FTP protocol implementation

[tabishimran]

Adding an FTP protocol implementation with a few primitive functions - ls, cd, pwd, upload and download to the framework. Metasploit already had ftp mixins under '/lib/metasploit/framework/ftp/client.rb', but there was no standalone class. I have used code from existing mixins to create this implementation.

[busterb]

This would be good to go ahead and add support in the FTP mixin for using this.

Also run rubocop on the library and fix any errors you see.

[tabishimran]

All right, I modified the code to reduce rubocop offenses from 99 to 52.
I followed metasploit's rubocop wiki to decide what to ignore.

Things changed

• offenses related to indentation
• offenses related to white spaces
• offenses related to improper use of parentheses

Things ignored

• Too many lines in the class
• Suggestions to use unless, modifications to 'if' statements
• Redundant self

That redundant self suggestion was ignored because I went through a lot of code written by many people and most of them seem to use self the way I did. It would be great if I could get some feedback about that!

As discussed, support for using this in the other two FTP mixins -

• lib/metasploit/framework/ftp/client.rb,
• lib/msf/core/exploit/ftp.rb

will be added in a separate PR after a little more testing.

[egypt]

This looks good; your rubocop decisions are spot on, I think.

I was thinking this would replace the copy-pasta versions in lib/msf/ and lib/metasploit/ -- basically instantiate this thing and call its methods instead of implementing them in both places. Do you think you could fit that into this pull request?

[tabishimran]

All right, I'll get started with that! Changing the code itself shouldn't be a big deal, I'm kind of worried about breaking things though! I will change the mixins to use this FTP client implementation and then maybe try out a couple of modules/exploits which used those mixins to make sure everything is fine.

[busterb]

Since this is pure library code, I'm going to go ahead and land it, with a follow-up PR expected for actually using it.