From ad2b39d4b95e32e1eb5110b42c6cc9c72f6fd4ee Mon Sep 17 00:00:00 2001
From: Knut Ahlers <knut@ahlers.me>
Date: Sat, 6 Mar 2021 17:42:38 +0100
Subject: [PATCH] Add source interface selection

Signed-off-by: Knut Ahlers <knut@ahlers.me>
---
 main.go  |  3 ++-
 spark.go | 35 +++++++++++++++++++++++++++++------
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/main.go b/main.go
index 692eeb0..cca0edd 100644
--- a/main.go
+++ b/main.go
@@ -18,6 +18,7 @@ var (
 		InfluxHost     string        `flag:"influx-host" default:"http://localhost:8086" description:"Host with protocol of the InfluxDB"`
 		InfluxPass     string        `flag:"influx-pass" default:"" description:"Password for the InfluxDB user"`
 		InfluxUser     string        `flag:"influx-user" default:"" description:"Username for the InfluxDB connection"`
+		Interface      string        `flag:"interface" default:"" description:"Bind to interface for testing a specific interface throughput"`
 		Interval       time.Duration `flag:"interval" default:"15m" description:"Interval to execute test in"`
 		LogLevel       string        `flag:"log-level" default:"info" description:"Set log level (debug, info, warning, error)"`
 		OneShot        bool          `flag:"oneshot,1" default:"false" description:"Execute one measurement and exit (for cron execution)"`
@@ -183,7 +184,7 @@ func writeTSV(t *testResult) error {
 func execTest() (*testResult, error) {
 	t := newTestResult()
 
-	sc := newSparkClient(cfg.Server, cfg.Port)
+	sc := newSparkClient(cfg.Server, cfg.Port, cfg.Interface)
 	if err := sc.ExecutePingTest(t); err != nil {
 		return nil, errors.Wrap(err, "Ping-test failed")
 	}
diff --git a/spark.go b/spark.go
index 5192853..e63b7bd 100644
--- a/spark.go
+++ b/spark.go
@@ -61,19 +61,42 @@ func (t testResult) String() string {
 }
 
 type sparkClient struct {
-	remote string
-	conn   net.Conn
-	reader *bufio.Reader
+	bindInterfaceName string
+	remote            string
+	conn              net.Conn
+	reader            *bufio.Reader
 }
 
-func newSparkClient(hostname string, port int) *sparkClient {
+func newSparkClient(hostname string, port int, bindInterfaceName string) *sparkClient {
 	return &sparkClient{
-		remote: fmt.Sprintf("%s:%d", hostname, port),
+		bindInterfaceName: bindInterfaceName,
+		remote:            fmt.Sprintf("%s:%d", hostname, port),
 	}
 }
 
 func (s *sparkClient) dial() error {
-	c, err := net.Dial("tcp", s.remote)
+	d := net.Dialer{}
+
+	if s.bindInterfaceName != "" {
+		iface, err := net.InterfaceByName(s.bindInterfaceName)
+		if err != nil {
+			return errors.Wrap(err, "select interface")
+		}
+
+		addrs, err := iface.Addrs()
+		if err != nil {
+			return errors.Wrap(err, "get interface IPs")
+		}
+
+		if len(addrs) == 0 {
+			return errors.New("no addresses found on interface")
+		}
+
+		d.LocalAddr = &net.TCPAddr{IP: addrs[0].(*net.IPNet).IP}
+		log.WithField("ip", d.LocalAddr).Warn("Set local address")
+	}
+
+	c, err := d.Dial("tcp", s.remote)
 	if err != nil {
 		return errors.Wrap(err, "Unable to dial")
 	}