Before this patch we would use `IO.copy_stream` with the tar entry
object rather than just straight to the IO.  That means every time
copy_stream wanted data, we would have to proxy the call.

The reason we did this is because every tar entry object _shares_ the
same IO object, and previous to https://github.com/rubygems/rubygems/commit/8927533b0a47
we would call `IO.copy_stream` _without_ a size.  Without passing a
size, copy_stream will just read until there is nothing left to read, so
these proxy object emulate finding "the end of the file" (where "end of
file" means "end of tar chunk").  Without emulating this "end of file"
behavior, copy_stream would just keep reading past the end of the tar
chunk.

However, now that we're passing the size to copy_stream, we can bypass
the proxy object overhead and just use the IO object directly because
copy_stream knows exactly the number of bytes it needs to read and will
stop when it reaches the goal.

https://github.com/rubygems/rubygems/commit/857002c135

Previously, `rake install` or `rake update` would fail if there was a non-tar format `.gem` file in the current working directory.

https://github.com/rubygems/rubygems/commit/f562788f1d

Gem::Package::TarReader::Entry now raises EOFError or returns nil
appropriately based on Ruby core IO.read and IO.readpartial behavior.

Zlib will respond accordingly by raising Zlib::GzipFile::Error on EOF.

When verifying a gem or extracting contents, raise FormatError similar
to other cases of corrupt gems.

Addresses a bug where Gem::Package would attempt to call size on nil
instead of raising a more descriptive and useful error, leading users
to assume the problem is internal to rubygems.

Remove unused error class TarReader::UnexpectedEOF that was never raised
since the NoMethodError on nil would happen first. Use EOFError instead.

https://github.com/rubygems/rubygems/commit/dc6129644b

https://github.com/rubygems/rubygems/commit/05cc97bdf8

https://github.com/rubygems/rubygems/commit/fba6e94de9

TarReader#each previously implemented a partial version of seek.
This code moved to Entry#seek for use from TarReader#each.

Entry#close now returns nil instead of true, like IO#close.

Closing an Entry now seeks to the end of the Entry, seeking past
any remaining zero byte tar file padding and moving the io to the
correcty position to read the next file in the archive.

Uses seek for Entry#rewind and #pos=, fixing the tar->gzip->tar nested
rewind that would break previous to this change.

Add Entry.open that behaves more like File.open.

https://github.com/rubygems/rubygems/commit/f5149565d5

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

https://github.com/rubygems/rubygems/commit/c74fc58695