Add mustache templating for email body (#51)

lib/logstash/outputs/email.rb

@@ -80,6 +80,9 @@ class LogStash::Outputs::Email < LogStash::Outputs::Base
   # Body for the email - plain text only.
   config :body, :validate => :string, :default => ""
 
+  # Email template file to be used - as mustache template.
+  config :template_file, :validate => :path
+
   # HTML Body for the email, which may contain HTML markup.
   config :htmlbody, :validate => :string, :default => ""
 
@@ -93,6 +96,7 @@ class LogStash::Outputs::Email < LogStash::Outputs::Base
   public
   def register
     require "mail"
+    require "mustache"
 
     options = {
       :address              => @address,
@@ -118,6 +122,7 @@ def register
         delivery_method :@via, options
       end
     end # @via tests
+    @htmlTemplate = File.open(@template_file, "r").read unless @template_file.nil?
     @logger.debug("Email Output Registered!", :config => options, :via => @via)
   end # def register
 
@@ -129,6 +134,7 @@ def receive(event)
       formatedSubject = event.sprintf(@subject)
       formattedBody = event.sprintf(@body)
       formattedHtmlBody = event.sprintf(@htmlbody)
+
       mail = Mail.new
       mail.from = event.sprintf(@from)
       mail.to = event.sprintf(@to)
@@ -137,18 +143,30 @@ def receive(event)
       end
       mail.cc = event.sprintf(@cc)
       mail.subject = formatedSubject
-      if @htmlbody.empty?
+
+      if @htmlbody.empty? and @template_file.nil?
         formattedBody.gsub!(/\\n/, "\n") # Take new line in the email
         mail.body = formattedBody
       else
+        # This handles multipart emails
+        # cf: https://github.com/mikel/mail/#writing-and-sending-a-multipartalternative-html-and-text-email
         mail.text_part = Mail::Part.new do
           content_type "text/plain; charset=UTF-8"
           formattedBody.gsub!(/\\n/, "\n") # Take new line in the email
           body formattedBody
         end
-        mail.html_part = Mail::Part.new do
-          content_type "text/html; charset=UTF-8"
-          body formattedHtmlBody
+
+        if @template_file.nil?
+          mail.html_part = Mail::Part.new do
+            content_type "text/html; charset=UTF-8"
+            body formattedHtmlBody
+          end
+        else
+          templatedHtmlBody = Mustache.render(@htmlTemplate, event.to_hash)
+          mail.html_part = Mail::Part.new do
+            content_type "text/html; charset=UTF-8"
+            body templatedHtmlBody
+          end
         end
       end
       @attachments.each do |fileLocation|

logstash-output-email.gemspec

@@ -26,6 +26,8 @@ Gem::Specification.new do |s|
   # mime-types >= 3 require ruby 2.0 support
   s.add_runtime_dependency 'mime-types', '< 3'
 
+  s.add_runtime_dependency 'mustache', '>= 0.99.8'
+
   s.add_development_dependency 'logstash-devutils'
   s.add_development_dependency 'rumbster'
   s.add_development_dependency 'logstash-input-generator'

spec/fixtures/template.mustache

@@ -0,0 +1 @@
+<h1>{{message}}</h1>

spec/outputs/email_spec.rb

@@ -89,5 +89,20 @@
 
       end
     end
+
+    context  "mustache template for email body" do
+      it "uses the template file" do
+        subject = plugin.new("to" => "me@host",
+                             "subject" => "Hello World",
+                             "template_file" => File.dirname(__FILE__) + "/../fixtures/template.mustache",
+                             "port" => port)
+        subject.register
+        subject.receive(LogStash::Event.new("message" => "hello"))
+
+        expect(message_observer.messages.size).to eq(1)
+        expect(message_observer.messages[0].subject).to eq("Hello World")
+        expect(message_observer.messages[0].body.decoded).to eq(craft_multi_part_email('', '<h1>hello</h1>', message_observer.messages[0].content_type))
+      end
+    end
   end
 end

spec/spec_helper.rb

@@ -12,3 +12,17 @@ def filter(event)
     filter_matched(event)
   end
 end
+
+def craft_multi_part_email(body, htmlbody, content_type)
+  charset = "charset=UTF-8"
+  content_encoding = "Content-Transfer-Encoding: 7bit"
+
+  # Have to get the generated part of the header, eg:
+  # --==_mimepart_5a462a1fda04b_efe7d032127
+  mimetype = content_type.split('; ')[1][10..-2]
+
+  plain_header = "\n--#{mimetype}\nContent-Type: text/plain;\n #{charset}\n#{content_encoding}\n\n"
+  html_header = "\n--#{mimetype}\nContent-Type: text/html;\n #{charset}\n#{content_encoding}\n\n"
+
+  "#{plain_header}#{body}#{html_header}#{htmlbody}\n\n--#{mimetype}--\n"
+end