fix(#1922): Allow to use instance variables defined in the endpoints inside rescue_from (#2377)

* fix(#1922): Allow to use instance variables defined in the endpoints when rescue_from

* fix(#1922): Update CHANGELOG and running rubocop

* fix(#1922): Updating UPGRADING and README files explaining the instance variables behavior. Extra tests added

* fix(#1922): Send endpoint parameter as the last param of the run_rescue_handler method

* fix(#1922): Adding short before/after example to UPGRADING

* fix(#1922): Fixing CHANGELOG format style

Author: jcagarcia

CHANGELOG.md

@@ -3,6 +3,7 @@
 #### Features
 
 * [#2371](https://github.com/ruby-grape/grape/pull/2371): Use a param value as the `default` value of other param - [@jcagarcia](https://github.com/jcagarcia).
+* [#2377](https://github.com/ruby-grape/grape/pull/2377): Allow to use instance variables values inside `rescue_from` - [@jcagarcia](https://github.com/jcagarcia).
 * Your contribution here.
 
 #### Fixes

README.md

@@ -121,6 +121,7 @@
 - [Current Route and Endpoint](#current-route-and-endpoint)
 - [Before, After and Finally](#before-after-and-finally)
 - [Anchoring](#anchoring)
+- [Instance Variables](#instance-variables)
 - [Using Custom Middleware](#using-custom-middleware)
   - [Grape Middleware](#grape-middleware)
   - [Rails Middleware](#rails-middleware)
@@ -3595,6 +3596,42 @@ end
 This will match all paths starting with '/statuses/'. There is one caveat though: the `params[:status]` parameter only holds the first part of the request url.
 Luckily this can be circumvented by using the described above syntax for path specification and using the `PATH_INFO` Rack environment variable, using `env['PATH_INFO']`. This will hold everything that comes after the '/statuses/' part.
 
+## Instance Variables
+
+You can use instance variables to pass information across the various stages of a request. An instance variable set within a `before` validator is accessible within the endpoint's code and can also be utilized within the `rescue_from` handler.
+
+```ruby
+class TwitterAPI < Grape::API
+  before do
+    @var = 1
+  end
+
+  get '/' do
+    puts @var # => 1
+    raise
+  end
+
+  rescue_from :all do
+    puts @var # => 1
+  end
+end
+```
+
+The values of instance variables cannot be shared among various endpoints within the same API. This limitation arises due to Grape generating a new instance for each request made. Consequently, instance variables set within an endpoint during one request differ from those set during a subsequent request, as they exist within separate instances.
+
+```ruby
+class TwitterAPI < Grape::API
+  get '/first' do
+    @var = 1
+    puts @var # => 1
+  end
+
+  get '/second' do
+    puts @var # => nil
+  end
+end
+```
+
 ## Using Custom Middleware
 
 ### Grape Middleware

UPGRADING.md

@@ -1,14 +1,56 @@
 Upgrading Grape
 ===============
 
-### Upgrading to >= 2.0.1
+### Upgrading to >= 2.1.0
 
 #### Grape::Router::Route.route_xxx methods have been removed
 
 - `route_method` is accessible through `request_method`
 - `route_path` is accessible through `path`
 - Any other `route_xyz` are accessible through `options[xyz]`
 
+#### Instance variables scope
+
+Due to the changes done in [#2377](https://github.com/ruby-grape/grape/pull/2377), the instance variables defined inside each of the endpoints (or inside a `before` validator) are now accessible inside the `rescue_from`. The behavior of the instance variables was undefined until `2.1.0`.
+
+If you were using the same variable name defined inside an endpoint or `before` validator inside a `rescue_from` handler, you need to take in mind that you can start getting different values or you can be overriding values.
+
+Before:
+```ruby
+class TwitterAPI < Grape::API
+  before do
+    @var = 1
+  end
+
+  get '/' do
+    puts @var # => 1
+    raise
+  end
+
+  rescue_from :all do
+    puts @var # => nil
+  end
+end
+```
+
+After:
+```ruby
+class TwitterAPI < Grape::API
+  before do
+    @var = 1
+  end
+
+  get '/' do
+    puts @var # => 1
+    raise
+  end
+
+  rescue_from :all do
+    puts @var # => 1
+  end
+end
+```
+
 ### Upgrading to >= 2.0.0
 
 #### Headers

lib/grape/dsl/inside_route.rb

@@ -167,6 +167,23 @@ def error!(message, status = nil, additional_headers = nil)
         throw :error, message: message, status: self.status, headers: headers
       end
 
+      # Creates a Rack response based on the provided message, status, and headers.
+      # The content type in the headers is set to the default content type unless provided.
+      # The message is HTML-escaped if the content type is 'text/html'.
+      #
+      # @param message [String] The content of the response.
+      # @param status [Integer] The HTTP status code.
+      # @params headers [Hash] (optional) Headers for the response
+      #                      (default: {Rack::CONTENT_TYPE => content_type}).
+      #
+      # Returns:
+      # A Rack::Response object containing the specified message, status, and headers.
+      #
+      def rack_response(message, status = 200, headers = { Rack::CONTENT_TYPE => content_type })
+        message = ERB::Util.html_escape(message) if headers[Rack::CONTENT_TYPE] == 'text/html'
+        Rack::Response.new([message], Rack::Utils.status_code(status), headers)
+      end
+
       # Redirect to a new url.
       #
       # @param url [String] The url to be redirect.

lib/grape/middleware/error.rb

@@ -46,7 +46,7 @@ def call!(env)
             rescue_handler_for_any_class(e.class) ||
             raise
 
-          run_rescue_handler(handler, e)
+          run_rescue_handler(handler, e, @env[Grape::Env::API_ENDPOINT])
         end
       end
 
@@ -119,21 +119,29 @@ def rescue_handler_for_any_class(klass)
         options[:all_rescue_handler] || :default_rescue_handler
       end
 
-      def run_rescue_handler(handler, error)
+      def run_rescue_handler(handler, error, endpoint)
         if handler.instance_of?(Symbol)
           raise NoMethodError, "undefined method '#{handler}'" unless respond_to?(handler)
 
           handler = public_method(handler)
         end
 
-        response = handler.arity.zero? ? instance_exec(&handler) : instance_exec(error, &handler)
+        response = (catch(:error) do
+          handler.arity.zero? ? endpoint.instance_exec(&handler) : endpoint.instance_exec(error, &handler)
+        end)
+
+        response = error!(response[:message], response[:status], response[:headers]) if error?(response)
 
         if response.is_a?(Rack::Response)
           response
         else
-          run_rescue_handler(:default_rescue_handler, Grape::Exceptions::InvalidResponse.new)
+          run_rescue_handler(:default_rescue_handler, Grape::Exceptions::InvalidResponse.new, endpoint)
         end
       end
+
+      def error?(response)
+        response.is_a?(Hash) && response[:message] && response[:status] && response[:headers]
+      end
     end
   end
 end

spec/grape/api_spec.rb

@@ -4352,4 +4352,61 @@ def uniqe_id_route
       expect(last_response.body).to be_eql('1-2')
     end
   end
+
+  context 'instance variables' do
+    context 'when setting instance variables in a before validation' do
+      it 'is accessible inside the endpoint' do
+        expected_instance_variable_value = 'wadus'
+
+        subject.before do
+          @my_var = expected_instance_variable_value
+        end
+
+        subject.get('/') do
+          { my_var: @my_var }.to_json
+        end
+
+        get '/'
+        expect(last_response.body).to eq({ my_var: expected_instance_variable_value }.to_json)
+      end
+    end
+
+    context 'when setting instance variables inside the endpoint code' do
+      it 'is accessible inside the rescue_from handler' do
+        expected_instance_variable_value = 'wadus'
+
+        subject.rescue_from(:all) do
+          body = { my_var: @my_var }
+          error!(body, 400)
+        end
+
+        subject.get('/') do
+          @my_var = expected_instance_variable_value
+          raise
+        end
+
+        get '/'
+        expect(last_response.status).to be 400
+        expect(last_response.body).to eq({ my_var: expected_instance_variable_value }.to_json)
+      end
+
+      it 'is NOT available in other endpoints of the same api' do
+        expected_instance_variable_value = 'wadus'
+
+        subject.get('/first') do
+          @my_var = expected_instance_variable_value
+          { my_var: @my_var }.to_json
+        end
+
+        subject.get('/second') do
+          { my_var: @my_var }.to_json
+        end
+
+        get '/first'
+        expect(last_response.body).to eq({ my_var: expected_instance_variable_value }.to_json)
+        get '/second'
+        expect(last_response.body).to eq({ my_var: nil }.to_json)
+      end
+    end
+  end
 end