How to get the "birth block" of a contract?

Question

How does one query the "birth block" of a contract using web3?

Answer 1

One possibility would be, taht the smart contract saves the block number / txid upon the call of the constructor

Otherwise, as stated here How to find contract creation block time with web3?, you will need to search for the creating transaction

Answer 2

Use binary search to scan the blockchain, here is the complete code in Golang

package main
import (
    "context"
    "log"
    "math/big"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/ethclient"

)
type ContractFinder struct {
    client      *ethclient.Client
    latestBlock int64
}
func NewContractFinder(provider string) (*ContractFinder, error) {
    conn, err := ethclient.Dial(provider)
    if err != nil {
        return nil, err
    }
    latestBlock, err := conn.BlockByNumber(context.Background(), nil)
    if err != nil {
        return nil, err
    }
return &ContractFinder{
    client:      conn,
    latestBlock: latestBlock.Number().Int64(),
}, nil

}
func (c *ContractFinder) codeLen(contractAddr string, blockNumber int64) int {
    ctx := context.Background()
    data, err := c.client.CodeAt(ctx, common.HexToAddress(contractAddr), big.NewInt(blockNumber))
    if err != nil {
        log.Fatal("Whoops something went wrong!", err)
    }
    return len(data)
}
func (c *ContractFinder) GetContractCreationBlock(contractAddr string) int64 {
    return c.getCreationBlock(contractAddr, 0, c.latestBlock)
}
// use binary search to find the block number where the contract was created
func (c *ContractFinder) getCreationBlock(contractAddr string, startBlock int64, endBlock int64) int64 {
    if startBlock == endBlock {
        return startBlock
    }
    // fmt.Println("contractAddr", contractAddr, "startBlock", startBlock, "endBlock", endBlock)
    midBlock := (startBlock + endBlock) / 2
    codeLen := c.codeLen(contractAddr, midBlock)
    if codeLen > 2 {
        return c.getCreationBlock(contractAddr, startBlock, midBlock)
    } else {
        return c.getCreationBlock(contractAddr, midBlock+1, endBlock)
    }
}
func main() {
    cttFinder, err := NewContractFinder("https://mainnet.infura.io/v3/[YOURKEY]")
    if err != nil {
        log.Fatal("Whoops something went wrong!", err)
    }
contracts := []string{
    "0x3a4f40631a4f906c2bad353ed06de7a5d3fcb430",
    "0xa4991609c508b6d4fb7156426db0bd49fe298bd8",
}

for _, contract := range contracts {
    creationBlock := cttFinder.GetContractCreationBlock(contract)
    log.Println(contract, creationBlock)
}


}

Remember to replace your provider URL before running.

Here is the complete post about the algorithm