wgengine/magicsock: drop a bytes.Buffer sync.Pool, use logger.ArgWriter instead

wgengine/magicsock/magicsock.go

@@ -7,7 +7,7 @@
 package magicsock
 
 import (
-	"bytes"
+	"bufio"
 	"context"
 	"encoding/binary"
 	"errors"
@@ -1362,37 +1362,29 @@ func (c *Conn) closeDerpLocked(node int, why string) {
 	}
 }
 
-var bufPool = sync.Pool{New: func() interface{} { return new(bytes.Buffer) }}
-
 // c.mu must be held.
 func (c *Conn) logActiveDerpLocked() {
-	buf := bufPool.Get().(*bytes.Buffer)
-	defer bufPool.Put(buf)
 	now := time.Now()
-	buf.Reset()
+	c.logf("magicsock: %v active derp conns%s", len(c.activeDerp), logger.ArgWriter(func(buf *bufio.Writer) {
+		if len(c.activeDerp) == 0 {
+			return
+		}
 		buf.WriteString(":")
 		c.foreachActiveDerpSortedLocked(func(node int, ad activeDerp) {
 			fmt.Fprintf(buf, " derp-%d=cr%v,wr%v", node, simpleDur(now.Sub(ad.createTime)), simpleDur(now.Sub(*ad.lastWrite)))
 		})
-	var details []byte
+	}))
-	if buf.Len() > len(": ") {
-		details = bytes.TrimSpace(buf.Bytes())
-	}
-	c.logf("magicsock: %v active derp conns%s", len(c.activeDerp), details)
 }
 
 func (c *Conn) logEndpointChange(endpoints []string, reasons map[string]string) {
-	buf := bufPool.Get().(*bytes.Buffer)
+	c.logf("magicsock: endpoints changed: %s", logger.ArgWriter(func(buf *bufio.Writer) {
-	defer bufPool.Put(buf)
-	buf.Reset()
-	buf.WriteString("magicsock: endpoints changed: ")
 		for i, ep := range endpoints {
 			if i > 0 {
 				buf.WriteString(", ")
 			}
 			fmt.Fprintf(buf, "%s (%s)", ep, reasons[ep])
 		}
-	c.logf("%s", buf.Bytes())
+	}))
 }
 
 // c.mu must be held.