000000000000002",
    "amountIn":"8952087000296027130940868",
    "amountOutMinimum":"41638694112306829",
    "sqrtPriceLimitX96":"0",
    "tokenIn":"0xe1283567345349942acdfad3692924a1b16cf3cc"
}

----------------unwrapWETH9----------------
amountMinimum: "41638694112306829"
recipient: "0x851b594033d57c98af753bcb3a7d0237a615de32"

If you are interested, you can modify and extend the example based on it to monitor more transactions and parse these on-chain operations.

From: https://blog.mathquant.com/2023/06/30/get-started-with-web3-development-easily-based-on-ethereum-using-fmz.html