[Solved] Unable to read compressed file

[alberto_lara]

Hi guys, I'm not fully familiarized with the math or filesystem API and I'm stuck here:

Code: Select all

function love.load()
    dataComp = love.math.compress("dsff sd  87sd f9f7 sd9 fsd")
    ok = love.filesystem.write("test1", dataComp)

    if ok then
        print("data compressed:")
        print(tostring(love.filesystem.read("test1")))
    end
end

function love.update(dt)

end

function love.draw()

end

I don't get any prints on the console (I'm on linux) and my intuition says I should get at least the "data compressed" text (if I comment the filesystem.read line then I get it, otherwise I get nothing, that's what confuses me more!). I can confirm the data is actually being written in a "test1" file.

Any help will be appreciated. Thanks in advance.

EDIT: If I don't compress the data then I can save it and get it again with no problems so I guess it has something to do with compress?

[raidho36]

Clearly your issue is that both of those prints are behind the if-guard, and it doesn't execute for one reason or another.

[alberto_lara]

That was the first thing I thought as well, but if you comment this line:

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print(tostring(love.filesystem.read("test1")))

then you get the "data compressed:" text, so the "ok" flag is = true. The weird thing is, if I try to read the file, then I get no prints, like if "ok" is = false, but if the read() function is causing it to be false, then that makes no sense for me (because it has to be true to call read() anyway... pretty weird)

[raidho36]

Oh right, I see. Compression creates all 256 single byte characters (which can in turn cause invalid multi byte characters) most of which are unprintable or otherwise break printing. Just don't print the compressed byte string. Convert it to hex format or base 64, if you need to print it anyway.

[Nixola]

Maybe there's some weird byte you print; try printing the uncompressed thata, or each of the bytes ( print(love.filesystem.read("test1"):gsub(".", function(c) return ("0x%x "):format(c:byte()) end)) )
EDIT - ninja'd by raidho, but answer is still kind of relevant

[alberto_lara]

I need to read the compressed data and then decompress it, sorry, I didn't mention that. Any ideas of how can I do this?

[zorg]

io.write may print it, but as raidho said, even then it's also dependent on the console/terminal language encoding and the font, so a hexdump would be better:

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-- from: http://lua-users.org/wiki/HexDump
function hex_dump(buf)
      for byte=1, #buf, 16 do
         local chunk = buf:sub(byte, byte+15)
         io.write(string.format('%08X  ',byte-1))
         chunk:gsub('.', function (c) io.write(string.format('%02X ',string.byte(c))) end)
         io.write(string.rep(' ',3*(16-#chunk)))
         io.write(' ',chunk:gsub('%c','.'),"\n") 
      end
   end

Also, for decompressing, there's the fittingly named love.math.decompress that goes with the compress function.

[alberto_lara]

Also, for decompressing, there's the fittingly named love.math.decompress that goes with the compress function.

I'm aware of this, but I don't really know if this is the right way (I guess not, should I do first the conversion thing? if so, how can I convert that dumped data to a lua table again?)

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function love.load()
    dataComp = love.math.compress("dsff sd  87sd f9f7 sd9 fsd")
    ok = love.filesystem.write("test1", dataComp)

    if ok then
        decompStr = love.math.decompress(love.filesystem.read("test1"))
        print(decompStr)
    end
end

function love.update(dt)

end

function love.draw()

end

this throws:

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Error: main.lua:338: Invalid compressed data format: 32

EDIT: I'm aware the file read returns "raw" content, so LÖVE doesn't really know if it's a CompressedData object (right?) so this is the part I care, how to save a compressed file (which type is CompressedData), get it again and somehow tell to LÖVE that it is an object of that type so I can get the original string.

[raidho36]

The read function returns string plus it's length. Both get passed into decompress, which needs second argument to be compression type, and of course "32" of not a valid one.

[alberto_lara]

Holy crap, thanks for that last comment! It works fine now with this approach:

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function love.load()
    dataComp = love.math.compress([[
        data = {
            {[1] = 32432, [2] = 3423},
            {[1] = 32432, [2] = 3423},
            {[1] = 32432, [2] = 3423},
            {[1] = 32432, [2] = 3423},
            {[1] = 32432, [2] = 3423},
            {[1] = 32432, [2] = 3423},
        }
    ]], "lz4")
    ok = love.filesystem.write("test1", dataComp)

    if ok then
        local data, size = love.filesystem.read("test1")
        decompStr = love.math.decompress(data, "lz4")
        print(decompStr)
    end
end

function love.update(dt)

end

function love.draw()

end