new content_type input

allow to set Content-Type HTTP header to a desired value

action.yml

@@ -29,6 +29,10 @@ inputs:
   from:
     description: Full name of mail sender
     required: true
+  content_type:
+    description: Content-Type HTTP header (MIME type)
+    required: false
+    default: text/plain
 runs:
   using: docker
   image: Dockerfile

main.rb

@@ -4,14 +4,15 @@
 require 'net/smtp'
 
 # Inputs
-address = ENV['INPUT_SERVER_ADDRESS']
-port = ENV['INPUT_SERVER_PORT']
+server_address = ENV['INPUT_SERVER_ADDRESS']
+server_port = ENV['INPUT_SERVER_PORT']
 username = ENV['INPUT_USERNAME']
 password = ENV['INPUT_PASSWORD']
 subject = ENV['INPUT_SUBJECT']
 body = ENV['INPUT_BODY']
 to = ENV['INPUT_TO']
 from = ENV['INPUT_FROM']
+content_type = ENV['INPUT_CONTENT_TYPE'] || 'text/plain'
 
 # Body
 prefix = 'file://'
@@ -24,6 +25,7 @@ body = if body.start_with?(prefix)
 
 # Message
 message = <<~END_OF_MESSAGE
+  Content-Type: #{content_type}; charset=utf-8
   Subject: #{subject}
   From: #{from} <#{username}>
 
@@ -32,9 +34,9 @@ END_OF_MESSAGE
 
 # Send
 begin
-  smtp = Net::SMTP.new(address, port.to_i)
+  smtp = Net::SMTP.new(server_address, server_port.to_i)
   smtp.enable_tls
-  smtp.start(address, username, password, :login)
+  smtp.start(server_address, username, password, :login)
   smtp.send_message(message, username, to.split(','))
 rescue StandardError => e
   puts "Error: #{e.message}"