Add length validator.

This validator validates that the length of the parameter (if the parameter supports `#length` is within the specified limits).

lib/grape/locale/en.yml

@@ -10,6 +10,9 @@ en:
         values: 'does not have a valid value'
         except_values: 'has a value not allowed'
         same_as: 'is not the same as %{parameter}'
+        length_mismatch_both: 'is expected to have a length within %{min_length} and %{max_length}'
+        length_mismatch_min_only: 'is expected to have a length greater than %{min_length}'
+        length_mismatch_max_only: 'is expected to have a length less than %{max_length}'
         missing_vendor_option:
           problem: 'missing :vendor option'
           summary: 'when version using header, you must specify :vendor option'

lib/grape/validations/attributes_doc.rb

@@ -28,6 +28,12 @@ def extract_details(validations)
         details[:documentation] = documentation if documentation
 
         details[:default] = validations[:default] if validations.key?(:default)
+
+        return unless validations.key?(:length)
+
+        length_validation = validations[:length]
+        details[:min_length] = length_validation[:min] if length_validation.key?(:min)
+        details[:max_length] = length_validation[:max] if length_validation.key?(:max)
       end
 
       def document(attrs)

lib/grape/validations/validators/length_validator.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+module Grape
+  module Validations
+    module Validators
+      class LengthValidator < Base
+        def initialize(attrs, options, required, scope, **opts)
+          @min_length = options[:min]
+          @max_length = options[:max]
+          super
+        end
+
+        def validate_param!(attr_name, params)
+          param = params[attr_name]
+          return unless param.respond_to?(:length)
+          return unless (@min_length && param.length < @min_length) || (@max_length && param.length > @max_length)
+
+          raise Grape::Exceptions::Validation.new(params: [@scope.full_name(attr_name)], message: build_message)
+        end
+
+        def build_message
+          if options_key?(:message)
+            @option[:message]
+          elsif @min_length && @max_length
+            format I18n.t(:length_mismatch_both, scope: 'grape.errors.messages'), min_length: @min_length, max_length: @max_length
+          elsif @min_length
+            format I18n.t(:length_mismatch_min_only, scope: 'grape.errors.messages'), min_length: @min_length
+          else
+            format I18n.t(:length_mismatch_max_only, scope: 'grape.errors.messages'), max_length: @max_length
+          end
+        end
+      end
+    end
+  end
+end

spec/grape/validations/attributes_doc_spec.rb

@@ -31,7 +31,8 @@
       presence: true,
       desc: 'Age of...',
       documentation: 'Age is...',
-      default: 1
+      default: 1,
+      length: { min: 1, max: 13 }
     }
   end
 
@@ -77,7 +78,9 @@
         documentation: validations[:documentation],
         default: validations[:default],
         type: 'Integer',
-        values: valid_values
+        values: valid_values,
+        min_length: validations[:length][:min],
+        max_length: validations[:length][:max]
       }
     end
 

spec/grape/validations/validators/length_spec.rb

@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+describe Grape::Validations::Validators::LengthValidator do
+  let_it_be(:app) do
+    Class.new(Grape::API) do
+      params do
+        requires :list, length: { min: 2, max: 3 }
+      end
+      post 'with_min_max' do
+      end
+
+      params do
+        requires :list, type: [Integer], length: { min: 2 }
+      end
+      post 'with_min_only' do
+      end
+
+      params do
+        requires :list, type: [Integer], length: { max: 3 }
+      end
+      post 'with_max_only' do
+      end
+
+      params do
+        requires :list, type: Integer, length: { max: 3 }
+      end
+      post 'type_is_not_array' do
+      end
+
+      params do
+        requires :list, type: [Integer], length: { min: 2, message: 'not match' }
+      end
+      post '/custom-message' do
+      end
+    end
+  end
+
+  describe '/with_min_max' do
+    context 'when length is within limits' do
+      it do
+        post '/with_min_max', list: [1, 2]
+        expect(last_response.status).to eq(201)
+        expect(last_response.body).to eq('')
+      end
+    end
+
+    context 'when length is exceeded' do
+      it do
+        post '/with_min_max', list: [1, 2, 3, 4, 5]
+        expect(last_response.status).to eq(400)
+        expect(last_response.body).to eq('list is expected to have a length within 2 and 3')
+      end
+    end
+
+    context 'when length is less than minimum' do
+      it do
+        post '/with_min_max', list: [1]
+        expect(last_response.status).to eq(400)
+        expect(last_response.body).to eq('list is expected to have a length within 2 and 3')
+      end
+    end
+  end
+
+  describe '/with_max_only' do
+    context 'when length is less than limits' do
+      it do
+        post '/with_max_only', list: [1, 2]
+        expect(last_response.status).to eq(201)
+        expect(last_response.body).to eq('')
+      end
+    end
+
+    context 'when length is exceeded' do
+      it do
+        post '/with_max_only', list: [1, 2, 3, 4, 5]
+        expect(last_response.status).to eq(400)
+        expect(last_response.body).to eq('list is expected to have a length less than 3')
+      end
+    end
+  end
+
+  describe '/with_min_only' do
+    context 'when length is greater than limit' do
+      it do
+        post '/with_min_only', list: [1, 2]
+        expect(last_response.status).to eq(201)
+        expect(last_response.body).to eq('')
+      end
+    end
+
+    context 'when length is less than limit' do
+      it do
+        post '/with_min_only', list: [1]
+        expect(last_response.status).to eq(400)
+        expect(last_response.body).to eq('list is expected to have a length greater than 2')
+      end
+    end
+  end
+
+  describe '/type_is_not_array' do
+    context 'is no op' do
+      it do
+        post 'type_is_not_array', list: 12
+        expect(last_response.status).to eq(201)
+        expect(last_response.body).to eq('')
+      end
+    end
+  end
+
+  describe '/custom-message' do
+    context 'is within limits' do
+      it do
+        post '/custom-message', list: [1, 2, 3]
+        expect(last_response.status).to eq(201)
+        expect(last_response.body).to eq('')
+      end
+    end
+
+    context 'is outside limit' do
+      it do
+        post '/custom-message', list: [1]
+        expect(last_response.status).to eq(400)
+        expect(last_response.body).to eq('list not match')
+      end
+    end
+  end
+end