Ruby zlib deflate and inflate not working as intended

Question

I have been trying to get a (relatively) simple compression and decompression functionality working on any sort of object (images, csv files, docs etc) and have had no success whatsoever.

I have tried many things and currently I think this code is close to it (not my code) however I have been having trouble getting it to work.

Hoge.txt content:

blahblah123

Ruby deflate class titled rubyfiletest.rb:

require "zlib"

file_name = "hoge.txt"
compressed_file = File.open(file_name +".gz", "w+")

zd = Zlib::Deflate.new(Zlib::BEST_COMPRESSION, 15, Zlib::MAX_MEM_LEVEL, Zlib::HUFFMAN_ONLY)


compressed_file << zd.deflate(File.read(file_name))
compressed_file.close
zd.close

So with this code what it does is create a .gz file entitled hoge.txt.gz which generates this in the command prompt

rubyfiletest.rb:9:in `read': No such file or directory - hoge.txt (Errno::ENOEN)

Also if I try to open the newly created file with winrar/7zip it will give me this error:

The archive is either in unknown format or damaged.

Ruby inflate class titled rubyinflate.rb:

require 'zlib'

File.open('hoge.txt.gz', 'rb') do |compressed|
    File.open('hoge.txt', 'w') do |decompressed|
        gz = Zlib::GzipReader.new(compressed)
        result = gz.read
        decompressed.write(result)
        gz.close
    end
end

I am guessing the compression is not working correctly since I cannot even open the compressed file and have been having so many problems with this. I think it is worth while to mention I am new to ruby. I also would like to know if the way this is implemented would enable images and all types of files to be compressed/decompressed fine.

* Update *

I was getting the error for wrong path because hoge was saved as hoge.txt.txt (doh!) and it was looking for hoge.txt in that path. So now I changed the ruby compression code a little so that the output creates a valid gzip file as pointed out by Matthew T.

This is what it looks like now

require "zlib"

file_name = "hoge.txt"
compressed_file = File.open(file_name +".gz", "w+b")

zd = Zlib::GzipWriter.new(compressed_file)

zd << File.read(file_name)
compressed_file.close
zd.close

With this as the new rubyfiletest.rb class to decompress using GzipWriter I receive this error when I run this class:

rubyfiletest.rb:8 in 'write': closed stream (IOError)

This will still generate the .gz file (and I can now open it in winrar/7zip without any problems however it is empty, should contain 'blahblah123'). After I compress it and run the rubyinflate.rb I receive this error from rubyinflate.rb:

rubyinflate.rb:6 in 'read': unecpected end of file (Zlib::GzipFile::Error)

I think these errors may be causing the data to not be copied over? If I used an image would that data be copied over assuming this code worked?

Answer 1

Is your hoge.txt file in your current directory when you run your program? The big error warning indicating that the file cannot be found would be the first thing that I would try to resolve before assuming that the compression and decompression is not working. I think that you will find that the "compressed" file cannot be read because it is an empty file.

---

After you resolve your program's inability to find the hoge.txt file, you are still going to have problems with your output. Deflate does not create a gzip file; it only does the compression. There is more that goes into a gzip file than just the compressed data. There is also header and footer information. I would recommend that you use the GzipWriter class instead of the Deflate class.

require "zlib"

file_name = "hoge.txt"
compressed_file = File.open(file_name +".gz", "w+")

zd = Zlib::GzipWriter.new(compressed_file)

zd << File.read(file_name)
compressed_file.close

Answer 2

Since you mentioned winrar, it sounds like you're on Windows. Once you get past finding hoge.txt, you will need a "w+b", not "w+" for the mode when writing the compressed data.