Expand Robots.txt parser with Allow rules

In this commit we exand the Robots.txt parser.
Now, `Allow` rules are parsed, they take precedence
over `Disallow` ones and the detection is case
insensitive.

lib/gitlab/robots_txt/parser.rb

@@ -3,34 +3,68 @@
 module Gitlab
   module RobotsTxt
     class Parser
-      attr_reader :disallow_rules
+      DISALLOW_REGEX = /^disallow: /i.freeze
+      ALLOW_REGEX = /^allow: /i.freeze
+
+      attr_reader :disallow_rules, :allow_rules
 
       def initialize(content)
         @raw_content = content
 
-        @disallow_rules = parse_raw_content!
+        @disallow_rules, @allow_rules = parse_raw_content!
       end
 
       def disallowed?(path)
+        return false if allow_rules.any? { |rule| path =~ rule }
+
         disallow_rules.any? { |rule| path =~ rule }
       end
 
       private
 
-      # This parser is very basic as it only knows about `Disallow:` lines,
-      # and simply ignores all other lines.
+      # This parser is very basic as it only knows about `Disallow:`
+      # and `Allow:` lines, and simply ignores all other lines.
       #
-      # Order of predecence, 'Allow:`, etc are ignored for now.
+      # Patterns ending in `$`, and `*` for 0 or more characters are recognized.
+      #
+      # It is case insensitive and `Allow` rules takes precedence
+      # over `Disallow`.
       def parse_raw_content!
-        @raw_content.each_line.map do |line|
-          if line.start_with?('Disallow:')
-            value = line.sub('Disallow:', '').strip
-            value = Regexp.escape(value).gsub('\*', '.*')
-            Regexp.new("^#{value}")
-          else
-            nil
+        disallowed = []
+        allowed = []
+
+        @raw_content.each_line.each do |line|
+          if disallow_rule?(line)
+            disallowed << get_disallow_pattern(line)
+          elsif allow_rule?(line)
+            allowed << get_allow_pattern(line)
           end
-        end.compact
+        end
+
+        [disallowed, allowed]
+      end
+
+      def disallow_rule?(line)
+        line =~ DISALLOW_REGEX
+      end
+
+      def get_disallow_pattern(line)
+        get_pattern(line, DISALLOW_REGEX)
+      end
+
+      def allow_rule?(line)
+        line =~ ALLOW_REGEX
+      end
+
+      def get_allow_pattern(line)
+        get_pattern(line, ALLOW_REGEX)
+      end
+
+      def get_pattern(line, rule_regex)
+        value = line.sub(rule_regex, '').strip
+        value = Regexp.escape(value).gsub('\*', '.*')
+        value = value.sub(/\\\$$/, '$')
+        Regexp.new("^#{value}")
       end
     end
   end

public/robots.txt

@@ -21,6 +21,7 @@ Disallow: /dashboard
 Disallow: /users
 Disallow: /help
 Disallow: /s/
+Disallow: /-/profile
 # Only specifically allow the Sign In page to avoid very ugly search results
 Allow: /users/sign_in
 

spec/lib/gitlab/robots_txt/parser_spec.rb

@@ -14,8 +14,13 @@ RSpec.describe Gitlab::RobotsTxt::Parser do
         <<~TXT
           User-Agent: *
           Disallow: /autocomplete/users
-          Disallow: /search
+          disallow: /search
           Disallow: /api
+          Allow: /users
+          Disallow: /help
+          allow: /help
+          Disallow: /test$
+          Disallow: /ex$mple$
         TXT
       end
 
@@ -28,6 +33,12 @@ RSpec.describe Gitlab::RobotsTxt::Parser do
         '/api/grapql' | true
         '/api/index.html' | true
         '/projects' | false
+        '/users' | false
+        '/help' | false
+        '/test' | true
+        '/testfoo' | false
+        '/ex$mple' | true
+        '/ex$mplefoo' | false
       end
 
       with_them do
@@ -47,6 +58,7 @@ RSpec.describe Gitlab::RobotsTxt::Parser do
           Disallow: /*/*.git
           Disallow: /*/archive/
           Disallow: /*/repository/archive*
+          Allow: /*/repository/archive/foo
         TXT
       end
 
@@ -61,6 +73,7 @@ RSpec.describe Gitlab::RobotsTxt::Parser do
         '/projects' | false
         '/git' | false
         '/projects/git' | false
+        '/project/repository/archive/foo' | false
       end
 
       with_them do

spec/requests/robots_txt_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Robots.txt Requests', :aggregate_failures do
+  before do
+    Gitlab::Testing::RobotsBlockerMiddleware.block_requests!
+  end
+
+  after do
+    Gitlab::Testing::RobotsBlockerMiddleware.allow_requests!
+  end
+
+  it 'allows the requests' do
+    requests = [
+      '/users/sign_in'
+    ]
+
+    requests.each do |request|
+      get request
+
+      expect(response).not_to have_gitlab_http_status(:service_unavailable), "#{request} must be allowed"
+    end
+  end
+
+  it 'blocks the requests' do
+    requests = [
+      '/autocomplete/users',
+      '/search',
+      '/admin',
+      '/profile',
+      '/dashboard',
+      '/users',
+      '/users/foo',
+      '/help',
+      '/s/',
+      '/-/profile',
+      '/foo/bar/new',
+      '/foo/bar/edit',
+      '/foo/bar/raw',
+      '/groups/foo/analytics',
+      '/groups/foo/contribution_analytics',
+      '/groups/foo/group_members',
+      '/foo/bar/project.git',
+      '/foo/bar/archive/foo',
+      '/foo/bar/repository/archive',
+      '/foo/bar/activity',
+      '/foo/bar/blame',
+      '/foo/bar/commits',
+      '/foo/bar/commit',
+      '/foo/bar/compare',
+      '/foo/bar/network',
+      '/foo/bar/graphs',
+      '/foo/bar/merge_requests/1.patch',
+      '/foo/bar/merge_requests/1.diff',
+      '/foo/bar/merge_requests/1/diffs',
+      '/foo/bar/deploy_keys',
+      '/foo/bar/hooks',
+      '/foo/bar/services',
+      '/foo/bar/protected_branches',
+      '/foo/bar/uploads/foo',
+      '/foo/bar/project_members',
+      '/foo/bar/settings'
+    ]
+
+    requests.each do |request|
+      get request
+
+      expect(response).to have_gitlab_http_status(:service_unavailable), "#{request} must be disallowed"
+    end
+  end
+end