Merge pull request #34505 from eileencodes/add-readonly-mode

Add ability to block writes to a database

10 files changed, 286 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 5b07d63684..d9488bd0f0 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,19 @@
+*   Add the ability to prevent writes to a database for the duration of a block.
+
+    Allows the application to prevent writes to a database. This can be useful when
+    you're building out multiple databases and want to make sure you're not sending
+    writes when you want a read.
+
+    If `while_preventing_writes` is called and the query is considered a write
+    query the database will raise an exception regardless of whether the database
+    user is able to write.
+
+    This is not meant to be a catch-all for write queries but rather a way to enforce
+    read-only queries without opening a second connection. One purpose of this is to
+    catch accidental writes, not all writes.
+
+    *Eileen M. Uchitelle*
+
 *   Allow aliased attributes to be used in `#update_columns` and `#update`.
 
     *Gannon McGibbon*
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index 0059f0b773..2299fc0214 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -98,6 +98,11 @@ module ActiveRecord
         exec_query(sql, name).rows
       end
 
+      # Determines whether the SQL statement is a write query.
+      def write_query?(sql)
+        raise NotImplementedError
+      end
+
       # Executes the SQL statement in the context of this connection and returns
       # the raw result from the connection adapter.
       # Note: depending on your database connector, the result returned by this
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index f73369ceef..31a994292e 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -76,7 +76,7 @@ module ActiveRecord
 
       SIMPLE_INT = /\A\d+\z/
 
-      attr_accessor :visitor, :pool
+      attr_accessor :visitor, :pool, :prevent_writes
       attr_reader :schema_cache, :owner, :logger, :prepared_statements, :lock
       alias :in_use? :owner
 
@@ -100,6 +100,13 @@ module ActiveRecord
         end
       end
 
+      def self.build_read_query_regexp(*parts) # :nodoc:
+        lambda do |*parts|
+          parts = parts.map { |part| /\A\s*#{part}/i }
+          Regexp.union(*parts)
+        end
+      end
+
       def initialize(connection, logger = nil, config = {}) # :nodoc:
         super()
 
@@ -133,6 +140,27 @@ module ActiveRecord
         @config[:replica] || false
       end
 
+      # Determines whether writes are currently being prevents.
+      #
+      # Returns true if the connection is a replica, or if +prevent_writes+
+      # is set to true.
+      def preventing_writes?
+        replica? || prevent_writes
+      end
+
+      # Prevent writing to the database  regardless of role.
+      #
+      # In some cases you may want to prevent writes to the database
+      # even if you are on a database that can write. `while_preventing_writes`
+      # will prevent writes to the database for the duration of the block.
+      def while_preventing_writes
+        original = self.prevent_writes
+        self.prevent_writes = true
+        yield
+      ensure
+        self.prevent_writes = original
+      end
+
       def migrations_paths # :nodoc:
         @config[:migrations_paths] || Migrator.migrations_paths
       end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
index 9ea237dd81..0ec9581c42 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
@@ -19,8 +19,18 @@ module ActiveRecord
           execute(sql, name).to_a
         end
 
+        READ_QUERY = ActiveRecord::ConnectionAdapters::AbstractAdapter.build_read_query_regexp.call(:begin, :select, :set, :show, :release, :savepoint) # :nodoc:
+
+        def write_query?(sql) # :nodoc:
+          !READ_QUERY.match?(sql)
+        end
+
         # Executes the SQL statement in the context of this connection.
         def execute(sql, name = nil)
+          if preventing_writes? && write_query?(sql)
+            raise ActiveRecord::StatementInvalid, "Write query attempted while in readonly mode: #{sql}"
+          end
+
           # make sure we carry over any changes to ActiveRecord::Base.default_timezone that have been
           # made since we established the connection
           @connection.query_options[:database_timezone] = ActiveRecord::Base.default_timezone
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
index 6bd6b67165..c8bc339e61 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -67,11 +67,21 @@ module ActiveRecord
           end
         end
 
+        READ_QUERY = ActiveRecord::ConnectionAdapters::AbstractAdapter.build_read_query_regexp.call(:select, :show, :set) # :nodoc:
+
+        def write_query?(sql) # :nodoc:
+          !READ_QUERY.match?(sql)
+        end
+
         # Executes an SQL statement, returning a PG::Result object on success
         # or raising a PG::Error exception otherwise.
         # Note: the PG::Result object is manually memory managed; if you don't
         # need it specifically, you may want consider the <tt>exec_query</tt> wrapper.
         def execute(sql, name = nil)
+          if preventing_writes? && write_query?(sql)
+            raise ActiveRecord::StatementInvalid, "Write query attempted while in readonly mode: #{sql}"
+          end
+
           materialize_transactions
 
           log(sql, name) do
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index b41bf2fc66..1bec8fbabd 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -209,6 +209,12 @@ module ActiveRecord
       # DATABASE STATEMENTS ======================================
       #++
 
+      READ_QUERY = ActiveRecord::ConnectionAdapters::AbstractAdapter.build_read_query_regexp.call(:select) # :nodoc:
+
+      def write_query?(sql) # :nodoc:
+        !READ_QUERY.match?(sql)
+      end
+
       def explain(arel, binds = [])
         sql = "EXPLAIN QUERY PLAN #{to_sql(arel, binds)}"
         SQLite3::ExplainPrettyPrinter.new.pp(exec_query(sql, "EXPLAIN", []))
@@ -257,6 +263,10 @@ module ActiveRecord
       end
 
       def execute(sql, name = nil) #:nodoc:
+        if preventing_writes? && write_query?(sql)
+          raise ActiveRecord::StatementInvalid, "Write query attempted while in readonly mode: #{sql}"
+        end
+
         materialize_transactions
 
         log(sql, name) do
diff --git a/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
index 0719baaa23..bddcd309cd 100644
--- a/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
@@ -69,6 +69,64 @@ class Mysql2AdapterTest < ActiveRecord::Mysql2TestCase
     @conn.exec_query("ALTER TABLE engines DROP COLUMN old_car_id")
   end
 
+  def test_errors_when_an_insert_query_is_called_while_preventing_writes
+    assert_raises(ActiveRecord::StatementInvalid) do
+      @conn.while_preventing_writes do
+        @conn.insert("INSERT INTO `engines` (`car_id`) VALUES ('138853948594')")
+      end
+    end
+  end
+
+  def test_errors_when_an_update_query_is_called_while_preventing_writes
+    @conn.insert("INSERT INTO `engines` (`car_id`) VALUES ('138853948594')")
+
+    assert_raises(ActiveRecord::StatementInvalid) do
+      @conn.while_preventing_writes do
+        @conn.update("UPDATE `engines` SET `engines`.`car_id` = '9989' WHERE `engines`.`car_id` = '138853948594'")
+      end
+    end
+  end
+
+  def test_errors_when_a_delete_query_is_called_while_preventing_writes
+    @conn.execute("INSERT INTO `engines` (`car_id`) VALUES ('138853948594')")
+
+    assert_raises(ActiveRecord::StatementInvalid) do
+      @conn.while_preventing_writes do
+        @conn.execute("DELETE FROM `engines` where `engines`.`car_id` = '138853948594'")
+      end
+    end
+  end
+
+  def test_errors_when_a_replace_query_is_called_while_preventing_writes
+    @conn.execute("INSERT INTO `engines` (`car_id`) VALUES ('138853948594')")
+
+    assert_raises(ActiveRecord::StatementInvalid) do
+      @conn.while_preventing_writes do
+        @conn.execute("REPLACE INTO `engines` SET `engines`.`car_id` = '249823948'")
+      end
+    end
+  end
+
+  def test_doesnt_error_when_a_select_query_is_called_while_preventing_writes
+    @conn.execute("INSERT INTO `engines` (`car_id`) VALUES ('138853948594')")
+
+    @conn.while_preventing_writes do
+      assert_equal 1, @conn.execute("SELECT `engines`.* FROM `engines` WHERE `engines`.`car_id` = '138853948594'").entries.count
+    end
+  end
+
+  def test_doesnt_error_when_a_show_query_is_called_while_preventing_writes
+    @conn.while_preventing_writes do
+      assert_equal 2, @conn.execute("SHOW FULL FIELDS FROM `engines`").entries.count
+    end
+  end
+
+  def test_doesnt_error_when_a_set_query_is_called_while_preventing_writes
+    @conn.while_preventing_writes do
+      assert_nil @conn.execute("SET NAMES utf8")
+    end
+  end
+
   private
 
     def with_example_table(definition = "id int auto_increment primary key, number int, data varchar(255)", &block)
diff --git a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
index cbb6cd42b5..59ddb8457e 100644
--- a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
@@ -376,6 +376,62 @@ module ActiveRecord
         end
       end
 
+      def test_errors_when_an_insert_query_is_called_while_preventing_writes
+        with_example_table do
+          assert_raises(ActiveRecord::StatementInvalid) do
+            @connection.while_preventing_writes do
+              @connection.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+            end
+          end
+        end
+      end
+
+      def test_errors_when_an_update_query_is_called_while_preventing_writes
+        with_example_table do
+          @connection.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+
+          assert_raises(ActiveRecord::StatementInvalid) do
+            @connection.while_preventing_writes do
+              @connection.execute("UPDATE ex SET data = '9989' WHERE data = '138853948594'")
+            end
+          end
+        end
+      end
+
+      def test_errors_when_a_delete_query_is_called_while_preventing_writes
+        with_example_table do
+          @connection.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+
+          assert_raises(ActiveRecord::StatementInvalid) do
+            @connection.while_preventing_writes do
+              @connection.execute("DELETE FROM ex where data = '138853948594'")
+            end
+          end
+        end
+      end
+
+      def test_doesnt_error_when_a_select_query_is_called_while_preventing_writes
+        with_example_table do
+          @connection.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+
+          @connection.while_preventing_writes do
+            assert_equal 1, @connection.execute("SELECT * FROM ex WHERE data = '138853948594'").entries.count
+          end
+        end
+      end
+
+      def test_doesnt_error_when_a_show_query_is_called_while_preventing_writes
+        @connection.while_preventing_writes do
+          assert_equal 1, @connection.execute("SHOW TIME ZONE").entries.count
+        end
+      end
+
+      def test_doesnt_error_when_a_set_query_is_called_while_preventing_writes
+        @connection.while_preventing_writes do
+          assert_equal [], @connection.execute("SET standard_conforming_strings = on").entries
+        end
+      end
+
       private
 
         def with_example_table(definition = "id serial primary key, number integer, data character varying(255)", &block)
diff --git a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
index 8536dcf183..3b7a28b757 100644
--- a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
@@ -573,6 +573,62 @@ module ActiveRecord
         end
       end
 
+      def test_errors_when_an_insert_query_is_called_while_preventing_writes
+        with_example_table "id int, data string" do
+          assert_raises(ActiveRecord::StatementInvalid) do
+            @conn.while_preventing_writes do
+              @conn.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+            end
+          end
+        end
+      end
+
+      def test_errors_when_an_update_query_is_called_while_preventing_writes
+        with_example_table "id int, data string" do
+          @conn.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+
+          assert_raises(ActiveRecord::StatementInvalid) do
+            @conn.while_preventing_writes do
+              @conn.execute("UPDATE ex SET data = '9989' WHERE data = '138853948594'")
+            end
+          end
+        end
+      end
+
+      def test_errors_when_a_delete_query_is_called_while_preventing_writes
+        with_example_table "id int, data string" do
+          @conn.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+
+          assert_raises(ActiveRecord::StatementInvalid) do
+            @conn.while_preventing_writes do
+              @conn.execute("DELETE FROM ex where data = '138853948594'")
+            end
+          end
+        end
+      end
+
+      def test_errors_when_a_replace_query_is_called_while_preventing_writes
+        with_example_table "id int, data string" do
+          @conn.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+
+          assert_raises(ActiveRecord::StatementInvalid) do
+            @conn.while_preventing_writes do
+              @conn.execute("REPLACE INTO ex (data) VALUES ('249823948')")
+            end
+          end
+        end
+      end
+
+      def test_doesnt_error_when_a_select_query_is_called_while_preventing_writes
+        with_example_table "id int, data string" do
+          @conn.execute("INSERT INTO ex (data) VALUES ('138853948594')")
+
+          @conn.while_preventing_writes do
+            assert_equal 1, @conn.execute("SELECT data from ex WHERE data = '138853948594'").count
+          end
+        end
+      end
+
       private
 
         def assert_logged(logs)
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index 63a73101c4..6c7f3a9c56 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -1488,4 +1488,40 @@ class BasicsTest < ActiveRecord::TestCase
   ensure
     ActiveRecord::Base.protected_environments = previous_protected_environments
   end
+
+  test "creating a record raises if preventing writes" do
+    assert_raises ActiveRecord::StatementInvalid do
+      ActiveRecord::Base.connection.while_preventing_writes do
+        bird = Bird.create! name: "Bluejay"
+      end
+    end
+  end
+
+  test "updating a record raises if preventing writes" do
+    bird = Bird.create! name: "Bluejay"
+
+    assert_raises ActiveRecord::StatementInvalid do
+      ActiveRecord::Base.connection.while_preventing_writes do
+        bird.update! name: "Robin"
+      end
+    end
+  end
+
+  test "deleting a record raises if preventing writes" do
+    bird = Bird.create! name: "Bluejay"
+
+    assert_raises ActiveRecord::StatementInvalid do
+      ActiveRecord::Base.connection.while_preventing_writes do
+        bird.destroy!
+      end
+    end
+  end
+
+  test "selecting a record does not raise if preventing writes" do
+    bird = Bird.create! name: "Bluejay"
+
+    ActiveRecord::Base.connection.while_preventing_writes do
+      assert_equal bird, Bird.where(name: "Bluejay").first
+    end
+  end
 end