Add validator 'declared_only' to reject undeclared params

CHANGELOG.md

@@ -6,6 +6,7 @@
 * [#1568](https://github.com/ruby-grape/grape/pull/1568): Add `proc` option to `values` validator to allow custom checks - [@jlfaber](https://github.com/jlfaber).
 * [#1575](https://github.com/ruby-grape/grape/pull/1575): Include nil values for missing nested params in declared - [@thogg4](https://github.com/thogg4).
 * [#1585](https://github.com/ruby-grape/grape/pull/1585): Bugs in declared method - make sure correct options var is used and respect include missing for non children params - [@thogg4](https://github.com/thogg4).
+* [#1606](https://github.com/ruby-grape/grape/pull/1606): Add `declared_only` validator to reject undeclared keys within block - [@jlfaber](https://github.com/jlfaber).
 * Your contribution here.
 
 #### Fixes

README.md

@@ -1251,7 +1251,20 @@ params do
 end
 ```
 
-#### Nested `mutually_exclusive`, `exactly_one_of`, `at_least_one_of`, `all_or_none_of`
+#### `declared_only`
+
+The method 'declared_only' may be used within any block to ensure that no undeclared parameters are allowed.
+
+```ruby
+params do
+  optional :beer
+  optional :wine
+  optional :juice
+  declared_only
+end
+```
+
+#### Nested `mutually_exclusive`, `exactly_one_of`, `at_least_one_of`, `all_or_none_of`, `declared_only`
 
 All of these methods can be used at any nested level.
 
@@ -1274,11 +1287,13 @@ params do
     optional :icecream
     mutually_exclusive :cake, :icecream
   end
-  optional :recipe, type: Hash do
+  optional :recipes, type: Array do
     optional :oil
     optional :meat
     all_or_none_of :oil, :meat
+    declared_only
   end
+  declared_only
 end
 ```
 

lib/grape.rb

@@ -182,6 +182,7 @@ module ServeFile
 require 'grape/validations/validators/default'
 require 'grape/validations/validators/exactly_one_of'
 require 'grape/validations/validators/mutual_exclusion'
+require 'grape/validations/validators/declared_only'
 require 'grape/validations/validators/presence'
 require 'grape/validations/validators/regexp'
 require 'grape/validations/validators/values'

lib/grape/dsl/parameters.rb

@@ -167,6 +167,12 @@ def all_or_none_of(*attrs)
         validates(attrs, all_or_none_of: { value: true, message: extract_message_option(attrs) })
       end
 
+      # Require that only declared params are present.
+      # @param (see #mutually_exclusive)
+      def declared_only(*attrs)
+        validates(attrs, declared_only: { value: true, message: extract_message_option(attrs) })
+      end
+
       # Define a block of validations which should be applied if and only if
       # the given parameter is present. The parameters are not nested.
       # @param attr [Symbol] the parameter which, if present, triggers the

lib/grape/locale/en.yml

@@ -35,6 +35,7 @@ en:
         at_least_one: 'are missing, at least one parameter must be provided'
         exactly_one: 'are missing, exactly one parameter must be provided'
         all_or_none: 'provide all or none of parameters'
+        declared_only: 'is not a declared parameter'
         missing_group_type: 'group type is required'
         unsupported_group_type: 'group type must be Array, Hash, JSON or Array[JSON]'
         invalid_message_body:

lib/grape/validations/params_scope.rb

@@ -2,7 +2,7 @@ module Grape
   module Validations
     class ParamsScope
       attr_accessor :element, :parent, :index
-      attr_reader :type
+      attr_reader :type, :declared_params
 
       include Grape::DSL::Parameters
 

lib/grape/validations/validators/declared_only.rb

@@ -0,0 +1,25 @@
+module Grape
+  module Validations
+    require 'grape/validations/validators/multiple_params_base'
+    class DeclaredOnlyValidator < MultipleParamsBase
+      attr_reader :extra_params
+
+      def validate!(params)
+        super
+        if extra_params_are_present
+          raise Grape::Exceptions::Validation, params: extra_params, message: message(:declared_only)
+        end
+        params
+      end
+
+      private
+
+      def extra_params_are_present
+        scoped_params.any? do |resource_params|
+          @extra_params = undeclared_keys(resource_params)
+          !@extra_params.empty?
+        end
+      end
+    end
+  end
+end

lib/grape/validations/validators/multiple_params_base.rb

@@ -19,6 +19,14 @@ def keys_in_common(resource_params)
         (all_keys & resource_params.stringify_keys.keys).map(&:to_s)
       end
 
+      def undeclared_keys(resource_params)
+        return [] unless resource_params.is_a?(Hash)
+        allowed_keys = @scope.declared_params.map do |k|
+          k.is_a?(Hash) ? k.keys.first.to_s : k.to_s
+        end
+        (resource_params.stringify_keys.keys - allowed_keys)
+      end
+
       def all_keys
         attrs.map(&:to_s)
       end