create error type for unsupported SO_MARK socket option

Signed-off-by: Jeremiah Millay <jmillay@fastly.com>

ping.go

@@ -82,6 +82,8 @@ const (
 var (
 	ipv4Proto = map[string]string{"icmp": "ip4:icmp", "udp": "udp4"}
 	ipv6Proto = map[string]string{"icmp": "ip6:ipv6-icmp", "udp": "udp6"}
+
+	ErrMarkNotSupported = errors.New("setting SO_MARK socket option is not supported on this platform")
 )
 
 // New returns a new Pinger struct pointer.
@@ -189,7 +191,7 @@ type Pinger struct {
 	ipaddr *net.IPAddr
 	addr   string
 
-	// Mark is a mark (fwmark) set on outgoing icmp packets
+	// mark is a SO_MARK (fwmark) set on outgoing icmp packets
 	mark uint
 
 	// trackerUUIDs is the list of UUIDs being used for sending packets.

utils_other.go

@@ -3,10 +3,6 @@
 
 package probing
 
-import (
-	"errors"
-)
-
 // Returns the length of an ICMP message.
 func (p *Pinger) getMessageLength() int {
 	return p.Size + 8
@@ -20,17 +16,17 @@ func (p *Pinger) matchID(ID int) bool {
 // SetMark sets the SO_MARK socket option on outgoing ICMP packets.
 // Setting this option requires CAP_NET_ADMIN.
 func (c *icmpConn) SetMark(mark uint) error {
-	return errors.New("setting SO_MARK socket option is not supported on this platform")
+	return ErrMarkNotSupported
 }
 
 // SetMark sets the SO_MARK socket option on outgoing ICMP packets.
 // Setting this option requires CAP_NET_ADMIN.
 func (c *icmpv4Conn) SetMark(mark uint) error {
-	return errors.New("setting SO_MARK socket option is not supported on this platform")
+	return ErrMarkNotSupported
 }
 
 // SetMark sets the SO_MARK socket option on outgoing ICMP packets.
 // Setting this option requires CAP_NET_ADMIN.
 func (c *icmpV6Conn) SetMark(mark uint) error {
-	return errors.New("setting SO_MARK socket option is not supported on this platform")
+	return ErrMarkNotSupported
 }

utils_windows.go

@@ -4,8 +4,6 @@
 package probing
 
 import (
-	"errors"
-
 	"golang.org/x/net/ipv4"
 	"golang.org/x/net/ipv6"
 )
@@ -29,17 +27,17 @@ func (p *Pinger) matchID(ID int) bool {
 // SetMark sets the SO_MARK socket option on outgoing ICMP packets.
 // Setting this option requires CAP_NET_ADMIN.
 func (c *icmpConn) SetMark(mark uint) error {
-	return errors.New("setting SO_MARK socket option is not supported on this platform")
+	return ErrMarkNotSupported
 }
 
 // SetMark sets the SO_MARK socket option on outgoing ICMP packets.
 // Setting this option requires CAP_NET_ADMIN.
 func (c *icmpv4Conn) SetMark(mark uint) error {
-	return errors.New("setting SO_MARK socket option is not supported on this platform")
+	return ErrMarkNotSupported
 }
 
 // SetMark sets the SO_MARK socket option on outgoing ICMP packets.
 // Setting this option requires CAP_NET_ADMIN.
 func (c *icmpV6Conn) SetMark(mark uint) error {
-	return errors.New("setting SO_MARK socket option is not supported on this platform")
+	return ErrMarkNotSupported
 }