# Rarely asked questions

### How can I run a standalone mock server?

By default, a mock service will be started automatically by the pact gem when running the consumer tests. A standalone mock service can be run locally and is useful for debugging purposes.

```ruby
Pact.service_consumer "My Service Consumer" do
  has_pact_with "My Service Provider" do
    mock_service :my_service_provider do
      port <port-num>
      standalone true #Tell the pact gem not to automatically start the mock service
    end
  end
end
```
    $ bundle exec pact service -p <port-num>

The service prints messages it recieves to stdout which can be really useful
when diagnosing issues with pacts.

### How can I specify multiple headers with the same name?

RFC 2616 states that two headers with the same name can interpreted as a single header with two comma-separated values. This is the safest way to specify multiple headers with the same name, as Rack will only pass the last value through when they are defined separately (see https://github.com/rack/rack/issues/436).

```ruby
my_service_provider.
  .given("it is RFC 2616 compliant")
  .upon_receiving("a request with a header with commas separated values")
  .with( method: :get, path: '/', headers: {'X-Request-Multival' => "A, B"} )
  .will_respond_with(
    status: 200, headers: {'X-Response-Multival' => "C, D"}
  )

```

### What is this pact file write mode?

By default, the pact file will be overwritten (started from scratch) every time any rspec runs any spec using pacts. This means that if there are interactions that haven't been executed in the most recent rspec run, they are effectively removed from the pact file. If you have long running pact specs (e.g. they are generated using the browser with Capybara) and you are developing both consumer and provider in parallel, or trying to fix a broken interaction, it can be tedius to run all the specs at once. In this scenario, you can set the pactfile_write_mode to :update. This will keep all existing interactions, and update only the changed ones, identified by description and provider state. The down side of this is that if either of those fields change, the old interactions will not be removed from the pact file. As a middle path, you can set pactfile_write_mode to :smart. This will use :overwrite mode when running rake (as determined by a call to system using 'ps') and :update when running an individual spec.