Chris made me aware that ASCII code 0 actually is a valid character (usually entered as Ctrl-Space or Ctrl-@) and that it is actually used (i.e. by EMACS).
The Apple II allows to natively enter the ASCII code 0 via Ctrl-@. However so far get_key_if_available returned 0 in accumulator to signal that no key was pressed. In order to allow the Apple II get_key_if_available to return the ASCII code 0 in the accumulator I changed it to use the carry flag to signal that no key was pressed.
Because get_key_if_available needs of course to behave the same on all targets I changed the other implementations to use the carry flag too.
Unfortunately I don't know enough about input capabilities of the C64 to decide on how to best get Telnet65 to send ASCII code 0 there.
It's imho in general a pretty unfortunate design to have IP65 check the keyboard during blocking operations. Rather it should call back into the application and have that decide what type of user abort it wants to offer.
Anyhow I don't want to change all that - at least not now. Therefore I just added the option to influence which key is considered the abort key - and provide a key value that isn't actually used and as such disables the abort check.
On the A2 get_key deletes any already pressed key. Therefore it's a bad idea(tm) to call it to retrieve the key detected in get_key_if_available. So now get_key_if_available insteads retrieves the key on its own via direct hw access. This was already done the very same way in check_for_abort_key. And apart from not working as expected the benefit of get_key displaying a cursor wasn't useful here anyway because get_key was supposed to return right away with the pressed key so the cursor wouldn't have been visible at all.
The pretty small check_for_abort_key is used by DHCP and DNS which means it is used by about every IP65 program. The pretty large get_filtered_input on the other hand is very seldom used so it makes sense to put the latter in a separate module to keep it from ending up in binaries unused.
- Tab chars were partially used with the unusual width of two blanks. I removed them altogether.
- Line endings were inconsistent even iniside individual files. I normalized them.
- I introduced a consistent coding style regarding comment indenting and blank line usage.
- I removed trailing spaces.
- I removed newlines following unnamed labels.
- ...
