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