[URN] HTTP Conventions draft

["Ronald E. Daniel" <[e-mail]>]

Hi,

Since I didn't hear any objections to the changes I planned for
the NAPTR and HTTP Conventions drafts, I made those changes.
The HTTP Conventions draft is appended, I will send the NAPTR
draft in another message.

Regards,
Ron
=====

INTERNET DRAFT                                                  Ron Daniel
draft-ietf-urn-http-conv-01.txt             Los Alamos National Laboratory
                                                              14 Feb, 1997


         A Trivial Convention for using HTTP in URN Resolution


Status of this Memo
===================

    This document is an Internet-Draft.  Internet-Drafts are working
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    This draft expires 22 August, 1997.
  
  

Abstract:
=========

The Uniform Resource Names Working Group (URN-WG) was formed to specify
persistent, location-independent names for network accessible
resources, as well as resolution mechanisms to retrive the resources
given such a name. At this time the URN-WG is considering one
particular resolution mechanism, the NAPTR proposal [1]. That proposal
specifies how a client may find a "resolver" for a URN. A resolver is a
database that can provide information about the resource identified by
a URN, such as the resource's location, a bibliographic description, or
even the resource itself. The protocol used for the client to
communicate with the resolver is not specified in the NAPTR proposal.
Instead, the NAPTR resource record provides a field that indicates the
"resolution protocol" and "resolution service requests" offered by the
resolver.

This document specifies the "THTTP" resolution protocol - a trivial
convention for encoding resolution service requests and responses as
HTTP 1.0 or 1.1 requests and responses.  The primary goal of THTTP is
to be simple to implement so that existing HTTP servers may easily add
support for URN resolution. We expect that the databases used by early
resolvers will be useful when more sophisticated resolution protocols
are developed later.


1.0  Introduction:
==================

The NAPTR specification[1] defined a new DNS resource record which may
be used to discover resolvers for Uniform Resource Identifiers. That
resource record provides the "services" field to specify the "resolution
protocol" spoken by the resolver, as well as the "resolution services"
it offers. Resolution protocols mentioned in that specification are
Z3950, THTTP, RCDS, HDL, and RWHOIS. (That list is expected to grow
over time). The NAPTR specification also lists a variety of resolution
services, such as N2L (given a URN, return a URL); N2R (Given a URN,
return the named resource), etc.

This document specifies the "THHTP" (Trivial HTTP) resolution protocol.
THHTP is a simple convention for encoding resolution service requests and
responses as HTTP 1.0 or 1.1 requests and responses. The primary goal
of THTTP is to have a URN resolution protocol that can easily be
added to existing HTTP daemons. Other resolution protocols are expected
to arise over time, so this document serves a secondary purpose of
illustrating the information that needs to be specified for a URN
resolution protocol. One of the resolution protocols we expect to be
developed is an extension of HTTP with new methods for the resolution
services. Therefore, we use "thhtp" as the identifier for this
protocol to leave "http" for later developments.

The reader is assumed to be familiar with the HTTP/1.0 [2] and 1.1 [3]
specifications. Implementors of this specification should be familiar with
CGI scripts, or server-specific interfaces, for database lookups.


2.0 General Approach:
=====================

The general approach used to encode resolution service requests in THTTP
is quite simple: 

    GET /uri-res/<service>?<uri>  HTTP/1.0

For example, if we have the URN "urn:foo:12345-54321" and want a URL,
we would send the request:

    GET /uri-res/N2L?urn:foo:12345-54321 HTTP/1.0

The request could also be encoded as an HTTP 1.1 request. This would look
like:

    GET /uri-res/N2L?urn:foo:12345-54321 HTTP/1.1
    Host: <whatever host we are sending the request to>

Responses from the HTTP server follow standard HTTP practice. Status
codes, such as 200 (OK) or 404 (Not Found) shall be returned.
The normal rules for determining cachability, negotiating formats, etc.
apply.

Handling these requests on the server side is easy to implement using
CGI or other, server-specific, extension mechanisms.
CGI scripts will see the incoming URI in the QUERY_STRING environment
variable. Any %encoded characters in the URN will remain in their
%encoded state in that string. The script can take the URN, look it
up in a database, and return the requested information.

One caveat should be kept in mind. The URN syntax draft[4] discusses
the notion of lexical equivalance. This means that two URIs are equivalent
under certain conditions of case-insensitivity. Resolvers MUST return
identical results for all lexically equivalent encodings of a URI. For
example, the requests below must return identical results:
    GET /uri-res/N2L?urn:cid:[e-mail] HTTP/1.0
    GET /uri-res/N2L?URN:CID:[e-mail] HTTP/1.0


3.0 Service-specific details:
=============================

This section goes through the various resolution services established
in the URN services draft[5] and states how to encode each of them,
how the results should be returned, and any special status codes that
are likely to arise.

Unless stated otherwise, the THTTP requests are formed according to
the simple convention above, either for HTTP/1.0 or HTTP/1.1. The response
is assumed to be an entity with normal headers and body unless stated
otherwise. (N2L is the only request that need not return a body).


3.1  N2L (URN to URL):
----------------------

The request is encoded as above. The URL MUST be returned in a Location:
header for the convienience of the user in the most common case of wanting
the resource. If the lookup is successful, a 30X status line SHOULD be
returned. HTTP/1.1 clients should be sent the 303 status code. HTTP/1.0
clients should be sent the 302 (Moved temporarily) status code unless the
resolver has particular reasons for using 301 (moved permanently) or 304
(not modified) codes.

Note that access controls may be applied to this, or any other, resolution
service request. Therefore the 401 (unauthorized) and 403 (forbidden)
status codes are legal responses. The server may wish to provide a body
in the response to explain the reason for refusing access, and/or to provide
alternate information about the resource, such as the price it will cost
to obtain the resource's URL.

3.2  N2Ls (URN to URLs):
------------------------

The request is encoded as above. The result is a list of 0 or
more URLs. The Internet Media Type (aka ContentType) of the result
may be negotiated using standard HTTP mechanisms if desired. At a
minimum the resolver should support the text/uri-list media type.
(See Appendix A for the definition of this media type). That media
type is suitable for machine-processing of the list of URLs. Resolvers
may also return the results as text/html, text/plain, or any other
media type they deem suitable.

No matter what the particular media type, the result MUST be a list
of the URLs which may be used to obtain an instance of the resource
identified by the URN. All URIs shall be encoded according to the
URI specification [6].

If the client has requested the result be returned as text/html or
application/html, the result should be a valid HTML docment containg
the fragment:
<UL>
<LI><A HREF="...url 1...">...url 1...</A>
<LI><A HREF="...url 2...">...url 2...</A>
 etc.
</UL>
where the strings ...url n... are replaced by the n'th URL in the list.


3.3  N2R (URN to Resource):
---------------------------

The request is encoded as above. The resource is returned using
standard HTTP mechanisms. The request may be modified using the
Accept: header as in normal HTTP to specify that the result
be given in a preferred Internet Media Type.


3.4  N2Rs (URN to Resources):
-----------------------------

This resolution service returns multiple instances of a resource,
for example, GIF and JPEG versions of an image. The judgment about
the resources being "the same" resides with the naming authority that
issued the URN.

The request is encoded as above. The result shall be a MIME
multipart/alternative message with the alternative versions of the
resource in seperate body parts. If there is only one version of
the resource identified by the URN, it MAY be returned without the
multipart/alternative wrapper. Resolver software SHOULD look at the
Accept: header, if any, and only return versions of the resource
that are acceptable according to that header. 


3.5  N2C (URN to URC):
----------------------

URCs (Uniform Resource Characteristics) are descriptions of other
resources. This request allows us to obtain a description of the
resource identified by a URN, as opposed to the resource itself.
The description might be a bibliographic citation, a digital signature,
a revision history, etc. This draft does not specify the content of
any response to a URC request. That content is expected to vary from
one resolver to another.

The format of any response to a N2C request MUST be communicated using the
ContentType header, as is standard HTTP practice. The Accept: header
SHOULD be honored.


3.6  N2Ns (URN to URNs):
------------------------

While URNs are supposed to identify one and only one resource, that
does not mean that a resource may have one and only one URN. For
example, consider a resource that has something like
"current-weather-map" for one URN and "weather-map-for-datetime-x" for
another URN. The N2Ns service request lets us obtain lists of URNs that
are believed equivalent at the time of the request. As the weathermap
example shows, some of the equivalances will be transitory, so the
standard HTTP mechanisms for communicating cachability MUST be honored.

The request is encoded as above. The result is a list of all the
URNs, known to the resolver, which identify the same resource as the
input URN. The result shall be encoded as for the N2Ls request
above (text/uri-list unless specified otherwise by an Accept: header).

3.7  L2Ns (URL to URNs):
----------------------

The request is encoded as above. The response is a list of any URNs
known to be assigned to the resource at the given URL. The result
shall be encoded as for the N2Ls and N2Ns requests.


3.8  L2Ls (URL to URLs):
------------------------

The request is encoded as described above. The result is a list of
all the URLs that the resolver knows are associated with the resource
located by the given URL. This is encoded as for the N2Ls, N2Ns, and L2Ns
requests.


3.9  L2C (URL to URC):
----------------------

The request is encoded as above, the response is the same as for the
N2C request.


Appendix A: The text/uri-list Internet Media Type
=================================================
[This appendix will be augmented or replaced by the registration
of the text/uri-list IMT once that registration has been performed].

Several of the resolution service requests, such as N2Ls, N2Ns, L2Ns,
L2Ls, result in a list of URIs being returned to the client. The
text/uri-list Internet Media Type is defined to provide a simple format
for the automatic processing of such lists of URIs.

The format of text/uri-list resources is:
1) Any lines beginning with the '#' character are comment lines
   and are ignored during processing. (Note that '#' is a character
   that may appear in URIs, so it only denotes a comment when it is the
   first character on a line).
2) The remaining non-comment lines MUST be URIs (URNs or URLs), encoded
   according to the URI specification RFC[6]. Each URI shall appear on
   one and only one line.
3) As for all text/* formats, lines are terminated with a CR LF pair,
   although clients should be liberal in accepting lines with only
   one of those characters.

In applications where one URI has been mapped to a list of URIs, such
as in response to the N2Ls request, the first line of the text/uri-list
response SHOULD be a comment giving the original URI. 

An example of such a result for the N2L request is shown below in figure 1.

     # urn:cid:[e-mail]
     http://www.huh.org/cid/foo.html
     http://www.huh.org/cid/foo.pdf
     ftp://ftp.foo.org/cid/foo.txt

               Figure 1: Example of the text/uri-list format


Appendix B:  n2l.pl script
==========================

This is a simple CGI script for the N2L resolution service. It
assumes the presence of a DBM database to store the URN to URL
mappings. This script does not specify standard behavior, it is
provided merely as a courtesy for implementors. In fact, this
script does not process incoming Accept: headers, nor does it
generate status codes. Such behavior should be part of a real
script for any of the resolution services.


    #!/bin/perl
    # N2L  - performs urn to url  resolution 

    $n2l_File = "...filename for DBM database...";


    $urn = $ENV{'QUERY_STRING'} ;

    # Sanity check on the URN. Minimum length of a valid URN is
    # 7 characters - "urn:", a 1-character Namespace ID, ":", and
    # a 1-character namespace-specific string. More elaborate
    # sanity checks should be part of a real resolver script.
    if(length($urn)<7)
    {
        $error=1;
    }

    if(!$error)
    {
        # Convert lexically equivalent versions of a URI into
        # a canonical version for DB lookups.
        $urn =~ s/^urn:([^:]*):(.*)$/sprintf("urn:%s:%s", lc $1, $2)/ie;

        dbmopen(%lu,$n2l_File,0444);
        if($lu{$urn})
        {
            $url=$lu{$urn};
            print STDOUT "Location: $url\n\n";
        }else{
            $error=2;
        }
        dbmclose(%lu);
    }

    if($error)
    {
        print "Content-Type: text/html \n\n";
        print "<html>\n";
        print "<head><title>URN Resolution: N2L</title></head>\n";
        print "<BODY>\n";
        print "<h1>URN to URL resolution failed for the URN:</h1>\n";
        print "<hr><h3>$urn</h3>\n";
        print "</body>\n";
        print "</html>\n";
    }

    exit;


References:
===========

[1] Ron Daniel and Michael Mealling, "Resolution of Uniform Resource
    Identifiers using the Domain Name System", draft-ietf-urn-naptr-02.txt,
    February, 1997.

[2] RFC 1945, "Hypertext Transfer Protocol -- HTTP/1.0", T. Berners-Lee,
    R. Fielding, H. Frystyk, May 1996.

[3] R. Fielding, J. Gettys, J.C. Mogul, H. Frystyk, T. Berners-Lee,
    "Hypertext Transfer Protocol -- HTTP/1.1", draft-ietf-http-v11-spec-06,
    July 1996.

[4] R. Moats, "URN Syntax", draft-ietf-urn-syntax-02, Jan. 1997.

[5] URN Resolution Services Draft -  (That document is in preparation.
    It will actually be strongly based on the content of this document and
    the NAPTR draft[1]). 

[6] RFC 1630, "Universal Resource Identifiers in WWW: A Unifying Syntax for
    the Expression of Names and Addresses of Objects on the Network as
    used in the World-Wide Web", T. Berners-Lee, June 1994.


Security Considerations
=======================
  Communications with a resolver may be of a sensitive nature. Some
  resolvers will hold information that should only be released to
  authorized users. The results from resolvers may be the target of
  spoofing, especially once electronic commerce transactions are common
  and there is money to be made by directing users to pirate repositories
  rather than repositories which pay royalties to rightsholders. Resolution
  requests may be of interest to traffic analysts. The requests may also
  be subject to spoofing.

  The requests and responses in this draft are amenable to encoding,
  signing, and authentication in the manner of any other HTTP traffic.


Author Contact Information:
===========================

Ron Daniel
Advanced Computing Lab, MS B287
Los Alamos National Laboratory
Los Alamos, NM, USA, 87545
voice:  [phone]
fax:    [phone]
email:  [e-mail]


    This draft expires 22 August, 1997.
Ron Daniel Jr.                   email: [e-mail]
Advanced Computing Lab, MS B287  voice: [phone]
Los Alamos National Laboratory     fax: [phone]
Los Alamos, NM, USA 87545         http://www.acl.lanl.gov/~rdaniel/
Want to buy: "The Five Laws of Library Science" by S.R. Ranganathan