- Add sha prefix for peer id in protocol

- Add magic cookie in hello msg
- Add tests

relay/messages/id.go

@@ -3,18 +3,25 @@ package messages
 import (
 	"crypto/sha256"
 	"encoding/base64"
+	"fmt"
 )
 
 const (
-	IDSize = sha256.Size
+	prefixLength = 4
+	IDSize       = sha256.Size + 4 // 4 is equal with len(prefix)
+)
+
+var (
+	prefix = []byte("sha-") // 4 bytes
 )
 
 func HashID(peerID string) ([]byte, string) {
 	idHash := sha256.Sum256([]byte(peerID))
-	idHashString := base64.StdEncoding.EncodeToString(idHash[:])
-	return idHash[:], idHashString
+	idHashString := string(prefix) + base64.StdEncoding.EncodeToString(idHash[:])
+	prefixedHash := append(prefix, idHash[:]...)
+	return prefixedHash, idHashString
 }
 
 func HashIDToString(idHash []byte) string {
-	return base64.StdEncoding.EncodeToString(idHash)
+	return fmt.Sprintf("%s%s", idHash[:prefixLength], base64.StdEncoding.EncodeToString(idHash[prefixLength:]))
 }