add a url whitelist

README.markdown

@@ -525,6 +525,13 @@ DatabaseCleaner.allow_production = true
 DatabaseCleaner.allow_remote_database_url = true
 ```
 
+In Ruby, a URL whitelist can be specified. When specified, DatabaseCleaner will only allow `DATABASE_URL` to be equal
+to one of the values specified in the url whitelist like so:
+
+```ruby
+DatabaseCleaner.url_whitelist = ['postgres://postgres@localhost', 'postgres://foo@bar']
+```
+
 ## Debugging
 
 In rare cases DatabaseCleaner will encounter errors that it will log.  By default it uses STDOUT set to the ERROR level but you can configure this to use whatever Logger you desire.

lib/database_cleaner.rb

@@ -3,7 +3,7 @@ require 'database_cleaner/configuration'
 
 module DatabaseCleaner
   class << self
-    attr_accessor :allow_remote_database_url, :allow_production
+    attr_accessor :allow_remote_database_url, :allow_production, :url_whitelist
 
     def can_detect_orm?
       DatabaseCleaner::Base.autodetect_orm

lib/database_cleaner/safeguard.rb

@@ -12,8 +12,35 @@ module DatabaseCleaner
           super("ENV['#{env}'] is set to production. Please refer to https://github.com/DatabaseCleaner/database_cleaner#safeguards")
         end
       end
+
+      class NotWhitelistedUrl < Error
+        def initialize
+          super("ENV['DATABASE_URL'] is set to a URL that is not on the whitelist. Please refer to https://github.com/DatabaseCleaner/database_cleaner#safeguards")
+        end
+      end
     end
 
+    class WhitelistedUrl
+      def run
+        raise Error::NotWhitelistedUrl if !skip? && given?
+      end
+
+      private
+
+        def given?
+          !whitelisted?(ENV['DATABASE_URL'])
+        end
+
+        def whitelisted?(url)
+          DatabaseCleaner.url_whitelist.include?(url)
+        end
+
+        def skip?
+          !DatabaseCleaner.url_whitelist
+        end
+    end
+
+
     class RemoteDatabaseUrl
       LOCAL = %w(localhost 127.0.0.1)
 
@@ -33,7 +60,8 @@ module DatabaseCleaner
 
         def skip?
           ENV['DATABASE_CLEANER_ALLOW_REMOTE_DATABASE_URL'] ||
-            DatabaseCleaner.allow_remote_database_url
+            DatabaseCleaner.allow_remote_database_url ||
+            DatabaseCleaner.url_whitelist
         end
     end
 
@@ -62,7 +90,8 @@ module DatabaseCleaner
 
     CHECKS = [
       RemoteDatabaseUrl,
-      Production
+      Production,
+      WhitelistedUrl
     ]
 
     def run