Handle slicer Toxic with zero SizeVariation (#359)

This change skips randomized size variation for the slicer toxic if the SizeVariation parameter is 0, which is also the default setting.

Additionally, it removes `rand.Intn(1)` was being added to mid to adjust for integer division rounding. However, rand.Intn(n) returns an integer in the range [0, n), so rand.Intn(1) always returns 0. It was removed.

Author: areveny

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Added verbose error on proxy upstream dialing (#355, @f-dg)
 * Improve server startup message (#358, @areveny)
 * Introduce yaml linter. (#362, @miry)
+* Handle slicer toxic with zero `SizeVariation` and fix slicing randomization (#359, @areveny)
 
 # [2.3.0] - 2021-12-23
 

toxics/slicer.go

@@ -37,10 +37,11 @@ func (t *SlicerToxic) chunk(start int, end int) []int {
 		return []int{start, end}
 	}
 
-	// +1 in the size variation to offset favoring of smaller
-	// numbers by integer division
+	mid := start + (end-start)/2
 	//#nosec
-	mid := start + (end-start)/2 + (rand.Intn(t.SizeVariation*2) - t.SizeVariation) + rand.Intn(1)
+	if t.SizeVariation > 0 {
+		mid += rand.Intn(t.SizeVariation*2) - t.SizeVariation
+	}
 	left := t.chunk(start, mid)
 	right := t.chunk(mid, end)
 

toxics/slicer_test.go

@@ -38,14 +38,14 @@ func TestSlicerToxic(t *testing.T) {
 
 	buf := make([]byte, 0, len(data))
 	reads := 0
-L:
-	for {
+
+	for timeout := false; !timeout; {
 		select {
 		case c := <-output:
 			reads++
 			buf = append(buf, c.Data...)
 		case <-time.After(10 * time.Millisecond):
-			break L
+			timeout = true
 		}
 	}
 
@@ -56,3 +56,51 @@ L:
 		t.Errorf("Server did not read correct buffer from client!")
 	}
 }
+
+func TestSlicerToxicZeroSizeVariation(t *testing.T) {
+	data := []byte(strings.Repeat("hello world ", 2)) // 24 bytes
+	// SizeVariation: 0 by default
+	slicer := &toxics.SlicerToxic{AverageSize: 1, Delay: 10}
+
+	input := make(chan *stream.StreamChunk)
+	output := make(chan *stream.StreamChunk)
+	stub := toxics.NewToxicStub(input, output)
+
+	done := make(chan bool)
+	go func() {
+		slicer.Pipe(stub)
+		done <- true
+	}()
+	defer func() {
+		close(input)
+		for {
+			select {
+			case <-done:
+				return
+			case <-output:
+			}
+		}
+	}()
+
+	input <- &stream.StreamChunk{Data: data}
+
+	buf := make([]byte, 0, len(data))
+	reads := 0
+
+	for timeout := false; !timeout; {
+		select {
+		case c := <-output:
+			reads++
+			buf = append(buf, c.Data...)
+		case <-time.After(10 * time.Millisecond):
+			timeout = true
+		}
+	}
+
+	if reads != 24 {
+		t.Errorf("Expected to read 24 times, but read %d times.", reads)
+	}
+	if !bytes.Equal(buf, data) {
+		t.Errorf("Server did not read correct buffer from client!")
+	}
+}