core: added basic chain configuration

Added chain configuration options and write out during genesis database
insertion. If no "config" was found, nothing is written to the database.

Configurations are written on a per genesis base. This means
that any chain (which is identified by it's genesis hash) can have their
own chain settings.

core/database_util.go

@@ -19,6 +19,7 @@ package core
 import (
 	"bytes"
 	"encoding/binary"
+	"encoding/json"
 	"fmt"
 	"math/big"
 
@@ -50,6 +51,8 @@ var (
 	MIPMapLevels = []uint64{1000000, 500000, 100000, 50000, 1000}
 
 	blockHashPrefix = []byte("block-hash-") // [deprecated by the header/block split, remove eventually]
+
+	configPrefix = []byte("ethereum-config-") // config prefix for the db
 )
 
 // GetCanonicalHash retrieves a hash assigned to a canonical block number.
@@ -527,3 +530,34 @@ func WriteBlockChainVersion(db ethdb.Database, vsn int) {
 	enc, _ := rlp.EncodeToBytes(uint(vsn))
 	db.Put([]byte("BlockchainVersion"), enc)
 }
+
+// WriteChainConfig writes the chain config settings to the database.
+func WriteChainConfig(db ethdb.Database, hash common.Hash, cfg *ChainConfig) error {
+	// short circuit and ignore if nil config. GetChainConfig
+	// will return a default.
+	if cfg == nil {
+		return nil
+	}
+
+	jsonChainConfig, err := json.Marshal(cfg)
+	if err != nil {
+		return err
+	}
+
+	return db.Put(append(configPrefix, hash[:]...), jsonChainConfig)
+}
+
+// GetChainConfig will fetch the network settings based on the given hash.
+func GetChainConfig(db ethdb.Database, hash common.Hash) (*ChainConfig, error) {
+	jsonChainConfig, _ := db.Get(append(configPrefix, hash[:]...))
+	if len(jsonChainConfig) == 0 {
+		return nil, ChainConfigNotFoundErr
+	}
+
+	var config ChainConfig
+	if err := json.Unmarshal(jsonChainConfig, &config); err != nil {
+		return nil, err
+	}
+
+	return &config, nil
+}