Raise Rack::Multipart::EmptyContentError instead of EOFError for parsing

This makes it simpler to catch this specific error.

Fixes rack#1603

CHANGELOG.md

@@ -11,6 +11,7 @@ All notable changes to this project will be documented in this file. For info on
 - Removed antiquated handlers: FCGI, LSWS, SCGI, Thin. ([#1658](https://github.com/rack/rack/pull/1658), [@ioquatix](https://github.com/ioquatix))
 - Removed options from `Rack::Builder.parse_file` and `Rack::Builder.load_file`. ([#1663](https://github.com/rack/rack/pull/1663), [@ioquatix](https://github.com/ioquatix))
 - HMAC argument for `Rack::Session::Cookie` doesn't accept a class constant anymore, but only a string recognized by OpenSSL (e.g. `"SHA256"`) or compatible instance (e.g. `OpenSSL::Digest.new("SHA256")`) ([#1676](https://github.com/rack/rack/pull/1676), [@bdewater](https://github.com/bdewater))
+- Attempting to parse a multipart response with an empty body now raises Rack::Multipart::EmptyContentError. ([#1603](https://github.com/rack/rack/issues/1603), [@jeremyevans](https://github.com/jeremyevans))
 
 ### Fixed
 

lib/rack/multipart/parser.rb

@@ -6,6 +6,10 @@ module Rack
   module Multipart
     class MultipartPartLimitError < Errno::EMFILE; end
 
+    # Use specific error class when parsing multipart request
+    # that ends early.
+    class EmptyContentError < ::EOFError; end
+
     class Parser
       (require_relative '../core_ext/regexp'; using ::Rack::RegexpExtensions) if RUBY_VERSION < '2.4'
 
@@ -356,7 +360,7 @@ def tag_multipart_encoding(filename, content_type, name, body)
 
       def handle_empty_content!(content)
         if content.nil? || content.empty?
-          raise EOFError
+          raise EmptyContentError
         end
       end
     end

test/spec_multipart.rb

@@ -151,7 +151,7 @@ def rd.rewind; end
     env = Rack::MockRequest.env_for '/', fixture
     lambda {
       Rack::Multipart.parse_multipart(env)
-    }.must_raise EOFError
+    }.must_raise Rack::Multipart::EmptyContentError
     rd.close
 
     err = thr.value