Handle IPv6 Fragment & Routing extension headers

Enables the reassembly of fragmented IPv6 packets and handling of the
Routing extension header with a Segments Left value of 0. Atomic
fragments are handled as described in RFC 6946 to not interfere with
"normal" fragment traffic. No specific routing header type is supported.

Note, the stack does not yet support sending ICMPv6 error messages in
response to IPv6 packets that cannot be handled/parsed. That will come
in a later change (Issue #2211).

Test:
- header_test.TestIPv6RoutingExtHdr
- header_test.TestIPv6FragmentExtHdr
- header_test.TestIPv6ExtHdrIterErr
- header_test.TestIPv6ExtHdrIter
- ipv6_test.TestReceiveIPv6ExtHdrs
- ipv6_test.TestReceiveIPv6Fragments

RELNOTES: n/a
PiperOrigin-RevId: 303189584

1 files changed, 20 insertions, 0 deletions

diff --git a/pkg/tcpip/buffer/view.go b/pkg/tcpip/buffer/view.go
index 17e94c562..8d42cd066 100644
--- a/pkg/tcpip/buffer/view.go
+++ b/pkg/tcpip/buffer/view.go
@@ -15,6 +15,10 @@
 // Package buffer provides the implementation of a buffer view.
 package buffer
 
+import (
+	"bytes"
+)
+
 // View is a slice of a buffer, with convenience methods.
 type View []byte
 
@@ -45,6 +49,13 @@ func (v *View) CapLength(length int) {
 	*v = (*v)[:length:length]
 }
 
+// Reader returns a bytes.Reader for v.
+func (v *View) Reader() bytes.Reader {
+	var r bytes.Reader
+	r.Reset(*v)
+	return r
+}
+
 // ToVectorisedView returns a VectorisedView containing the receiver.
 func (v View) ToVectorisedView() VectorisedView {
 	return NewVectorisedView(len(v), []View{v})
@@ -162,3 +173,12 @@ func (vv *VectorisedView) AppendView(v View) {
 	vv.views = append(vv.views, v)
 	vv.size += len(v)
 }
+
+// Readers returns a bytes.Reader for each of vv's views.
+func (vv *VectorisedView) Readers() []bytes.Reader {
+	readers := make([]bytes.Reader, 0, len(vv.views))
+	for _, v := range vv.views {
+		readers = append(readers, v.Reader())
+	}
+	return readers
+}