This extension is part of the Sinatra::Contrib project. Run gem install sinatra-contrib to have it available.

Sinatra::RespondWith

These extensions let Sinatra automatically choose what template to render or action to perform depending on the request’s Accept header.

Example:

# Without Sinatra::RespondWith
get '/' do
  data = { :name => 'example' }
  request.accept.each do |type|
    case type
    when 'text/html'
      halt haml(:index, :locals => data)
    when 'text/json'
      halt data.to_json
    when 'application/atom+xml'
      halt nokogiri(:'index.atom', :locals => data)
    when 'application/xml', 'text/xml'
      halt nokogiri(:'index.xml', :locals => data)
    when 'text/plain'
      halt 'just an example'
    end
  end
  error 406
end

# With Sinatra::RespondWith
get '/' do
  respond_with :index, :name => 'example' do |f|
    f.txt { 'just an example' }
  end
end

Both helper methods respond_to and respond_with let you define custom handlers like the one above for text/plain. respond_with additionally takes a template name and/or an object to offer the following default behavior:

If a template name is given, search for a template called name.format.engine (index.xml.nokogiri in the above example).
If a template name is given, search for a templated called name.engine for engines known to result in the requested format (index.haml).
If a file extension associated with the mime type is known to Sinatra, and the object responds to to_extension, call that method and use the result (data.to_json).

Security

Since methods are triggered based on client input, this can lead to security issues (but not as severe as those might appear in the first place: keep in mind that only known file extensions are used). You should limit the possible formats you serve.

This is possible with the provides condition:

get '/', :provides => [:html, :json, :xml, :atom] do
  respond_with :index, :name => 'example'
end

However, since you have to set provides for every route, this extension adds an app global (class method) `respond_to`, that lets you define content types for all routes:

respond_to :html, :json, :xml, :atom
get('/a') { respond_with :index, :name => 'a' }
get('/b') { respond_with :index, :name => 'b' }

Custom Types

Use the on method for defining actions for custom types:

get '/' do
  respond_to do |f|
    f.xml { nokogiri :index }
    f.on('application/custom') { custom_action }
    f.on('text/*') { data.to_s }
    f.on('*/*') { "matches everything" }
  end
end

Definition order does not matter.