Automate clearing of broken LDAP configurations (fixes #2140)

app/models/setting.rb

@@ -51,7 +51,7 @@ get config setting
 
   def self.get(name)
     load
-    @@current[name]
+    @@current[name].deep_dup # prevents accidental modification of settings in console
   end
 
 =begin

db/migrate/20180911064647_issue_2140_reset_ldap_config.rb

@@ -0,0 +1,15 @@
+class Issue2140ResetLdapConfig < ActiveRecord::Migration[5.1]
+  def up
+    # return if it's a new setup
+    return if !Setting.find_by(name: 'system_init_done')
+
+    ldap_config = Setting.get('ldap_config')
+
+    # finish if LDAP config isn't broken
+    ldap_config.to_json
+  rescue Encoding::UndefinedConversionError
+    ldap_config[:wizardData].delete(:backend_user_attributes)
+
+    Setting.set('ldap_config', ldap_config)
+  end
+end

spec/db/migrate/issue_2140_reset_ldap_config_spec.rb

@@ -0,0 +1,35 @@
+require 'rails_helper'
+
+RSpec.describe Issue2140ResetLdapConfig, type: :db_migration do
+  before { Setting.set('ldap_config', config) }
+
+  context 'when LDAP config isn’t broken' do
+    let(:config) do
+      { 'wizardData' =>
+          { 'backend_user_attributes' =>
+              { 'foo' => 'bar' },
+            'user_attributes' =>
+              { 'baz' => 'qux' } } }.with_indifferent_access
+    end
+
+    it 'makes no changes' do
+      expect { migrate }.not_to change { Setting.get('ldap_config') }
+    end
+  end
+
+  context 'when LDAP config is broken' do
+    let(:config) do
+      { 'wizardData' =>
+          { 'backend_user_attributes' =>
+              { 'foo' => "\u0001\u0001\u0004€" },
+            'user_attributes' =>
+              { 'baz' => 'qux' } } }.with_indifferent_access
+    end
+
+    it 'removes the offending backend_user_attributes sub-hash' do
+      expect { migrate }
+        .to change { Setting.get('ldap_config') }
+        .to(config.tap { |c| c[:wizardData].delete(:backend_user_attributes) })
+    end
+  end
+end