From b6ecf29d9812d2c4a8c200dd736d275bb74b981e Mon Sep 17 00:00:00 2001
From: Tom Thorogood <me+github@tomthorogood.co.uk>
Date: Thu, 2 Feb 2017 18:03:49 +1030
Subject: [PATCH] Improve performance by addressing some low hanging fruit.
 (#444)

* Remove unused bytes.Buffer from dns/idn.encode.

This buffer is truncated and written to but never read from. It
serves no purpose and all tests pass with it removed.

It appears to have been introduced when puncycode.go was first
added in miekg/dns@e3c2c07.

* Produce less pointless garbage.

This change:
- removes several needless []byte -> string conversions,
- removes two needless append calls in HashName, and
- writes the hash to the same nsec3 []byte in HashName rather
  than creating a new []byte on each of the k iterations.

These are all minor performance improvements that will likely
go entirely unnoticed. The changes will reduce the ammount of
garbage produced when calling CertificateToDANE, HashName,
(*SIG).Sign and TsigGenerate.
---
 dane.go         |  9 ++++-----
 idn/punycode.go |  3 ---
 nsecx.go        | 11 +++++------
 sig0.go         |  5 ++---
 tsig.go         |  3 +--
 5 files changed, 12 insertions(+), 19 deletions(-)

diff --git a/dane.go b/dane.go
index cdaa833f..8c4a14ef 100644
--- a/dane.go
+++ b/dane.go
@@ -6,7 +6,6 @@ import (
 	"crypto/x509"
 	"encoding/hex"
 	"errors"
-	"io"
 )
 
 // CertificateToDANE converts a certificate to a hex string as used in the TLSA or SMIMEA records.
@@ -23,20 +22,20 @@ func CertificateToDANE(selector, matchingType uint8, cert *x509.Certificate) (st
 		h := sha256.New()
 		switch selector {
 		case 0:
-			io.WriteString(h, string(cert.Raw))
+			h.Write(cert.Raw)
 			return hex.EncodeToString(h.Sum(nil)), nil
 		case 1:
-			io.WriteString(h, string(cert.RawSubjectPublicKeyInfo))
+			h.Write(cert.RawSubjectPublicKeyInfo)
 			return hex.EncodeToString(h.Sum(nil)), nil
 		}
 	case 2:
 		h := sha512.New()
 		switch selector {
 		case 0:
-			io.WriteString(h, string(cert.Raw))
+			h.Write(cert.Raw)
 			return hex.EncodeToString(h.Sum(nil)), nil
 		case 1:
-			io.WriteString(h, string(cert.RawSubjectPublicKeyInfo))
+			h.Write(cert.RawSubjectPublicKeyInfo)
 			return hex.EncodeToString(h.Sum(nil)), nil
 		}
 	}
diff --git a/idn/punycode.go b/idn/punycode.go
index 7e5c263f..1d03bf6a 100644
--- a/idn/punycode.go
+++ b/idn/punycode.go
@@ -242,11 +242,8 @@ func encode(input []byte) []byte {
 		t, k, cp     rune // weight and codepoint calculation
 	)
 
-	s := &bytes.Buffer{}
 	for h := basiclen; h < fulllen; n, delta = n+1, delta+1 {
 		nextltr = next(b, n)
-		s.Truncate(0)
-		s.WriteRune(nextltr)
 		delta, n = delta+(nextltr-n)*rune(h+1), nextltr
 
 		for _, ltr = range b {
diff --git a/nsecx.go b/nsecx.go
index 6f10f3e6..51ce7f8b 100644
--- a/nsecx.go
+++ b/nsecx.go
@@ -3,7 +3,6 @@ package dns
 import (
 	"crypto/sha1"
 	"hash"
-	"io"
 	"strings"
 )
 
@@ -36,15 +35,15 @@ func HashName(label string, ha uint8, iter uint16, salt string) string {
 	}
 
 	// k = 0
-	name = append(name, wire...)
-	io.WriteString(s, string(name))
+	s.Write(name)
+	s.Write(wire)
 	nsec3 := s.Sum(nil)
 	// k > 0
 	for k := uint16(0); k < iter; k++ {
 		s.Reset()
-		nsec3 = append(nsec3, wire...)
-		io.WriteString(s, string(nsec3))
-		nsec3 = s.Sum(nil)
+		s.Write(nsec3)
+		s.Write(wire)
+		nsec3 = s.Sum(nsec3[:0])
 	}
 	return toBase32(nsec3)
 }
diff --git a/sig0.go b/sig0.go
index 2dce06af..f31e9e68 100644
--- a/sig0.go
+++ b/sig0.go
@@ -60,16 +60,15 @@ func (rr *SIG) Sign(k crypto.Signer, m *Msg) ([]byte, error) {
 	}
 
 	rr.Signature = toBase64(signature)
-	sig := string(signature)
 
-	buf = append(buf, sig...)
+	buf = append(buf, signature...)
 	if len(buf) > int(^uint16(0)) {
 		return nil, ErrBuf
 	}
 	// Adjust sig data length
 	rdoff := len(mbuf) + 1 + 2 + 2 + 4
 	rdlen := binary.BigEndian.Uint16(buf[rdoff:])
-	rdlen += uint16(len(sig))
+	rdlen += uint16(len(signature))
 	binary.BigEndian.PutUint16(buf[rdoff:], rdlen)
 	// Adjust additional count
 	adc := binary.BigEndian.Uint16(buf[10:])
diff --git a/tsig.go b/tsig.go
index 78365e1c..24013096 100644
--- a/tsig.go
+++ b/tsig.go
@@ -9,7 +9,6 @@ import (
 	"encoding/binary"
 	"encoding/hex"
 	"hash"
-	"io"
 	"strconv"
 	"strings"
 	"time"
@@ -124,7 +123,7 @@ func TsigGenerate(m *Msg, secret, requestMAC string, timersOnly bool) ([]byte, s
 	default:
 		return nil, "", ErrKeyAlg
 	}
-	io.WriteString(h, string(buf))
+	h.Write(buf)
 	t.MAC = hex.EncodeToString(h.Sum(nil))
 	t.MACSize = uint16(len(t.MAC) / 2) // Size is half!