Jekyll Build Tools Part II - Gzipping files

Google's PageSpeed tool says:

All modern browsers support and automatically negotiate gzip compression for all HTTP requests. Enabling gzip compression can reduce the size of the transferred response by up to 90%, which can significantly reduce the amount of time to download the resource, reduce data usage for the client, and improve the time to first render of your pages.

https://developers.google.com/speed/docs/insights/EnableCompression

I tried (and failed) to do this with the shell commands ls and gzip. I couldn't find an elegant way to

• List all the files recursively
• Ignore the directories

I needed a script that could do some intelligent directory traversal and then gzip the files in place.

Here's the solution I came up with

# jekyll-gzip.rb
# Compresses all the files in a directory using gzip compression

require 'zlib'

# Get a list of files in folder, recursively
folder = '_site'

Dir[File.join(folder, '**', '*')].reject { |filename| File.directory? filename }
.each do |filename|
  old_file_text = File.read(filename)
  open(filename, 'wb') do |file|
    gzip = Zlib::GzipWriter.new(file)
    gzip << old_file_text
    gzip.close
  end
end

Getting the proper file list.

The following Ruby code, using the Dir class, recursively gets a list of all the contents of a directory and returns an array of strings.

Dir[File.join(folder, '**', '*')]

Filtering out directories.

Now that we have an array of filenames as strings, we can use the File class to test if it points to a directory, and reject elements of the array that are directories.

.reject { |filename| File.directory? filename }

Gzipping the files

Now that we have an array of just filenames (free of directory names) as strings. We can use Ruby's File class to read the file in as a string, and use Ruby's Zlib module to compress the strings and write them to the opened file.

.each do |filename|
  old_file_text = File.read(filename)
  open(filename, 'wb') do |file|
    gzip = Zlib::GzipWriter.new(file)
    gzip << old_file_text
    gzip.close
  end
end