device: optimize Peer.String

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

diff --git a/device/peer.go b/device/peer.go
index 005976bd83d1a701bcc7de31a71282bcfb82348f..d2f6d0773e3895ee5c7001e244ff33cf76661602 100644 (file)
--- a/device/peer.go
+++ b/device/peer.go
@@ -9,7 +9,6 @@ import (
        "container/list"
        "encoding/base64"
        "errors"
-       "fmt"
        "sync"
        "sync/atomic"
        "time"
@@ -144,12 +143,26 @@ func (peer *Peer) SendBuffer(buffer []byte) error {
 }
 
 func (peer *Peer) String() string {
-       base64Key := base64.StdEncoding.EncodeToString(peer.handshake.remoteStatic[:])
-       abbreviatedKey := "invalid"
-       if len(base64Key) == 44 {
-               abbreviatedKey = base64Key[0:4] + "…" + base64Key[39:43]
-       }
-       return fmt.Sprintf("peer(%s)", abbreviatedKey)
+       // 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.
+       const prefix = "peer("
+       b := make([]byte, len(prefix)+44)
+       copy(b, prefix)
+       r := b[len(prefix):]
+       base64.StdEncoding.Encode(r, peer.handshake.remoteStatic[:])
+       r = r[4:]
+       copy(r, "…")
+       r = r[len("…"):]
+       copy(r, b[len(prefix)+39:len(prefix)+43])
+       r = r[4:]
+       r[0] = ')'
+       r = r[1:]
+       return string(b[:len(b)-len(r)])
 }
 
 func (peer *Peer) Start() {