webrick: support Proc objects as body responses

	* lib/webrick/httpresponse.rb (send_body): call send_body_proc
	  (send_body_proc): new method
	  (class ChunkedWrapper): new class

	* test/webrick/test_httpresponse.rb (test_send_body_proc): new test
	  (test_send_body_proc_chunked): ditto
	  [Feature #855]

	webrick: favor .write over << method

	This will make the next change to use IO.copy_stream
	easier-to-read.  When we can drop Ruby 2.4 support in a few
	years, this will allow us to use writev(2) with multiple
	arguments for headers and chunked responses.

	* lib/webrick/cgi.rb (write): new wrapper method
	  lib/webrick/httpresponse.rb: (send_header): use socket.write
	  (send_body_io): ditto
	  (send_body_string): ditto
	  (send_body_proc): ditto
	  (_write_data): ditto
	  (ChunkedWrapper#write): ditto
	  (_send_file): ditto
	------------------------------------------------------------------------
	r62954 | normal | 2018-03-28 17:05:52 +0900 (水, 28 3 2018) | 14 lines

	webrick/httpresponse: IO.copy_stream for regular files

	Remove the redundant _send_file method since its functionality
	is unnecessary with IO.copy_stream.  IO.copy_stream also allows
	the use of sendfile under some OSes to speed up copies to
	non-TLS sockets.

	Testing with "curl >/dev/null" and "ruby -run -e httpd" to
	read a 1G file over Linux loopback reveals a reduction from
	around ~0.770 to ~0.490 seconds on the client side.

	* lib/webrick/httpresponse.rb (send_body_io): use IO.copy_stream
	  (_send_file): remove
	  [Feature #14237]
	------------------------------------------------------------------------
	r62955 | normal | 2018-03-28 17:05:57 +0900 (水, 28 3 2018) | 10 lines

	webrick: use IO.copy_stream for single range response

	This is also compatible with range responses generated
	by Rack::File (tested with rack 2.0.3).

	* lib/webrick/httpresponse.rb (send_body_io): use Content-Range
	* lib/webrick/httpservlet/filehandler.rb (make_partial_content):
	  use File object for the single range case
	* test/webrick/test_filehandler.rb (get_res_body): use send_body
	  to test result
	------------------------------------------------------------------------
	r62956 | normal | 2018-03-28 17:06:02 +0900 (水, 28 3 2018) | 7 lines

	test/webrick/test_filehandler.rb: stricter multipart range test

	We need to ensure we generate compatibile output in
	the face of future changes

	* test/webrick/test_filehandler.rb (test_make_partial_content):
	  check response body
	------------------------------------------------------------------------
	r62957 | normal | 2018-03-28 17:06:08 +0900 (水, 28 3 2018) | 8 lines

	webrick: quiet warning for multi-part ranges

	Content-Length is ignored by WEBrick::HTTPResponse even if we
	calculate it, so instead we chunk responses to HTTP/1.1 clients
	and terminate HTTP/1.0 connections.

	* lib/webrick/httpservlet/filehandler.rb (make_partial_content):
	  quiet warning
	------------------------------------------------------------------------
	r62958 | normal | 2018-03-28 17:06:13 +0900 (水, 28 3 2018) | 7 lines

	webrick/httpresponse: make ChunkedWrapper copy_stream-compatible

	The .write method needs to return the number of bytes written
	to avoid confusing IO.copy_stream.

	* lib/webrick/httpresponse.rb (ChunkedWrapper#write): return bytes written
	  (ChunkedWrapper#<<): return self
	------------------------------------------------------------------------
	r62959 | normal | 2018-03-28 17:06:18 +0900 (水, 28 3 2018) | 9 lines

	webrick: use IO.copy_stream for multipart response

	Use the new Proc response body feature to generate a multipart
	range response dynamically.  We use a flat array to minimize
	object overhead as much as possible; as many ranges may fit
	into an HTTP request header.

	* lib/webrick/httpservlet/filehandler.rb (multipart_body): new method
	  (make_partial_content): use multipart_body

	get rid of test error/failure on Windows introduced at r62955

	* lib/webrick/httpresponse.rb (send_body_io): use seek if NotImplementedError
	  is raised in IO.copy_stream with offset.

	* lib/webrick/httpservlet/filehandler.rb (multipart_body): ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@63014 b2dd03c8-39d4-4d8f-98ff-823fe69b080e