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follower.go
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follower.go
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package dht
import (
"errors"
"io"
"log"
"net"
"github.com/golang/protobuf/proto"
)
// Follower is an implementation dht.Role that is dependent upon a Leader.
type Follower struct {
*Node
}
// NewFollower initializes a new Follower.
func NewFollower(node *Node) (follower *Follower, err error) {
if node == nil {
return nil, errors.New("Node may not be nil.")
}
return &Follower{
Node: node,
}, nil
}
// Register registers a Follower with a Leader under the address leaderHost.
func (follower *Follower) Register(leaderHost string) (err error) {
log.Printf("Registring with Leader...\n")
conn, err := net.Dial("tcp", leaderHost)
if err != nil {
return err
}
message := &Message{
Action: Message_REGISTER.Enum(),
Id: follower.id[:],
Host: proto.String(follower.host),
}
data, err := proto.Marshal(message)
if err != nil {
return err
}
if _, err := conn.Write(data); err != nil {
return err
}
return nil
}
// Handle handles all message types a Follower must respond to.
func (follower *Follower) Handle(m *Message, w io.Writer) (err error) {
switch m.GetAction() {
case Message_GET:
log.Printf("[EVENT]Follower handling GET.\n")
err = follower.OnGet(m, w)
case Message_SET:
log.Printf("[EVENT]Follower handling SET.\n")
err = follower.OnSet(m, w)
case Message_DELETE:
log.Printf("[EVENT]Follower handling DELETE.\n")
err = follower.OnDelete(m, w)
case Message_NOOP:
log.Printf("[EVENT]Follower handling NOOP.\n")
err = follower.OnNoop(m, w)
default:
log.Printf("[EVENT]Follower handling fell through.\n")
err = errors.New("Unrecognized action in message.")
}
return err
}
// OnGet is called when a message with type Message_GET is received.
func (follower *Follower) OnGet(m *Message, w io.Writer) (err error) {
follower.mutex.Lock()
value, ok := follower.table[m.GetKey()]
follower.mutex.Unlock()
message := Message{
Action: Message_GET.Enum(),
Value: &value,
Success: &ok,
}
data, err := proto.Marshal(&message)
if err != nil {
return err
}
if _, err := w.Write(data); err != nil {
return err
}
return nil
}
// OnSet is called when a message with type Message_SET is received.
func (follower *Follower) OnSet(m *Message, w io.Writer) (err error) {
follower.mutex.Lock()
follower.table[m.GetKey()] = m.GetValue()
follower.mutex.Unlock()
log.Printf("Table after Set: %v\n", follower.table)
return nil
}
// OnDelete is called when a message with type Message_DELETE is received.
func (follower *Follower) OnDelete(m *Message, w io.Writer) (err error) {
follower.mutex.Lock()
delete(follower.table, m.GetKey())
follower.mutex.Unlock()
log.Printf("Table after Delete: %v\n", follower.table)
return nil
}
// OnNoop is called when a message with type Message_NOOP is received.
func (follower *Follower) OnNoop(m *Message, w io.Writer) error {
return nil
}