[Ruby] sample: Send Mail Using the Gmail API

smuga.rb

APP_NAME = 'Send Mail Using the Gmail API'
#
# To run this program, we need two files.
#
#   1. clent_secret.json
#
#      Create credentials in your Google Developers Console and download it.
#      Details for see 'Google Developers Console' web page.
#
#   2. credential.yaml
#
#      When authorization is required, this program will get and store it.
#      In that case, plese operate according to the message of this program.
#
#
require 'mail'                                  # gem install mail
require 'google/apis/gmail_v1'                  # gem install google-api-client
require 'googleauth'                            # (same as above)
require 'googleauth/stores/file_token_store'    # (same as above)
require 'zip'                                   # gem install rubyzip
require 'find'
require 'tmpdir'
require 'pathname'
require 'optparse'

SCOPE         = Google::Apis::GmailV1::AUTH_GMAIL_SEND
CHARSET       = 'UTF-8'
OOB_URI       = 'urn:ietf:wg:oauth:2.0:oob'
APP_HOME      = Pathname.new(Dir.home) + ".#{APP_NAME.gsub(/\s+/){'_'}}"
CLIENT_SECRET = Pathname.new('client_secret.json')
CREDENTIALS   = Pathname.new('credentials.yaml')

app = {
  user:          ENV['LOGNAME'] || `hostname`.chomp,
  client_secret: APP_HOME + CLIENT_SECRET,
  credentials:   APP_HOME + CREDENTIALS,
} 

message = Google::Apis::GmailV1::Message.new

Dir.mktmpdir do |tmpdir|
  make_zip = -> path {
    zip_path = Pathname.new(tmpdir) + "#{path.basename}.zip"
    Zip::File.open(zip_path, Zip::File::CREATE) do |zip|
      Dir.chdir(path.dirname) do
        Find.find(path.basename) do |ent|
          zip.add(ent, Pathname.new(ent).realpath)
        end
      end
    end
    zip_path.to_s
  }

  OptionParser.new.instance_eval do
    mail = Mail.new(charset: CHARSET)
    on('--to=TO'             ) {|to  | mail.to             = to                }
    on('--cc=CC'             ) {|cc  | mail.cc             = cc                }
    on('--subject=SUBJECT'   ) {|text| mail.subject        = text              }
    on('--body=BODY'         ) {|text| mail.body           = text              }
    on('--user=USER'         ) {|user| app[:user         ] = user              }
    on('--client_secret=PATH') {|path| app[:client_secret] = Pathname.new path }
    on('--credentials=PATH'  ) {|path| app[:credentials  ] = Pathname.new path }
    parse! ARGV
    raise "Not specified 'to'" unless mail.to

    ARGV.map{|f| Pathname.new f }.each do |path|
      mail.add_file(path.to_s)       if path.file?
      mail.add_file(make_zip.(path)) if path.directory?
    end

    message.raw = mail.to_s
  end
end

app[:credentials].dirname.mkpath
client_id   = Google::Auth::ClientId.from_file(app[:client_secret])
token_store = Google::Auth::Stores::FileTokenStore.new(file: app[:credentials])
authorizer  = Google::Auth::UserAuthorizer.new(client_id, SCOPE, token_store)

authorization = authorizer.instance_eval do
  get_code = -> {
    puts <<-ATTENTION
!!! NEEDS AUTHORIZATION !!!

    1) At first, sign in with your Google account in your browser
    2) then open the following URL and click 'Authorize' button.
    3) At last, enter the resulting code that display on the browser.

--[URL]---------------------------------------------------------------
#{get_authorization_url base_url:OOB_URI}
----------------------------------------------------------------------

    ATTENTION
    print "[Enter the resulting code]==>> " ; gets
  }

  get_credentials(app[:user]) ||
  get_and_store_credentials_from_code(user_id:  app[:user],
                                      code:     get_code.(),
                                      base_url: OOB_URI)
end

Google::Apis::GmailV1::GmailService.new.tap do |gmail|
  gmail.client_options.application_name = APP_NAME
  gmail.authorization                   = authorization
  gmail.send_user_message(user_id='me', message)
end