🏪 conn: add separate pktinfo struct

Author: database64128

conn/cmsg.go

@@ -6,11 +6,13 @@ import "net/netip"
 const SocketControlMessageBufferSize = socketControlMessageBufferSize
 
 // SocketControlMessage contains information that can be parsed from or put into socket control messages.
+//
+// Fields of [Pktinfo] are manually embedded to avoid wasting space.
 type SocketControlMessage struct {
-	// PktinfoAddr is the IP address of the network interface the packet was received from.
+	// PktinfoAddr is the IP address of the network interface the packet was received on, or to send the packet from.
 	PktinfoAddr netip.Addr
 
-	// PktinfoIfindex is the index of the network interface the packet was received from.
+	// PktinfoIfindex is the index of the network interface the packet was received on, or to send the packet from.
 	PktinfoIfindex uint32
 
 	// SegmentSize is the UDP GRO/GSO segment size.
@@ -29,3 +31,16 @@ func ParseSocketControlMessage(cmsg []byte) (m SocketControlMessage, err error)
 func (m SocketControlMessage) AppendTo(b []byte) []byte {
 	return m.appendTo(b)
 }
+
+// Pktinfo represents packet information as specified in RFC 3542.
+//
+// For received packets, it contains the destination IP address and the arriving interface index.
+//
+// For outgoing packets, it can specify the source IP address and the outgoing interface index.
+type Pktinfo struct {
+	// Addr is the IP address of the network interface the packet was received on, or to send the packet from.
+	Addr netip.Addr
+
+	// Ifindex is the index of the network interface the packet was received on, or to send the packet from.
+	Ifindex uint32
+}