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Fix flaky TestSetAndGetUUIDValue: big.Int drops leading zero bytes #518

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Merged
lemire merged 1 commit into from
Mar 9, 2026
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Fix flaky TestSetAndGetUUIDValue: big.Int drops leading zero bytes #518

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32 changes: 31 additions & 1 deletion roaring64/bsi64_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -86,12 +86,42 @@ func TestSetAndGetUUIDValue(t *testing.T) {
bv, _ := bsi.GetBigValue(1)
assert.Equal(t, bigUUID, bv)

newUUID, err := uuid.FromBytes(bv.Bytes())
// big.Int.Bytes() drops leading zero bytes; use FillBytes to restore the
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@lemire lemire Mar 9, 2026

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correct: https://pkg.go.dev/math/big#Int.Bytes

// original length so uuid.FromBytes receives exactly len(b) bytes.
bvBytes := make([]byte, len(b))
bv.FillBytes(bvBytes)
newUUID, err := uuid.FromBytes(bvBytes)
assert.Nil(t, err)

assert.Equal(t, uuidVal.String(), newUUID.String())
}

// TestSetAndGetUUIDValueLeadingZero is a deterministic regression test for the
// case where the UUID binary representation has a leading zero byte, which
// big.Int.Bytes() would silently drop.
func TestSetAndGetUUIDValueLeadingZero(t *testing.T) {
// Construct a UUID whose MarshalBinary starts with 0x00.
var uuidVal uuid.UUID
uuidVal[0] = 0x00
uuidVal[6] = 0x40 // version 4
uuidVal[8] = 0x80 // variant bits
b, errx := uuidVal.MarshalBinary()
require.Nil(t, errx)
require.Equal(t, 0x00, int(b[0]), "test requires leading zero byte")

bigUUID := new(big.Int)
bigUUID.SetBytes(b)
bsi := NewDefaultBSI()
bsi.SetBigValue(1, bigUUID)
bv, _ := bsi.GetBigValue(1)

bvBytes := make([]byte, len(b))
bv.FillBytes(bvBytes)
newUUID, err := uuid.FromBytes(bvBytes)
assert.Nil(t, err)
assert.Equal(t, uuidVal.String(), newUUID.String())
}

func secondsAndNanosToBigInt(seconds int64, nanos int32) *big.Int {
b := make([]byte, 12)
binary.BigEndian.PutUint64(b[:8], uint64(seconds))
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