types/wgkey: simplify Key.UnmarshalJSON

Instead of calling ParseHex, do the hex.Decode directly.

name             old time/op    new time/op    delta
UnmarshalJSON-8    86.9ns ± 0%    42.6ns ± 0%   -50.94%  (p=0.000 n=15+14)

name             old alloc/op   new alloc/op   delta
UnmarshalJSON-8      128B ± 0%        0B       -100.00%  (p=0.000 n=15+15)

name             old allocs/op  new allocs/op  delta
UnmarshalJSON-8      2.00 ± 0%      0.00       -100.00%  (p=0.000 n=15+15)

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

types/wgkey/key.go

@@ -106,11 +106,10 @@ func (k *Key) UnmarshalJSON(b []byte) error {
 		return errors.New("wgkey.Key: UnmarshalJSON not given a string")
 	}
 	b = b[1 : len(b)-1]
-	key, err := ParseHex(string(b))
-	if err != nil {
-		return fmt.Errorf("wgkey.Key: UnmarshalJSON: %v", err)
+	if len(b) != 2*Size {
+		return fmt.Errorf("wgkey.Key: UnmarshalJSON input wrong size: %d", len(b))
 	}
-	copy(k[:], key[:])
+	hex.Decode(k[:], b)
 	return nil
 }
 

types/wgkey/key_test.go

@@ -156,3 +156,18 @@ func BenchmarkMarshalJSON(b *testing.B) {
 		}
 	}
 }
+
+func BenchmarkUnmarshalJSON(b *testing.B) {
+	b.ReportAllocs()
+	var k Key
+	buf, err := k.MarshalJSON()
+	if err != nil {
+		b.Fatal(err)
+	}
+	for i := 0; i < b.N; i++ {
+		err := k.UnmarshalJSON(buf)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}