Merge pull request #27 from mroth/fuzz

Implement fuzz testing

fuzz_test.go

@@ -0,0 +1,100 @@
+//go:build go1.18
+// +build go1.18
+
+package weightedrand
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+// Fuzz testing does not support slices as a corpus type in go1.18, thus we
+// write a bunch of boilerplate here to allow us to encode []uint64 as []byte
+// for kicks.
+
+func bEncodeSlice(xs []uint64) []byte {
+	bs := make([]byte, len(xs)*8)
+	for i, x := range xs {
+		n := i * 8
+		binary.LittleEndian.PutUint64(bs[n:], x)
+	}
+	return bs
+}
+
+func bDecodeSlice(bs []byte) []uint64 {
+	n := len(bs) / 8
+	xs := make([]uint64, 0, n)
+	for i := 0; i < n; i++ {
+		x := binary.LittleEndian.Uint64(bs[8*i:])
+		xs = append(xs, x)
+	}
+	return xs
+}
+
+// test our own encoder to make sure we didn't introduce errors.
+func Test_bEncodeSlice(t *testing.T) {
+	var testcases = [][]uint64{
+		{},
+		{1},
+		{42},
+		{912346},
+		{1, 2},
+		{1, 1, 1},
+		{1, 2, 3},
+		{1, 1000000},
+		{1, 2, 3, 4, 5, 6, 7, 8, 9},
+	}
+	for _, tc := range testcases {
+		t.Run(fmt.Sprintf("%v", tc), func(t *testing.T) {
+			before := tc
+			encoded := bEncodeSlice(before)
+			if want, got := len(before)*8, len(encoded); want != got {
+				t.Errorf("encoded length not as expected: want %d got %d", want, got)
+			}
+			decoded := bDecodeSlice(encoded)
+			if !reflect.DeepEqual(before, decoded) {
+				t.Errorf("want %v got %v", before, decoded)
+			}
+		})
+	}
+}
+
+func FuzzNewChooser(f *testing.F) {
+	var fuzzcases = [][]uint64{
+		{},
+		{0},
+		{1},
+		{1, 1},
+		{1, 2, 3},
+		{0, 1, 2},
+	}
+	for _, tc := range fuzzcases {
+		f.Add(bEncodeSlice(tc))
+	}
+
+	f.Fuzz(func(t *testing.T, encodedWeights []byte) {
+		weights := bDecodeSlice(encodedWeights)
+		const sentinel = 1
+
+		cs := make([]Choice[int, uint64], 0, len(weights))
+		for _, w := range weights {
+			cs = append(cs, Choice[int, uint64]{Item: sentinel, Weight: w})
+		}
+
+		// fuzz for error or panic on NewChooser
+		c, err := NewChooser(cs...)
+		if err != nil && !errors.Is(err, errNoValidChoices) && !errors.Is(err, errWeightOverflow) {
+			t.Fatal(err)
+		}
+
+		if err == nil {
+			result := c.Pick()      // fuzz for panic on Panic
+			if result != sentinel { // fuzz for returned value unexpected (just use same non-zero sentinel value for all choices)
+				t.Fatalf("expected %v got %v", sentinel, result)
+			}
+		}
+	})
+}

testdata/fuzz/FuzzNewChooser/a547669aeb7ca0ca

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("0000000\x8f00000000")

weightedrand.go

@@ -48,11 +48,16 @@ func NewChooser[T any, W integer](choices ...Choice[T, W]) (*Chooser[T, W], erro
 	totals := make([]int, len(choices))
 	runningTotal := 0
 	for i, c := range choices {
-		weight := int(c.Weight)
-		if weight < 0 {
+		if c.Weight < 0 {
 			continue // ignore negative weights, can never be picked
 		}
 
+		// case of single ~uint64 or similar value that exceeds maxInt on its own
+		if uint64(c.Weight) >= maxInt {
+			return nil, errWeightOverflow
+		}
+
+		weight := int(c.Weight) // convert weight to int for internal counter usage
 		if (maxInt - runningTotal) <= weight {
 			return nil, errWeightOverflow
 		}
@@ -68,8 +73,9 @@ func NewChooser[T any, W integer](choices ...Choice[T, W]) (*Chooser[T, W], erro
 }
 
 const (
-	intSize = 32 << (^uint(0) >> 63) // cf. strconv.IntSize
-	maxInt  = 1<<(intSize-1) - 1
+	intSize   = 32 << (^uint(0) >> 63) // cf. strconv.IntSize
+	maxInt    = 1<<(intSize-1) - 1
+	maxUint64 = 1<<64 - 1
 )
 
 // Possible errors returned by NewChooser, preventing the creation of a Chooser

weightedrand_test.go

@@ -81,10 +81,42 @@ func TestNewChooser(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			_, err := NewChooser(tt.cs...)
+			c, err := NewChooser(tt.cs...)
 			if err != tt.wantErr {
 				t.Errorf("NewChooser() error = %v, wantErr %v", err, tt.wantErr)
 			}
+
+			if err == nil { // run a few Picks to make sure there are no panics
+				for i := 0; i < 10; i++ {
+					_ = c.Pick()
+				}
+			}
+		})
+	}
+
+	u64tests := []struct {
+		name    string
+		cs      []Choice[rune, uint64]
+		wantErr error
+	}{
+		{
+			name:    "weight overflow from single uint64 exceeding system maxInt",
+			cs:      []Choice[rune, uint64]{{Item: 'a', Weight: maxInt + 1}},
+			wantErr: errWeightOverflow,
+		},
+	}
+	for _, tt := range u64tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c, err := NewChooser(tt.cs...)
+			if err != tt.wantErr {
+				t.Errorf("NewChooser() error = %v, wantErr %v", err, tt.wantErr)
+			}
+
+			if err == nil { // run a few Picks to make sure there are no panics
+				for i := 0; i < 10; i++ {
+					_ = c.Pick()
+				}
+			}
 		})
 	}
 }