Add length validator (#2437)

CHANGELOG.md

@@ -29,6 +29,7 @@
 * [#2436](https://github.com/ruby-grape/grape/pull/2436): Update coverallsapp github-action - [@ericproulx](https://github.com/ericproulx).
 * [#2434](https://github.com/ruby-grape/grape/pull/2434): Implement nested `with` support in parameter dsl - [@numbata](https://github.com/numbata).
 * [#2438](https://github.com/ruby-grape/grape/pull/2438): Fix some Rack::Lint - [@ericproulx](https://github.com/ericproulx).
+* [#2437](https://github.com/ruby-grape/grape/pull/2437): Add length validator - [@dhruvCW](https://github.com/dhruvCW).
 * Your contribution here.
 
 #### Fixes

README.md

@@ -56,6 +56,7 @@
     - [values](#values)
     - [except_values](#except_values)
     - [same_as](#same_as)
+    - [length](#length)
     - [regexp](#regexp)
     - [mutually_exclusive](#mutually_exclusive)
     - [exactly_one_of](#exactly_one_of)
@@ -69,6 +70,7 @@
   - [Custom Validation messages](#custom-validation-messages)
     - [presence, allow_blank, values, regexp](#presence-allow_blank-values-regexp)
     - [same_as](#same_as-1)
+    - [length](#length-1)
     - [all_or_none_of](#all_or_none_of-1)
     - [mutually_exclusive](#mutually_exclusive-1)
     - [exactly_one_of](#exactly_one_of-1)
@@ -1709,6 +1711,20 @@ params do
 end
 ```
 
+#### `length`
+
+Parameters with types that support `#length` method can be restricted to have a specific length with the `:length` option.
+
+The validator accepts `:min` or `:max` or both options to validate that the value of the parameter is within the given limits.
+
+```ruby
+params do
+  requires :str, type: String, length: { min: 3 }
+  requires :list, type: [Integer], length: { min: 3, max: 5 }
+  requires :hash, type: Hash, length: { max: 5 }
+end
+```
+
 #### `regexp`
 
 Parameters can be restricted to match a specific regular expression with the `:regexp` option. If the value does not match the regular expression an error will be returned. Note that this is true for both `requires` and `optional` parameters.
@@ -2026,6 +2042,15 @@ params do
 end
 ```
 
+#### `length`
+
+```ruby
+params do
+  requires :str, type: String, length: { min: 5, message: 'str is expected to be atleast 5 characters long' }
+  requires :list, type: [Integer], length: { min: 2, max: 3, message: 'list is expected to have between 2 and 3 elements' }
+end
+```
+
 #### `all_or_none_of`
 
 ```ruby

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: 'is expected to have length within %{min} and %{max}'
+        length_min: 'is expected to have length greater than or equal to %{min}'
+        length_max: 'is expected to have length less than or equal to %{max}'
         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 +28,9 @@ def extract_details(validations)
         details[:documentation] = documentation if documentation
 
         details[:default] = validations[:default] if validations.key?(:default)
+
+        details[:min_length] = validations[:length][:min] if validations.key?(:length) && validations[:length].key?(:min)
+        details[:max_length] = validations[:length][:max] if validations.key?(:length) && validations[:length].key?(:max)
       end
 
       def document(attrs)

lib/grape/validations/validators/length_validator.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module Grape
+  module Validations
+    module Validators
+      class LengthValidator < Base
+        def initialize(attrs, options, required, scope, **opts)
+          @min = options[:min]
+          @max = options[:max]
+
+          super
+
+          raise ArgumentError, 'min must be an integer greater than or equal to zero' if !@min.nil? && (!@min.is_a?(Integer) || @min.negative?)
+          raise ArgumentError, 'max must be an integer greater than or equal to zero' if !@max.nil? && (!@max.is_a?(Integer) || @max.negative?)
+          raise ArgumentError, "min #{@min} cannot be greater than max #{@max}" if !@min.nil? && !@max.nil? && @min > @max
+        end
+
+        def validate_param!(attr_name, params)
+          param = params[attr_name]
+
+          raise ArgumentError, "parameter #{param} does not support #length" unless param.respond_to?(:length)
+
+          return unless (!@min.nil? && param.length < @min) || (!@max.nil? && param.length > @max)
+
+          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 && @max
+            format I18n.t(:length, scope: 'grape.errors.messages'), min: @min, max: @max
+          elsif @min
+            format I18n.t(:length_min, scope: 'grape.errors.messages'), min: @min
+          else
+            format I18n.t(:length_max, scope: 'grape.errors.messages'), max: @max
+          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