[REBOL] Re: hook while downloading from html port
From: Gary:Jones:usap:gov at: 15-Apr-2004 15:38
From: Maxim Olivier-Adlhoch
....
I was wondering, if its possible to put a hook somewhere (even if deep) within
the port or more specifically the html port handler, so that we can update
something elsewhere, do statistics or print out transfer rate for example...
....
Hi, Max,
Since no one has offered anything any more specific, I can suggest a general way to put
in your own hooks, but some of the services are at a lower level than you can access
through the standard service.
First, you'll need a working copy of the scheme. For example, for http:
echo %/path/to/my-http.txt
probe system/schemes/http
echo off
With this text file, first place:
system/schemes/http:
near the top before the make, like:
system/schemes/http: make object! [
scheme: 'HTTP
host: none
port-id: 80
....
Then go to the end of the file and erase everything after the last "]" and resave the
file. This file can be loaded in as a replacement for the http scheme. If reloaded
as such, there will be no change.
Now, you have to begin to understand how the schemes work. As the port for a scheme
is read, it goes through these stages (or functions):
init
open-proto
open
close
The lowest level functions, accessed more "invisibly," are read and write.
By playing with probe or print statements and then accessing a web page, one can begin
to get more information at a stage of the process as needed. You will find after a lot
of experimentation that much of the reading is done at a very low level, like through
'read-io. This function stores its data in temporary spaces in this protocol, like the
port/state object that is used during the access. If you try to access these data, you
inadvertently end up botching the operation, so care must be used and there are definitely
limits to what can be used. The only way to bypass some of the limits would be to extensively
modify the scheme, which can be done with some work and care, or to create your own,
which is reinventing the wheel.
It may be enough to get you going, but I would not be overenthusiastic about thinking
you will be able the scrounge things like transfer rates!
Hope this gives you some help.
--Scott Jones
