Example test for Frozen Bitmap fault when using Frozen Bitmaps as regular/mutable bitmaps with a read-only buffer

go.mod

@@ -6,4 +6,5 @@ require (
 	github.com/bits-and-blooms/bitset v1.2.0
 	github.com/mschoch/smat v0.2.0
 	github.com/stretchr/testify v1.4.0
+	golang.org/x/sys v0.0.0-20220622161953-175b2fd9d664
 )

go.sum

@@ -9,6 +9,8 @@ github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZN
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+golang.org/x/sys v0.0.0-20220622161953-175b2fd9d664 h1:wEZYwx+kK+KlZ0hpvP2Ls1Xr4+RWnlzGFwPP0aiDjIU=
+golang.org/x/sys v0.0.0-20220622161953-175b2fd9d664/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=

serialization_frozen_test.go

@@ -5,8 +5,13 @@ package roaring
 
 import (
 	"bytes"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/unix"
 	"io/ioutil"
+	"os"
 	"reflect"
+	"runtime/debug"
 	"testing"
 )
 
@@ -126,3 +131,90 @@ func TestFrozenFormat(t *testing.T) {
 		})
 	}
 }
+
+type frozenTestCase struct {
+	name        string
+	useMMapped  bool
+	useFrozen   bool
+	shouldPanic bool
+}
+
+func TestFrozenCases(t *testing.T) {
+	cases := []frozenTestCase{
+		{name: "in-memory-frozen", useMMapped: false,
+			useFrozen:   true,
+			shouldPanic: false},
+		{name: "mmap-frozen", useMMapped: true,
+			useFrozen: true,
+			// THIS SHOULD NOT BE PANIC/FAULTING
+			shouldPanic: true},
+		{name: "in-memory", useMMapped: false,
+			useFrozen:   false,
+			shouldPanic: false},
+		{name: "mmap", useMMapped: true,
+			useFrozen:   false,
+			shouldPanic: false},
+	}
+	for _, testCase := range cases {
+		testFrozenCase(t, testCase)
+	}
+}
+func testFrozenCase(t *testing.T, testCase frozenTestCase) {
+
+	startingBitmap := NewBitmap()
+	startingBitmap.highlowcontainer.appendContainer(0, &runContainer16{iv: []interval16{{0, 0},
+		{2, 5}}}, false)
+
+	primary := getBitmap(t, testCase, startingBitmap)
+	assert.True(t, startingBitmap.Equals(primary))
+	clone := primary.Clone()
+	primary.Xor(clone)
+	res := primary.GetCardinality()
+	assert.Equal(t, res, uint64(0))
+	if testCase.shouldPanic {
+		assert.Panics(t, func() {
+			debug.SetPanicOnFault(true)
+			primary.Xor(clone)
+		})
+	} else {
+		primary.Xor(clone)
+	}
+}
+
+func getBitmap(t *testing.T, testCase frozenTestCase, startingBitmap *Bitmap) *Bitmap {
+	receiver := NewBitmap()
+	if testCase.useFrozen {
+		frozenBytes, err := startingBitmap.Freeze()
+		require.NoError(t, err)
+		if testCase.useMMapped {
+			require.NoError(t, receiver.FrozenView(getBytesAsMMap(t, frozenBytes)))
+			return receiver
+		}
+		require.NoError(t, receiver.FrozenView(frozenBytes))
+		return receiver
+	}
+	nonFrozenBytes, err := startingBitmap.ToBytes()
+	require.NoError(t, err)
+
+	if testCase.useMMapped {
+		_, err = receiver.FromBuffer(getBytesAsMMap(t, nonFrozenBytes))
+		require.NoError(t, err)
+		return receiver
+	}
+	_, err = receiver.FromBuffer(nonFrozenBytes)
+	require.NoError(t, err)
+	return receiver
+}
+
+func getBytesAsMMap(t *testing.T, startingBytes []byte) []byte {
+	os.WriteFile("data", startingBytes, 0777)
+	file, err := os.OpenFile("data", os.O_RDONLY, 0)
+	require.NoError(t, err)
+	fileinfo, err := file.Stat()
+	require.NoError(t, err)
+
+	bytes, err := unix.Mmap(int(file.Fd()), 0, int(fileinfo.Size()),
+		unix.PROT_READ, unix.MAP_PRIVATE)
+	require.NoError(t, err)
+	return bytes
+}