Why is Net::HTTP timing out when I try to access a Prawn Generated PDF?

Question

I am using Prawn to generate a PDF from my controller, and when accessed directly at the url, it works flawlessly, I.E. localhost:3000/responses/1.pdf

However, when I try to generate this file on the fly for inclusion in a Mailer, everything freezes up and it times out.

I have tried various methods for generating / attaching the file and none have changed the outcome.

I also tried modifying the timeout for Net::HTTP to no avail, it just takes LONGER to time out.

If I run this command on the Rails Console, I receive a PDF data stream.

Net::HTTP.get('127.0.0.1',"/responses/1.pdf", 3000)

But if I include this code in my controller, it times out.

I have tried two different methods, and both fail repeatedly.

Method 1 Controller:

http = Net::HTTP.new('localhost', 3000)
http.read_timeout = 6000
file = http.get(response_path(@response, :format => 'pdf')) #timeout here
ResponseMailer.confirmComplete(@response,file).deliver #deliver the mail!

Method 1 Mailer:

def confirmComplete(response,file)
  email_address = response.supervisor_id
  attachments["test.pdf"] = {:mime_type => "application/pdf", :content=> file}
  mail to: email_address, subject: 'Thank you for your feedback!'
end

The above code times out.

Method 2 Controller:

ResponseMailer.confirmComplete(@response).deliver #deliver the mail!

Method 2 Mailer:

def confirmComplete(response)
email_address = response.supervisor_id
attachment "application/pdf" do |a|
    a.body = Net::HTTP.get('127.0.0.1',"/responses/1.pdf", 3000) #timeout here
    a.filename = "test.pdf" 
end
mail to: email_address, subject: 'Thank you for your feedback!'

end

If I switch the a.body and a.filename, it errors out first with

undefined method `filename=' for #<Mail::Part:0x007ff620e05678>

Every example I find has a different syntax or suggestion but none fix the problem that Net::HTTP times out. Rails 3.1, Ruby 1.9.2

Wget also gets stuck `Resolving localhost... 127.0.0.1 Connecting to localhost|127.0.0.1|:3000... connected. HTTP request sent, awaiting response... ` and just hangs there. the same command works on the command line, though. — Oranges13, Dec 14 '11 at 20:26
looks like weird problems with Web Server, try to use other one, f.ex. if you currently use WEBrick, try to check with Mongrel or Passenger — zed_0xff, Dec 15 '11 at 07:11

Jon Garvin · Answer 1 · 2011-12-14T21:48:40.580

The problem is that, in development, you're only running one server process, which is busy generating the email. That process is sending another request (to itself) to generate a PDF and waiting for a response. The request for the PDF is basically standing in line at the server so that it can get it's PDF, but the server is busy generating the email and waiting to get the PDF before it can finish. And thus, you're waiting forever.

What you need to do is start up a second server process...

script/rails server -p 3001

and then get your PDF with something like ...

args = ['127.0.0.1','/responses/1.pdf']
args << 3001 unless Rails.env == 'production'
file = Net::HTTP.get(*args)

As an aside, depending on what server you're running on your production machine, you might run into issues with pointing at 127.0.0.1. You might need to make that dynamic and point to the full domain when in production, but that should be easy.

score 1 · Accepted Answer · edited May 23 '17 at 11:55

I agree with https://stackoverflow.com/users/811172/jon-garvin's analysis that you're only running one server process, but I would mention another solution. Refactor your PDF generation so you don't depend on your controller.

If you're using Prawnto, I'm guessing you have a view like

# app/views/response.pdf.prawn
pdf.text "Hello world"

Move this to your Response model: (or somewhere else more appropriate, like a presenter)

# app/models/response.rb
require 'tmpdir'
class Response < ActiveRecord::Base
  def pdf_path
    return @pdf_path if @pdf_generated == true
    @pdf_path = File.join(Dir.tmpdir, rand(1e11).to_s)
    Prawn::Document.generate(@pdf_path) do |pdf|
      pdf.text "Hello world"
    end
    @pdf_generated = true
    @pdf_path
  end

  def pdf_cleanup
    if @pdf_generated and File.exist?(@pdf_path.to_s)
      File.unlink @pdf_path
    end
  end
end

Then in your ResponsesController you can do:

# app/controllers/responses_controller.rb
def show
  @response = Response.find params[:id]
  respond_to do |format|
    # this sends the PDF to the browser (doesn't email it)
    format.pdf { send_file @response.pdf_path, :type => 'application/pdf', :disposition => 'attachment', :filename => 'test.pdf' }
  end
end

And in your mailer you can do:

# this sends an email with the PDF attached
def confirm_complete(response)
  email_address = response.supervisor_id
  attachments['test.pdf'] = {:mime_type => "application/pdf", :content => File.read(response.pdf_path, :binmode => true) }
  mail to: email_address, subject: 'Thank you for your feedback!'
end

Since you created it in the tmpdir, it will be automatically deleted when your server restarts. You can also call the cleanup function.

One final note: you might want to use a different model name like SupervisorReport or something - Response might get you in namespacing trouble later)

Why is Net::HTTP timing out when I try to access a Prawn Generated PDF?

2 Answers2