feat: add square wave latency summand (#17)

* feat: add square wave summand

* test: ensure that speedbump has started before dialing TCP in echo server test

* docs: add square wave latency flags in cli arg reference

* format: fix LatencyCfg struct initialization indent

* refactor: simplify square wave formula

README.md

@@ -1,4 +1,5 @@
 # speedbump - TCP proxy with variable latency
+
 <div align="center">
   <img alt="speedbump logo" src="https://github.com/kffl/speedbump/raw/HEAD/assets/speedbump.gif" width="480" height="auto"/>
 </div>
@@ -32,6 +33,7 @@ Spawn a new instance with a base latency of 300ms and a sawtooth wave latency su
 ```
 speedbump --latency=300ms --saw-amplitude=200ms --saw-period=2m --port=2000 localhost:80
 ```
+
 <div align="center">
   <img alt="speedbump sawtooth wave graph" src="https://github.com/kffl/speedbump/raw/HEAD/assets/sawtooth.svg" width="800" height="auto"/>
 </div>
@@ -54,17 +56,19 @@ usage: speedbump [<flags>] <destination>
 TCP proxy for simulating variable network latency.
 
 Flags:
-  --help              Show context-sensitive help (also try --help-long and --help-man).
-  --port=8000         Port number to listen on.
-  --buffer=64KB       Size of the buffer used for TCP reads.
-  --queue-size=1024   Size of the delay queue storing read buffers.
-  --latency=5ms       Base latency added to proxied traffic.
-  --log-level=INFO    Log level. Possible values: DEBUG, TRACE, INFO, WARN, ERROR.
-  --sine-amplitude=0  Amplitude of the latency sine wave.
-  --sine-period=0     Period of the latency sine wave.
-  --saw-amplitude=0   Amplitude of the latency sawtooth wave.
-  --saw-period=0      Period of the latency sawtooth wave.
-  --version           Show application version.
+  --help                Show context-sensitive help (also try --help-long and --help-man).
+  --port=8000           Port number to listen on.
+  --buffer=64KB         Size of the buffer used for TCP reads.
+  --queue-size=1024     Size of the delay queue storing read buffers.
+  --latency=5ms         Base latency added to proxied traffic.
+  --log-level=INFO      Log level. Possible values: DEBUG, TRACE, INFO, WARN, ERROR.
+  --sine-amplitude=0    Amplitude of the latency sine wave.
+  --sine-period=0       Period of the latency sine wave.
+  --saw-amplitude=0     Amplitude of the latency sawtooth wave.
+  --saw-period=0        Period of the latency sawtooth wave.
+  --square-amplitude=0  Amplitude of the latency square wave.
+  --square-period=0     Period of the latency square wave.
+  --version             Show application version.
 
 Args:
   <destination>  TCP proxy destination in host:post format.
@@ -78,4 +82,4 @@ Speedbump can be used as a Go library via its `lib` package. Check `lib` [README
 
 Copyright Paweł Kuffel 2022, licensed under Apache 2.0 License.
 
-Speedbump logo contains the Go Gopher mascot which was originally designed by Renee French (http://reneefrench.blogspot.com/) and licensed under Creative Commons 3.0 Attributions license.
+Speedbump logo contains the Go Gopher mascot which was originally designed by Renee French (http://reneefrench.blogspot.com/) and licensed under Creative Commons 3.0 Attributions license.

args.go

@@ -34,6 +34,12 @@ func parseArgs(args []string) (*lib.SpeedbumpCfg, error) {
 		sawPeriod = app.Flag("saw-period", "Period of the latency sawtooth wave.").
 				PlaceHolder("0").
 				Duration()
+		squareAmplitude = app.Flag("square-amplitude", "Amplitude of the latency square wave.").
+				PlaceHolder("0").
+				Duration()
+		suqarePeriod = app.Flag("square-period", "Period of the latency square wave.").
+				PlaceHolder("0").
+				Duration()
 		destAddr = app.Arg("destination", "TCP proxy destination in host:post format.").
 				Required().
 				String()
@@ -52,11 +58,13 @@ func parseArgs(args []string) (*lib.SpeedbumpCfg, error) {
 		BufferSize: int(*bufferSize),
 		QueueSize:  *queueSize,
 		Latency: &lib.LatencyCfg{
-			Base:          *latency,
-			SineAmplitude: *sineAmplitude,
-			SinePeriod:    *sinePeriod,
-			SawAmplitute:  *sawAmplitute,
-			SawPeriod:     *sawPeriod,
+			Base:            *latency,
+			SineAmplitude:   *sineAmplitude,
+			SinePeriod:      *sinePeriod,
+			SawAmplitute:    *sawAmplitute,
+			SawPeriod:       *sawPeriod,
+			SquareAmplitude: *squareAmplitude,
+			SquarePeriod:    *suqarePeriod,
 		},
 		LogLevel: *logLevel,
 	}

args_test.go

@@ -30,6 +30,8 @@ func TestParseArgsAll(t *testing.T) {
 			"--latency=100ms",
 			"--sine-amplitude=50ms",
 			"--sine-period=1m",
+			"--square-amplitude=123ms",
+			"--square-period=3m",
 			"host:777",
 		},
 	)
@@ -42,4 +44,6 @@ func TestParseArgsAll(t *testing.T) {
 	assert.Equal(t, time.Minute, cfg.Latency.SinePeriod)
 	assert.Equal(t, time.Duration(0), cfg.Latency.SawAmplitute)
 	assert.Equal(t, time.Duration(0), cfg.Latency.SawPeriod)
+	assert.Equal(t, time.Millisecond*123, cfg.Latency.SquareAmplitude)
+	assert.Equal(t, time.Minute*3, cfg.Latency.SquarePeriod)
 }

lib/latency_generator.go

@@ -9,11 +9,13 @@ type LatencyGenerator interface {
 }
 
 type LatencyCfg struct {
-	Base          time.Duration
-	SineAmplitude time.Duration
-	SinePeriod    time.Duration
-	SawAmplitute  time.Duration
-	SawPeriod     time.Duration
+	Base            time.Duration
+	SineAmplitude   time.Duration
+	SinePeriod      time.Duration
+	SawAmplitute    time.Duration
+	SawPeriod       time.Duration
+	SquareAmplitude time.Duration
+	SquarePeriod    time.Duration
 }
 
 type latencySummand interface {
@@ -39,6 +41,12 @@ func newSimpleLatencyGenerator(start time.Time, cfg *LatencyCfg) simpleLatencyGe
 			cfg.SawPeriod,
 		})
 	}
+	if cfg.SquareAmplitude > 0 && cfg.SquarePeriod > 0 {
+		summands = append(summands, squareLatencySummand{
+			cfg.SquareAmplitude,
+			cfg.SquarePeriod,
+		})
+	}
 	return simpleLatencyGenerator{
 		start:    start,
 		summands: summands,

lib/speedbump_test.go

@@ -140,7 +140,20 @@ func TestSpeedbumpWithEchoServer(t *testing.T) {
 	assert.Nil(t, err)
 
 	tcpAddr, _ := net.ResolveTCPAddr("tcp", "localhost:8000")
-	conn, _ := net.DialTCP("tcp", nil, tcpAddr)
+
+	var conn *net.TCPConn
+
+	// Wait for the speedbump instance to start listening
+	// since it is started in a separate goroutine, we don't know
+	// if it has already started listening by this point
+	for {
+		conn, err = net.DialTCP("tcp", nil, tcpAddr)
+		if err != nil {
+			time.Sleep(10 * time.Millisecond)
+		} else {
+			break
+		}
+	}
 
 	firstOpStart := time.Now()
 

lib/square.go

@@ -0,0 +1,15 @@
+package lib
+
+import "time"
+
+
+type squareLatencySummand struct {
+	amplitude time.Duration
+	period    time.Duration
+}
+
+func (s squareLatencySummand) getLatency(elapsed time.Duration) time.Duration {
+	return time.Duration(
+		(4 * (elapsed / s.period) - 2 * ((2 * elapsed) / s.period) + 1) * s.amplitude,
+	)
+}

lib/square_test.go

@@ -0,0 +1,23 @@
+package lib
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSquareLatencySummand(t *testing.T) {
+	s := squareLatencySummand{
+		amplitude: time.Second * 2,
+		period:    time.Minute,
+	}
+
+	assert.Equal(t, s.getLatency(time.Duration(0)), time.Second * 2)
+	assert.Equal(t, s.getLatency(time.Second * 15), time.Second * 2)
+	assert.Equal(t, s.getLatency(time.Second * 30), time.Second * -2)
+	assert.Equal(t, s.getLatency(time.Second * 45), time.Second * -2)
+	assert.Equal(t, s.getLatency(time.Second * 60), time.Second * 2)
+	assert.Equal(t, s.getLatency(time.Second * 84), time.Second * 2)
+	assert.Equal(t, s.getLatency(time.Second * 90), time.Second * -2)
+}