Rack handler should use provided default host

[schneems]

This issue is somewhat tricky. When Rails is booted via rails server there are two types of configuration options passed, ones specified directly by a user like rails s -p 3001 will always "win".

For any other config that is not explicitly passed in, puma will consider it a "default". For example when you run rails s (without -p) then the default port will be 3000.

There is one other way to configure puma though, and that is via a config file:

# config/puma.rb
port 3002

This is the order of precedence for configuration

1. Anything the user explicitly passes to rails s
2. Config specified in config/puma.rb file
3. Default values passed in via rails s
4. Defaults values stored in puma

This fallback mechanism works well except in the case of calling port in a config/puma.rb file. To understand look at the old method definition:

def port(port, host=nil)
  host ||= Configuration::DefaultTCPHost
  bind "tcp://#{host}:#{port}"
end

When the port method gets called, even if the user did not specify a host the Configuration::DefaultTCPHost will be used, which is a problem for local development because it defaults to 0.0.0.0. SO about 0.0.0.0 versus localhost.

In this case, while a user did directly specify a port, they did not specify a host, so you would expect the rails s defaults passed in to take affect.

To make Puma respect that the host coming from rails s has more precedence than it's own default host, we must introduce the ability to set and retrieve a default_host value.

This is then used in the rack handler so when rails s passes in :Host => "localhost" then it is used instead of reverting to 0.0.0.0.

The issue with #1699 is the test was wrong, it would have failed if a config file was present with a port invocation.

[Fjan]

I agree this is a good change (safe bij default) but for anyone looking to restore the old behaviour because you need rails accessible to the outside world most of the time, you can do that by setting a new default for the host in puma.rb like this:

port        ENV.fetch("PORT") { 3000 }, ENV.fetch("HOST") { '0.0.0.0' }

[nicovak]

@rafaelfranca @schneems I think this kind of behavior's change should have been notified to the community. I searched for hours why I wasn't able anymore to access my application through local network while developing ... The problem could have been network, proxy or anything else.
Anyway thank you for the change, security first.