From 4422db389ae1ace61344150195260a1847ee8a65 Mon Sep 17 00:00:00 2001
From: Gyu-Ho Lee <gyuhox@gmail.com>
Date: Thu, 3 Mar 2016 02:24:14 -0800
Subject: [PATCH] pkg/netutil: add linux netem functions

This is useful for simulating bad networks by introducing
latencies to wide area networks.

Reference:
http://www.linuxfoundation.org/collaborate/workgroups/networking/netem
---
 pkg/netutil/isolate_linux.go | 24 ++++++++++++++++++++++++
 pkg/netutil/isolate_stub.go  |  4 ++++
 2 files changed, 28 insertions(+)

diff --git a/pkg/netutil/isolate_linux.go b/pkg/netutil/isolate_linux.go
index 31727a83f..c61f16c58 100644
--- a/pkg/netutil/isolate_linux.go
+++ b/pkg/netutil/isolate_linux.go
@@ -40,3 +40,27 @@ func RecoverPort(port int) error {
 	_, err := exec.Command("/bin/sh", "-c", cmdStr).Output()
 	return err
 }
+
+// SetLatency adds latency in millisecond scale with random variations.
+func SetLatency(ms, rv int) error {
+	if rv > ms {
+		rv = 1
+	}
+	cmdStr := fmt.Sprintf("sudo tc qdisc add dev eth0 root netem delay %dms %dms distribution normal", ms, rv)
+	_, err := exec.Command("/bin/sh", "-c", cmdStr).Output()
+	if err != nil {
+		// the rule has already been added. Overwrite it.
+		cmdStr = fmt.Sprintf("sudo tc qdisc change dev eth0 root netem delay %dms %dms distribution normal", ms, rv)
+		_, err = exec.Command("/bin/sh", "-c", cmdStr).Output()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// RemoveLatency resets latency configurations.
+func RemoveLatency() error {
+	_, err := exec.Command("/bin/sh", "-c", "sudo tc qdisc del dev eth0 root netem").Output()
+	return err
+}
diff --git a/pkg/netutil/isolate_stub.go b/pkg/netutil/isolate_stub.go
index c8f70f9b6..d517fd688 100644
--- a/pkg/netutil/isolate_stub.go
+++ b/pkg/netutil/isolate_stub.go
@@ -19,3 +19,7 @@ package netutil
 func DropPort(port int) error { return nil }
 
 func RecoverPort(port int) error { return nil }
+
+func SetLatency(ms, rv int) error { return nil }
+
+func RemoveLatency() error { return nil }