[hsbt]

After breaking out of the block given to Zlib::Deflate#deflate, Zlib::Deflate#params compresses the input left by the break a second time, so the output no longer inflates to the original.

z = Zlib::Deflate.new(Zlib::DEFAULT_COMPRESSION, 9, 1)
input = Random.new(0).bytes(20000)
out = +""
z.deflate(input) { |chunk| out << chunk; break }
z.params(Zlib::BEST_SPEED, Zlib::DEFAULT_STRATEGY)
out << z.finish
Zlib.inflate(out).bytesize # => 23616, expected 20000

The rest of the input is already kept for the next call, so I clear next_in and avail_in once it is. Zlib::Inflate#inflate("") used the stale avail_in to tell whether such input was left, so it now checks the kept input instead.

Generated with Claude Code