Raise ActionController::BadRequest for malformed parameter hashes.

Currently Rack raises a TypeError when it encounters a malformed or
ambiguous hash like `foo[]=bar&foo[4]=bar`. Rather than pass this
through to the application this commit captures the exception and
re-raises it using a new ActionController::BadRequest exception.

The new ActionController::BadRequest exception returns a 400 error
instead of the 500 error that would've been returned by the original
TypeError. This allows exception notification libraries to ignore
these errors if so desired.

Closes #3051

1 files changed, 11 insertions, 0 deletions

diff --git a/actionpack/test/dispatch/request/url_encoded_params_parsing_test.rb b/actionpack/test/dispatch/request/url_encoded_params_parsing_test.rb
index 568e220b15..e9b59f55a7 100644
--- a/actionpack/test/dispatch/request/url_encoded_params_parsing_test.rb
+++ b/actionpack/test/dispatch/request/url_encoded_params_parsing_test.rb
@@ -126,6 +126,17 @@ class UrlEncodedParamsParsingTest < ActionDispatch::IntegrationTest
     assert_parses expected, query
   end
 
+  test "ambiguous params returns a bad request" do
+    with_routing do |set|
+      set.draw do
+        post ':action', :to => ::UrlEncodedParamsParsingTest::TestController
+      end
+
+      post "/parse", "foo[]=bar&foo[4]=bar"
+      assert_response :bad_request
+    end
+  end
+
   private
     def with_test_routing
       with_routing do |set|