[Web-SIG] Request and Response objects

[Gregory (Grisha) Trubetskoy]

On Wed, 5 Nov 2003, Stuart Bishop wrote:

> The "response"-type class is the interesting bit - the API for setting
> status codes, headers, cookies etc. And you do want multiples, of
> which only one is sent to the client. In particular, if you catch an
> exception and are preparing an error message you will want a clean
> response to work with rather than, for example, accidently sending
> your error message with the wrong content-type. The alternative would
> be a reset() method on the response buffer, although this isn't as
> flexible.
>
> def handler(request):
> 	try:
> 		response = Reponse(request)
> 		filename = response.request.getFirst('filename')
> 		response.headers['Content-Type'] = 'image/jpeg'
> 		response.cookies['latest'] = filename
> 		response.write(open(filename,'rb').read()) # A filelike object
> 	except IOError:
> 		response = Response(request)
> 		response.status = 404
> 		print >> response, 'File not found'
> 	response.close() # No more data - compute content-length header
> 	response.send() # Send to client.


The functional equivalent of the above would look like this in mod_python.

def handler(req):

	req.content_type = 'image/jpeg'

	try:
		req.sendfile(req.filename)
	except IOError:
		return apache.HTTP_NOT_FOUND

	return apache.OK


1. This is a pretty good example of the fact that dual objects don't do
much other than introduce extra typing.

2. This is too low level of an example:

The specifics of how an HTTP error is handled are going to vary from
server to server - e.g. Apache httpd will furnish it's own error text.
(BTW, HTTP errors shouldn't happen if your application is written well.)

Response.close() and response.send() also assume too much control over the
server. Unless we abstract completely by providing our own buffering
(which would do little other than introduce inefficiency), the buffering
is handled by the server, and whether and when content-length is set
depends on encoding used (chunked doesn't need content-length), which is
something also best left for the server to decide.

Whatever we come up with needs to be at a higher level.

having flush() would be appropriate I think.

sendfile() is another nice thing to have - if the environment has a
native implementation (e.g. mod_python), then it could be used, otherwise
it'd just be req.write(open(file)read())

Grisha