Concatenated problem about go-smpp HOT 1 OPEN

func (t *Transmitter) SubmitLongMsg8bit(sm *ShortMessage) ([]ShortMessage, error) {
	maxLen := 134 // 140-6 (UDH)
	rawMsg := sm.Text.Encode()
	countParts := int((len(rawMsg)-1)/maxLen) + 1
	ri := uint8(t.r.Intn(128))
	UDHHeader := make([]byte, 6)
	UDHHeader[0] = 5
	UDHHeader[1] = 0
	UDHHeader[2] = 3
	UDHHeader[3] = ri
	UDHHeader[4] = uint8(countParts)
	responses := []ShortMessage{}
	for i := 0; i < countParts; i++ {
		UDHHeader[5] = uint8(i + 1) // current message part
		p := pdu.NewSubmitSM(sm.TLVFields)
		f := p.Fields()
		f.Set(pdufield.SourceAddr, sm.Src)
		f.Set(pdufield.DestinationAddr, sm.Dst)
		if i != countParts-1 {
			f.Set(pdufield.ShortMessage, pdutext.Raw(append(UDHHeader, rawMsg[i*maxLen:(i+1)*maxLen]...)))
		} else {
			f.Set(pdufield.ShortMessage, pdutext.Raw(append(UDHHeader, rawMsg[i*maxLen:]...)))
		}
		f.Set(pdufield.RegisteredDelivery, uint8(sm.Register))
		if sm.Validity != time.Duration(0) {
			f.Set(pdufield.ValidityPeriod, convertValidity(sm.Validity))
		}
		f.Set(pdufield.ServiceType, sm.ServiceType)
		f.Set(pdufield.SourceAddrTON, sm.SourceAddrTON)
		f.Set(pdufield.SourceAddrNPI, sm.SourceAddrNPI)
		f.Set(pdufield.DestAddrTON, sm.DestAddrTON)
		f.Set(pdufield.DestAddrNPI, sm.DestAddrNPI)
		f.Set(pdufield.ESMClass, 0x40)
		f.Set(pdufield.ProtocolID, sm.ProtocolID)
		f.Set(pdufield.PriorityFlag, sm.PriorityFlag)
		f.Set(pdufield.ScheduleDeliveryTime, sm.ScheduleDeliveryTime)
		f.Set(pdufield.ReplaceIfPresentFlag, sm.ReplaceIfPresentFlag)
		f.Set(pdufield.SMDefaultMsgID, sm.SMDefaultMsgID)
		f.Set(pdufield.DataCoding, uint8(sm.Text.Type()))
		//set the optional parameters in the submit pdu from sm
		optParams := p.TLVFields()
		for tag, value := range sm.TLVFields {
			err := optParams.Set(tag, value)
			if err != nil {
				return nil, err
			}
		}

		resp, err := t.do(p)
		if err != nil {
			return nil, err
		}
		sm.resp.Lock()
		sm.resp.p = resp.PDU
		sm.resp.Unlock()
		// checking for errors in the responses will be left to the client
		responses = append(responses, *sm)
	}
	return responses, nil
}