Add revision param validator

changelogs/unreleased/ref-params-validator.yml

+---
+title: Add grape custom validator for git reference params
+merge_request: 26102
+author: Rajendra Kadam
+type: added

lib/api/helpers/custom_validators.rb

@@ -56,6 +56,35 @@ module API
                                                message: "should be an array, 'None' or 'Any'"
         end
       end
+
+      class GitRef < Grape::Validations::Base
+        # There are few checks that a Git reference should pass through to be valid reference.
+        # The link contains some rules that have been added to this validator.
+        # https://mirrors.edge.kernel.org/pub/software/scm/git/docs/git-check-ref-format.html
+        # We have skipped some checks that are optional and can be skipped for exception.
+        # We also check for control characters, More info on ctrl chars - https://ruby-doc.org/core-2.7.0/Regexp.html#class-Regexp-label-Character+Classes
+        INVALID_CHARS = Regexp.union('..', '\\', '@', '@{', ' ', '~', '^', ':', '*', '?', '[', /[[:cntrl:]]/).freeze
+        GIT_REF_LENGTH = (1..1024).freeze
+
+        def validate_param!(attr_name, params)
+          revision = params[attr_name]
+
+          return unless invalid_character?(revision)
+
+          raise Grape::Exceptions::Validation, params: [@scope.full_name(attr_name)],
+                                               message: 'should be a valid reference path'
+        end
+
+        private
+
+        def invalid_character?(revision)
+          revision.nil? ||
+            revision.start_with?('-') ||
+            revision.end_with?('.') ||
+            GIT_REF_LENGTH.exclude?(revision.length) ||
+            INVALID_CHARS.match?(revision)
+        end
+      end
     end
   end
 end
@@ -65,3 +94,4 @@ Grape::Validations.register_validator(:git_sha, ::API::Helpers::CustomValidators
 Grape::Validations.register_validator(:absence, ::API::Helpers::CustomValidators::Absence)
 Grape::Validations.register_validator(:integer_none_any, ::API::Helpers::CustomValidators::IntegerNoneAny)
 Grape::Validations.register_validator(:array_none_any, ::API::Helpers::CustomValidators::ArrayNoneAny)
+Grape::Validations.register_validator(:git_ref, ::API::Helpers::CustomValidators::GitRef)

spec/lib/api/helpers/custom_validators_spec.rb

@@ -61,6 +61,47 @@ describe API::Helpers::CustomValidators do
     end
   end
 
+  describe API::Helpers::CustomValidators::GitRef do
+    subject do
+      described_class.new(['test'], {}, false, scope.new)
+    end
+
+    context 'valid revision param' do
+      it 'does not raise a validation error' do
+        expect_no_validation_error('test' => '4e963fe')
+        expect_no_validation_error('test' => 'foo/bar/baz')
+        expect_no_validation_error('test' => "heads/fu\303\237")
+        expect_no_validation_error('test' => 'a' * 1024)
+      end
+    end
+
+    context "revision param contains invalid chars" do
+      it 'raises a validation error' do
+        expect_validation_error('test' => '-4e963fe')
+        expect_validation_error('test' => '4e963fe..ed4ef')
+        expect_validation_error('test' => '4e96\3fe')
+        expect_validation_error('test' => '4e96@3fe')
+        expect_validation_error('test' => '4e9@{63fe')
+        expect_validation_error('test' => '4e963 fe')
+        expect_validation_error('test' => '4e96~3fe')
+        expect_validation_error('test' => '^4e963fe')
+        expect_validation_error('test' => '4:e963fe')
+        expect_validation_error('test' => '4e963fe.')
+        expect_validation_error('test' => 'heads/foo..bar')
+        expect_validation_error('test' => 'foo/bar/.')
+        expect_validation_error('test' => 'heads/v@{ation')
+        expect_validation_error('test' => 'refs/heads/foo.')
+        expect_validation_error('test' => 'heads/foo\bar')
+        expect_validation_error('test' => 'heads/f[/bar')
+        expect_validation_error('test' => "heads/foo\t")
+        expect_validation_error('test' => "heads/foo\177")
+        expect_validation_error('test' => "#{'a' * 1025}")
+        expect_validation_error('test' => nil)
+        expect_validation_error('test' => '')
+      end
+    end
+  end
+
   describe API::Helpers::CustomValidators::FilePath do
     subject do
       described_class.new(['test'], {}, false, scope.new)