Handle and log invalid IP address errors

If the filter get any invalid input for the anonymize_ipv4_network
mode, it will crash the whole Logstash pipeline because of an
unhandled ArgumentError thrown by the IPAddr class.
Furthermore, the causing event got lost during the crash, so
post-mortem analysis were not possible.

Now, ArgumentError is catched and an error message is logged.
The value to be anonymized is kept in the event in the identified form
and the event gets processed further as usual.

Fixes logstash-plugins#3.

lib/logstash/filters/anonymize.rb

@@ -39,26 +39,31 @@ def filter(event)
     @fields.each do |field|
       next unless event.include?(field)
       if event.get(field).is_a?(Array)
-        event.set(field, event.get(field).collect { |v| anonymize(v) })
+        event.set(field, event.get(field).collect { |v| anonymize(event, field, v) })
       else
-        event.set(field, anonymize(event.get(field)))
+        event.set(field, anonymize(event, field, event.get(field)))
       end
     end
   end # def filter
 
   private
-  def anonymize_ipv4_network(ip_string)
-    # in JRuby 1.7.11 outputs as US-ASCII
-    IPAddr.new(ip_string).mask(@key.to_i).to_s.force_encoding(Encoding::UTF_8)
+  def anonymize_ipv4_network(event, field, ip_string)
+    begin
+      # in JRuby 1.7.11 outputs as US-ASCII
+      IPAddr.new(ip_string).mask(@key.to_i).to_s.force_encoding(Encoding::UTF_8)
+    rescue ArgumentError => e
+      @logger.error("Anonymize: Invalid IP address received", :field => field, :value => ip_string, :exception => e, :backtrace => e.backtrace)
+      return ip_string
+    end
   end
 
-  def anonymize_openssl(data)
+  def anonymize_openssl(event, field, data)
     digest = algorithm()
     # in JRuby 1.7.11 outputs as ASCII-8BIT
     OpenSSL::HMAC.hexdigest(digest, @key, data).force_encoding(Encoding::UTF_8)
   end
 
-  def anonymize_murmur3(value)
+  def anonymize_murmur3(event, field, value)
     case value
     when Fixnum
       MurmurHash3::V32.int_hash(value)