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

@@ -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
 		}
 	}

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 {

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)
 }

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:])

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!