cmd/geth: make dumpgenesis load genesis datadir if it exists (#25135)

`geth dumpgenesis` currently does not respect the content of the data directory. Instead, it outputs the genesis block created by command-line flags. This PR fixes it to read the genesis from the database, if the database already exists.


Co-authored-by: Martin Holst Swende <martin@swende.se>

core/genesis.go

@@ -65,6 +65,41 @@ type Genesis struct {
 	BaseFee    *big.Int    `json:"baseFeePerGas"`
 }
 
+func ReadGenesis(db ethdb.Database) (*Genesis, error) {
+	var genesis Genesis
+	stored := rawdb.ReadCanonicalHash(db, 0)
+	if (stored == common.Hash{}) {
+		return nil, fmt.Errorf("invalid genesis hash in database: %x", stored)
+	}
+	blob := rawdb.ReadGenesisStateSpec(db, stored)
+	if blob == nil {
+		return nil, fmt.Errorf("genesis state missing from db")
+	}
+	if len(blob) != 0 {
+		if err := genesis.Alloc.UnmarshalJSON(blob); err != nil {
+			return nil, fmt.Errorf("could not unmarshal genesis state json: %s", err)
+		}
+	}
+	genesis.Config = rawdb.ReadChainConfig(db, stored)
+	if genesis.Config == nil {
+		return nil, fmt.Errorf("genesis config missing from db")
+	}
+	genesisBlock := rawdb.ReadBlock(db, stored, 0)
+	if genesisBlock == nil {
+		return nil, fmt.Errorf("genesis block missing from db")
+	}
+	genesisHeader := genesisBlock.Header()
+	genesis.Nonce = genesisHeader.Nonce.Uint64()
+	genesis.Timestamp = genesisHeader.Time
+	genesis.ExtraData = genesisHeader.Extra
+	genesis.GasLimit = genesisHeader.GasLimit
+	genesis.Difficulty = genesisHeader.Difficulty
+	genesis.Mixhash = genesisHeader.MixDigest
+	genesis.Coinbase = genesisHeader.Coinbase
+
+	return &genesis, nil
+}
+
 // GenesisAlloc specifies the initial state that is part of the genesis block.
 type GenesisAlloc map[common.Address]GenesisAccount