Implement SO_NO_CHECK socket option.

SO_NO_CHECK is used to skip the UDP checksum generation on a TX socket
(UDP checksum is optional on IPv4).

Test:
 - TestNoChecksum
 - SoNoCheckOffByDefault (UdpSocketTest)
 - SoNoCheck (UdpSocketTest)

Fixes #3055

PiperOrigin-RevId: 318575215

1 files changed, 16 insertions, 0 deletions

diff --git a/pkg/tcpip/checker/checker.go b/pkg/tcpip/checker/checker.go
index c1745ba6a..ee264b726 100644
--- a/pkg/tcpip/checker/checker.go
+++ b/pkg/tcpip/checker/checker.go
@@ -320,6 +320,22 @@ func DstPort(port uint16) TransportChecker {
 	}
 }
 
+// NoChecksum creates a checker that checks if the checksum is zero.
+func NoChecksum(noChecksum bool) TransportChecker {
+	return func(t *testing.T, h header.Transport) {
+		t.Helper()
+
+		udp, ok := h.(header.UDP)
+		if !ok {
+			return
+		}
+
+		if b := udp.Checksum() == 0; b != noChecksum {
+			t.Errorf("bad checksum state, got %t, want %t", b, noChecksum)
+		}
+	}
+}
+
 // SeqNum creates a checker that checks the sequence number.
 func SeqNum(seq uint32) TransportChecker {
 	return func(t *testing.T, h header.Transport) {