Hi Andrew,

> Note that the sms_tpdu member could be of type struct sms_deliver, but the
> users may more often have access to the raw tpdu so there's no point
> decoding and reencoding it.

Overall patch looks fine, but using a raw pdu is not preferable.  Couple of 
reasons:

- When SMS is delivered, it is delivered in tpdu form, e.g. sc_address + 
deliver pdu.  To obtain the sc_address, we need to decode the deliver tpdu 
anyway.
- Before we know this is an SMS-PP download, we must check the dcs / pid.  In 
order to check those, we must again decode the tpdu.
- SMS sc_address can actually be non-numeric.  In that case the SMS-PP 
download should simply be dropped.
- Consistency with Send SMS proactive command.

> +
> +/* Returns TRUE on success */
> +ofono_bool_t stk_pdu_from_envelope(const struct stk_envelope *envelope,
> +					unsigned char *pdu, unsigned int size,
> +					unsigned char **out_pdu,
> +					unsigned int *out_size);
> 

This part just looks ugly.  Can't we hide the details of char buf[512] 
somewhere inside stk_pdu_from_envelope?  Or perhaps make **out_pdu and 
*out_size in/out arguments instead of just out.

Regards,
-Denis