Merge segments in sender's writeList

PiperOrigin-RevId: 220185891
Change-Id: Iaea73fd7b2fa8c399b989cdcaabf4885f370df4b

2 files changed, 36 insertions, 4 deletions

diff --git a/pkg/tcpip/header/BUILD b/pkg/tcpip/header/BUILD
index 8f22ba3a5..66b37720c 100644
--- a/pkg/tcpip/header/BUILD
+++ b/pkg/tcpip/header/BUILD
@@ -22,6 +22,7 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
         "//pkg/tcpip/seqnum",
     ],
 )
diff --git a/pkg/tcpip/header/checksum.go b/pkg/tcpip/header/checksum.go
index 12f208fde..2c2fcbd9b 100644
--- a/pkg/tcpip/header/checksum.go
+++ b/pkg/tcpip/header/checksum.go
@@ -18,12 +18,11 @@ package header
 
 import (
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
 )
 
-// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
-// given byte array.
-func Checksum(buf []byte, initial uint16) uint16 {
-	v := uint32(initial)
+func calculateChecksum(buf []byte, initial uint32) uint16 {
+	v := initial
 
 	l := len(buf)
 	if l&1 != 0 {
@@ -38,8 +37,40 @@ func Checksum(buf []byte, initial uint16) uint16 {
 	return ChecksumCombine(uint16(v), uint16(v>>16))
 }
 
+// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
+// given byte array.
+//
+// The initial checksum must have been computed on an even number of bytes.
+func Checksum(buf []byte, initial uint16) uint16 {
+	return calculateChecksum(buf, uint32(initial))
+}
+
+// ChecksumVV calculates the checksum (as defined in RFC 1071) of the bytes in
+// the given VectorizedView.
+//
+// The initial checksum must have been computed on an even number of bytes.
+func ChecksumVV(vv buffer.VectorisedView, initial uint16) uint16 {
+	var odd bool
+	sum := initial
+	for _, v := range vv.Views() {
+		if len(v) == 0 {
+			continue
+		}
+		s := uint32(sum)
+		if odd {
+			s += uint32(v[0])
+			v = v[1:]
+		}
+		odd = len(v)&1 != 0
+		sum = calculateChecksum(v, s)
+	}
+	return sum
+}
+
 // ChecksumCombine combines the two uint16 to form their checksum. This is done
 // by adding them and the carry.
+//
+// Note that checksum a must have been computed on an even number of bytes.
 func ChecksumCombine(a, b uint16) uint16 {
 	v := uint32(a) + uint32(b)
 	return uint16(v + v>>16)