generalListDecoder panics when iterator timeout on decoding message

[xnslong]

When decoding a message, the Decoder.Decode method is called. (the following code snippet)

Line 24 (L24) tries to decode the message, and it will check the error of iter on decoding finished (L25). However, the L24 may panic (instead of return normally). When the L24 panics, the whole method will panic, not returning the expected error.

go/decoder.go

Lines 16 to 29 in 9b5a675

	func (decoder *Decoder) Decode(val interface{}) error {
	cfg := decoder.cfg
	valType := reflect.TypeOf(val)
	valDecoder := cfg.getGenDecoder(valType)
	if valDecoder == nil {
	valDecoder = cfg.decoderOf(valType)
	cfg.addGenDecoder(valType, valDecoder)
	}
	valDecoder.Decode(val, decoder.iter)
	if decoder.iter.Error() != nil {
	return decoder.iter.Error()
	}
	return nil
	}

Following is the method where panic may occur.

The underlying Reader of iter may read from a TCP connection (L13). But TCP connection can run timeout, then the underlying Reader will get an error. When such error occurs, the iter will return zero values and set an error. (thus elemType == TypeStop && length == 0 && iter.Error() != nil) When trying to get the generalReaderOf(TypeStop) (L14), this method will panic (See the code snippet, go/general/decode.go#L31).

go/general/decode_list.go

Lines 8 to 20 in 9b5a675

	func (decoder *generalListDecoder) Decode(val interface{}, iter spi.Iterator) {
	*val.(*List) = readList(iter).(List)
	}
	func readList(iter spi.Iterator) interface{} {
	elemType, length := iter.ReadListHeader()
	generalReader := generalReaderOf(elemType)
	var generalList List
	for i := 0; i < length; i++ {
	generalList = append(generalList, generalReader(iter))
	}
	return generalList
	}

go/general/decode.go

Lines 8 to 33 in 9b5a675

	func generalReaderOf(ttype protocol.TType) func(iter spi.Iterator) interface{} {
	switch ttype {
	case protocol.TypeBool:
	return readBool
	case protocol.TypeI08:
	return readInt8
	case protocol.TypeI16:
	return readInt16
	case protocol.TypeI32:
	return readInt32
	case protocol.TypeI64:
	return readInt64
	case protocol.TypeString:
	return readString
	case protocol.TypeDouble:
	return readFloat64
	case protocol.TypeList:
	return readList
	case protocol.TypeMap:
	return readMap
	case protocol.TypeStruct:
	return readStruct
	default:
	panic("unsupported type")
	}
	}