cmd/geth, rpc/api: extend metrics API, add a basic monitor command

rpc/api/debug_args.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"math/big"
+	"reflect"
 
 	"github.com/ethereum/go-ethereum/rpc/shared"
 )
@@ -45,3 +46,26 @@ func (args *WaitForBlockArgs) UnmarshalJSON(b []byte) (err error) {
 
 	return nil
 }
+
+type MetricsArgs struct {
+	Raw bool
+}
+
+func (args *MetricsArgs) UnmarshalJSON(b []byte) (err error) {
+	var obj []interface{}
+	if err := json.Unmarshal(b, &obj); err != nil {
+		return shared.NewDecodeParamError(err.Error())
+	}
+	if len(obj) > 1 {
+		return fmt.Errorf("metricsArgs needs 0, 1 arguments")
+	}
+	// default values when not provided
+	if len(obj) >= 1 && obj[0] != nil {
+		if value, ok := obj[0].(bool); !ok {
+			return fmt.Errorf("invalid argument %v", reflect.TypeOf(obj[0]))
+		} else {
+			args.Raw = value
+		}
+	}
+	return nil
+}