cache2: uncrustify
stream: rename cache2.c to cache.c

I never found cache1.c (whatever it was named, if it ever existed).

cache2.h will be deleted later, so don't go through the trouble of
renaming it.
core: use STREAM_CTRL instead of accessing stream_dvd internals

Some code in mplayer.c did stuff like accessing (dvd_priv_t *)st->priv.
Do this indirectly by introducing STREAM_CTRL_GET_DVD_INFO. This is
extremely specific to DVD, so it's not worth abstracting this further.

This is a preparation for turning the cache into an actual stream, which
simply wraps the cached stream. There are other streams which are
accessed in the way DVD was, at least TV/radio/DVB. We assume these
can't be used with the cache. The code doesn't look thread-safe or fork
aware.
stream: misleading statement
stream_dvd: remove some deadly insane code

Of course all of stream_dvd.c (as well as libdvdread) is completely
insane, but at least this hack for ancient broken compilers on really
obscure platforms should be safe to remove.
stream_cdda, stream_vcd: check read buffer size

These assumed that the buffer provided with fill_buffer() was at least
sector sized, instead of checking the size parameter.

This is just a cleanup, since every caller made sure to align everything
on sector sizes, if a stream has the sector size set.
stream: move VCD specific stuff to stream_vcd

I don't even know what VCDs are. A prehistoric version of the DVD or so.
stream: remove unused function
stream: remove pointless check
cache: make the stream cache a proper stream that wraps other streams

Before this commit, the cache was franken-hacked on top of the stream
API. You had to use special functions (like cache_stream_fill_buffer()
instead of stream_fill_buffer()), which would access the stream in a
cached manner.

The whole idea about the previous design was that the cache runs in a
thread or in a forked process, while the cache awa functions made sure
the stream instance looked consistent to the user. If you used the
normal functions instead of the special ones while the cache was
running, you were out of luck.

Make it a bit more reasonable by turning the cache into a stream on its
own. This makes it behave exactly like a normal stream. The stream
callbacks call into the original (uncached) stream to do work. No
special cache functions or redirections are needed. The only different
thing about cache streams is that they are created by special functions,
instead of being part of the auto_open_streams[] array.

To make things simpler, remove the threading implementation, which was
messed into the code. The threading code could perhaps be kept, but I
don't really want to have to worry about this special case. A proper
threaded implementation will be added later.

Remove the cache enabling code from stream_radio.c. Since enabling the
cache involves replacing the old stream with a new one, the code as-is
can't be kept. It would be easily possible to enable the cache by
requesting a cache size (which is also much simpler). But nobody uses
stream_radio.c and I can't even test this thing, and the cache is
probably not really important for it either.
stream: add stream_unread_buffer()

demux_lavf probes up to 2 MB of data in the worst case. When the ffmpeg
demuxer is actually opened, the stream is seeked back to 0, and the
previously read data is thrown away.

This wasn't a problem for playback of local files, but it's less than
ideal for playing from slow media (like web streams), and breaks
completely if the media is not seekable (pipes, some web streams).

This new function is intended to allow fixing this. demux_lavf will use
it to put the read probe data back into the buffer.

The simplest way of implementing this function is by making it
transparently extend the normal stream buffer. This makes sure no
existing code is broken by new weird special cases. For simplicity
and to avoid possible performance loss due to extra dereferencing
when accessing the buffer, we just extend the static buffer from
8 KB to 2 MB. Normally, most of these 2 MB will stay uncommitted, so
there's no associated waste of memory. If demux_lavf really reads all
2 MB, the memory will be committed and stay unused, though.
demux_lavf: change probing, use stream_unread_buffer()

This fixes a longstanding issue with demux_lavf probing.
See previous commit.
stream: add partial read function

This is a nice way to avoid an additional copy of the data when reading
with stream_read().
cache: use threads instead of fork()

Basically rewrite all the code supporting the cache (i.e. anything other
than the ringbuffer logic). The underlying design is untouched.

Note that the old cache2.c (on which this code is based) already had a
threading implementation. This was mostly unused on Linux, and had some
problems, such as using shared volatile variables for communication and
uninterruptible timeouts, instead of using locks for synchronization.

This commit does use proper locking, while still retaining the way the
old cache worked. It's basically a big refactor.

Simplify the code too. Since we don't need to copy stream ctrl args
anymore (we're always guaranteed a shared address space now), lots of
annoying code just goes away. Likewise, we don't need to care about
sector sizes. The cache uses the high-level stream API to read from
other streams, and sector sizes are handled transparently.
stream: reset buffer even on EOF/error

This probably didn't matter anywhere, but it's more proper.
stream: cosmetics
stream: check for interruption when trying to reconnect stream

This happens with something like "mpv https://www.youtube.com/watch".
The URL is obviously not valid, but the stream layer tries to reconnect.
This commit at least allows to use the terminal to abort gracefully.
(Other than killing the process.)
stream: remove stream_reset()

This function was called in various places. Most time, it was used
before a seek. In other cases, the purpose was apparently resetting
the EOF flag. As far as I can see, this makes no sense anymore. At
least the stream_reset() calls paired with stream_seek() are completely
pointless. A seek will either seek inside the buffer (and reset the
EOF flag), or do an actual seek and reset all state.
stream: don't set EOF flag in stream implementations

EOF should be set when reading more data fails. The stream
implementations have nothing to say here and should behave correctly
when trying to read when EOF was actually read.

Even when seeking, a correct EOF flag should be guaranteed. stream_seek()
(or actually stream_seek_long()) calls stream_fill_buffer() at least
once, which also updates the EOF flag.
stream: fix some aspects of EOF handling

The stream EOF flag should only be set when trying to read past the end
of the file (relatively similar to unix files). Always clear the EOF
flag on seeking. Trying to set it "properly" (depending whether data is
available at seek destination or not) might be an ok idea, but would
require attention to too many special cases. I suspect before this
commit (and in MPlayer etc. too), the EOF flag wasn't handled
consistently when the stream position was at the end of the file.

Fix one special case in ebml.c and stream_skip(): this function couldn't
distinguish between at-EOF and past-EOF either.