56 lines
2.0 KiB
Lua
56 lines
2.0 KiB
Lua
--
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-- zlib.lua: ZLIB Compressed Data Format
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--
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-- Copyright (c) 2017, Přemysl Eric Janouch <p@janouch.name>
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--
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-- Permission to use, copy, modify, and/or distribute this software for any
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-- purpose with or without fee is hereby granted.
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--
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-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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-- MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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-- SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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-- WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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-- OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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-- CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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--
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-- Based on RFC 1950, this format isn't very widely used
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local decode = function (c)
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c.endianity = 'le'
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local deflate_levels = { "fastest", "fast", "default", "slowest" }
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local deflate
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local cmf = c:u8 ("compression method and flags: %s", function (u8)
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local cm, cm_name = u8 & 0xf, "unknown"
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local cinfo, cinfo_name = u8 >> 4, "unknown"
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if cm == 8 then
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deflate = true
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cm_name = "deflate"
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cinfo_name = ("window size = %d"):format (2 ^ (cinfo + 8))
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end
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return "%s (%d), %s (%d)", cm_name, cm, cinfo_name, cinfo
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end)
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local have_dict
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local flags = c:u8 ("flags: %s", function (u8)
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local check = (cmf * 256 + u8) % 31 == 0
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if check then check = "ok" else check = "failed" end
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local level, level_name = (u8 >> 6) & 3, "unknown"
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if deflate then level_name = deflate_levels[level + 1] end
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have_dict = (u8 >> 5) & 1 == 1
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local info = "preset dictionary"
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if not have_dict then info = "no " .. info end
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return "level %s (%d), check %s, %s", level_name, level, check, info
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end)
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if have_dict then
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c:u16 ("dictionary Adler-32 checksum: %04x")
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end
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-- Compressed data follows immediately
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-- Not going to decompress it, so we don't know where the final checksum is
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end
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hex.register { type="zlib", detect=nil, decode=decode }
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