Teach netstack how to add options to IPv4 packets

Most packets don't have options but they are an integral part of the
standard. Teaching the ipv4 code how to handle them will simplify future
testing and use.  Because Options are so rare it is worth making sure
that the extra work is kept out of the fast path as much as possible.

Prior to this change, all usages of the IHL field of the IPv4Fields/Encode
system set it to the same constant value except in a couple of tests
for bad values. From this change IHL will not be a constant as it will
depend on the size of any Options. Since ipv4.Encode() now handles the
options it becomes a possible source of errors to let the callers set
this value, so remove it entirely and calculate the value from the size
of the Options if present (or not) therefore guaranteeing a correct value.

Fixes #4709
RELNOTES: n/a
PiperOrigin-RevId: 341864765

1 files changed, 10 insertions, 11 deletions

diff --git a/test/packetimpact/testbench/connections.go b/test/packetimpact/testbench/connections.go
index 8fa585804..030a73c3c 100644
--- a/test/packetimpact/testbench/connections.go
+++ b/test/packetimpact/testbench/connections.go
@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package testbench has utilities to send and receive packets and also command
-// the DUT to run POSIX functions.
 package testbench
 
 import (
@@ -74,7 +72,7 @@ func pickPort(domain, typ int) (fd int, port uint16, err error) {
 	}
 	sa, err = unix.Getsockname(fd)
 	if err != nil {
-		return -1, 0, fmt.Errorf("Getsocketname(%d): %w", fd, err)
+		return -1, 0, fmt.Errorf("fail in Getsocketname(%d): %w", fd, err)
 	}
 	port, err = portFromSockaddr(sa)
 	if err != nil {
@@ -102,9 +100,9 @@ type layerState interface {
 	// as it was sent is available.
 	sent(sent Layer) error
 
-	// received updates the layerState based on a Layer that is receieved. The
+	// received updates the layerState based on a Layer that is received. The
 	// input is a Layer with all prev and next pointers populated so that the
-	// entire frame as it was receieved is available.
+	// entire frame as it was received is available.
 	received(received Layer) error
 
 	// close frees associated resources held by the LayerState.
@@ -475,12 +473,12 @@ func (conn *Connection) Close(t *testing.T) {
 	}
 }
 
-// CreateFrame builds a frame for the connection with defaults overriden
+// CreateFrame builds a frame for the connection with defaults overridden
 // from the innermost layer out, and additionalLayers added after it.
 //
 // Note that overrideLayers can have a length that is less than the number
 // of layers in this connection, and in such cases the innermost layers are
-// overriden first. As an example, valid values of overrideLayers for a TCP-
+// overridden first. As an example, valid values of overrideLayers for a TCP-
 // over-IPv4-over-Ethernet connection are: nil, [TCP], [IPv4, TCP], and
 // [Ethernet, IPv4, TCP].
 func (conn *Connection) CreateFrame(t *testing.T, overrideLayers Layers, additionalLayers ...Layer) Layers {
@@ -711,7 +709,7 @@ func (conn *TCPIPv4) ConnectWithOptions(t *testing.T, options []byte) {
 }
 
 // ExpectData is a convenient method that expects a Layer and the Layer after
-// it. If it doens't arrive in time, it returns nil.
+// it. If it doesn't arrive in time, it returns nil.
 func (conn *TCPIPv4) ExpectData(t *testing.T, tcp *TCP, payload *Payload, timeout time.Duration) (Layers, error) {
 	t.Helper()
 
@@ -1046,7 +1044,7 @@ func (conn *UDPIPv4) Expect(t *testing.T, udp UDP, timeout time.Duration) (*UDP,
 }
 
 // ExpectData is a convenient method that expects a Layer and the Layer after
-// it. If it doens't arrive in time, it returns nil.
+// it. If it doesn't arrive in time, it returns nil.
 func (conn *UDPIPv4) ExpectData(t *testing.T, udp UDP, payload Payload, timeout time.Duration) (Layers, error) {
 	t.Helper()
 
@@ -1174,7 +1172,7 @@ func (conn *UDPIPv6) Expect(t *testing.T, udp UDP, timeout time.Duration) (*UDP,
 }
 
 // ExpectData is a convenient method that expects a Layer and the Layer after
-// it. If it doens't arrive in time, it returns nil.
+// it. If it doesn't arrive in time, it returns nil.
 func (conn *UDPIPv6) ExpectData(t *testing.T, udp UDP, payload Payload, timeout time.Duration) (Layers, error) {
 	t.Helper()
 
@@ -1234,13 +1232,14 @@ func NewTCPIPv6(t *testing.T, outgoingTCP, incomingTCP TCP) TCPIPv6 {
 	}
 }
 
+// SrcPort returns the source port from the given Connection.
 func (conn *TCPIPv6) SrcPort() uint16 {
 	state := conn.layerStates[2].(*tcpState)
 	return *state.out.SrcPort
 }
 
 // ExpectData is a convenient method that expects a Layer and the Layer after
-// it. If it doens't arrive in time, it returns nil.
+// it. If it doesn't arrive in time, it returns nil.
 func (conn *TCPIPv6) ExpectData(t *testing.T, tcp *TCP, payload *Payload, timeout time.Duration) (Layers, error) {
 	t.Helper()