How to render rails mailer views in Mailgun HTTP API - ruby-on-rails

Question

I'm using Mailgun HTTP API to send emails from rails application.But I'm not able to render the mailer views. This is my mailer class.
class MailgunMails < ActionMailer::Base
def send_complex_message
data = Multimap.new
data[:from] = "Excited User <postmasters##{##domain}>"
data[:to] = "alice#example.com"
data[:subject] = "Hello"
data[:html] = File.open("#{Rails.root}/app/views/mailgun_mails/send_complex_message.html.erb", 'r').to_s.html_safe
## also tried
data[:html] = render(template: "send_complex_message.html.erb")
response = RestClient.post "https://api:#{##private_key}"\
"#api.mailgun.net/v2/#{##domain}/messages", data
response = JSON.parse(response)
end
end
But that throws:
NoMethodError: undefined method `each_byte' for nil:NilClass
How do I use mailer views with Mailgun API.
PS: I know there are many gems available to use mailgun with rails but none of them gives full functionality as the API does.
IF there is any alternative way to send emails from the api using the rails views, I'm waiting for that answer. I just don't know how to do that (even if it doesn't use actionmailer)
FULL error trace
NoMethodError: undefined method `each_byte' for nil:NilClass
from /Users/example/.rvm/rubies/ruby-2.0.0-p451/lib/ruby/2.0.0/uri/common.rb:307:in `block in escape'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/core_ext/string/output_safety.rb:177:in `gsub'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/core_ext/string/output_safety.rb:177:in `gsub'
from /Users/example/.rvm/rubies/ruby-2.0.0-p451/lib/ruby/2.0.0/uri/common.rb:304:in `escape'
from /Users/example/.rvm/rubies/ruby-2.0.0-p451/lib/ruby/2.0.0/uri/common.rb:623:in `escape'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:150:in `handle_key'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:143:in `block in build_stream'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:142:in `collect'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:142:in `build_stream'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:53:in `initialize'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:18:in `new'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/payload.rb:18:in `generate'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/request.rb:45:in `initialize'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/request.rb:33:in `new'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient/request.rb:33:in `execute'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/rest-client-1.6.7/lib/restclient.rb:72:in `post'
... 2 levels...
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/callbacks.rb:18:in `block in process_action'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/callbacks.rb:373:in `_run__1281843520849433682__process_action__callbacks'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/activesupport-4.0.4/lib/active_support/callbacks.rb:80:in `run_callbacks'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/callbacks.rb:17:in `process_action'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/base.rb:136:in `process'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionpack-4.0.4/lib/abstract_controller/rendering.rb:44:in `process'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:503:in `process'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:497:in `initialize'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:480:in `new'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/actionmailer-4.0.4/lib/action_mailer/base.rb:480:in `method_missing'
from (irb):1
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/railties-4.0.4/lib/rails/commands/console.rb:90:in `start'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/railties-4.0.4/lib/rails/commands/console.rb:9:in `start'
from /Users/example/.rvm/gems/ruby-2.0.0-p451/gems/railties-4.0.4/lib/rails/commands.rb:62:in `<top (required)>'
from bin/rails:4:in `require'

Answer 1

How about using the render_to_string method? I believe you want to dynamically generate the view content. Reading up the view template by opening up the file would not run any Ruby code in it.
class MailgunMails < ActionMailer::Base
def send_complex_message
data = Multimap.new
data[:from] = "Excited User <postmasters##{##domain}>"
data[:to] = "alice#example.com"
data[:subject] = "Hello"
html_output = render_to_string template: "mailgun_mails/send_complex_message"
data[:html] = html_output.to_str
response = RestClient.post "https://api:#{##private_key}"\
"#api.mailgun.net/v2/#{##domain}/messages", data
response = JSON.parse(response)
end
end