How to calculate the amount of data downloaded and the total data to be downloaded in Ruby

I'm trying to build a desktop client that manages some downloads with Ruby. I would like to know how to go about trying to identify how much of the data is downloaded and the size of the entire data that is to be downloaded.

Im trying to do 开发者_高级运维this with Ruby so any help would be useful.

Thanks in advance.

Like Wayne said in his comment, it depends on the protocol that is used to transfer the files. With HTTP for example, the HTTP response will include a Content-Length header which will tell you the length of the file that you are downloading. After you know that you will have to keep track of the number of bytes that you've read from the HTTP connection.

Something like this seems to work (for HTTP), but I wouldn't be surprised if it could be done more elegantly:

require 'net/http' 

url = URI.parse('http://www.google.com/index.html')
req = Net::HTTP::Get.new(url.path)
res = Net::HTTP.start(url.host, url.port) do |http|
  http.request(req) do |res|
    remaining = res.content_length
    puts "total length: #{remaining}"
    res.read_body do |segment|
      puts "read #{segment.length} bytes"
      remaining = remaining - segment.length
      puts "#{remaining} bytes remaining"
    end
  end
end

www.google.com/index.html is a bad example since the content gets returned in one segment, but try it on a larger object and you should see multiple "read..." lines.

If you're using Net::HTTP then the length of whatever you're requesting should be in the response header. Net::HTTP mixin NET::HTTPHeader, in it you'll find content_length(). Although it only works if the size is determined before the transfer happens.

Net::HTTPResponse has a method that reads the body in chunks, so you can use that to determine the progress. Start at 0 and add the length of each chunk, compare it to the total size and you're done.

http.request_get('/index.html') {|res|
res.read_body do |segment|
  print segment
end
} #Example taken from Ruby-Documentation

If you're using FTP then it should be easier through NET::FTP. Connect to the server, get the size of a given file with size(filename), and then download the file with get, getbinaryfile or gettextfile.

This is the signature of the get method: get(remotefile, localfile = File.basename(remotefile), blocksize = DEFAULT_BLOCKSIZE) {|data| ...}

ftp.get('file.something', 'file.something.local', 1024){ |data|
     puts "Downloaded 1024 more bytes"
}