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