refactor: move app/util/* to app/lib/

app/lib/dns_resolver.rb

@@ -0,0 +1,149 @@
+# frozen_string_literal: true
+
+class DNSResolver
+
+  attr_reader :nameservers
+  attr_reader :timeout
+
+  def initialize(nameservers: nil, timeout: 5)
+    @nameservers = nameservers
+    @timeout = timeout
+  end
+
+  # Return all A records for the given name
+  #
+  # @param [String] name
+  # @return [Array<String>]
+  def a(name)
+    dns do |dns|
+      dns.getresources(name, Resolv::DNS::Resource::IN::A).map do |s|
+        s.address.to_s
+      end
+    end
+  end
+
+  # Return all AAAA records for the given name
+  #
+  # @param [String] name
+  # @return [Array<String>]
+  def aaaa(name)
+    dns do |dns|
+      dns.getresources(name, Resolv::DNS::Resource::IN::AAAA).map do |s|
+        s.address.to_s
+      end
+    end
+  end
+
+  # Return all TXT records for the given name
+  #
+  # @param [String] name
+  # @return [Array<String>]
+  def txt(name)
+    dns do |dns|
+      dns.getresources(name, Resolv::DNS::Resource::IN::TXT).map do |s|
+        s.data.to_s.strip
+      end
+    end
+  end
+
+  # Return all CNAME records for the given name
+  #
+  # @param [String] name
+  # @return [Array<String>]
+  def cname(name)
+    dns do |dns|
+      dns.getresources(name, Resolv::DNS::Resource::IN::CNAME).map do |s|
+        s.name.to_s.downcase
+      end
+    end
+  end
+
+  # Return all MX records for the given name
+  #
+  # @param [String] name
+  # @return [Array<Array<Integer, String>>]
+  def mx(name)
+    dns do |dns|
+      records = dns.getresources(name, Resolv::DNS::Resource::IN::MX).map do |m|
+        [m.preference.to_i, m.exchange.to_s]
+      end
+      records.sort do |a, b|
+        if a[0] == b[0]
+          [-1, 1].sample
+        else
+          a[0] <=> b[0]
+        end
+      end
+    end
+  end
+
+  # Return the effective nameserver names for a given domain name.
+  #
+  # @param [String] name
+  # @return [Array<String>]
+  def effective_ns(name)
+    records = []
+    dns do |dns|
+      parts = name.split(".")
+      (parts.size - 1).times do |n|
+        d = parts[n, parts.size - n + 1].join(".")
+
+        records = dns.getresources(d, Resolv::DNS::Resource::IN::NS).map do |s|
+          s.name.to_s
+        end
+
+        break if records.present?
+      end
+    end
+
+    records
+  end
+
+  # Return the hostname for a given IP address.
+  # Returns the IP address itself if no hostname can be determined.
+  #
+  # @param [String] ip_address
+  # @return [String]
+  def ip_to_hostname(ip_address)
+    dns do |dns|
+      dns.getname(ip_address)&.to_s
+    end
+  rescue Resolv::ResolvError
+    ip_address
+  end
+
+  private
+
+  def dns
+    kwargs = @nameservers ? { nameserver: @nameservers } : {}
+    Resolv::DNS.open(**kwargs) do |dns|
+      dns.timeouts = [@timeout, @timeout / 2]
+      yield dns
+    end
+  end
+
+  class << self
+
+    # Return a resolver which will use the nameservers for the given domain
+    #
+    # @param [String] name
+    # @return [DNSResolver]
+    def for_domain(name)
+      resolver = new
+      nameservers = resolver.effective_ns(name)
+      ips = nameservers.map do |ns|
+        resolver.a(ns)
+      end.flatten.uniq
+      new(nameservers: ips)
+    end
+
+    # Return a local resolver to use for lookups
+    #
+    # @return [DNSResolver]
+    def local
+      @local ||= new
+    end
+
+  end
+
+end