Question

I am trying to decompress a file with following Ruby code.

File.open("file_compressed.gz") do |compressed|
  File.open("file_decomp","w") do |decompressed|
    gz = Zlib::GzipReader.new(compressed)
    result = gz.read
    decompressed.write(result)
    gz.close
  end
end

But I am getting following error –

 not in gzip format (Zlib::GzipFile::Error)
 ./features/support/abc/abc_file.rb:44:in `initialize'

When I decompress the same file using gzip command on Mac it produced the correct uncompressed output.
For following command I can see –

 $file file_compressed.gz
 file_compressed.gz: gzip compressed data, from FAT filesystem (MS-DOS, OS/2, NT)

Do I need to put any header data while I create the compressed file with Zlib? Because when I use the inflate method instead of the GzipReader I get following error –

 incorrect header check (Zlib::DataError)
  ./features/support/abc/abc_file.rb:69:in `inflate'

Answer 1

If you’re on a platform that doesn’t use LF delimiters, but CR+LF, you may need to open the file in binary mode for reading:

File.open("file_compressed.gz", "rb") do |compressed|
  # ...
end

This should also avoid interpreting the input stream as anything but 8-bit binary.

Be sure to open your output file the same way using "wb" as the flag.