From 6a845e40b485465d972b7f22b37bd0d1a1641b40 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C5=99emysl=20Janouch?= <p.janouch@gmail.com>
Date: Sun, 5 Feb 2017 22:29:55 +0100
Subject: Add a partial decoder for ZIP

---
 plugins/zip.lua | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 plugins/zip.lua

diff --git a/plugins/zip.lua b/plugins/zip.lua
new file mode 100644
index 0000000..a1b61de
--- /dev/null
+++ b/plugins/zip.lua
@@ -0,0 +1,81 @@
+--
+-- zip.lua: ZIP archives
+--
+-- 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.
+--
+
+-- Heuristics required, see https://en.wikipedia.org/wiki/Zip_(file_format)
+local detect = function (c)
+	c.endianity = "le"
+	for o = #c - 22 + 1, #c - 65535 - 22 + 1, -1 do
+		if o < 1 then break end
+		c.position = o
+		if c:u32 () == 0x06054b50 then return o end
+	end
+end
+
+local decode = function (c)
+	local eocd = detect (c ())
+	if not eocd then error ("not a ZIP file") end
+	c.endianity = "le"
+
+	c.position = eocd
+	c:u32 ("end of CD magic: %#x")
+	c:u16 ("# of this disk: %d")
+	c:u16 ("disk # where CD starts: %d")
+	local cd_len = c:u16 ("# of CD records on this disk: %d")
+	c:u16 ("total # of CD records: %d")
+	c:u32 ("size of CD: %d")
+	local cd_offset = c:u32 ("offset of (start of CD - start of archive): %d")
+	local comment_len = c:u16 ("comment length: %d")
+	c (c.position, c.position + comment_len - 1):mark ("comment")
+
+	-- TODO: decode the fields better
+	-- TODO: also mark actual file data if someone wants to put in the effort
+	c.position = cd_offset + 1
+	for i = 1, cd_len do
+		local p, magic = c.position, c:u32 ()
+		if magic ~= 0x02014b50 then break end
+		c (p, c.position - 1):mark ("CD file header magic: %#x", magic)
+		c:u16 ("version made by: %d")
+		c:u16 ("version needed to extract: %d")
+		c:u16 ("general purpose bit flag: %#x")
+		c:u16 ("compression method: %d")
+		c:u16 ("file last modification time: %d")
+		c:u16 ("file last modification date: %d")
+		c:u32 ("CRC-32: %#x")
+		c:u32 ("compressed size: %d")
+		c:u32 ("uncompressed size: %d")
+		local filename_len = c:u16 ("file name length: %d")
+		local extra_len = c:u16 ("extra field length: %d")
+		local comment_len = c:u16 ("file comment length: %d")
+		c:u16 ("disk # where file starts: %d")
+		c:u16 ("internal file attributes: %#x")
+		c:u32 ("external file attributes: %#x")
+		c:u32 ("offset of (start of local file header - start of archive): %d")
+
+		c (c.position, c.position + filename_len - 1):mark ("filename")
+		c.position = c.position + filename_len
+
+		c (c.position, c.position + extra_len - 1):mark ("extra field")
+		c.position = c.position + extra_len
+
+		c (c.position, c.position + comment_len - 1):mark ("file comment")
+		c.position = c.position + comment_len
+	end
+end
+
+hex.register { type="zip", detect=detect, decode=decode }
+
-- 
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