Do not write empty lines to IO and File adapters

If a line is completely empty, it is not useful to log it at all since
it would be invisible on the created logstream anyway. If we get passed
an empty String from the encoder, we can thus silently ignore it.

lib/rackstash/adapters/adapter.rb

@@ -96,16 +96,17 @@ module Rackstash
 
       private
 
-      # Helper method to ensure that a log line passed to {#write} is a string
-      # that ends in a newline character by mutating the object is required.
+      # Helper method to ensure that a log line passed to {#write} is either a
+      # String that ends in a newline character or is completely empty.
       #
       # @param line [#to_s] a log line
       # @return [String] `line` with a trailing newline character (`"\n"`)
       #   appended if necessary
       def normalize_line(line)
         line = line.to_s
-        line = "#{line}\n" unless line.end_with?("\n".freeze)
-        line
+        return line if line.empty? || line.end_with?("\n".freeze)
+
+        "#{line}\n"
       end
     end
   end

lib/rackstash/adapters/file.rb

@@ -104,9 +104,12 @@ module Rackstash
       # @param log [#to_s] the encoded log event
       # @return [nil]
       def write_single(log)
+        line = normalize_line(log)
+        return if line.empty?
+
         @mutex.synchronize do
           auto_reopen
-          @file.write normalize_line(log)
+          @file.write(line)
         end
         nil
       end

lib/rackstash/adapters/io.rb

@@ -88,8 +88,11 @@ module Rackstash
       # @param log [#to_s] the encoded log event
       # @return [nil]
       def write_single(log)
+        line = normalize_line(log)
+        return if line.empty?
+
         @io.synchronize_for_rackstash do
-          @io.write normalize_line(log)
+          @io.write line
           @io.flush if @flush_immediately
         end
         nil

spec/rackstash/adapters/file_spec.rb

@@ -92,6 +92,13 @@ describe Rackstash::Adapters::File do
       expect(logfile.tap(&:rewind).read).to eql "a full line.\n"
     end
 
+    it 'ignores empty log lines' do
+      adapter.write('')
+      adapter.write(nil)
+
+      expect(logfile.tap(&:rewind).read).to eql ''
+    end
+
     context 'with auto_reopen: true' do
       let(:adapter_args) { { auto_reopen: true } }
 

spec/rackstash/adapters/io_spec.rb

@@ -77,5 +77,11 @@ describe Rackstash::Adapters::IO do
         adapter.write('bar')
       end
     end
+
+    it 'ignores empty log lines' do
+      expect(io).to_not receive(:write)
+      adapter.write('')
+      adapter.write(nil)
+    end
   end
 end