download-url-to-file.rb

#!/usr/bin/env ruby
#
# Ruby script to download a number of files
# from individual URLs via HTTP/HTTPS/FTP
# specified in an external file.
#
# Author: Tobias Preuss
# Revision: 2013-04-18 16:26 +0100 UTC
# License: Creative Commons Attribution-ShareAlike 3.0 Unported

require 'net/http'
require 'net/ftp'
require 'uri'
require 'date'


def create_directory(dirname)
  unless Dir.exists?(dirname)
    Dir.mkdir(dirname)
  else
    puts "Skipping creating directory " + dirname + ". It already exists."
  end
end

def read_uris_from_file(file)
  uris = Array.new
  File.open(file).each do |line|
    line = line.strip
    next if line == nil || line.length == 0
    parts = line.split(' ')
    pair = Hash[ [:resource, :filename].zip(parts) ]
    uris.push(pair)
  end
  uris
end

def download_resource(resource, filename)
  uri = URI.parse(resource)
  case uri.scheme.downcase
  when /http|https/
    http_download_uri(uri, filename)
  when /ftp/
    ftp_download_uri(uri, filename)
  else
    puts "Unsupported URI scheme for resource " + resource + "."
  end
end

def http_download_uri(uri, filename)
  puts "Starting HTTP download for: " + uri.to_s
  http_object = Net::HTTP.new(uri.host, uri.port)
  http_object.use_ssl = true if uri.scheme == 'https'
  begin
    http_object.start do |http|
      request = Net::HTTP::Get.new uri.request_uri
      http.read_timeout = 500
      http.request request do |response|
        open filename, 'w' do |io|
          response.read_body do |chunk|
            io.write chunk
          end
        end
      end
    end
  rescue Exception => e
    puts "=> Exception: '#{e}'. Skipping download."
    return
  end
  puts "Stored download as " + filename + "."
end

def ftp_download_uri(uri, filename)
  puts "Starting FTP download for: " + uri.to_s + "."
  dirname = File.dirname(uri.path)
  basename = File.basename(uri.path)
  begin
    Net::FTP.open(uri.host) do |ftp|
      ftp.login
      ftp.chdir(dirname)
      ftp.getbinaryfile(basename)
    end
  rescue Exception => e
    puts "=> Exception: '#{e}'. Skipping download."
    return
  end
  puts "Stored download as " + filename + "."
end

def download_resources(pairs)
  pairs.each do |pair|
    filename = pair[:filename].to_s
    resource = pair[:resource].to_s
    unless File.exists?(filename)
      download_resource(resource, filename)
    else
      puts "Skipping download for " + filename + ". It already exists."
    end
  end
end


def main
  sources_file = ARGV.first
  uris = read_uris_from_file(sources_file)

  target_dir_name = Date.today.strftime('%y%m%d')
  create_directory(target_dir_name)
  Dir.chdir(target_dir_name)
  puts "Changed directory: " + Dir.pwd

  download_resources(uris)
end


if __FILE__ == $0
  usage = <<-EOU

usage: ruby #{File.basename($0)} sources.txt

  The file sources.txt should contain an URL and the target file name.
  The expected file format is:

  http://www.domain.com/file target_file_name
  ftp://www.domain.com/file target_file_name

  EOU

  abort usage if ARGV.length != 1

  main

end