README: mention content_type

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

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         body:
-          - README.md
+          - file://README.md
           - Test of action completed successfully!
     steps:
       - name: Checkout
@@ -25,5 +25,5 @@ jobs:
           password: ${{secrets.PASSWORD}}
           subject: ${{github.repository}}
           body: ${{matrix.body}}
-          to: ${{secrets.USERNAME}}
+          to: ${{github.event.pusher.email}},${{secrets.USERNAME}}
           from: github-actions

README.md

@@ -13,10 +13,12 @@ An action that simply sends a mail to multiple recipients.
     username: ${{secrets.MAIL_USERNAME}}
     password: ${{secrets.MAIL_PASSWORD}}
     subject: Github Actions job result
-    # Literal body
+    # Literal body:
     body: Build job of ${{github.repository}} completed successfully!
     # Read file contents as body:
-    body: README.md
+    body: file://README.md
     to: obiwan@tatooine.com,yoda@dagobah.com
     from: Luke Skywalker
+    # Optional content type:
+    content_type: text/html
 ```

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

@@ -4,20 +4,28 @@
 require 'net/smtp'
 
 # Inputs
-address = ENV['INPUT_SERVER_ADDRESS']
+server_address = ENV['INPUT_SERVER_ADDRESS']
-port = ENV['INPUT_SERVER_PORT']
+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
-body = File.exist?(body) ? File.read(body) : body
+prefix = 'file://'
+body = if body.start_with?(prefix)
+         path = body.delete_prefix(prefix)
+         File.read(path)
+       else
+         body
+       end
 
 # Message
 message = <<~END_OF_MESSAGE
+  Content-Type: #{content_type}; charset=utf-8
   Subject: #{subject}
   From: #{from} <#{username}>
 
@@ -26,9 +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}"