Fix lint errors

internal/gtcpip/header/ndp_options.go

@@ -878,7 +878,7 @@ func (o NDPDNSSearchList) iterDomainNames(fn func(string)) error {
 			}
 
 			// Copy the label and add a trailing period.
-			for i := 0; i < labelLen; i++ {
+			for i := range labelLen {
 				b, err := searchList.ReadByte()
 				if err != nil {
 					if err != io.EOF {

internal/gtcpip/header/tcp.go

@@ -476,20 +476,14 @@ func ParseSynOptions(opts []byte, isAck bool) TCPSynOptions {
 			if mss == 0 {
 				return synOpts
 			}
-			synOpts.MSS = mss
-			if mss < TCPMinimumSendMSS {
-				synOpts.MSS = TCPMinimumSendMSS
-			}
+			synOpts.MSS = max(mss, TCPMinimumSendMSS)
 			i += 4
 
 		case TCPOptionWS:
 			if i+3 > limit || opts[i+1] != 3 {
 				return synOpts
 			}
-			ws := int(opts[i+2])
-			if ws > MaxWndScale {
-				ws = MaxWndScale
-			}
+			ws := min(int(opts[i+2]), MaxWndScale)
 			synOpts.WS = ws
 			i += 3
 
@@ -561,7 +555,7 @@ func ParseTCPOptions(b []byte) TCPOptions {
 			}
 			numBlocks := (sackOptionLen - 2) / 8
 			opts.SACKBlocks = []SACKBlock{}
-			for j := 0; j < numBlocks; j++ {
+			for j := range numBlocks {
 				start := binary.BigEndian.Uint32(b[i+2+j*8:])
 				end := binary.BigEndian.Uint32(b[i+2+j*8+4:])
 				opts.SACKBlocks = append(opts.SACKBlocks, SACKBlock{
@@ -646,10 +640,7 @@ func EncodeSACKBlocks(sackBlocks []SACKBlock, b []byte) int {
 	if len(sackBlocks) == 0 {
 		return 0
 	}
-	l := len(sackBlocks)
-	if l > TCPMaxSACKBlocks {
-		l = TCPMaxSACKBlocks
-	}
+	l := min(len(sackBlocks), TCPMaxSACKBlocks)
 	if ll := (len(b) - 2) / 8; ll < l {
 		l = ll
 	}

internal/gtcpip/tcpip.go

@@ -245,6 +245,53 @@ func (a Address) Len() int {
 	return a.length
 }
 
+// String implements the fmt.Stringer interface.
+func (a Address) String() string {
+	switch l := a.Len(); l {
+	case 4:
+		return fmt.Sprintf("%d.%d.%d.%d", int(a.addr[0]), int(a.addr[1]), int(a.addr[2]), int(a.addr[3]))
+	case 16:
+		// Find the longest subsequence of hexadecimal zeros.
+		start, end := -1, -1
+		for i := 0; i < a.Len(); i += 2 {
+			j := i
+			for j < a.Len() && a.addr[j] == 0 && a.addr[j+1] == 0 {
+				j += 2
+			}
+			if j > i+2 && j-i > end-start {
+				start, end = i, j
+			}
+		}
+
+		var b strings.Builder
+		for i := 0; i < a.Len(); i += 2 {
+			if i == start {
+				b.WriteString("::")
+				i = end
+				if end >= a.Len() {
+					break
+				}
+			} else if i > 0 {
+				b.WriteByte(':')
+			}
+			v := uint16(a.addr[i+0])<<8 | uint16(a.addr[i+1])
+			if v == 0 {
+				b.WriteByte('0')
+			} else {
+				const digits = "0123456789abcdef"
+				for i := uint(3); i < 4; i-- {
+					if v := v >> (i * 4); v != 0 {
+						b.WriteByte(digits[v&0xf])
+					}
+				}
+			}
+		}
+		return b.String()
+	default:
+		return fmt.Sprintf("%x", a.addr[:l])
+	}
+}
+
 // WithPrefix returns the address with a prefix that represents a point subnet.
 func (a Address) WithPrefix() AddressWithPrefix {
 	return AddressWithPrefix{
@@ -541,7 +588,7 @@ func (a AddressWithPrefix) Subnet() Subnet {
 			address: a.Address,
 			mask:    AddressMask{length: addrLen},
 		}
-		for i := 0; i < addrLen; i++ {
+		for i := range addrLen {
 			sub.mask.mask[i] = 0xff
 		}
 		return sub
@@ -550,7 +597,7 @@ func (a AddressWithPrefix) Subnet() Subnet {
 	sa := Address{length: addrLen}
 	sm := AddressMask{length: addrLen}
 	n := uint(a.PrefixLen)
-	for i := 0; i < addrLen; i++ {
+	for i := range addrLen {
 		if n >= 8 {
 			sa.addr[i] = a.Address.addr[i]
 			sm.mask[i] = 0xff