Allow specifying a handler for grape_exceptions (ruby-grape#2342)

* Allow specifying a handler for grape_exceptions

This allows you to customize the format of the error response for grape exceptions:

For example, you could do something like this:

```rb
rescue_from :grape_exceptions do |e|
  error!({ errors: [{ code: 'Error', message: e.message.squish }] }, e.status)
end
```

which would render like this:

```
{
  "errors": [
    {
      "code": "Error",
      "message": "Problem: message body does not match declared format Resolution: when specifying application/json as content-type, you must pass valid application/json in the request's 'body'"
    }
  ]
}
```

* match format

* Fix issue caught by tests

* Update README & CHANGELOG

* Add spec to demonstrate usage

* Fix rubocop offenses

* Fix rubocop offences

.rubocop_todo.yml

@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config --auto-gen-only-exclude --exclude-limit 5000`
-# on 2023-05-27 20:47:15 UTC using RuboCop version 1.50.2.
+# on 2023-07-01 15:43:53 UTC using RuboCop version 1.50.2.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -100,6 +100,12 @@ Lint/MissingSuper:
     - 'lib/grape/router/pattern.rb'
     - 'lib/grape/validations/validators/base.rb'
 
+# Offense count: 1
+# Configuration parameters: CountComments, Max, CountAsOne, AllowedMethods, AllowedPatterns.
+Metrics/MethodLength:
+  Exclude:
+    - 'lib/grape/endpoint.rb'
+
 # Offense count: 2
 # Configuration parameters: EnforcedStyleForLeadingUnderscores.
 # SupportedStylesForLeadingUnderscores: disallowed, required, optional
@@ -134,7 +140,7 @@ RSpec/AnyInstance:
     - 'spec/grape/api_spec.rb'
     - 'spec/grape/middleware/base_spec.rb'
 
-# Offense count: 342
+# Offense count: 343
 # Configuration parameters: Prefixes, AllowedPatterns.
 # Prefixes: when, with, without
 RSpec/ContextWording:
@@ -324,7 +330,7 @@ RSpec/MessageChain:
   Exclude:
     - 'spec/grape/middleware/formatter_spec.rb'
 
-# Offense count: 136
+# Offense count: 147
 # Configuration parameters: .
 # SupportedStyles: have_received, receive
 RSpec/MessageSpies:
@@ -335,7 +341,7 @@ RSpec/MissingExampleGroupArgument:
   Exclude:
     - 'spec/grape/middleware/exception_spec.rb'
 
-# Offense count: 765
+# Offense count: 772
 # Configuration parameters: Max.
 RSpec/MultipleExpectations:
   Exclude:
@@ -413,7 +419,7 @@ RSpec/MultipleMemoizedHelpers:
     - 'spec/grape/request_spec.rb'
     - 'spec/grape/validations/attributes_doc_spec.rb'
 
-# Offense count: 2137
+# Offense count: 2150
 # Configuration parameters: EnforcedStyle, IgnoreSharedExamples.
 # SupportedStyles: always, named_only
 RSpec/NamedSubject:
@@ -478,7 +484,7 @@ RSpec/NamedSubject:
     - 'spec/grape/validations/validators/presence_spec.rb'
     - 'spec/grape/validations_spec.rb'
 
-# Offense count: 174
+# Offense count: 173
 # Configuration parameters: Max, AllowedGroups.
 RSpec/NestedGroups:
   Exclude:
@@ -527,11 +533,10 @@ RSpec/RepeatedDescription:
     - 'spec/grape/validations/validators/allow_blank_spec.rb'
     - 'spec/grape/validations/validators/values_spec.rb'
 
-# Offense count: 10
+# Offense count: 8
 RSpec/RepeatedExample:
   Exclude:
     - 'spec/grape/api_spec.rb'
-    - 'spec/grape/dsl/request_response_spec.rb'
     - 'spec/grape/middleware/versioner/accept_version_header_spec.rb'
     - 'spec/grape/validations/validators/allow_blank_spec.rb'
 
@@ -559,7 +564,7 @@ RSpec/StubbedMock:
     - 'spec/grape/middleware/formatter_spec.rb'
     - 'spec/grape/parser_spec.rb'
 
-# Offense count: 114
+# Offense count: 122
 RSpec/SubjectStub:
   Exclude:
     - 'spec/grape/api_spec.rb'

CHANGELOG.md

@@ -9,6 +9,7 @@
 * [#2332](https://github.com/ruby-grape/grape/pull/2332): Use ActiveSupport configurable - [@ericproulx](https://github.com/ericproulx).
 * [#2333](https://github.com/ruby-grape/grape/pull/2333): Use custom messages in parameter validation with arity 1 - [@thedevjoao](https://github.com/TheDevJoao).
 * [#2341](https://github.com/ruby-grape/grape/pull/2341): Stop yielding skip value - [@ericproulx](https://github.com/ericproulx).
+* [#2342](https://github.com/ruby-grape/grape/pull/2342): Allow specifying a handler for grape_exceptions - [@mscrivo](https://github.com/mscrivo).
 * Your contribution here.
 
 #### Fixes

README.md

@@ -2626,6 +2626,14 @@ class Twitter::API < Grape::API
 end
 ```
 
+If you want to customize the shape of grape exceptions returned to the user, to match your `:all` handler for example, you can pass a block to `rescue_from :grape_exceptions`.
+
+```ruby
+rescue_from :grape_exceptions do |e|
+  error!(e, e.status)
+end
+```
+
 You can also rescue specific exceptions.
 
 ```ruby

lib/grape/dsl/request_response.rb

@@ -112,10 +112,11 @@ def rescue_from(*args, &block)
 
           if args.include?(:all)
             namespace_inheritable(:rescue_all, true)
-            namespace_inheritable :all_rescue_handler, handler
+            namespace_inheritable(:all_rescue_handler, handler)
           elsif args.include?(:grape_exceptions)
             namespace_inheritable(:rescue_all, true)
             namespace_inheritable(:rescue_grape_exceptions, true)
+            namespace_inheritable(:grape_exceptions_rescue_handler, handler)
           else
             handler_type =
               case options[:rescue_subclasses]

lib/grape/endpoint.rb

@@ -292,7 +292,8 @@ def build_stack(helpers)
                 rescue_options: namespace_stackable_with_hash(:rescue_options) || {},
                 rescue_handlers: namespace_reverse_stackable_with_hash(:rescue_handlers) || {},
                 base_only_rescue_handlers: namespace_stackable_with_hash(:base_only_rescue_handlers) || {},
-                all_rescue_handler: namespace_inheritable(:all_rescue_handler)
+                all_rescue_handler: namespace_inheritable(:all_rescue_handler),
+                grape_exceptions_rescue_handler: namespace_inheritable(:grape_exceptions_rescue_handler)
 
       stack.concat namespace_stackable(:middleware)
 

lib/grape/middleware/error.rb

@@ -109,7 +109,7 @@ def rescue_handler_for_grape_exception(klass)
         return :error_response if klass == Grape::Exceptions::InvalidVersionHeader
         return unless options[:rescue_grape_exceptions] || !options[:rescue_all]
 
-        :error_response
+        options[:grape_exceptions_rescue_handler] || :error_response
       end
 
       def rescue_handler_for_any_class(klass)

spec/grape/dsl/request_response_spec.rb

@@ -148,13 +148,32 @@ def self.imbue(key, value)
           it 'sets rescue all to true' do
             expect(subject).to receive(:namespace_inheritable).with(:rescue_all, true)
             expect(subject).to receive(:namespace_inheritable).with(:rescue_grape_exceptions, true)
+            expect(subject).to receive(:namespace_inheritable).with(:grape_exceptions_rescue_handler, nil)
             subject.rescue_from :grape_exceptions
           end
 
-          it 'sets rescue_grape_exceptions to true' do
+          it 'sets given proc as rescue handler' do
+            rescue_handler_proc = proc {}
             expect(subject).to receive(:namespace_inheritable).with(:rescue_all, true)
             expect(subject).to receive(:namespace_inheritable).with(:rescue_grape_exceptions, true)
-            subject.rescue_from :grape_exceptions
+            expect(subject).to receive(:namespace_inheritable).with(:grape_exceptions_rescue_handler, rescue_handler_proc)
+            subject.rescue_from :grape_exceptions, rescue_handler_proc
+          end
+
+          it 'sets given block as rescue handler' do
+            rescue_handler_proc = proc {}
+            expect(subject).to receive(:namespace_inheritable).with(:rescue_all, true)
+            expect(subject).to receive(:namespace_inheritable).with(:rescue_grape_exceptions, true)
+            expect(subject).to receive(:namespace_inheritable).with(:grape_exceptions_rescue_handler, rescue_handler_proc)
+            subject.rescue_from :grape_exceptions, &rescue_handler_proc
+          end
+
+          it 'sets a rescue handler declared through :with option' do
+            with_block = -> { 'hello' }
+            expect(subject).to receive(:namespace_inheritable).with(:rescue_all, true)
+            expect(subject).to receive(:namespace_inheritable).with(:rescue_grape_exceptions, true)
+            expect(subject).to receive(:namespace_inheritable).with(:grape_exceptions_rescue_handler, an_instance_of(Proc))
+            subject.rescue_from :grape_exceptions, with: with_block
           end
         end
 

spec/grape/exceptions/body_parse_errors_spec.rb

@@ -91,6 +91,46 @@ def app
     end
   end
 
+  context 'api with rescue_from :grape_exceptions handler with block' do
+    subject { Class.new(Grape::API) }
+
+    before do
+      subject.rescue_from :grape_exceptions do |e|
+        rack_response "Custom Error Contents, Original Message: #{e.message}", 400
+      end
+
+      subject.params do
+        requires :beer
+      end
+
+      subject.post '/beer' do
+        'beer received'
+      end
+    end
+
+    def app
+      subject
+    end
+
+    context 'with content_type json' do
+      it 'returns body parsing error message' do
+        post '/beer', 'test', 'CONTENT_TYPE' => 'application/json'
+        expect(last_response.status).to eq 400
+        expect(last_response.body).to include 'message body does not match declared format'
+        expect(last_response.body).to include 'Custom Error Contents, Original Message'
+      end
+    end
+
+    context 'with content_type xml' do
+      it 'returns body parsing error message' do
+        post '/beer', 'test', 'CONTENT_TYPE' => 'application/xml'
+        expect(last_response.status).to eq 400
+        expect(last_response.body).to include 'message body does not match declared format'
+        expect(last_response.body).to include 'Custom Error Contents, Original Message'
+      end
+    end
+  end
+
   context 'api without a rescue handler' do
     subject { Class.new(Grape::API) }