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 Zero value is no
longer valid.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

2 files changed, 16 insertions, 18 deletions

diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index 31a242482..1ad788a17 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -99,7 +99,7 @@ func (e *endpoint) WriteHeaderIncludedPacket(r *stack.Route, pkt *stack.PacketBu
 }
 
 func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
-	h := header.ARP(pkt.NetworkHeader)
+	h := header.ARP(pkt.NetworkHeader().View())
 	if !h.IsValid() {
 		return
 	}
@@ -110,17 +110,17 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 		if e.linkAddrCache.CheckLocalAddress(e.nicID, header.IPv4ProtocolNumber, localAddr) == 0 {
 			return // we have no useful answer, ignore the request
 		}
-		hdr := buffer.NewPrependable(int(e.linkEP.MaxHeaderLength()) + header.ARPSize)
-		packet := header.ARP(hdr.Prepend(header.ARPSize))
+		pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+			ReserveHeaderBytes: int(e.linkEP.MaxHeaderLength()) + header.ARPSize,
+		})
+		packet := header.ARP(pkt.NetworkHeader().Push(header.ARPSize))
 		packet.SetIPv4OverEthernet()
 		packet.SetOp(header.ARPReply)
 		copy(packet.HardwareAddressSender(), r.LocalLinkAddress[:])
 		copy(packet.ProtocolAddressSender(), h.ProtocolAddressTarget())
 		copy(packet.HardwareAddressTarget(), h.HardwareAddressSender())
 		copy(packet.ProtocolAddressTarget(), h.ProtocolAddressSender())
-		e.linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, &stack.PacketBuffer{
-			Header: hdr,
-		})
+		_ = e.linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, pkt)
 		fallthrough // also fill the cache from requests
 	case header.ARPReply:
 		addr := tcpip.Address(h.ProtocolAddressSender())
@@ -168,17 +168,17 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAdd
 		r.RemoteLinkAddress = header.EthernetBroadcastAddress
 	}
 
-	hdr := buffer.NewPrependable(int(linkEP.MaxHeaderLength()) + header.ARPSize)
-	h := header.ARP(hdr.Prepend(header.ARPSize))
+	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+		ReserveHeaderBytes: int(linkEP.MaxHeaderLength()) + header.ARPSize,
+	})
+	h := header.ARP(pkt.NetworkHeader().Push(header.ARPSize))
 	h.SetIPv4OverEthernet()
 	h.SetOp(header.ARPRequest)
 	copy(h.HardwareAddressSender(), linkEP.LinkAddress())
 	copy(h.ProtocolAddressSender(), localAddr)
 	copy(h.ProtocolAddressTarget(), addr)
 
-	return linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, &stack.PacketBuffer{
-		Header: hdr,
-	})
+	return linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, pkt)
 }
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.ResolveStaticAddress.
@@ -210,12 +210,10 @@ func (*protocol) Wait() {}
 
 // Parse implements stack.NetworkProtocol.Parse.
 func (*protocol) Parse(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNumber, hasTransportHdr bool, ok bool) {
-	hdr, ok := pkt.Data.PullUp(header.ARPSize)
+	_, ok = pkt.NetworkHeader().Consume(header.ARPSize)
 	if !ok {
 		return 0, false, false
 	}
-	pkt.NetworkHeader = hdr
-	pkt.Data.TrimFront(header.ARPSize)
 	return 0, false, true
 }
 
diff --git a/pkg/tcpip/network/arp/arp_test.go b/pkg/tcpip/network/arp/arp_test.go
index a35a64a0f..c2c3e6891 100644
--- a/pkg/tcpip/network/arp/arp_test.go
+++ b/pkg/tcpip/network/arp/arp_test.go
@@ -106,9 +106,9 @@ func TestDirectRequest(t *testing.T) {
 
 	inject := func(addr tcpip.Address) {
 		copy(h.ProtocolAddressTarget(), addr)
-		c.linkEP.InjectInbound(arp.ProtocolNumber, &stack.PacketBuffer{
+		c.linkEP.InjectInbound(arp.ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
 			Data: v.ToVectorisedView(),
-		})
+		}))
 	}
 
 	for i, address := range []tcpip.Address{stackAddr1, stackAddr2} {
@@ -118,9 +118,9 @@ func TestDirectRequest(t *testing.T) {
 			if pi.Proto != arp.ProtocolNumber {
 				t.Fatalf("expected ARP response, got network protocol number %d", pi.Proto)
 			}
-			rep := header.ARP(pi.Pkt.Header.View())
+			rep := header.ARP(pi.Pkt.NetworkHeader().View())
 			if !rep.IsValid() {
-				t.Fatalf("invalid ARP response pi.Pkt.Header.UsedLength()=%d", pi.Pkt.Header.UsedLength())
+				t.Fatalf("invalid ARP response: len = %d; response = %x", len(rep), rep)
 			}
 			if got, want := tcpip.LinkAddress(rep.HardwareAddressSender()), stackLinkAddr1; got != want {
 				t.Errorf("got HardwareAddressSender = %s, want = %s", got, want)