Pass on specific error message returned from Mailgun

If Mailgun raises a RestClient::BadRequest "400 Bad Request" error, for example, there is also
probably (always?) the specific error message (for example, "'to' parameter is missing") from
Mailgun embedded in the JSON response.

However, there was no easy way to see what that specific error message actually was, and you'd end
up with a BadRequest error from your Rails app that you had no idea the actual cause of.

This change causes it to automatically extract that specific message from the JSON response and use
that as the Ruby exception message.

Author: TylerRick

lib/mailgun_rails/deliverer.rb

@@ -21,7 +21,13 @@ def verify_ssl
     end
 
     def deliver!(rails_message)
-      response = mailgun_client.send_message build_mailgun_message_for(rails_message)
+      begin
+        response = mailgun_client.send_message build_mailgun_message_for(rails_message)
+      rescue Exception => mailgun_error
+        json = JSON.parse(mailgun_error.http_body.to_s) rescue raise(mailgun_error)
+        mailgun_error.define_singleton_method(:message) { json["message"] }
+        raise mailgun_error
+      end
       if response.code == 200
         mailgun_message_id = JSON.parse(response.to_str)["id"]
         rails_message.message_id = mailgun_message_id

spec/lib/mailgun_rails/deliverer_spec.rb

@@ -115,12 +115,30 @@
       msg.message_id.should eq "20111114174239.25659.5817@samples.mailgun.org"
     end
 
+    it "should include the error message returned from Mailgun in the Ruby exception message" do
+      msg = Mail::Message.new(to: [], cc: 'cc@email.com', from: 'from@email.com')
+      expectation = { to: [], cc: ['cc@email.com'], from: ['from@email.com']}
+      check_mailgun_error msg, expectation, RestClient::BadRequest, "'to' parameter is missing"
+    end
+
     def check_mailgun_message(rails_message, mailgun_message)
       rest_response = double(:code => 200, :to_str => '{"message": "Queued. Thank you.","id": "<20111114174239.25659.5817@samples.mailgun.org>"}')
       mailgun_client.should_receive(:send_message).with(mailgun_message).and_return(rest_response)
       MailgunRails::Deliverer.new(api_key: api_key, domain: domain).deliver!(rails_message)
     end
 
+    def check_mailgun_error(rails_message, mailgun_message, exception, message)
+      body = %{{"message": #{JSON.dump message}}}
+      response = double(code: 400, body: body)
+      exception = exception.new(response)
+      allow(mailgun_client).to receive(:send_message).and_raise(exception)
+      expect {
+        MailgunRails::Deliverer.new(api_key: api_key, domain: domain).deliver!(rails_message)
+      }.to raise_exception(RestClient::BadRequest) {|exception|
+        expect(exception.message).to eq message
+      }
+    end
+
     def rails_message_with_attachment
       msg = basic_multipart_rails_message
       msg.attachments["attachment.jpg"] = "\312\213\254\232"