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Step Estimation

In your transaction request, you must specify the stepLimit, the maximum amount of steps you are willing to pay for the transaction. stepLimit must be greater than the actual steps required and less than the maximum value, 0x9502f900.
In this document, we will explain how you choose the right stepLimit for your transaction.

Pre-reading

Transaction Fee

Transaction fee is calculated as usedStep * stepPrice, where stepPrice is the ICX exchange rate, and usedStep is the sum of stepCost for each action processed in the transaction.

  • If usedStep reaches the stepLimit before finishing the execution, the transaction will fail with out of step error, but the amount of stepLimit is deducted from your balance.
  • Before executing your transaction, your account must hold at least stepLimit * stepPrice amount of ICX. If you do not have sufficient ICX, your transaction will fail immediately.
  • Therefore, it is important to set appropriate stepLimit, neither too large nor too small, to guarantee the successful execution of the transaction without wasting your ICX.

You can query the stepCost of each action, the maximum possible stepLimit value you can set, and the stepPrice to the Governance SCORE.

$ cat stepcost.json 
{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "icx_call",
    "params": {
        "to": "cx0000000000000000000000000000000000000001",
        "dataType": "call",
        "data": {
            "method": "getStepCosts"
        }
    }
}

$ curl -H "Content-Type: application/json" -d @stepcost.json https://bicon.net.solidwallet.io/api/v3 
{
    "jsonrpc": "2.0",
    "result": {
        "default": "0x186a0",
        "contractCall": "0x61a8",
        "contractCreate": "0x3b9aca00",
        "contractUpdate": "0x5f5e1000",
        "contractDestruct": "-0x11170",
        "contractSet": "0x7530",
        "get": "0x0",
        "set": "0x140",
        "replace": "0x50",
        "delete": "-0xf0",
        "input": "0xc8",
        "eventLog": "0x64",
        "apiCall": "0x0"
    },
    "id": 1
}
$ cat maxsteplimit.json 
{
    "jsonrpc": "2.0",
    "id": 2,
    "method": "icx_call",
    "params": {
        "to": "cx0000000000000000000000000000000000000001",
        "dataType": "call",
        "data": {
            "method": "getMaxStepLimit",
            "params": {
                "contextType": "invoke"
            }
        }
    }
}

$ curl -H "Content-Type: application/json" -d @maxsteplimit.json https://bicon.net.solidwallet.io/api/v3 
{
    "jsonrpc": "2.0",
    "result": "0x9502f900",
    "id": 2
}
$ cat stepprice.json 
{
    "jsonrpc": "2.0",
    "id": 3,
    "method": "icx_call",
    "params": {
        "to": "cx0000000000000000000000000000000000000001",
        "dataType": "call",
        "data": {
            "method": "getStepPrice"
            }
        }
    }
}

$ curl -H "Content-Type: application/json" -d @stepprice.json https://bicon.net.solidwallet.io/api/v3 
{
    "jsonrpc": "2.0",
    "result": "0x2540be400",
    "id": 3
}

Step Estimation using the JSON RPC API

debug_estimateStep API will estimate the required steps of the given transaction. You can create the transaction data without stepLimit and signature, and pass it to the API endpoint <scheme>://<host>/api/debug/v3. The transaction is not added to the blockchain but simply returns the estimated steps. Sample request messages will look like the bellows.

// transaction request - send ICX
{
    "jsonrpc": "2.0",
    "method": "icx_sendTransaction",
    "id": 1234,
    "params": {
        "version": "0x3",
        "from": "hxbe258ceb872e08851f1f59694dac2558708ece11",
        "to": "hx5bfdb090f43a808005ffc27c25b213145e80b7cd",
        "value": "0xde0b6b3a7640000",
        "timestamp": "0x563a6cf330136",
        "nid": "0x3",
        "nonce": "0x1",
        "stepLimit": "0x30d40",
        "signature": "rBaH0U6y85y1CWp/JbalUbzLVGjtGYG+hut/G5o30vBxhWoxPYtSYBQu6X0Tak1SdcnlZSCJL7DeOeKmI4y+5wE="
    }
}

// debug.json for step estimation request - send ICX
{
    "jsonrpc": "2.0",
    "method": "debug_estimateStep",
    "id": 1234,
    "params": {
        "version": "0x3",
        "from": "hxbe258ceb872e08851f1f59694dac2558708ece11",
        "to": "hx5bfdb090f43a808005ffc27c25b213145e80b7cd",
        "value": "0xde0b6b3a7640000",
        "timestamp": "0x563a6cf330136",
        "nid": "0x3",
        "nonce": "0x1"
    }
}

Request debug_estimateStep using curl from CLI

$ curl -H "Content-Type: application/json" -d @debug.json https://bicon.net.solidwallet.io/api/debug/v3
{"jsonrpc": "2.0", "result": "0x186a0", "id": 1234}

Reference