resolve gosec suggestion, use crypo package for randomness (#357)

operator/builtin/transformer/filter/filter.go

@@ -2,8 +2,9 @@ package filter
 
 import (
 	"context"
+	"crypto/rand"
 	"fmt"
-	"math/rand"
+	"math/big"
 
 	"github.com/antonmedv/expr"
 	"github.com/antonmedv/expr/vm"
@@ -17,6 +18,10 @@ func init() {
 	operator.Register("filter", func() operator.Builder { return NewFilterOperatorConfig("") })
 }
 
+var upperBound = big.NewInt(1000)
+
+var randInt = rand.Int // allow override for testing
+
 // NewFilterOperatorConfig creates a filter operator config with default values
 func NewFilterOperatorConfig(operatorID string) *FilterOperatorConfig {
 	return &FilterOperatorConfig{
@@ -51,7 +56,7 @@ func (c FilterOperatorConfig) Build(context operator.BuildContext) ([]operator.O
 	filterOperator := &FilterOperator{
 		TransformerOperator: transformer,
 		expression:          compiledExpression,
-		dropRatio:           c.DropRatio,
+		dropCutoff:          big.NewInt(int64(c.DropRatio * 1000)),
 	}
 
 	return []operator.Operator{filterOperator}, nil
@@ -61,7 +66,7 @@ func (c FilterOperatorConfig) Build(context operator.BuildContext) ([]operator.O
 type FilterOperator struct {
 	helper.TransformerOperator
 	expression *vm.Program
-	dropRatio  float64
+	dropCutoff *big.Int // [0..1000)
 }
 
 // Process will drop incoming entries that match the filter expression
@@ -81,7 +86,17 @@ func (f *FilterOperator) Process(ctx context.Context, entry *entry.Entry) error
 		return nil
 	}
 
-	if !filtered || rand.Float64() > f.dropRatio {
+	if !filtered {
+		f.Write(ctx, entry)
+		return nil
+	}
+
+	i, err := randInt(rand.Reader, upperBound)
+	if err != nil {
+		return err
+	}
+
+	if i.Cmp(f.dropCutoff) >= 0 {
 		f.Write(ctx, entry)
 	}
 

operator/builtin/transformer/filter/filter_test.go

@@ -2,7 +2,8 @@ package filter
 
 import (
 	"context"
-	"math/rand"
+	"io"
+	"math/big"
 	"os"
 	"testing"
 
@@ -141,14 +142,21 @@ func TestFilterDropRatio(t *testing.T) {
 		},
 	}
 
+	nextIndex := 0
+	randos := []int64{250, 750}
+	randInt = func(io.Reader, *big.Int) (*big.Int, error) {
+		defer func() {
+			nextIndex = (nextIndex + 1) % len(randos)
+		}()
+		return big.NewInt(randos[nextIndex]), nil
+	}
+
 	for i := 1; i < 11; i++ {
-		rand.Seed(1)
 		err = filterOperator.Process(context.Background(), testEntry)
 		require.NoError(t, err)
 	}
 
 	for i := 1; i < 11; i++ {
-		rand.Seed(2)
 		err = filterOperator.Process(context.Background(), testEntry)
 		require.NoError(t, err)
 	}