# Rack

VCR provides a rack middleware that uses a cassette for the duration of a request. Simply provide `VCR::Middleware::Rack` with a block that sets the cassette name and options. You can set these based on the rack env if your block accepts two arguments.

This is useful in a couple different ways:

*   In a rails app, you could use this to log all HTTP API calls made by

    the rails app (using the `:all` record mode).  Of course, this will only

    record HTTP API calls made in the request-response cycle--API calls that

    are offloaded to a background job will not be logged.
*   This can be used as middleware in a simple rack HTTP proxy, to record

    and replay the proxied requests.

## Background ()

_Given_ a file named "remote\_server.rb" with:

```
request_count = 0
$server = start_sinatra_app do
  get('/:path') { "Hello #{params[:path]} #{request_count += 1}" }
end
```

_And_ a file named "client.rb" with:

```
require 'remote_server'
require 'proxy_server'
require 'cgi'

url = URI.parse("http://localhost:#{$proxy.port}?url=#{CGI.escape("http://localhost:#{$server.port}/foo")}")

puts "Response 1: #{Net::HTTP.get_response(url).body}"
puts "Response 2: #{Net::HTTP.get_response(url).body}"
```

_And_ the directory "cassettes" does not exist.

## Use VCR rack middleware to record HTTP responses for a simple rack proxy app

_Given_ a file named "proxy\_server.rb" with:

```
require 'vcr'

$proxy = start_sinatra_app do
  use VCR::Middleware::Rack do |cassette|
    cassette.name    'proxied'
    cassette.options :record => :new_episodes
  end

  get('/') { Net::HTTP.get_response(URI.parse(params[:url])).body }
end

VCR.configure do |c|
  c.cassette_library_dir = 'cassettes'
  c.hook_into :webmock
  c.allow_http_connections_when_no_cassette = true
end
```

_When_ I run `ruby client.rb`

_Then_ the output should contain:

```
Response 1: Hello foo 1
Response 2: Hello foo 1
```

_And_ the file "cassettes/proxied.yml" should contain "Hello foo 1".

## Set cassette name based on rack request env

_Given_ a file named "proxy\_server.rb" with:

```
require 'vcr'

$proxy = start_sinatra_app do
  use VCR::Middleware::Rack do |cassette, env|
    cassette.name    env['SERVER_NAME']
  end

  get('/') { Net::HTTP.get_response(URI.parse(params[:url])).body }
end

VCR.configure do |c|
  c.cassette_library_dir = 'cassettes'
  c.hook_into :webmock
  c.allow_http_connections_when_no_cassette = true
end
```

_When_ I run `ruby client.rb`

_Then_ the output should contain:

```
Response 1: Hello foo 1
Response 2: Hello foo 1
```

_And_ the file "cassettes/localhost.yml" should contain "Hello foo 1".
