Raise exception when building invalid mime type

This allows mime types in the form text/html, text/*, or */*

This required a few minor test/code changes where previously nil was
used as a mime string.

2 files changed, 11 insertions, 2 deletions

diff --git a/actionpack/lib/action_dispatch/http/mime_type.rb b/actionpack/lib/action_dispatch/http/mime_type.rb
index c3e0ea3c89..296a36ad28 100644
--- a/actionpack/lib/action_dispatch/http/mime_type.rb
+++ b/actionpack/lib/action_dispatch/http/mime_type.rb
@@ -170,6 +170,7 @@ module Mime
       def parse(accept_header)
         if !accept_header.include?(",")
           accept_header = accept_header.split(PARAMETER_SEPARATOR_REGEXP).first
+          return [] unless accept_header
           parse_trailing_star(accept_header) || [Mime::Type.lookup(accept_header)].compact
         else
           list, index = [], 0
@@ -221,7 +222,15 @@ module Mime
 
     attr_reader :hash
 
+    MIME_NAME = "[a-zA-Z0-9][a-zA-Z0-9#{Regexp.escape('!#$&-^_.+')}]{0,126}"
+    MIME_REGEXP = /\A(?:\*\/\*|#{MIME_NAME}\/(?:\*|#{MIME_NAME}))\z/
+
+    class InvalidMimeType < StandardError; end
+
     def initialize(string, symbol = nil, synonyms = [])
+      unless MIME_REGEXP.match?(string)
+        raise InvalidMimeType, "#{string.inspect} is not a valid MIME type"
+      end
       @symbol, @synonyms = symbol, synonyms
       @string = string
       @hash = [@string, @synonyms, @symbol].hash
diff --git a/actionpack/lib/action_dispatch/testing/request_encoder.rb b/actionpack/lib/action_dispatch/testing/request_encoder.rb
index 9889f61951..6c65bec62f 100644
--- a/actionpack/lib/action_dispatch/testing/request_encoder.rb
+++ b/actionpack/lib/action_dispatch/testing/request_encoder.rb
@@ -38,8 +38,8 @@ module ActionDispatch
     end
 
     def self.parser(content_type)
-      mime = Mime::Type.lookup(content_type)
-      encoder(mime ? mime.ref : nil).response_parser
+      type = Mime::Type.lookup(content_type).ref if content_type
+      encoder(type).response_parser
     end
 
     def self.encoder(name)