Add gzip.lua
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--
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-- gzip.lua: GZIP File Format
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--
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-- Copyright (c) 2017, Přemysl Janouch <p.janouch@gmail.com>
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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, provided that the above
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-- copyright notice and this permission notice appear in all copies.
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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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local detect = function (c)
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return c:read (2) == "\x1f\x8b"
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end
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local function latin1_to_utf8 (s)
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local u = ""
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for _, c in ipairs (table.pack (s:byte (1, #s))) do
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if c < 0x80 then
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u = u .. string.char (c)
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else
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u = u .. string.char (0xc0 | c >> 6, 0x80 | c & 0x3f)
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end
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end
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return u
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end
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-- Everything here is based on RFC 1952 and some bits of dictzip
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local crc32_table = function ()
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local table = {}
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for n = 0, 255 do
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local c = n
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for k = 0, 7 do
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if c & 1 ~= 0 then
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c = 0xedb88320 ~ (c >> 1)
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else
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c = c >> 1
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end
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end
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table[n] = c
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end
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return table
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end
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local crc32 = function (s)
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local table, c = crc32_table (), 0xffffffff
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for n = 1, #s do c = table[(c ~ s:byte (n)) & 0xff] ~ (c >> 8) end
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return c ~ 0xffffffff
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end
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local os_table = {
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[0] = "FAT filesystem",
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[1] = "Amiga",
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[2] = "VMS",
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[3] = "Unix",
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[4] = "VM/CMS",
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[5] = "Atari TOS",
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[6] = "HPFS filesystem",
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[7] = "Macintosh",
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[8] = "Z-System",
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[9] = "CP/M",
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[10] = "TOPS-20",
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[11] = "NTFS filesystem",
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[12] = "QDOS",
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[13] = "Acord RISCOS",
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[255] = "unknown"
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}
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local decode = function (c)
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if not detect (c ()) then error ("not a GZIP file") end
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local start = c.position
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c.endianity = 'le'
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c:u16 ("GZIP magic")
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local deflate
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c:u8 ("compression method: %s", function (u8)
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if u8 ~= 8 then return "unknown: %d", u8 end
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deflate = true
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return "deflate"
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end)
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local text, hcrc, extra, name, comment
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c:u8 ("flags: %s", function (u8)
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text = u8 & 1 == 1
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hcrc = (u8 >> 1) & 1 == 1
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extra = (u8 >> 2) & 1 == 1
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name = (u8 >> 3) & 1 == 1
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comment = (u8 >> 4) & 1 == 1
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local flags = ""
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if text then flags = flags .. ", text" end
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if hcrc then flags = flags .. ", header CRC" end
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if extra then flags = flags .. ", extra" end
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if name then flags = flags .. ", filename" end
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if comment then flags = flags .. ", comment" end
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if flags == "" then
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return "none"
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else
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return "%s", flags:sub (3)
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end
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end)
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c:u32 ("modified time: %s", function (u32)
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if u32 == 0 then return "none" end
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return os.date ("!%F %T", u32)
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end)
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c:u8 ("extra flags: %s", function (u8)
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if deflate then
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if u8 == 2 then return "slowest (%d)", u8 end
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if u8 == 4 then return "fastest (%d)", u8 end
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end
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return "unknown: %d", u8
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end)
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c:u8 ("OS: %s", function (u8)
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os = os_table[u8]
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if os then return os end
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return "unknown: %d", u8
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end)
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local extra_table = {}
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if extra then
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local len = c:u16 ("extra field length: %d")
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c (c.position, c.position + len - 1):mark ("extra field")
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-- This will handle even overflowing subfields
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while len >= 4 do
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local p, sid = c.position, c:read (2)
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c (p, c.position - 1):mark ("subfield ID: %s", sid)
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local sid_len = c:u16 ("subfield length: %d")
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local subfield = c (c.position, c.position + sid_len - 1)
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subfield:mark ("subfield data")
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extra_table[sid] = subfield
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c.position = c.position + sid_len
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len = len - 4 - sid_len
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end
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c.position = c.position + len
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end
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if name then
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c:cstring ("filename: %s", latin1_to_utf8)
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end
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if comment then
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c:cstring ("comment: %s", latin1_to_utf8)
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end
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if hcrc then
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c:u16 ("CRC-16: %s", function (u16)
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local crc = 0xffff & crc32 (c (start):read (c.position - 1))
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if crc == u16 then check = "ok" else check = "failed" end
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return "%#06x (%s)", u16, check
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end)
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end
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-- Compressed data follows immediately
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-- We can jump through it without decompression in dictzip v1 archives
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local ra = extra_table["RA"]
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if not ra then return end
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local ra_ver = ra:u16 ("RA version: %d")
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if ra_ver ~= 1 then return end
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local ra_chunk = ra:u16 ("chunk length: %d")
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local ra_count = ra:u16 ("chunk count: %d")
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for i = 1, ra_count do
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local len = ra:u16 ("chunk " .. i .. " compressed length: %d")
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c (c.position, c.position + len - 1):mark ("chunk " .. i)
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c.position = c.position + len
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end
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-- 1 final, 01 static, 0000000 end of block, padding discarded
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-- This is the kind of block that dictzip finalizes archives with
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if c:u16 () & 0x03ff == 0x0003 then
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c:u32 ("CRC-32: %#010x")
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c:u32 ("input size: %d")
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end
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end
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hex.register { type="gzip", detect=detect, decode=decode }
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