New zipwriter module (wrapping zlib via ffi)

Needed for wikipedia epub generation

ffi/zipwriter.lua

@@ -0,0 +1,201 @@
+-- Zip packing workflow & code from luarocks' zip.lua :
+--   https://github.com/luarocks/luarocks/blob/master/src/luarocks/tools/zip.lua
+-- Modified to not require lua-zlib (we can wrap zlib with ffi)
+--   cf: http://luajit.org/ext_ffi_tutorial.html, which uses zlib as an example !
+-- Simplified to take filename and content from strings and not from disk
+
+-- We only need a few functions from zlib
+local ffi = require "ffi"
+ffi.cdef([[
+unsigned long crc32(unsigned long crc, const char *buf, unsigned len);
+unsigned long compressBound(unsigned long sourceLen);
+int compress2(uint8_t *dest, unsigned long *destLen, const uint8_t *source, unsigned long sourceLen, int level);
+]])
+
+-- We only need to wrap 2 zlib functions to make a zip file
+local _zlib = ffi.load(ffi.os == "Windows" and "zlib1" or "z")
+local function zlibCompress(data)
+    local n = _zlib.compressBound(#data)
+    local buf = ffi.new("uint8_t[?]", n)
+    local buflen = ffi.new("unsigned long[1]", n)
+    local res = _zlib.compress2(buf, buflen, data, #data, 9)
+    assert(res == 0)
+    return ffi.string(buf, buflen[0])
+end
+local function zlibCrc32(data, chksum)
+    chksum = chksum or 0
+    data = data or ""
+    return _zlib.crc32(chksum, data, #data)
+end
+
+local function numberToByteString(number, nbytes)
+    local out = {}
+    for _ = 1, nbytes do
+        local byte = number % 256
+        table.insert(out, string.char(byte))
+        number = (number - byte) / 256
+    end
+    return table.concat(out)
+end
+
+
+-- Pure lua zip writer
+local ZipWriter = {}
+
+function ZipWriter:new()
+    local o = {}
+    setmetatable(o, self)
+    self.__index = self
+    return o
+end
+
+--- Begin a new file to be stored inside the zipfile.
+function ZipWriter:_open_new_file_in_zip(filename)
+    if self.in_open_file then
+        self:_close_file_in_zip()
+        return nil
+    end
+    local lfh = {}
+    self.local_file_header = lfh
+    lfh.last_mod_file_time = self.started_time -- 0 = 00:00
+    lfh.last_mod_file_date = self.started_date -- 0 = 1980-00-00 00:00
+    lfh.file_name_length = #filename
+    lfh.extra_field_length = 0
+    lfh.file_name = filename:gsub("\\", "/")
+    lfh.external_attr = 0
+    self.in_open_file = true
+    return true
+end
+
+--- Write data to the file currently being stored in the zipfile.
+function ZipWriter:_write_file_in_zip(data)
+    if not self.in_open_file then
+        return nil
+    end
+    local lfh = self.local_file_header
+    local compressed = zlibCompress(data):sub(3, -5)
+    lfh.crc32 = tonumber(zlibCrc32(data))
+    lfh.compressed_size = #compressed
+    lfh.uncompressed_size = #data
+    self.data = compressed
+    return true
+end
+
+--- Complete the writing of a file stored in the zipfile.
+function ZipWriter:_close_file_in_zip()
+    local zh = self.ziphandle
+    if not self.in_open_file then
+        return nil
+    end
+    -- Local file header
+    local lfh = self.local_file_header
+    lfh.offset = zh:seek()
+    zh:write(numberToByteString(0x04034b50, 4)) -- signature
+    zh:write(numberToByteString(20, 2)) -- version needed to extract: 2.0
+    zh:write(numberToByteString(0, 2)) -- general purpose bit flag
+    zh:write(numberToByteString(8, 2)) -- compression method: deflate
+    zh:write(numberToByteString(lfh.last_mod_file_time, 2))
+    zh:write(numberToByteString(lfh.last_mod_file_date, 2))
+    zh:write(numberToByteString(lfh.crc32, 4))
+    zh:write(numberToByteString(lfh.compressed_size, 4))
+    zh:write(numberToByteString(lfh.uncompressed_size, 4))
+    zh:write(numberToByteString(lfh.file_name_length, 2))
+    zh:write(numberToByteString(lfh.extra_field_length, 2))
+    zh:write(lfh.file_name)
+    -- File data
+    zh:write(self.data)
+    -- Data descriptor
+    zh:write(numberToByteString(lfh.crc32, 4))
+    zh:write(numberToByteString(lfh.compressed_size, 4))
+    zh:write(numberToByteString(lfh.uncompressed_size, 4))
+    -- Done, add it to list of files
+    table.insert(self.files, lfh)
+    self.in_open_file = false
+    return true
+end
+
+--- Complete the writing of the zipfile.
+function ZipWriter:close()
+    local zh = self.ziphandle
+    local central_directory_offset = zh:seek()
+    local size_of_central_directory = 0
+    -- Central directory structure
+    for _, lfh in ipairs(self.files) do
+        zh:write(numberToByteString(0x02014b50, 4)) -- signature
+        zh:write(numberToByteString(3, 2)) -- version made by: UNIX
+        zh:write(numberToByteString(20, 2)) -- version needed to extract: 2.0
+        zh:write(numberToByteString(0, 2)) -- general purpose bit flag
+        zh:write(numberToByteString(8, 2)) -- compression method: deflate
+        zh:write(numberToByteString(lfh.last_mod_file_time, 2))
+        zh:write(numberToByteString(lfh.last_mod_file_date, 2))
+        zh:write(numberToByteString(lfh.crc32, 4))
+        zh:write(numberToByteString(lfh.compressed_size, 4))
+        zh:write(numberToByteString(lfh.uncompressed_size, 4))
+        zh:write(numberToByteString(lfh.file_name_length, 2))
+        zh:write(numberToByteString(lfh.extra_field_length, 2))
+        zh:write(numberToByteString(0, 2)) -- file comment length
+        zh:write(numberToByteString(0, 2)) -- disk number start
+        zh:write(numberToByteString(0, 2)) -- internal file attributes
+        zh:write(numberToByteString(lfh.external_attr, 4)) -- external file attributes
+        zh:write(numberToByteString(lfh.offset, 4)) -- relative offset of local header
+        zh:write(lfh.file_name)
+        size_of_central_directory = size_of_central_directory + 46 + lfh.file_name_length
+    end
+    -- End of central directory record
+    zh:write(numberToByteString(0x06054b50, 4)) -- signature
+    zh:write(numberToByteString(0, 2)) -- number of this disk
+    zh:write(numberToByteString(0, 2)) -- number of disk with start of central directory
+    zh:write(numberToByteString(#self.files, 2)) -- total number of entries in the central dir on this disk
+    zh:write(numberToByteString(#self.files, 2)) -- total number of entries in the central dir
+    zh:write(numberToByteString(size_of_central_directory, 4))
+    zh:write(numberToByteString(central_directory_offset, 4))
+    zh:write(numberToByteString(0, 2)) -- zip file comment length
+    zh:close()
+    return true
+end
+
+-- Open zipfile
+function ZipWriter:open(zipfilepath)
+    self.files = {}
+    self.in_open_file = false
+    -- set modification date and time of files to now
+    local t = os.date("*t")
+    self.started_date = bit.bor(
+        bit.lshift(t.year-1980, 9),
+        bit.lshift(t.month,     5),
+        bit.lshift(t.day,       0)
+    )
+    self.started_time = bit.bor(
+        bit.lshift(t.hour,     11),
+        bit.lshift(t.min,       5),
+        bit.rshift(t.sec+2,     1)
+    )
+    self.ziphandle = io.open(zipfilepath, "wb")
+    if not self.ziphandle then
+        return nil
+    end
+    return true
+end
+
+-- Add to zipfile content with the name in_zip_filepath
+function ZipWriter:add(in_zip_filepath, content)
+    self:_open_new_file_in_zip(in_zip_filepath)
+    self:_write_file_in_zip(content)
+    self:_close_file_in_zip()
+end
+
+-- Convenience function
+-- function ZipWriter.createZipWithFiles(zipfilename, files)
+--     local zw = ZipWriter:new()
+--     zw:open(zipfilename)
+--     for _, f in pairs(files) do
+--         zw:add(f.filename, f.content)
+--     end
+--     zw:close()
+-- end
+-- files = {}
+-- files[1] = {filename="tutu.txt", content="this is tutu"}
+-- files[2] = {filename="subtoto/toto.txt", content="this is toto in subtoto directory"}
+-- createZipWithFiles("tata.zip", files)
+
+return ZipWriter