INTERNET-DRAFT MIME Handler Detection
August 1999
Expires February 2000
draft-ietf-trade-mime-detector-01.txt
HTTP MIME Type Handler Detection
---- ---- ---- ------- ---------
Donald E. Eastlake 3rd
Chris J. Smith
David M. Soroka
Status of This Document
This draft, file name draft-ietf-trade-mime-detector-01.txt, is
intended to become an Informational RFC. Distribution of this
document is unlimited. Comments should be sent to the TRADE WG
mailing list <ietf-trade@eListX.com> or to the authors.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of [RFC 2026]. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
D. Eastlake, C. Smith, D. Soroka [Page 1]
INTERNET-DRAFT MIME Handler Detection August 1999
Abstract
Entities composing web pages to provide services over HTTP frequently
have the problem of not knowing what MIME types have handlers
installed at a user's browser. For example, whether an IOTP or VRML
or SET or some streaming media handler is available. In many cases
they would want to display different web pages or content depending
on a MIME handler's availability. This document summarizes a
reasonable technique to solve this problem for most of the browsers
actually deployed on the Internet as of August 1999. It is intended
to be of practical use to implementors during the period before the
wide deployment of superior standards based techniques which may be
developed.
Table of Contents
Status of This Document....................................1
Abstract...................................................2
Table of Contents..........................................2
1. Introduction............................................3
2. The HTTP 'Accept' Header................................3
3. JavaScript..............................................3
4. Microsoft ActiveX and the Windows Registry..............4
5. ECML, The Electronic Commerce Modeling Language.........5
6. Putting It All Together.................................5
7. Future Development......................................6
8. Security Considerations.................................6
9. IANA Considerations.....................................7
References.................................................8
Appendix A: Browser Version Sniffer Code...................9
Authors Addresses.........................................13
Expiration and File Name..................................13
D. Eastlake, C. Smith, D. Soroka [Page 2]
INTERNET-DRAFT MIME Handler Detection August 1999
1. Introduction
Entities composing web pages to provide services over [HTTP]
frequently have the problem of not knowing what [MIME] types have
handlers installed at a user's browser. For example, whether an
[IOTP] or VRML or [SET] or some streaming media handler is available.
In many cases they would want to display different web pages or
content depending on a MIME handler's availability. Sending a
response with a MIME type that is not supported frequently results in
interrupting the flow of the user experience, browser queries as to
what to do with the data being provided, and, of course, failure to
provide the behavior that would have occurred had the correct MIME
type handler been installed.
This document describes reasonable techniques to solve this problem
for most of the browsers actually deployed on the Internet as of
August 1999. It is intended to be of practical use to implementors
during the period before the wide deployment of superior standards
based techniques which may be developed. It is written in terms of
determining whether a handler for application/iotp or application/x-
iotp exists but is equally applicable to other MIME types.
2. The HTTP 'Accept' Header
The problem should be solved by the Hyper Text Transport Protocol
[HTTP] request "Accept" header which lists accepted [MIME] types.
This header is present in both Version 1.0 and 1.1 of HTTP and its
content is supposed to be a list of MIME types and subtypes that are
accepted. The only problem is that many browsers just send "*/*".
If the particular MIME type you are looking for is present in the
Accept header, it is generally safe to assume that some specific
handler for it is actually installed or part of the browser.
NOTE: Although not part of the main topic of this document, if you
are designing MIME type handler software and have access to a browser
interface that allows you to request the insertion of the MIME type
or types your software handles into the Accept header, you generally
should do so. It will make it easier for servers sensitive to that
MIME type to respond correctly.
3. JavaScript
Most recent browsers support one or more scripting languages of which
the most widely deployed is "JavaScript". These scripting languages
appear in web pages and permit the interpretive execution of
D. Eastlake, C. Smith, D. Soroka [Page 3]
INTERNET-DRAFT MIME Handler Detection August 1999
programing language constructs that can probe the browser
environment, conditionally cause different page contents to be
displayed, etc. For example, Appendix A shows JavaScript available
from the Netscape web site for determining what operating system,
browser, and version you are running on.
NOTE: JavaScript is a trademark of SUN Microsystems, Inc. It was
originally called LiveScript. It has nothing to do with the Java
language.
The syntax for script use appears to be a Hyper Text Markup Language
(HTML) comment so that bowsers that do not support scripting will
ignore such items. That is, script use if preceeded by "<!--" and
terminated by "-->". The following is a simple example of
conditional execution of parts of a web page based on JavaScript MIME
type handler detection.
<SCRIPT LANGUAGE=JAVASCRIPT>
<!-- hide it
if (navigator.appName=="netscape") { // wise precaution
if ( navigator.mimeTypes["application/iotp"] ||
navigator.mimeTypes["application/x-iotp"]) {
// here if IOTP handler exists
}
else {
// here if IOTP handler does not exist
}
}
// end and hide -->
</SCRIPT>
4. Microsoft ActiveX and the Windows Registry
If running on Internet Explorer version 3 or 4, it is necessary to
query to Windows Registry to determine local MIME type support.
Although these broswers support JavaScript, in v3 the mimeTypes array
is not present and in v4 the mimeTypes array is present but always
empty. For example, executing the following code will test for
support of the IOTP types:
D. Eastlake, C. Smith, D. Soroka [Page 4]
INTERNET-DRAFT MIME Handler Detection August 1999
CString iotpString, xiotpString;
char* Key, Keyx;
int rc, rcx;
iotpString =
"SOFTWARE\Classes\MIME\Database\Content Type\application/iotp";
xiotpString =
"SOFTWARE\Classes\MIME\Database\Content Type\application/x-iotp";
Key = iotpString.GetBuffer(1);
Keyx = xiotpString.GetBuffer(1);
rc = RegOpenKeyEx(HKEY_LOCAL_MACHINE, Key, 0, KEY_READ, hDefKey);
rcx = RegOpenKeyEx(HKEY_LOCAL_MACHINE, Key, 0, KEY_READ, hDefKey);
if ( ( rc == ERROR_SUCCESS ) || ( rcx == ERROR_SUCCESS ) )
{
// IOTP Handler exists
}
else
{
// No IOTP Handler
}
NOTE: Active X is a trademark of Microsoft and was originally called
Sweeper.
[TBD Stuff about ActiveX glue...?]
5. ECML, The Electronic Commerce Modeling Language
A industry group has recently proposed a standard for fields used in
electronic commerce. This fields allow "wallet" software acting for
the consumer to convey standardized information to a merchant,
including information as to what payment related protocols are
supported at the customer site. See [ECML].
6. Putting It All Together
[..]
D. Eastlake, C. Smith, D. Soroka [Page 5]
INTERNET-DRAFT MIME Handler Detection August 1999
start>-----+
|
+------------------+
| Was desired type | NO +-------------------------+
|found in Accept? |------------>| Is JavaScript available |
+------------------+ |and does it show type? |
| +-------------------------+
YES | | | |
|<---------------------------+ | NO |
| YES | |
| +---<explorer<--+ |
| | |
| +----------------------+ |
| | Is ActiveX available | |
| |and does it show type?| |
| +----------------------+ |
| YES | | | NO |
|<-----------+ | +----------------->|
| V |
remember | Indeterminate remember |
that |. take default that type |
type IS | action. is NOT |
supported| supported |
X done X
[...]
7. Future Development
Active work is proceeding in the IETF, World Wide Web Consortium
[W3C], and Electronic Commerce Modeling Language Alliance [ECML]
concerning content and capabilities negotiation. This work is likely
to lead to superior methods to implement the functionality described
herein. However, near universal deployment of such new
standards/features will take some time. Thus you should expect the
methods given herein to be obsoleted, but perhaps not for a few
years.
8. Security Considerations
It should be noted that the variety of Active X control suggested
above is reading the user's registry, that is, examining their
computer and reporting back some information it has discovered. This
may be a concern among some users.
Security of web interactions is normally provided by adopting channel
D. Eastlake, C. Smith, D. Soroka [Page 6]
INTERNET-DRAFT MIME Handler Detection August 1999
encryption on the browser to server connections, such as [TLS]. In
the absence of some such additional security outside of HTTP,
requests and/or responses may be forged or tampered with.
9. IANA Considerations
None specific to the techniques described herein. For MIME types and
type registration procedures, see [RFCs 2046, 2048].
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References
[ECML] draft-eastlake-ecom-fields-*.txt, D. Eastlake, T. Goldstein,
<www.ecml.org>.
[HTTP] RFC 1945 - "Hypertext Transfer Protocol -- HTTP/1.0", T.
Berners-Lee, R. Fielding & H. Frystyk. May 1996.
RFC 2616 - "Hypertext Transfer Protocol -- HTTP/1.1", R.
Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, T.
Berners-Lee. June 1999.
[IOTP] draft-ietf-trade-iotp-v1.0-protocol-*.txt - David Burdett,
1999.
[MIME] RFC 2045 - "Multipurpose Internet Mail Extensions (MIME) Part
One: Format of Internet Message Bodies", N. Freed & N. Borenstein.
November 1996.
RFC 2046 - "Multipurpose Internet Mail Extensions (MIME) Part
Two: Media Types", N. Freed & N. Borenstein. November 1996.
RFC 2047 - "MIME (Multipurpose Internet Mail Extensions) Part
Three: Message Header Extensions for Non-ASCII Text", K. Moore.
November 1996.
RFC 2048 - "Multipurpose Internet Mail Extensions (MIME) Part
Four: Registration Procedures", N. Freed, J. Klensin & J. Postel.
November 1996.
[SET]- Secure Electronic Transaction (SET) Specification, Version
1.0, May 31, 1997, available from <http://www.setco.org>.
Book 1: Business Description
Book 2: Programmer's Guide
Book 3: Formal Protocol Definition
[TLS] RFC 2246 - "The TLS Protocol Version 1.0", T. Dierks, C. Allen.
[W3C] Wolrd Wide Web Constortium, <www.w3.org>
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Appendix A: Browser Version Sniffer Code
<SCRIPT LANGUAGE="JavaScript">
<!-- hide JavaScript from non-JavaScript browsers
//Ultimate client-side JavaScript client sniff.
//(C)Netscape Communications 1998. Permission granted to reuse and distribute.
//Revised 20 April 98 to add is.nav4up and is.ie4up (see below).
// Everything you always wanted to know about your JavaScript client
// but were afraid to ask ... "Is" is the constructor function for "is" object,
// which has properties indicating:
//(1) browser vendor:
// is.nav, is.ie, is.opera
//(2) browser version number:
// is.major (integer indicating major version number: 2, 3, 4 ...)
// is.minor (float indicating full version number: 2.02, 3.01, 4.04...)
//(3) browser vendor AND major version number
// is.nav2, is.nav3, is.nav4, is.nav4up, is.ie3, is.ie4, is.ie4up
//(4) JavaScript version number:
// is.js (float indicating full JavaScript version number: 1, 1.1, 1.2...)
//(5) OS platform and version:
// is.win, is.win16, is.win32, is.win31, is.win95, is.winnt, is.win98
// is.os2
// is.mac, is.mac68k, is.macppc
// is.unix
// is.sun, is.sun4, is.sun5, is.suni86
// is.irix, is.irix5, is.irix6
// is.hpux, is.hpux9, is.hpux10
// is.aix, is.aix1, is.aix2, is.aix3, is.aix4
// is.linux, is.sco, is.unixware, is.mpras, is.reliant
// is.dec, is.sinix, is.freebsd, is.bsd
// is.vms
//
//See http://www.it97.de/JavaScript/JS_tutorial/obj_hierarchy/navobjFr.html
//for a detailed list of userAgent strings.
//
//Note: you don't want your Nav4 or IE4 code to "turn off" or
//stop working when Nav5 and IE5 (or later) are released, so
//in conditional code forks, use is.nav4up ("Nav4 or greater")
//and is.ie4up ("IE4 or greater") instead of is.nav4 or is.ie4
//to check version in code which you want to work on future
//versions.
function Is ()
{ // convert all characters to lowercase to simplify testing
var agt=navigator.userAgent.toLowerCase()
// *** BROWSER VERSION ***
this.major = parseInt(navigator.appVersion)
this.minor = parseFloat(navigator.appVersion)
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this.nav = ((agt.indexOf('mozilla')!=-1) &&
((agt.indexOf('spoofer')==-1) &&
(agt.indexOf('compatible') == -1)))
this.nav2 = (this.nav && (this.major == 2))
this.nav3 = (this.nav && (this.major == 3))
this.nav4 = (this.nav && (this.major == 4))
this.nav4up = this.nav && (this.major >= 4)
this.navonly = (this.nav && (agt.indexOf(";nav") != -1))
this.ie = (agt.indexOf("msie") != -1)
this.ie3 = (this.ie && (this.major == 2))
this.ie4 = (this.ie && (this.major == 4))
this.ie4up = this.ie && (this.major >= 4)
this.opera = (agt.indexOf("opera") != -1)
// *** JAVASCRIPT VERSION CHECK ***
// Useful to workaround Nav3 bug in which Nav3
// loads <SCRIPT LANGUAGE="JavaScript1.2">.
if (this.nav2 || this.ie3) this.js = 1.0
else if (this.nav3 || this.opera) this.js = 1.1
else if (this.nav4 || this.ie4) this.js = 1.2
// NOTE: In the future, update this code when newer versions of JS
// are released. For now, we try to provide some upward compatibility
// so that future versions of Nav and IE will show they are at
// *least* JS 1.2 capable. Always check for JS version compatibility
// with > or >=.
else if ((this.nav && (this.minor > 4.05)) || (this.ie && (this.major > 4)))
this.js = 1.2
else this.js = 0.0 // HACK: always check for JS version with > or >=
// *** PLATFORM ***
this.win = ( (agt.indexOf("win")!=-1) || (agt.indexOf("16bit")!=-1) )
// NOTE: On Opera 3.0, the userAgent string includes "Windows 95/NT4" on all
// Win32, so you can't distinguish between Win95 and WinNT.
this.win95 = ((agt.indexOf("win95")!=-1) || (agt.indexOf("windows 95")!=-1))
// is this a 16 bit compiled version?
this.win16 = ((agt.indexOf("win16")!=-1)
|| (agt.indexOf("16bit")!=-1) || (agt.indexOf("windows 3.1")!=-1)
|| (agt.indexOf("windows 16-bit")!=-1) )
this.win31 = (agt.indexOf("windows 3.1")!=-1) ||
(agt.indexOf("win16")!=-1) ||
(agt.indexOf("windows 16-bit")!=-1)
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// NOTE: Reliable detection of Win98 may not be possible. It appears that:
// - On Nav 4.x and before you'll get plain "Windows" in userAgent.
// - On Mercury client, the 32-bit version will return "Win98", but
// the 16-bit version running on Win98 will still return "Win95".
this.win98 =
((agt.indexOf("win98")!=-1)||(agt.indexOf("windows 98")!=-1))
this.winnt =
((agt.indexOf("winnt")!=-1)||(agt.indexOf("windows nt")!=-1))
this.win32 = this.win95 || this.winnt || this.win98 ||
((this.major >= 4) && (navigator.platform == "Win32")) ||
(agt.indexOf("win32")!=-1) || (agt.indexOf("32bit")!=-1)
this.os2 = (agt.indexOf("os/2")!=-1)
|| (navigator.appVersion.indexOf("OS/2")!=-1)
|| (agt.indexOf("ibm-webexplorer")!=-1)
this.mac= (agt.indexOf("mac")!=-1)
this.mac68k = this.mac && ((agt.indexOf("68k")!=-1) ||
(agt.indexOf("68000")!=-1))
this.macppc = this.mac && ((agt.indexOf("ppc")!=-1) ||
(agt.indexOf("powerpc")!=-1))
this.sun = (agt.indexOf("sunos")!=-1)
this.sun4 = (agt.indexOf("sunos 4")!=-1)
this.sun5 = (agt.indexOf("sunos 5")!=-1)
this.suni86= this.sun && (agt.indexOf("i86")!=-1)
this.irix = (agt.indexOf("irix") !=-1) // SGI
this.irix5 = (agt.indexOf("irix 5") !=-1)
this.irix6 =
((agt.indexOf("irix 6") !=-1) || (agt.indexOf("irix6")!=-1))
this.hpux = (agt.indexOf("hp-ux")!=-1)
this.hpux9 = this.hpux && (agt.indexOf("09.")!=-1)
this.hpux10= this.hpux && (agt.indexOf("10.")!=-1)
this.aix = (agt.indexOf("aix") !=-1) // IBM
this.aix1 = (agt.indexOf("aix 1") !=-1)
this.aix2 = (agt.indexOf("aix 2") !=-1)
this.aix3 = (agt.indexOf("aix 3") !=-1)
this.aix4 = (agt.indexOf("aix 4") !=-1)
this.linux = (agt.indexOf("inux")!=-1)
this.sco = (agt.indexOf("sco")!=-1) || (agt.indexOf("unix_sv")!=-1)
this.unixware = (agt.indexOf("unix_system_v")!=-1)
this.mpras= (agt.indexOf("ncr")!=-1)
this.reliant = (agt.indexOf("reliantunix")!=-1)
this.dec =
(agt.indexOf("dec")!=-1) || (agt.indexOf("osf1")!=-1)
|| (agt.indexOf("dec_alpha")!=-1) || (agt.indexOf("alphaserver")!=-1)
|| (agt.indexOf("ultrix")!=-1) || (agt.indexOf("alphastation")!=-1)
this.sinix = (agt.indexOf("sinix")!=-1)
this.freebsd = (agt.indexOf("freebsd")!=-1)
this.bsd = (agt.indexOf("bsd")!=-1)
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this.unix =
(agt.indexOf("x11")!=-1) || this.sun || this.irix || this.hpux ||
this.sco ||this.unixware || this.mpras || this.reliant ||
this.dec || this.sinix || this.aix || this.linux || this.freebsd
this.vms = (agt.indexOf("vax")!=-1) || (agt.indexOf("openvms")!=-1)
}
var is;
var isIE3Mac = false;
// this section is designed specifically for IE3 for the Mac
if ((navigator.appVersion.indexOf("Mac")!=-1) &&
(navigator.userAgent.indexOf("MSIE")!=-1) &&
(parseInt(navigator.appVersion)==3))
isIE3Mac = true;
else
is = new Is();
//--> end hide JavaScript
</SCRIPT>
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Authors Addresses
Donald E. Eastlake 3rd
IBM
65 Shindegan Hill Road
Carmel, NY 10512 USA
Telephone: +1 914-276-2668(h)
+1 914-784-7913(w)
FAX: +1 914-784-3833(w)
email: dee3@us.ibm.com
Chris J. Smith
Royal Bank of Canada
277 Front Street West
Toronto, Ontario M5V 3A4 CANADA
Telephone: +1 416-348-6090
FAX: +1 416-348-2210
email: chris.smith@royalbank.com
David M. Soroka
IBM
Raleigh, NC
Telephone: +1 919-486-2684
Fax: +1 919-543-4653
email: dsoroka@us.ibm.com
Expiration and File Name
This draft expires February 2000.
Its file name is draft-ietf-trade-mime-detector-01.txt.
D. Eastlake, C. Smith, D. Soroka [Page 13]
