MONGOID-5099 Improve error when loading an empty or invalid config file (#5032)

* Fixes MONGOID-5099

Improves error when loading an empty or invalid file and adds specs to #load_yaml method. Note that certain errors (file missing, ERB, YAML parsing) bubble up as per existing behavior.

This change is only intended to avoid an internal cryptic error happening within Mongoid's code (NoMethodError (undefined method `[]' for false:FalseClass). Please also note that this does not change the conditions under which an exception occurs, it just changes the class of the exception.

* repair exception docstring

* fix test setup

* tweak exception message

* raise a specific exception for the case of empty config file

* exception constructors are private

* fix the test

Co-authored-by: shields <[email protected]>
Co-authored-by: Oleg Pudeyev <[email protected]>

Author: johnnyshields

lib/config/locales/en.yml

@@ -80,6 +80,12 @@ en:
             different collections so a simple id lookup is not sufficient enough."
           resolution: "Don't attempt to perform this action and have patience,
             maybe this will be supported in the future."
+        empty_config_file:
+          message: "Empty configuration file: %{path}."
+          summary: "Your mongoid.yml configuration file appears to be empty."
+          resolution: "Ensure your configuration file contains the correct contents.
+            Please consult the following page with respect to Mongoid's configuration:
+            https://docs.mongodb.com/mongoid/current/reference/configuration/"
         invalid_collection:
           message: "Access to the collection for %{klass} is not allowed."
           summary: "%{klass}.collection was called, and %{klass} is an embedded
@@ -94,6 +100,13 @@ en:
             A collation option is only supported if the query is executed on a MongoDB server
             with version >= 3.4."
           resolution: "Remove the collation option from the query."
+        invalid_config_file:
+          message: "Invalid configuration file: %{path}."
+          summary: "Your mongoid.yml configuration file does not contain the
+            correct file structure."
+          resolution: "Ensure your configuration file contains the correct contents.
+            Please consult the following page with respect to Mongoid's configuration:
+            https://docs.mongodb.com/mongoid/current/reference/configuration/"
         invalid_config_option:
           message: "Invalid configuration option: %{name}."
           summary: "A invalid configuration option was provided in your

lib/mongoid/config/environment.rb

@@ -52,7 +52,15 @@ def env_name
       # @api private
       def load_yaml(path, environment = nil)
         env = environment ? environment.to_s : env_name
-        YAML.load(ERB.new(File.new(path).read).result)[env]
+        contents = File.new(path).read
+        if contents.empty?
+          raise Mongoid::Errors::EmptyConfigFile.new(path)
+        end
+        data = YAML.load(ERB.new(contents).result)
+        unless data.is_a?(Hash)
+          raise Mongoid::Errors::InvalidConfigFile.new(path)
+        end
+        data[env]
       end
     end
   end

lib/mongoid/errors.rb

@@ -8,8 +8,10 @@
 require "mongoid/errors/document_not_destroyed"
 require "mongoid/errors/document_not_found"
 require "mongoid/errors/eager_load"
+require "mongoid/errors/empty_config_file"
 require "mongoid/errors/in_memory_collation_not_supported"
 require "mongoid/errors/invalid_collection"
+require "mongoid/errors/invalid_config_file"
 require "mongoid/errors/invalid_config_option"
 require "mongoid/errors/invalid_dependent_strategy"
 require "mongoid/errors/invalid_field"

lib/mongoid/errors/empty_config_file.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+# encoding: utf-8
+
+module Mongoid
+  module Errors
+
+    # This error is raised when an empty configuration file is attempted to be
+    # loaded.
+    class EmptyConfigFile < MongoidError
+
+      # Create the new error.
+      #
+      # @param [ String ] path The path of the config file used.
+      #
+      # @api private
+      def initialize(path)
+        super(
+          compose_message(
+            "empty_config_file",
+            { path: path }
+          )
+        )
+      end
+    end
+  end
+end

lib/mongoid/errors/invalid_config_file.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+# encoding: utf-8
+
+module Mongoid
+  module Errors
+
+    # This error is raised when a bad configuration file is attempted to be
+    # loaded.
+    class InvalidConfigFile < MongoidError
+
+      # Create the new error.
+      #
+      # @param [ String ] path The path of the config file used.
+      #
+      # @api private
+      def initialize(path)
+        super(
+          compose_message(
+            "invalid_config_file",
+            { path: path }
+          )
+        )
+      end
+    end
+  end
+end

spec/mongoid/config/environment_spec.rb

@@ -5,9 +5,19 @@
 
 describe Mongoid::Config::Environment do
 
-  after(:all) do
-    Rails = RailsTemp
-    Object.send(:remove_const, :RailsTemp)
+  around do |example|
+    if defined?(Rails)
+      SavedRails = Rails
+      example.run
+      Object.send(:remove_const, :Rails) if defined?(Rails)
+      Rails = SavedRails
+      Object.send(:remove_const, :SavedRails)
+    else
+      example.run
+      if defined?(Rails)
+        Object.send(:remove_const, :Rails)
+      end
+    end
   end
 
   describe "#env_name" do
@@ -24,11 +34,6 @@ def env; "production"; end
           end
         end
 
-        after do
-          RailsTemp = Rails
-          Object.send(:remove_const, :Rails)
-        end
-
         it "returns the rails environment" do
           expect(described_class.env_name).to eq("production")
         end
@@ -86,4 +91,77 @@ def environment; :staging; end
       end
     end
   end
+
+  describe "#load_yaml" do
+    let(:path) { 'mongoid.yml' }
+    let(:environment) {}
+    before { allow(Rails).to receive('env').and_return('test') }
+
+    subject { described_class.load_yaml(path, environment) }
+
+    context 'when file not found' do
+      let(:path) { 'not/a/valid/path'}
+
+      it { expect { subject }.to raise_error(Errno::ENOENT) }
+    end
+
+    context 'when file found' do
+      before do
+        allow(File).to receive(:new).with('mongoid.yml').and_return(StringIO.new(file_contents))
+      end
+
+      let(:file_contents) do
+        <<~FILE
+          test:
+            clients: ['test']
+          development:
+            clients: ['dev']
+        FILE
+      end
+
+      context 'when file cannot be parsed as YAML' do
+        let(:file_contents) { "*\nbad:%123abc" }
+
+        it { expect { subject }.to raise_error(Psych::SyntaxError) }
+      end
+
+      context 'when file contains ERB errors' do
+        let(:file_contents) { '<%= foo %>' }
+
+        it { expect { subject }.to raise_error(NameError) }
+      end
+
+      context 'when file is empty' do
+        let(:file_contents) { '' }
+
+        it { expect { subject }.to raise_error(Mongoid::Errors::EmptyConfigFile) }
+      end
+
+      context 'when file does not contain a YAML Hash object' do
+        let(:file_contents) { '["this", "is", "an", "array"]' }
+
+        it { expect { subject }.to raise_error(Mongoid::Errors::InvalidConfigFile) }
+      end
+
+      context 'when environment not specified' do
+        it 'uses the rails environment' do
+          is_expected.to eq("clients"=>["test"])
+        end
+      end
+
+      context 'when environment is specified' do
+        let(:environment) { 'development' }
+
+        it 'uses the specified environment' do
+          is_expected.to eq("clients"=>["dev"])
+        end
+      end
+
+      context 'when environment is missing' do
+        let(:environment) { 'staging' }
+
+        it { is_expected.to be_nil }
+      end
+    end
+  end
 end

spec/mongoid/errors/invalid_config_file_spec.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+# encoding: utf-8
+
+require "spec_helper"
+
+describe Mongoid::Errors::InvalidConfigFile do
+
+  describe "#message" do
+
+    let(:error) do
+      described_class.new('/my/path')
+    end
+
+    it "contains the problem in the message" do
+      expect(error.message).to include(
+        "Invalid configuration file: /my/path."
+      )
+    end
+
+    it "contains the summary in the message" do
+      expect(error.message).to include(
+        "Your mongoid.yml configuration file does not contain the"
+      )
+    end
+
+    it "contains the resolution in the message" do
+      expect(error.message).to include(
+        "Ensure your configuration file contains the correct contents."
+      )
+    end
+  end
+end