Unfortunately we have mixed up the concept of TPDUs and APDUs in earlier versions of pySim-shell. This lead to problems with detecteding the APDU case properly (see also ISO/IEC 7816-3) and also prevented us from adding support for T=1.
This problem has been fixed long time ago and all APDUs sent from the pySim-shell code should be well formed and valid according to ISO/IEC 7816-3.
To ensure that we continue to format APDUs correctly as APDUs (and not TPDUs) we have added a mechanism to the LinkBase class that would either raise an exception or print a warning if someone mistakenly tries to send an APDU that is really a TPDU. Whether a warning is printed or an exception is raised is controlled via the apdu_strict member in the LinkBase class, which is false (print warning only) by default.
The reason why we have implemneted the mechanism this way was because we wanted to ensure that existing APDU scripts (pySim-shell apdu command) keep working, even though when those scripts uses APDUs which are formally invalid.
Sending a TPDU instead of an APDU via a T=0 link will still work in almost all cases. This is also the reason why this problem slipped through unnoticed for long time. However, there may still be subtile problems araising from this practice. The root of the problem is that it is impossible to distinguish between APDU case 3 and 4 when a TPDU instead of an APDU is sent. However in order to handle a case 4 APDU correctly we must be able to distinguish the APDU case correctly to handle the case correctly. ETSI TS 102 221, section 7.3.1.1.4, clause 4 is very clear about the fact that not (only) the status word (e.g. 61xx) but the APDU case is what matters.
To complete the logic in LinkBaseTpdu and to maintain compatibility (older APDU scripts), we must still be able to switch between the 'apdu_strict' mode and the non-strict mode. However, it makes sense to do this on a per-api-call basis instead globally via a class property.
At the same time we will limit the effect of pySim-shell's apdu_strict setable to the apdu command only. By doing so, the bahviour of the apdu command is not altered. Users will still have to enable the 'strict' mode explicitly. At the same time all the internal functionality of pySim-shell will always use the 'strict' mode.
