Re: IPP> Re: New IPP Scheme

[Robert Herriot <[e-mail]>]

Action item from Robert Herriot and Tom Hastings:

The IPP working group reached an agreement with Keith Moore in this 
morning's teleconference. This document is our best understanding of the 
details of this agreement.

Summary:

The quick summary is that IPP should support a new scheme 'ipp', which 
clients and servers use in IPP attributes. Such attributes are in a message 
body whose Content-Type is application/ipp.  A client maps 'ipp' URLs to 
'http' URLs, and then follows the HTTP/1.1 rules for constructing a 
Request-Line and HTTP headers. The IPP document will not prohibit 
implementations from supporting other schemes in IPP attributes, but such 
support is not defined by this document.  

Now for the details.

A client and an IPP object (i.e. the server) SHOULD support the 'ipp' scheme 
in the following IPP attributes.  Each of these attributes identifies a 
printer or job object. The 'ipp' scheme is not intended for use in 'uri' 
valued attributes not in this list.

     job attributes - 
        job-uri 
        job-printer-uri
    printer attributes - 
        printer-uri-supported
    operation attributes - 
        job-uri 
        printer-uri

If the scheme of the target URL in a request (i.e. the value of  
"printer-uri" or "job-uri" operation attribute) is some scheme 'x', other 
than 'ipp', the behavior of the IPP object is not defined by this document.  
However, it is RECOMMENDED that if an operation on an IPP object creates a 
new value for any of the above attributes, that attribute has the same 
scheme 'x'. It is also RECOMMENDED that if an IPP object returns any of the 
seven attributes above in the response, that the IPP object returns those 
URL values as is, regardless of the scheme of the target URL.

If the client obtains a target URL from a directory service, the scheme of 
the target URL SHOULD be 'ipp'.  If the scheme is not 'ipp', the behavior of 
the client is not defined by this document, but it is RECOMMENDED that the 
client use the URL as is as the target URL.

Although user interfaces are beyond the scope of this document, it is 
RECOMMENDED that if software exposes the URL values of any of the above 
seven attributes to a human user, that the human see the URL as is.  

When a client sends a request, it MUST convert an 'ipp' target URL to an 
'http' target URL for use in the HTTP Request-Line and HTTP headers as 
specified by HTTP/1.1. However, the 'ipp' target URL remains as is for the 
value of the "printer-uri" or "job-uri" attribute in the message body.  If 
the scheme of the target URL is not 'ipp', the behavior of the client is not 
defined by this document, but it is RECOMMENDED that the client use the 
target URL as is in the Request-Line and HTTP headers.
 
A client converts an 'ipp' URL to an 'http' URL by 
    1) replacing the 'ipp' scheme by 'http' 
    2) adding an explicit port 631 if the URL does not contain an explicit 
port.

When an IPP client sends a request directly (i.e. no proxy) to an ‘ipp’ URL 
such as “ipp://myhost.com/myprinter/myqueue”, it MUST open a TCP connection 
to some port (this example uses the IPP default port 631) on some host 
(“myhost.com” in this example) with the following headers:

POST /myprinter/myqueue HTTP/1.1 
Host: myhost.com:631 
Content-type: application/ipp 
Transfer-Encoding: chunked 
...
"printer-uri" "ipp://myhost.com/myprinter/myqueue"   
(encoded in application/ipp message body) 
...

When an IPP client sends a request via a proxy, such as “myproxy.com”, to an 
‘ipp’  URL, such as “ipp://myhost.com/myprinter/myqueue”, it MUST open a TCP 
connection to some port (8080 in this example) on some proxy (“myproxy.com” 
in this example) with the following headers:


POST http://myhost.com:631/myprinter/myqueue   HTTP/1.1 
Host: myproxy.com:8080 
Content-type: application/ipp 
Transfer-Encoding: chunked 
...
"printer-uri" "ipp://myhost.com/myprinter/myqueue"   
(encoded in application/ipp message body) 
...

The proxy then connects to the IPP origin server with headers that are the 
same as the "no-proxy" example above.