decimal: incorrect MP_DECIMAL decoding with scale < 0

[oleg-jukovec]

The scale value in MP_DECIMAL may be negative [1]. We need to handle the case.

1. https://www.tarantool.io/en/doc/latest/dev_guide/internals/msgpack_extensions/#the-decimal-type

I didn't forget about (remove if it is not applicable):

• Tests (see documentation for a testing package)
• Changelog (see documentation for changelog format)

[ArtDu]

May you return values from tarantool as etalon response. It's hard to validate that d501fe1c is correct response

[oleg-jukovec]

I've added TestUnmarshal_from_decimal_new where we create a decimal inside a Tarantool instance with eval:

return require('decimal').new(str)

[ArtDu]

Should add limits. 1e37, 1e-38 is max values for decimal

[oleg-jukovec]

We have tests for min/max:

go-tarantool/decimal/decimal_test.go

Lines 251 to 278 in 337ca73

	func TestEncodeMaxNumber(t *testing.T) {
	referenceErrMsg := "msgpack: decimal number is bigger than maximum supported number (10^38 - 1)"
	decNum := decimal.New(1, DecimalPrecision) // // 10^DecimalPrecision
	tuple := TupleDecimal{number: *NewDecimal(decNum)}
	_, err := msgpack.Marshal(&tuple)
	if err == nil {
	t.Fatalf("It is possible to msgpack.Encoder a number unsupported by Tarantool")
	}
	if err.Error() != referenceErrMsg {
	t.Fatalf("Incorrect error message on attempt to msgpack.Encoder number unsupported by Tarantool")
	}
	}
	func TestEncodeMinNumber(t *testing.T) {
	referenceErrMsg := "msgpack: decimal number is lesser than minimum supported number (-10^38 - 1)"
	two := decimal.NewFromInt(2)
	decNum := decimal.New(1, DecimalPrecision).Neg().Sub(two) // -10^DecimalPrecision - 2
	tuple := TupleDecimal{number: *NewDecimal(decNum)}
	_, err := msgpack.Marshal(&tuple)
	if err == nil {
	t.Fatalf("It is possible to msgpack.Encoder a number unsupported by Tarantool")
	}
	if err.Error() != referenceErrMsg {
	fmt.Println("Actual message: ", err.Error())
	fmt.Println("Expected message: ", referenceErrMsg)
	t.Fatalf("Incorrect error message on attempt to msgpack.Encoder number unsupported by Tarantool")
	}
	}

[DifferentialOrange]

See comment above