How to use the go API provided by geth to call smart contracts?

Question

    msg := ethereum.CallMsg{
        To:        &contractAddr,
        Gas:       uint64(21000),
        GasTipCap: tipCap,
        GasFeeCap: feeCap,
        Data:
    }
    client.CallContract(context.Background(), msg, nil)

I want to use this API to call smart contracts, but I don't know what to fill in the "Data" field. Can someone provide an example for my reference? Thans very much!

Answer 1

Here ethereum.CallMsg is struct this

type CallMsg struct {
    From      common.Address  // the sender of the 'transaction'
    To        *common.Address // the destination contract (nil for contract creation)
    Gas       uint64          // if 0, the call executes with near-infinite gas
    GasPrice  *big.Int        // wei <-> gas exchange ratio
    GasFeeCap *big.Int        // EIP-1559 fee cap per gas.
    GasTipCap *big.Int        // EIP-1559 tip per gas.
    Value     *big.Int        // amount of wei sent along with the call
    Data      []byte          // input data, usually an ABI-encoded contract method invocation

    AccessList types.AccessList // EIP-2930 access list.
}

and here Data have a type of []byte

but I don't know what to fill in the "Data" field

in the Data field, you need to provide ABI-encoded contract method invocation

To create ABI-encoded contract method you need to import "github.com/ethereum/go-ethereum/accounts/abi" and use abi.Pack method

for your reference, you can look at test cases abi_test.go