[hsbt]

Zlib::Inflate#sync did not check whether the stream was in progress. Called from the block of Zlib::Inflate#inflate, it pointed next_in at its argument, and the inflate loop kept reading from there after the block returned, even after the argument was freed.

require "zlib"

z = Zlib::Inflate.new
z.inflate(Zlib.deflate("x" * 400_000)) do
  s = "\0\0\xff\xff".b + "\1".b * 50_000_000
  z.sync(s)
  s.clear
end
#=> [BUG] Segmentation fault (mswin)

It now raises Zlib::InProgressError, as #<< and #finish already do there. The last chunk is yielded after the loop has returned, so #sync from that yield keeps working.

I also fixed the rdoc of #sync, which described the return values the other way around.

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