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| -rw-r--r-- | plugins/gzip.lua | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/plugins/gzip.lua b/plugins/gzip.lua new file mode 100644 index 0000000..8cc93a1 --- /dev/null +++ b/plugins/gzip.lua @@ -0,0 +1,185 @@ +-- +-- gzip.lua: GZIP File 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. +-- + +local detect = function (c) + return 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) + 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 } |