Improve remote CI/CD config file extension validation

lib/gitlab/ci/config/external/file/base.rb

@@ -10,7 +10,7 @@ module Gitlab
 
             attr_reader :location, :opts, :errors
 
-            YAML_WHITELIST_EXTENSION = /(yml|yaml)$/i.freeze
+            YAML_WHITELIST_EXTENSION = /.+\.(yml|yaml)$/i.freeze
 
             def initialize(location, opts = {})
               @location = location
@@ -21,7 +21,7 @@ module Gitlab
             end
 
             def invalid_extension?
-              !location.match(YAML_WHITELIST_EXTENSION)
+              !::File.basename(location).match(YAML_WHITELIST_EXTENSION)
             end
 
             def valid?

spec/lib/gitlab/ci/config/external/file/base_spec.rb

+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+describe Gitlab::Ci::Config::External::File::Base do
+  subject { described_class.new(location) }
+
+  before do
+    allow_any_instance_of(described_class)
+      .to receive(:content).and_return('key: value')
+  end
+
+  describe '#valid?' do
+    context 'when location is not a YAML file by extension' do
+      let(:location) { 'some/file.txt' }
+
+      it { is_expected.not_to be_valid }
+    end
+
+    context 'when location is not an invalid YAML extension' do
+      let(:location) { 'some/file/.yml' }
+
+      it { is_expected.not_to be_valid }
+    end
+
+    context 'when location is not an valid YAML extension' do
+      let(:location) { 'some/file/config.yml' }
+
+      it { is_expected.to be_valid }
+    end
+
+    context 'when location is not an valid YAML extension' do
+      let(:location) { 'some/file/config.yaml' }
+
+      it { is_expected.to be_valid }
+    end
+
+    context 'when there are YAML syntax errors' do
+      let(:location) { 'some/file/config.yml' }
+
+      before do
+        allow_any_instance_of(described_class)
+          .to receive(:content).and_return('invalid_syntax')
+      end
+
+      it 'is not a valid file' do
+        expect(subject).not_to be_valid
+        expect(subject.error_message).to match /does not have valid YAML syntax/
+      end
+    end
+  end
+end