2 files changed, 60 insertions, 0 deletions
diff --git a/pkg/tcpip/internal/tcp/BUILD b/pkg/tcpip/internal/tcp/BUILD
new file mode 100644
index 000000000..9ae258a0b
--- /dev/null
+++ b/pkg/tcpip/internal/tcp/BUILD
@@ -0,0 +1,12 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "tcp",
+    srcs = ["tcp.go"],
+    visibility = ["//pkg/tcpip:__subpackages__"],
+    deps = [
+        "//pkg/tcpip",
+    ],
+)
diff --git a/pkg/tcpip/internal/tcp/tcp.go b/pkg/tcpip/internal/tcp/tcp.go
new file mode 100644
index 000000000..0616d368c
--- /dev/null
+++ b/pkg/tcpip/internal/tcp/tcp.go
@@ -0,0 +1,48 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package tcp contains internal type definitions that are not expected to be
+// used by anyone else outside pkg/tcpip.
+package tcp
+
+import (
+	"time"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+)
+
+// TSOffset is an offset applied to the value of the TSVal field in the TCP
+// Timestamp option.
+//
+// +stateify savable
+type TSOffset struct {
+	milliseconds uint32
+}
+
+// NewTSOffset creates a new TSOffset from milliseconds.
+func NewTSOffset(milliseconds uint32) TSOffset {
+	return TSOffset{
+		milliseconds: milliseconds,
+	}
+}
+
+// TSVal applies the offset to now and returns the timestamp in milliseconds.
+func (offset TSOffset) TSVal(now tcpip.MonotonicTime) uint32 {
+	return uint32(now.Sub(tcpip.MonotonicTime{}).Milliseconds()) + offset.milliseconds
+}
+
+// Elapsed calculates the elapsed time given now and the echoed back timestamp.
+func (offset TSOffset) Elapsed(now tcpip.MonotonicTime, tsEcr uint32) time.Duration {
+	return time.Duration(offset.TSVal(now)-tsEcr) * time.Millisecond
+}