Dialog with FTP using Ruby

Question

I want to start an FTP process, issue commands, check for a specially formatted response strings and capture them, then issue commands based on the captured strings.

So the flow is:

1. start ftp

2. echo the welcome text

3. for each ftp subcommand

   a) issue subcommand

   b) echo the response for the subcommand

   c) scan the response for a pattern and save the matches for later

4. perform a computation on the saved patterns

5. issue more ftp commands

6. echo the response

Here is my script, which does not read ftp output and hangs after attempting to write the first ftp subcommand:

require 'io/wait'
require 'open3'

# Define the commands to send to FTP
commands = [
  'ascii',
  'quote site filetype=jes',
  'put amblist.jcl',
  'dir'
]

user_id = 'mikes01'.downcase
program_command = "ftp ftp://#{user_id}:mypwd@bigiron"
Open3.popen2(program_command) do |stdin, stdout, wait_thread|
  Thread.new do
    stdout.each do |line|
      # I want to scan the line for a pattern but we never get here
      puts line
      stdout.flush
    end
  end

  commands.each do |command| # Issue command
    stdin.puts command
    # Hopefully the output resulting from the ftp command is captured in the above thread
  end
  # Do something with previously processed output before closing the FTP session
  stdin.close
  wait_thread.value # exit status
end
# Do more processing

Answer 1

My original approach was unworkable, so I followed the suggestion from @Stefan and looked into the Ruby Net::FTP gem. I modified the gem to include the necessary functionality, present in the Linux FTP command. I made a pull request.

The modifications in the pull request have been tested against an IBM z/OS Communications Server. The following code fragment uses FTP to submit a batch job to the mainframe, and collects the results.

def parse_job_number_from(line)
  tokens = line.split('JOB')
  raise StandardError, "Error: The string 'JOB' was not found in the FTP response." unless tokens.length == 2

  job_number = tokens[1].split.first
  job_number.sub(/^0+/, '') # Remove leading zeros
end
    
Net::FTP.open(@ip_or_domain) do |ftp|
  ftp.login @uid, @pwd
  ftp.quote 'site filetype=jes'
  job_info = ftp.puttextfile @local_jcl_filepath
  job_number = parse_job_number_from job_info
  ftp.gettextfile "J#{job_number}", @local_results_file
end