Simplify the driver interface

[jsonn]

Consider the abstract state machine and there are four states:

1. Waiting for further input
2. Waiting for further output
3. Stream has been processed successfully.
4. Stream has been processed unsuccessfully.

Those states should be reflected in the exit codes of the inflate driver function. That simplifies the logic for caller as well as it avoids most address calculations to see which state the library is currently in.

[dunhor]

To make sure I understand the request completely, do you have any specific suggestions (e.g. in this scenario X happens). Some of these seem to have overlaps. E.g. 1 & 2 can both be true at the same time as well as 2 & 3. Which suggests I'm likely mis-understanding the ask.

That simplifies the logic for caller as well as it avoids most address calculations to see which state the library is currently in.

The pointer-arithmetic logic is probably the thing I dislike the most about the current implementation, though I'm not sure the return code would necessarily help here (more of an indication I'm probably mis-understanding the request). One thing I've thought about is to add some fields like last_in / last_out (names not finalized) that communicate the most recent number of bytes read/written respectively.