Support mark / reset in InputStreamReader

[nishihatapalmer]

InputStreamReader gives up if it can't find a Window in the cache from a position which has already been read, and throws a WindowMissingException. This is because you can't rewind streams, so if it isn't in the cache, we can't get the data.

If the underlying InputStream supported mark / reset, we have the possibility of rewinding the stream.

It still may fail, but then we just might get another IOException - instead of the guaranteed WindowMissingException (which is an IOException).

If it succeeds, we can read forward again in the stream to obtain the missing data.

[nishihatapalmer]

The simple implementation is to call mark() immediately on any stream we get (which we also assume is position 0).

Then we are relying on the underlying implementation being able to rewind the stream back to the point we got it, even if we've subsequently read a lot of data.

If it can't do that, it will fail sometimes. Whether failing every time is better than failing sometimes is something which only a user can answer - it depends on what is being used for.

[nishihatapalmer]

Another consideration is that in order to be able to rewind the stream, the stream must be performing some kind of caching.

If the stream supports caching, should we even bother doing our own caching?

I guess if we don't want to do our own caching, we can just pass a NoCache into the cache constructor.