refactor to support testing from_json and legacy parser

lib/logstash/codecs/json_lines.rb

@@ -34,6 +34,14 @@ def register
     @buffer = FileWatch::BufferedTokenizer.new(@delimiter)
     @converter = LogStash::Util::Charset.new(@charset)
     @converter.logger = @logger
+
+    # pick the correct parser here and not at class evaluation so that we can control this
+    # mechanism in rspec and actually force use both strategies.
+    self.class.module_eval do
+      # keep compatibility with all v2.x distributions. only in 2.3 will the Event#from_json method be introduced
+      # and we need to keep compatibility for all v2 releases.
+      alias_method :parse, from_json_exposed? ? :from_json_parse : :legacy_parse
+    end
   end
 
   def decode(data, &block)
@@ -48,6 +56,12 @@ def encode(event)
     @on_event.call(event, "#{event.to_json}#{@delimiter}")
   end # def encode
 
+  # this method is made public to that we can mock it in rspec and control
+  # testing using from_json or legacy mechanism.
+  def self.from_json_exposed?
+    LogStash::Event.respond_to?(:from_json)
+  end
+
   private
 
   # from_json_parse uses the Event#from_json method to deserialize and directly produce events
@@ -63,9 +77,4 @@ def legacy_parse(json, &block)
   rescue LogStash::Json::ParserError
     yield LogStash::Event.new("message" => json, "tags" => ["_jsonparsefailure"])
   end
-
-  # keep compatibility with all v2.x distributions. only in 2.3 will the Event#from_json method be introduced
-  # and we need to keep compatibility for all v2 releases.
-  alias_method :parse, LogStash::Event.respond_to?(:from_json) ? :from_json_parse : :legacy_parse
-
 end # class LogStash::Codecs::JSONLines

spec/codecs/json_lines_spec.rb

@@ -6,9 +6,10 @@
 require "insist"
 
 describe LogStash::Codecs::JSONLines do
-  subject do
-    next LogStash::Codecs::JSONLines.new
-  end
+
+  let(:codec_options) { {} }
+
+  shared_examples :codec do
 
   context "#decode" do
     it "should return an event from json data" do
@@ -37,9 +38,7 @@
     context "when using custom delimiter" do
       let(:delimiter) { "|" }
       let(:line) { "{\"hey\":1}|{\"hey\":2}|{\"hey\":3}|" }
-      subject do
-        next LogStash::Codecs::JSONLines.new("delimiter" => delimiter)
-      end
+      let(:codec_options) { { "delimiter" => delimiter } }
 
       it "should decode multiple lines separated by the delimiter" do
         result = []
@@ -122,9 +121,7 @@
 
     context "when using custom delimiter" do
       let(:delimiter) { "|" }
-      subject do
-        next LogStash::Codecs::JSONLines.new("delimiter" => delimiter)
-      end
+      let(:codec_options) { { "delimiter" => delimiter } }
 
       it "should decode multiple lines separated by the delimiter" do
         subject.on_event do |e, d|
@@ -170,4 +167,27 @@
       expect(collector.last['field']).to eq('value2')
     end
   end
+
+  end
+
+  context "forcing legacy parsing" do
+    it_behaves_like :codec do
+      subject do
+        expect(LogStash::Codecs::JSONLines).to receive(:from_json_exposed?).and_return(false)
+        # register method is called in the constructor
+        LogStash::Codecs::JSONLines.new(codec_options)
+      end
+    end
+  end
+
+  context "default parser choice" do
+    # here we cannot force the use of the Event#from_json since if this test is run in the
+    # legacy context (no Java Event) it will fail but if in the new context, it will be picked up.
+    it_behaves_like :codec do
+      subject do
+        # register method is called in the constructor
+        LogStash::Codecs::JSONLines.new(codec_options)
+      end
+    end
+  end
 end