(RFC) hostname reader

library/network/src/lib/y2network/config_reader/hostname.rb

@@ -0,0 +1,130 @@
+# Copyright (c) [2019] SUSE LLC
+#
+# All Rights Reserved.
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of version 2 of the GNU General Public License as published
+# by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+# more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, contact SUSE LLC.
+#
+# To contact SUSE LLC about this file by physical or electronic mail, you may
+# find current contact information at www.suse.com.
+
+require "yast"
+require "y2network/hostname"
+
+Yast.import "IP"
+Yast.import "Mode"
+Yast.import "Hostname"
+Yast.import "String"
+
+module Y2Network
+  module ConfigReader
+    class Hostname
+      include Yast::Logger
+
+      def self.from_system
+        # In installation (standard, or AutoYaST one), prefer /etc/install.inf
+        # (because HOSTNAME comes with netcfg.rpm already, #144687)
+        if (Yast::Mode.installation || Yast::Mode.autoinst) && File.exists?("/etc/install.inf")
+          fqhostname = read_hostname_from_install_inf
+        end
+
+        # reads setup from /etc/HOSTNAME, returns a default if nothing found
+        fqhostname = Yast::Hostname.CurrentFQ if fqhostname.nil? || fqhostname.empty?
+
+        Y2Network::Hostname.new(fqdn: fqhostname)
+      end
+
+    private
+
+      def read_hostname_from_install_inf
+        install_inf_hostname = Yast::SCR.Read(path(".etc.install_inf.Hostname")) || ""
+        log.info("Got #{install_inf_hostname} from install.inf")
+
+        return "" if install_inf_hostname.empty?
+
+        # if the name is actually IP, try to resolve it (bnc#556613, bnc#435649)
+        if Yast::IP.Check(install_inf_hostname)
+          fqhostname = ResolveIP(install_inf_hostname)
+          log.info("Got #{fqhostname} after resolving IP from install.inf")
+        else
+          fqhostname = install_inf_hostname
+        end
+
+        fqhostname
+      end
+
+      # Resolve IP to canonical hostname
+      #
+      # @param [String] ip given IP address
+      # @return resolved canonical hostname (FQDN) for given IP or empty string in case of failure.
+      def ResolveIP(ip)
+        getent = Yast::SCR.Execute(path(".target.bash_output"), "/usr/bin/getent hosts #{ip.shellescape}")
+        exit_code = getent.fetch("exit", -1)
+
+        if exit_code != 0
+          log.error("ResolveIP: getent call failed (#{getent})")
+
+          return ""
+        end
+
+        GetHostnameFromGetent(getent.fetch("stdout", ""))
+      end
+
+      # Handles input as one line of getent output. Returns first hostname found
+      # on the line (= canonical hostname).
+      #
+      # @param [String] line in /etc/hosts format
+      # @return canonical hostname from given line
+      def GetHostnameFromGetent(line)
+        #  line is expected same format as is used in /etc/hosts without additional
+        #  comments (getent removes comments from the end).
+        #
+        #  /etc/hosts line is formatted this way (man 5 hosts):
+        #
+        #      <ip address> <canonical hostname> [<alias> ...]
+        #
+        #  - field separators are at least one space and/or tab.
+        #  - <canonical hostname>, in generic it is "a computer's unique name". In case
+        #  of DNS world, <canonical hostname> is FQDN ("A" record), then <hostname> is
+        #  <canonical hostname> without domain part. For example:
+        #
+        #      foo.example.com. IN A 1.2.3.4
+        #
+        #  <canonical hostname> => foo.example.com
+        #  <hostname> => foo
+        #
+        canonical_hostname = Yast::Builtins.regexpsub(
+          line,
+          Yast::Builtins.sformat("^[%1]+[[:blank:]]+(.*)", Yast::IP.ValidChars),
+          "\\1"
+        )
+
+        canonical_hostname = Yast::String.FirstChunk(canonical_hostname, " \t\n")
+        canonical_hostname = Yast::String.CutBlanks(canonical_hostname)
+
+        if !Yast::Hostname.CheckDomain(canonical_hostname) &&
+            !Yast::Hostname.Check(canonical_hostname)
+          log.error("GetHostnameFromGetent: Invalid hostname detected (#{canonical_hostname})")
+          log.error("GetHostnameFromGetent: input params - begin")
+          log.error(line)
+          log.error("GetHostnameFromGetent: input params - end")
+
+          return ""
+        end
+
+        log.info("GetHostnameFromGetEnt: canonical hostname => (#{canonical_hostname})")
+
+        canonical_hostname
+      end
+    end
+  end
+end