3 files changed, 95 insertions, 0 deletions
diff --git a/pkg/tcpip/network/testutil/BUILD b/pkg/tcpip/network/testutil/BUILD
index d0ffc299a..652b92a21 100644
--- a/pkg/tcpip/network/testutil/BUILD
+++ b/pkg/tcpip/network/testutil/BUILD
@@ -6,6 +6,7 @@ go_library(
     name = "testutil",
     srcs = [
         "testutil.go",
+        "testutil_unsafe.go",
     ],
     visibility = [
         "//pkg/tcpip/network/fragmentation:__pkg__",
diff --git a/pkg/tcpip/network/testutil/testutil.go b/pkg/tcpip/network/testutil/testutil.go
index 3af44991f..9bd009374 100644
--- a/pkg/tcpip/network/testutil/testutil.go
+++ b/pkg/tcpip/network/testutil/testutil.go
@@ -19,6 +19,8 @@ package testutil
 import (
 	"fmt"
 	"math/rand"
+	"reflect"
+	"strings"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
@@ -127,3 +129,69 @@ func MakeRandPkt(transportHeaderLength int, extraHeaderReserveLength int, viewSi
 	}
 	return pkt
 }
+
+func checkFieldCounts(ref, multi reflect.Value) error {
+	refTypeName := ref.Type().Name()
+	multiTypeName := multi.Type().Name()
+	refNumField := ref.NumField()
+	multiNumField := multi.NumField()
+
+	if refNumField != multiNumField {
+		return fmt.Errorf("type %s has an incorrect number of fields: got = %d, want = %d (same as type %s)", multiTypeName, multiNumField, refNumField, refTypeName)
+	}
+
+	return nil
+}
+
+func validateField(ref reflect.Value, refName string, m tcpip.MultiCounterStat, multiName string) error {
+	s, ok := ref.Addr().Interface().(**tcpip.StatCounter)
+	if !ok {
+		return fmt.Errorf("expected ref type's to be *StatCounter, but its type is %s", ref.Type().Elem().Name())
+	}
+
+	// The field names are expected to match (case insensitive).
+	if !strings.EqualFold(refName, multiName) {
+		return fmt.Errorf("wrong field name: got = %s, want = %s", multiName, refName)
+	}
+
+	base := (*s).Value()
+	m.Increment()
+	if (*s).Value() != base+1 {
+		return fmt.Errorf("updates to the '%s MultiCounterStat' counters are not reflected in the '%s CounterStat'", multiName, refName)
+	}
+
+	return nil
+}
+
+// ValidateMultiCounterStats verifies that every counter stored in multi is
+// correctly tracking its counterpart in the given counters.
+func ValidateMultiCounterStats(multi reflect.Value, counters []reflect.Value) error {
+	for _, c := range counters {
+		if err := checkFieldCounts(c, multi); err != nil {
+			return err
+		}
+	}
+
+	for i := 0; i < multi.NumField(); i++ {
+		multiName := multi.Type().Field(i).Name
+		multiUnsafe := unsafeExposeUnexportedFields(multi.Field(i))
+
+		if m, ok := multiUnsafe.Addr().Interface().(*tcpip.MultiCounterStat); ok {
+			for _, c := range counters {
+				if err := validateField(unsafeExposeUnexportedFields(c.Field(i)), c.Type().Field(i).Name, *m, multiName); err != nil {
+					return err
+				}
+			}
+		} else {
+			var countersNextField []reflect.Value
+			for _, c := range counters {
+				countersNextField = append(countersNextField, c.Field(i))
+			}
+			if err := ValidateMultiCounterStats(multi.Field(i), countersNextField); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
diff --git a/pkg/tcpip/network/testutil/testutil_unsafe.go b/pkg/tcpip/network/testutil/testutil_unsafe.go
new file mode 100644
index 000000000..5ff764800
--- /dev/null
+++ b/pkg/tcpip/network/testutil/testutil_unsafe.go
@@ -0,0 +1,26 @@
+// Copyright 2020 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 testutil
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// unsafeExposeUnexportedFields takes a Value and returns a version of it in
+// which even unexported fields can be read and written.
+func unsafeExposeUnexportedFields(a reflect.Value) reflect.Value {
+	return reflect.NewAt(a.Type(), unsafe.Pointer(a.UnsafeAddr())).Elem()
+}