Enable IPv6 WriteHeaderIncludedPacket

Allow writing an IPv6 packet where the IPv6 header is a provided by
the user.

* Introduce an error to let callers know a header is malformed.
We previously useed tcpip.ErrInvalidOptionValue but that did not seem
appropriate for generic malformed header errors.

* Populate network header in WriteHeaderIncludedPacket
IPv4's implementation of WriteHeaderIncludedPacket did not previously
populate the packet buffer's network header. This change fixes that.

Fixes #4527

Test: ip_test.TestWriteHeaderIncludedPacket
PiperOrigin-RevId: 337534548

1 files changed, 18 insertions, 0 deletions

diff --git a/pkg/tcpip/checker/checker.go b/pkg/tcpip/checker/checker.go
index d4d785cca..6f81b0164 100644
--- a/pkg/tcpip/checker/checker.go
+++ b/pkg/tcpip/checker/checker.go
@@ -178,6 +178,24 @@ func PayloadLen(payloadLength int) NetworkChecker {
 	}
 }
 
+// IPPayload creates a checker that checks the payload.
+func IPPayload(payload []byte) NetworkChecker {
+	return func(t *testing.T, h []header.Network) {
+		t.Helper()
+
+		got := h[0].Payload()
+
+		// cmp.Diff does not consider nil slices equal to empty slices, but we do.
+		if len(got) == 0 && len(payload) == 0 {
+			return
+		}
+
+		if diff := cmp.Diff(payload, got); diff != "" {
+			t.Errorf("payload mismatch (-want +got):\n%s", diff)
+		}
+	}
+}
+
 // IPv4Options returns a checker that checks the options in an IPv4 packet.
 func IPv4Options(want []byte) NetworkChecker {
 	return func(t *testing.T, h []header.Network) {