Rails: Missing host to link to! Please provide :host parameter or set default_url_options[:host]

You need to add the following line at every environment:

config.action_mailer.default_url_options = { :host => "yourhost" }

That way, it can work in all environments and could be different from environment to environment. For example:

development.rb

config.action_mailer.default_url_options = { :host => "dev.yourhost.com" }

test.rb

config.action_mailer.default_url_options = { :host => "test.yourhost.com" }

production.rb

config.action_mailer.default_url_options = { :host => "www.yourhost.com" }

---

Your::Application.routes.draw do
  default_url_options :host => "example.com"

  # ... snip ...
end

Somewhere in routes.rb :)

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The host should be specified in each environment's config file. Eg:

config/environments/development.rb

See this question and this question.

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Set default_url_options to use your action_mailer.default_url_options.

In each of your environment files (e.g. development.rb, production.rb, etc.) you can specify the default_url_options to use for action_mailer:

config.action_mailer.default_url_options = { host: 'lvh.me', port: '3000' }

However, these are not set for MyApp:Application.default_url_options:

$ MyApp::Application.config.action_mailer.default_url_options
#=> {:host=>"lvh.me", :port=>"3000"}

$ MyApp::Application.default_url_options
#=> {}

That's why you are getting that error in anything outside of ActionMailer.

You can set your Application's default_url_options to use what you defined for action_mailer in the appropriate environment file (development.rb, production.rb, etc.).

To keep things as DRY as possible, do this in your config/environment.rb file so you only have to do this once:

# Initialize the rails application
MyApp::Application.initialize!

# Set the default host and port to be the same as Action Mailer.
MyApp::Application.default_url_options = MyApp::Application.config.action_mailer.default_url_options

Now when you boot up your app, your entire Application's default_url_options will match your action_mailer.default_url_options:

$ MyApp::Application.config.action_mailer.default_url_options
#=> {:host=>"lvh.me", :port=>"3000"}

$ MyApp::Application.default_url_options
#=> {:host=>"lvh.me", :port=>"3000"}

Hat tip to @pduersteler for leading me down this path.

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When you use any listing_url method the full URL will be returned(not a relative one as normal). That's why rails is asking you for the host, to compute the whole URL.

How you can tell rails the host? You can do it in several ways:

1.Adding this option to each environment:

[/config/development.rb]
config.action_mailer.default_url_options = { host: "localhost:3000" }
[/config/test.rb]
config.action_mailer.default_url_options = { host: "localhost:3000" }
[/config/production.rb]
config.action_mailer.default_url_options = { host: "www.example.com" }

NOTE: If you are working inside a rails engine remember to do the same for your dummy app inside the engine tests: path_to_your_engine/test/dummy/config/environments/* because when you test the engine it's what rails is testing against.

2.Add the host option to the foo_url method like this:

listing_url(listing, host: request.host) # => 'http://localhost:3000/listings/1'

3.Not output the host with the option :only_path to true.

listing_url(listing, only_path: true ) # => '/listings/1'   

IMHO I don't see the point on this one because in this case I would use the listing_path method

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Rails.application.routes.default_url_options[:host]= 'localhost:3000'

In the developemnt.rb / test.rb, can be more concise as following:

Rails.application.configure do
  # ... other config ...

  routes.default_url_options[:host] = 'localhost:3000'
end

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Funny thing, that setting config.action_mailer.default_url_options does not help for me. Also, messing around with environment-independent settings in places I felt like it does not belong was not satisfying for me. Additionally, I wanted a solution that worked when generating urls in sidekiq/resque workers.

My approach so far, which goes into config/environments/{development, production}.rb:

MyApp::Application.configure do
    # Stuff omitted...

    config.action_mailer.default_url_options = {
      # Set things here as usual
    }
end

MyApp::Application.default_url_options = MyApp::Application.config.action_mailer.default_url_options

This works for me in rails >= 3.2.x.

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You can always pass host as a parameter to the URL helper:

listing_url(listing, host: request.host)

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go to config/environments/test.rb

Rails.application.routes.default_url_options[:host] = 'localhost:3000'

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just in case someone finds this searching for errors concerning ActiveStorage:

if you have a controller-action where you want to generate upload-urls etc with the local disc-service (most likely in test environment), you need to include ActiveStorage::SetCurrent in the controller in order to allow blob.service_url_for_direct_upload to work correctly.

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The above answer did not work for me, at least not as I wanted. I realised config.action_mailer.default_url_options = { host: "localhost", port: 3000 } after installing devise. Hope it will help someone with the same problem.

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You can set default url options in the Application Controller:

class ApplicationController < ActionController::Base
  def default_url_options
    {:locale => I18n.locale}
  end
end

http://guides.rubyonrails.org/action_controller_overview.html#default_url_options

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I had this same error. I had everything written in correctly, including the Listing 10.13 from the tutorial.

Rails.application.configure do
.
.
.
config.action_mailer.raise_delivery_errors = true
config.action_mailer.delevery_method :test
host = 'example.com'
config.action_mailer.default_url_options = { host: host }
.
.
.
end

obviously with "example.com" replaced with my server url.

What I had glossed over in the tutorial was this line:

After restarting the development server to activate the configuration...

So the answer for me was to turn the server off and back on again.

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Adding the default_url in routes not the right solution although, it works for some cases.

You've to set the default_url in each environment(development, test, production).

You need make these changes.

    config/environments/development.rb
     config.action_mailer.default_url_options = 
      { :host => 'your-host-name' }  #if it is local then 'localhost:3000'

 config/environments/test.rb
      config.action_mailer.default_url_options = 
      { :host => 'your-host-name' }  #if it is local then 'localhost:3000'

  config/environments/development.rb
     config.action_mailer.default_url_options = 
      { :host => 'your-host-name' }  #if it is local then 'localhost:3000'

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I solved the issue by configuring environment.rb as

YourApp::Application.default_url_options = YourApp::Application.config.action_mailer.default_url_options

You need to set default_url_options for action mailer against each environment like development, testing, staging and production etc.

Reference: Missing host to link to! Please provide :host parameter or set default_url_options[:host]

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Didn't want to change the behavior for other environments, so I used:

development.rb

Rails.application.configure do
...
end

Rails.application.default_url_options = Rails.application.config.action_mailer.default_url_options

Works in Rails 6.

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