update-ssh-config

#!/usr/bin/env ruby

require 'erb'
require 'ipaddr'

class HostParseError < StandardError; end

class Host
  
  attr_accessor :fqhn, :port, :user, :name, :proxy
  
  def proxied?
    !!@proxy
  end
  
  def ip?
    !(IPAddr.new(@fqhn) rescue nil).nil?
  end
end

class ERBContext
  def initialize(hash)
    hash.each_pair do |key, value|
      instance_variable_set('@' + key.to_s, value)
    end
  end
  
  def get_binding
    binding
  end
end

FQDN_RE = /([^\.]+)/
HOST_SPEC_RE = /(?:(?<proxy>[^\s]+)\s+->\s+)?(?:(?<user>[^@]+)@)?(?<fqhn>[^\s:]+)(?:\:(?<port>\d+))?(?:\s+\((?<name>[^\)]+)\))?/

def parse_host_spec(spec)
  data = HOST_SPEC_RE.match(spec)
  raise HostParseError, 'Malformed syntax' unless data

  host = Host.new
  host.fqhn = data['fqhn']
  host.proxy = data['proxy']
  host.port = data['port'] || 22
  host.user = data['user']
  host.name = 
    if data['name']
      data['name']
    elsif not host.ip?
      FQDN_RE.match(data['fqhn'])[1]
    else
      raise HostParseError, 'Cannot infer name'
    end
  
  host
end

def render_hosts
  Dir.glob(File.expand_path('~/.ssh/hosts.d/*.hosts')).each do |hosts_file|
    config_file = File.join(File.expand_path('~/.ssh/config.d'), File.basename(hosts_file, '.hosts'))
    config = ERB.new(File.new(config_file + '.config').read, nil, '%')
    
    File.readlines(hosts_file).each_with_index do |spec, i|
      line = i + 1
      spec = spec.chomp

      begin
        host = parse_host_spec(spec)
        yield config.result(ERBContext.new(host: host).get_binding)
      rescue HostParseError => e
        STDERR.puts "warning: parse error in #{hosts_file}:#{line} \"#{spec}\" (#{e.message}), skipping."
      end
    end
  end
end

File.open(File.expand_path('~/.ssh/config'), File::CREAT|File::TRUNC|File::RDWR, 0644) do |io|
  render_hosts do |host|
    io.puts host
  end
end