fix: Non-privileged (UDP) ping response parsing for OSes not supporting STRIPHDR sock option

Signed-off-by: Gaius <gaius.qi@gmail.com>

ping.go

@@ -49,7 +49,6 @@
 // it calls the OnFinish callback.
 //
 // For a full ping example, see "cmd/ping/ping.go".
-//
 package ping
 
 import (
@@ -580,7 +579,8 @@ func (p *Pinger) recvICMP(
 		case <-p.done:
 			return nil
 		default:
-			bytes := make([]byte, p.getMessageLength())
+			messageLength := p.getMessageLength()
+			bytes := make([]byte, messageLength)
 			if err := conn.SetReadDeadline(time.Now().Add(delay)); err != nil {
 				return err
 			}
@@ -598,10 +598,25 @@ func (p *Pinger) recvICMP(
 				return err
 			}
 
+			// syscall.SetsockoptInt dose not work with sysIP_STRIPHDR on the darwin,
+			// we need to check the bytes, if there is an IP header, we needs to strip it.
+			// Refer to https://go.googlesource.com/net/+/master/icmp/listen_posix.go#75.
+			if !p.Privileged() && n >= messageLength {
+				if p.ipv4 {
+					if hdr, err := ipv4.ParseHeader(bytes); err == nil && hdr != nil && hdr.TotalLen == n && hdr.Len == ipv4.HeaderLen {
+						bytes = bytes[ipv4.HeaderLen:]
+					}
+				} else {
+					if hdr, err := ipv6.ParseHeader(bytes); err == nil && hdr.PayloadLen == p.Size && hdr.NextHeader == protocolIPv6ICMP {
+						bytes = bytes[ipv6.HeaderLen:]
+					}
+				}
+			}
+
 			select {
 			case <-p.done:
 				return nil
-			case recv <- &packet{bytes: bytes, nbytes: n, ttl: ttl}:
+			case recv <- &packet{bytes: bytes, nbytes: len(bytes), ttl: ttl}:
 			}
 		}
 	}

utils_linux.go

@@ -3,9 +3,22 @@
 
 package ping
 
+import (
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
 // Returns the length of an ICMP message.
 func (p *Pinger) getMessageLength() int {
-	return p.Size + 8
+	if p.Privileged() {
+		return p.Size + 8
+	}
+
+	if p.ipv4 {
+		return p.Size + 8 + ipv4.HeaderLen
+	}
+
+	return p.Size + 8 + ipv6.HeaderLen
 }
 
 // Attempts to match the ID of an ICMP packet.

utils_other.go

@@ -3,9 +3,22 @@
 
 package ping
 
+import (
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
 // Returns the length of an ICMP message.
 func (p *Pinger) getMessageLength() int {
-	return p.Size + 8
+	if p.Privileged() {
+		return p.Size + 8
+	}
+
+	if p.ipv4 {
+		return p.Size + 8 + ipv4.HeaderLen
+	}
+
+	return p.Size + 8 + ipv6.HeaderLen
 }
 
 // Attempts to match the ID of an ICMP packet.