device: cache peer string

I am not sure why it must be fast but there were previous efforts
25ad08a and 9087e44
to speed it up; and I even did my own WireGuard#60.

If that is so important lets cache peer string to make it fast and readable again.

Signed-off-by: Alexander Yastrebov <[email protected]>

Author: AlexanderYastrebov

device/peer.go

@@ -7,6 +7,7 @@ package device
 
 import (
 	"container/list"
+	"encoding/base64"
 	"errors"
 	"sync"
 	"sync/atomic"
@@ -24,6 +25,7 @@ type Peer struct {
 	txBytes           atomic.Uint64  // bytes send to peer (endpoint)
 	rxBytes           atomic.Uint64  // bytes received from peer
 	lastHandshakeNano atomic.Int64   // nano seconds since epoch
+	string            string         // cached [Peer.String]
 
 	endpoint struct {
 		sync.Mutex
@@ -107,6 +109,9 @@ func (device *Device) NewPeer(pk NoisePublicKey) (*Peer, error) {
 	// init timers
 	peer.timersInit()
 
+	base64Key := base64.StdEncoding.EncodeToString(pk[:])
+	peer.string = "peer(" + base64Key[0:4] + "…" + base64Key[39:43] + ")"
+
 	// add
 	device.peers.keyMap[pk] = peer
 
@@ -145,29 +150,7 @@ func (peer *Peer) SendBuffers(buffers [][]byte) error {
 }
 
 func (peer *Peer) String() string {
-	// The awful goo that follows is identical to:
-	//
-	//   base64Key := base64.StdEncoding.EncodeToString(peer.handshake.remoteStatic[:])
-	//   abbreviatedKey := base64Key[0:4] + "…" + base64Key[39:43]
-	//   return fmt.Sprintf("peer(%s)", abbreviatedKey)
-	//
-	// except that it is considerably more efficient.
-	src := peer.handshake.remoteStatic
-	b64 := func(input byte) byte {
-		return input + 'A' + byte(((25-int(input))>>8)&6) - byte(((51-int(input))>>8)&75) - byte(((61-int(input))>>8)&15) + byte(((62-int(input))>>8)&3)
-	}
-	b := []byte("peer(____…____)")
-	const first = len("peer(")
-	const second = len("peer(____…")
-	b[first+0] = b64((src[0] >> 2) & 63)
-	b[first+1] = b64(((src[0] << 4) | (src[1] >> 4)) & 63)
-	b[first+2] = b64(((src[1] << 2) | (src[2] >> 6)) & 63)
-	b[first+3] = b64(src[2] & 63)
-	b[second+0] = b64(src[29] & 63)
-	b[second+1] = b64((src[30] >> 2) & 63)
-	b[second+2] = b64(((src[30] << 4) | (src[31] >> 4)) & 63)
-	b[second+3] = b64((src[31] << 2) & 63)
-	return string(b)
+	return peer.string
 }
 
 func (peer *Peer) Start() {