Add ability to run using chain json file

internal/cli/server/chains/chain.go

@@ -1,6 +1,9 @@
 package chains
 
 import (
+	"encoding/json"
+	"io/ioutil"
+
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 )
@@ -19,6 +22,29 @@ var chains = map[string]*Chain{
 }
 
 func GetChain(name string) (*Chain, bool) {
-	chain, ok := chains[name]
-	return chain, ok
+	chain, err := ImportFromFile(name)
+	if err != nil {
+		chain, ok := chains[name]
+		return chain, ok
+	}
+	return chain, true
+}
+
+func ImportFromFile(filename string) (*Chain, error) {
+	data, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+
+	return importChain(data)
+}
+
+func importChain(content []byte) (*Chain, error) {
+	var chain *Chain
+
+	if err := json.Unmarshal(content, &chain); err != nil {
+		return nil, err
+	}
+
+	return chain, nil
 }