Return body on upgrade.

lib/protocol/http1/connection.rb

@@ -503,6 +503,11 @@ def read_request_body(method, headers)
 					return read_tunnel_body
 				end
 
+				# A successful upgrade response implies that the connection will become a tunnel immediately after the empty line that concludes the header fields.
+				if headers[UPGRADE]
+					return read_tunnel_body
+				end
+
 				# 6.  If this is a request message and none of the above are true, then
 				# the message body length is zero (no message body is present).
 				return read_body(headers)

test/protocol/http1/upgrade.rb

@@ -24,7 +24,7 @@
 
 			expect(version).to be == request_version
 			expect(headers['upgrade']).to be == [protocol]
-			expect(body).to be_nil
+			expect(body).to be_a(Protocol::HTTP1::Body::Remainder)
 
 			stream = server.hijack!
 			expect(stream.read).to be == "Hello World"