Make body not respond to to_path to Rack::Files range requests

If the body responds to to_path, the server is allowed to serve
the file at that path and ignore the body.  That works well for
most requests, but not for range requests, since the correct
byte range won't be served.

Work around this issue by using a separate body class for the
partial content responses that does not respond to to_path, and
the current body class for non-partial content responses.

Fixes #1235

lib/rack/files.rb

@@ -90,6 +90,7 @@ def serving(request, path)
         return response
       else
         # Partial content:
+        partial_content = true
         range = ranges[0]
         response[0] = 206
         response[1]["Content-Range"] = "bytes #{range.begin}-#{range.end}/#{size}"
@@ -99,13 +100,18 @@ def serving(request, path)
       response[2] = [response_body] unless response_body.nil?
 
       response[1][CONTENT_LENGTH] = size.to_s
-      response[2] = make_body request, path, range
+      response[2] = if request.head?
+        []
+      elsif partial_content
+        BaseIterator.new path, range
+      else
+        Iterator.new path, range
+      end
       response
     end
 
-    class Iterator
+    class BaseIterator
       attr_reader :path, :range
-      alias :to_path :path
 
       def initialize path, range
         @path  = path
@@ -129,16 +135,12 @@ def each
       def close; end
     end
 
-    private
-
-    def make_body request, path, range
-      if request.head?
-        []
-      else
-        Iterator.new path, range
-      end
+    class Iterator < BaseIterator
+      alias :to_path :path
     end
 
+    private
+
     def fail(status, body, headers = {})
       body += "\n"
 

test/spec_files.rb

@@ -165,6 +165,15 @@ def files(*args)
     body.to_path.must_equal path
   end
 
+  it "return bodies that do not respond to #to_path if a byte range is requested" do
+    env = Rack::MockRequest.env_for("/cgi/test")
+    env["HTTP_RANGE"] = "bytes=22-33"
+    status, _, body = Rack::Files.new(DOCROOT).call(env)
+
+    status.must_equal 206
+    body.wont_respond_to :to_path
+  end
+
   it "return correct byte range in body" do
     env = Rack::MockRequest.env_for("/cgi/test")
     env["HTTP_RANGE"] = "bytes=22-33"