Rack::JSONBodyParser: rescue all parser exceptions (#184)

Rescue all exceptions raised by the parser as long as it is StandardError
subclass (which should be all the exceptions raised by different libraries).

This is specially needed when using a parser other than JSON. Otherwise we need
to rescue the corresponding exception and raise JSON:ParseError inside the
block.

Co-authored-by: Juan Manuel Cuello <[email protected]>
Co-authored-by: Samuel Williams <[email protected]>

lib/rack/contrib/json_body_parser.rb

@@ -61,7 +61,7 @@ def call(env)
 
           update_form_hash_with_json_body(env)
         end
-      rescue JSON::ParserError
+      rescue ParserError
         body = { error: 'Failed to parse body as JSON' }.to_json
         header = { 'content-type' => 'application/json' }
         return Rack::Response.new(body, 400, header).finish
@@ -71,13 +71,22 @@ def call(env)
 
     private
 
+    class ParserError < StandardError; end
+
     def update_form_hash_with_json_body(env)
       body = env[Rack::RACK_INPUT]
       return unless (body_content = body.read) && !body_content.empty?
 
       body.rewind if body.respond_to?(:rewind) # somebody might try to read this stream
+
+      begin
+        parsed_body = @parser.call(body_content)
+      rescue StandardError
+        raise ParserError
+      end
+
       env.update(
-        Rack::RACK_REQUEST_FORM_HASH => @parser.call(body_content),
+        Rack::RACK_REQUEST_FORM_HASH => parsed_body,
         Rack::RACK_REQUEST_FORM_INPUT => body
       )
     end

test/spec_rack_json_body_parser_spec.rb

@@ -64,6 +64,17 @@ def create_parser(app, **args, &block)
     _( -> { create_parser(app).call(env) }).must_raise JSON::ParserError
   end
 
+  specify "should rescue StandardError subclasses raised by the parser" do
+    class CustomParserError < StandardError; end
+
+    parser = create_parser(app) do |_body|
+      raise CustomParserError.new
+    end
+
+    res = parser.call(mock_env)
+    _(res[0]).must_equal 400
+  end
+
   describe "contradiction between body and type" do
     specify "should return bad request with a JSON-encoded error message" do
       env = mock_env(input: 'This is not JSON')