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package raft
import (
var commandTypes map[string]Command
func init() {
commandTypes = map[string]Command{}
// Command represents an action to be taken on the replicated state machine.
type Command interface {
CommandName() string
// CommandApply represents the interface to apply a command to the server.
type CommandApply interface {
Apply(Context) (interface{}, error)
// deprecatedCommandApply represents the old interface to apply a command to the server.
type deprecatedCommandApply interface {
Apply(Server) (interface{}, error)
type CommandEncoder interface {
Encode(w io.Writer) error
Decode(r io.Reader) error
// Creates a new instance of a command by name.
func newCommand(name string, data []byte) (Command, error) {
// Find the registered command.
command := commandTypes[name]
if command == nil {
return nil, fmt.Errorf("raft.Command: Unregistered command type: %s", name)
// Make a copy of the command.
v := reflect.New(reflect.Indirect(reflect.ValueOf(command)).Type()).Interface()
copy, ok := v.(Command)
if !ok {
panic(fmt.Sprintf("raft: Unable to copy command: %s (%v)", command.CommandName(), reflect.ValueOf(v).Kind().String()))
// If data for the command was passed in the decode it.
if data != nil {
if encoder, ok := copy.(CommandEncoder); ok {
if err := encoder.Decode(bytes.NewReader(data)); err != nil {
return nil, err
} else {
return copy, nil
// Registers a command by storing a reference to an instance of it.
func RegisterCommand(command Command) {
if command == nil {
panic(fmt.Sprintf("raft: Cannot register nil"))
} else if commandTypes[command.CommandName()] != nil {
panic(fmt.Sprintf("raft: Duplicate registration: %s", command.CommandName()))
commandTypes[command.CommandName()] = command
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