Migrate to PacketHeader API for PacketBuffer.

Formerly, when a packet is constructed or parsed, all headers are set by the
client code. This almost always involved prepending to pk.Header buffer or
trimming pk.Data portion. This is known to prone to bugs, due to the complexity
and number of the invariants assumed across netstack to maintain.

In the new PacketHeader API, client will call Push()/Consume() method to
construct/parse an outgoing/incoming packet. All invariants, such as slicing
and trimming, are maintained by the API itself.

NewPacketBuffer() is introduced to create new PacketBuffer. Zero value is no
longer valid.

PacketBuffer now assumes the packet is a concatenation of following portions:
* LinkHeader
* NetworkHeader
* TransportHeader
* Data
Any of them could be empty, or zero-length.

PiperOrigin-RevId: 326507688

1 files changed, 17 insertions, 18 deletions

diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index df478115d..1b03ad6bb 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -433,9 +433,9 @@ func (ep *endpoint) HandlePacket(nicID tcpip.NICID, localAddr tcpip.LinkAddress,
 	// Push new packet into receive list and increment the buffer size.
 	var packet packet
 	// TODO(gvisor.dev/issue/173): Return network protocol.
-	if len(pkt.LinkHeader) > 0 {
+	if !pkt.LinkHeader().View().IsEmpty() {
 		// Get info directly from the ethernet header.
-		hdr := header.Ethernet(pkt.LinkHeader)
+		hdr := header.Ethernet(pkt.LinkHeader().View())
 		packet.senderAddr = tcpip.FullAddress{
 			NIC:  nicID,
 			Addr: tcpip.Address(hdr.SourceAddress()),
@@ -458,9 +458,14 @@ func (ep *endpoint) HandlePacket(nicID tcpip.NICID, localAddr tcpip.LinkAddress,
 		case tcpip.PacketHost:
 			packet.data = pkt.Data
 		case tcpip.PacketOutgoing:
-			// Strip Link Header from the Header.
-			pkt.Header = buffer.NewPrependableFromView(pkt.Header.View()[len(pkt.LinkHeader):])
-			combinedVV := pkt.Header.View().ToVectorisedView()
+			// Strip Link Header.
+			var combinedVV buffer.VectorisedView
+			if v := pkt.NetworkHeader().View(); !v.IsEmpty() {
+				combinedVV.AppendView(v)
+			}
+			if v := pkt.TransportHeader().View(); !v.IsEmpty() {
+				combinedVV.AppendView(v)
+			}
 			combinedVV.Append(pkt.Data)
 			packet.data = combinedVV
 		default:
@@ -471,9 +476,8 @@ func (ep *endpoint) HandlePacket(nicID tcpip.NICID, localAddr tcpip.LinkAddress,
 		// Raw packets need their ethernet headers prepended before
 		// queueing.
 		var linkHeader buffer.View
-		var combinedVV buffer.VectorisedView
 		if pkt.PktType != tcpip.PacketOutgoing {
-			if len(pkt.LinkHeader) == 0 {
+			if pkt.LinkHeader().View().IsEmpty() {
 				// We weren't provided with an actual ethernet header,
 				// so fake one.
 				ethFields := header.EthernetFields{
@@ -485,19 +489,14 @@ func (ep *endpoint) HandlePacket(nicID tcpip.NICID, localAddr tcpip.LinkAddress,
 				fakeHeader.Encode(&ethFields)
 				linkHeader = buffer.View(fakeHeader)
 			} else {
-				linkHeader = append(buffer.View(nil), pkt.LinkHeader...)
+				linkHeader = append(buffer.View(nil), pkt.LinkHeader().View()...)
 			}
-			combinedVV = linkHeader.ToVectorisedView()
-		}
-		if pkt.PktType == tcpip.PacketOutgoing {
-			// For outgoing packets the Link, Network and Transport
-			// headers are in the pkt.Header fields normally unless
-			// a Raw socket is in use in which case pkt.Header could
-			// be nil.
-			combinedVV.AppendView(pkt.Header.View())
+			combinedVV := linkHeader.ToVectorisedView()
+			combinedVV.Append(pkt.Data)
+			packet.data = combinedVV
+		} else {
+			packet.data = buffer.NewVectorisedView(pkt.Size(), pkt.Views())
 		}
-		combinedVV.Append(pkt.Data)
-		packet.data = combinedVV
 	}
 	packet.timestampNS = ep.stack.Clock().NowNanoseconds()