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Rewrite file systems to use ByteChannels #575

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@SquidDev SquidDev commented Sep 21, 2018

This replaces the existing IMount openFor* method with openChannelFor* ones, which return an appropriate byte channel instead. I've put a little more detail in the commit message about the implications of this, but there's a couple of user-facing benefits:

  • Add support for seekable handles. This works for any main filesystem or HTTP handle opened in binary mode.
  • Rewrite the io library to more accurately emulate PUC Lua's implementation. This passes a large portion of the the test suite - the remaining issues mainly involve their use of os.date and setvbuf, neither of which are implemented.
This replaces the existing IMount openFor* method with openChannelFor*
ones, which return an appropriate byte channel instead.

As channels are not correctly closed when GCed, we introduce a
FileSystemWrapper. We store a weak reference to this, and when it is
GCed or the file closed, we will remove it from our "open file" set and
ensure any underlying buffers are closed.

While this change may seem a little odd, it does introduce some
benefits:

 - We can replace JarMount with a more general FileSystemMount. This
   does assume a read-only file system, but could technically be used
   for other sources.

 - Add support for seekable (binary) handles. We can now look for
   instances of SeekableByteChannel and dynamically add it. This works
   for all binary filesystem and HTTP streams.

 - Rewrite the io library to more accurately emulate PUC Lua's
   implementation. We do not correctly implement some elements (most
   noticably "*n", but it's a definite improvement.
@SquidDev SquidDev force-pushed the SquidDev-CC:feature/file-seeking branch from d6c5631 to 518eefb Sep 26, 2018
SquidDev added 3 commits Oct 24, 2018
 - Rename openStreamFor* methods to more accurate openChannelFor*
 - Fix ArrayByteChannel having an incorrect .position() implementation
 - Fix stdin not being considered a "readable" input
 - Return an unsigned byte rather than a signed one for no-args .read()
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@SquidDev SquidDev commented Nov 3, 2018

Possibly worth noting that seekable binary handles do not work for Jar mounts - namely the rom and any treasure disks.

It would be possible to implement this by reading the entire contents of the file into memory and exposing it as an ArrayByteChannel, but I think it's worth discussing whether it's worth it.

ccserver pushed a commit to ccserver/ComputerCraft that referenced this pull request Sep 16, 2019
…file-seeking

Rewrite file systems to use ByteChannels
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