RFC2936 - HTTP MIME Type Handler Detection

Network Working Group D. Eastlake

Request for Comments: 2936 Motorola

Category: Informational C. Smith

Royal Bank of Canada

D. Soroka

IBM

September 2000

HTTP MIME Type Handler Detection

Status of this Memo

This memo provides information for the Internet community. It does

not specify an Internet standard of any kind. Distribution of this

memo is unlimited.

Abstract

Entities composing web pages to provide services over the Hypertext

Transfer Protocol (HTTP) frequently have the problem of not knowing

what Multipurpose Internet Mail Extensions (MIME) types have handlers

installed at a user's browser. For example, whether an Internet Open

Trading Protocol (IOTP) or VRML or SET or some streaming media

handler is available. In some cases they would want to display

different web pages or content depending on a MIME handler's

availability. This document summarizes reasonable techniques to

solve this problem for most of the browsers actually deployed on the

Internet as of early 2000. 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.

Acknowledegements

Helpful comments by Tony Lewis of Visa have been incorporated.

Table of Contents

1. IntrodUCtion................................................. 2

2. The HTTP 'Accept' Header..................................... 2

3. javascript................................................... 3

4. ActiveX and the Windows Registry............................. 4

5. ECML, The Electronic Commerce Modeling Language.............. 4

6. Putting It All Together...................................... 5

7. Future Development........................................... 5

8. Security Considerations...................................... 5

9. IANA Considerations.......................................... 6

References...................................................... 6

Appendix A: Browser Version Sniffer Code........................ 8

Authors' Addresses.............................................. 12

Full Copyright Statement........................................ 13

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

early 2000. 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 "*/*" or

the like.

If the particular MIME type you are looking for is specifically

present in the Accept header, it is generally safe to assume that a

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

programming 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 on which a web page is appearing.

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 browsers that do not support scripting will

ignore such items. That is, script use is preceded 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.

<!-- hide it

if (navigator.mimeTypes && navigator.mimeTypes.length > 0) {

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. ActiveX and the Windows Registry

If running on Microsoft Windows Internet Explorer version 3 or 4, it

is necessary to query the 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:

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, Keyx, 0, KEY_READ, hDefKey);

if ( ( rc == ERROR_SUCCESS ) ( rcx == ERROR_SUCCESS ) )

{

// IOTP Handler exists

}

else

{

// No IOTP Handler

}

NOTE: ActiveX is a trademark of Microsoft and was originally called

Sweeper.

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

The following diagram indicates how these techniques can be put

together.

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

<-----------+ +----------------->

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 other standards and industry groups 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 some time.

8. Security Considerations

It should be noted that the variety of ActiveX 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.

In general, the use of JavaScript and, even more so, ActiveX is

dangerous because they are so powerful. JavaScript or ActiveX from a

web page could be invisibly damaging to the client.

Security of web interactions is normally provided by adopting channel

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 [MIME: RFCs 2046, 2048].

References

[ECML] Eastlake, D. and T. Goldstein, "ECML v1: Field Names for E-

Commerce", RFC2706, October 1999.

[HTTP] Berners-Lee, T., Fielding, R. and H. Frystyk, "Hypertext

Transfer Protocol -- HTTP/1.0", RFC1945, May 1996.

[HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,

L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol

-- HTTP/1.1", RFC2616, June 1999.

[IOTP] Burdett, D., "Internet Open Trading Protocol - IOTP Version

1.0", RFC2801, April 2000.

[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail

Extensions (MIME) Part One: Format of Internet Message

Bodies", RFC2045, November 1996.

[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail

Extensions (MIME) Part Two: Media Types", RFC2046, November

1996.

[MIME] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part

Three: Message Header Extensions for Non-ASCII Text", RFC

2047, November 1996.

[MIME] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet

Mail Extensions (MIME) Part Four: Registration Procedures",

RFC2048, 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] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC

2246, January 1999.

[W3C] World Wide Web Consortium, <www.w3.org>

Appendix A: Browser Version Sniffer Code

<!-- hide JavaScript from non-JavaScript browsers

// Ultimate client-side JavaScript client sniff.

// (C) Netscape Communications 1999.

// Permission granted to reuse and distribute.

// Revised 17 May 99 to add is_nav5up and is_ie5up (see below).

// Everything you always wanted to know about your JavaScript client

// but were afraid to ask. Creates "is_" variables 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_nav5, is_nav5up,

// 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/bstat/navobj.html and

// http://www.it97.de/JavaScript/JS_tutorial/bstat/Browseraol.html

// for detailed lists 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.

// convert all characters to lowercase to simplify testing

var agt=navigator.userAgent.toLowerCase();

// *** BROWSER VERSION ***

// Note: On IE5, these return 4, so use is_ie5up to detect IE5.

var is_major = parseInt(navigator.appVersion);

var is_minor = parseFloat(navigator.appVersion);

// Note: Opera and WebTV spoof Navigator. We do strict client

// detection. If you want to allow spoofing, take out the tests

// for opera and webtv.

var is_nav = ((agt.indexOf('mozilla')!=-1)

&& (agt.indexOf('spoofer')==-1)

&& (agt.indexOf('compatible') == -1)

&& (agt.indexOf('opera')==-1)

&& (agt.indexOf('webtv')==-1));

var is_nav2 = (is_nav && (is_major == 2));

var is_nav3 = (is_nav && (is_major == 3));

var is_nav4 = (is_nav && (is_major == 4));

var is_nav4up = (is_nav && (is_major >= 4));

var is_navonly = (is_nav && ((agt.indexOf(";nav") != -1)

(agt.indexOf("; nav") != -1)) );

var is_nav5 = (is_nav && (is_major == 5));

var is_nav5up = (is_nav && (is_major >= 5));

var is_ie = (agt.indexOf("msie") != -1);

var is_ie3 = (is_ie && (is_major < 4));

var is_ie4 = (is_ie && (is_major == 4)

&& (agt.indexOf("msie 5.0")==-1) );

var is_ie4up = (is_ie && (is_major >= 4));

var is_ie5 = (is_ie && (is_major == 4)

&& (agt.indexOf("msie 5.0")!=-1) );

var is_ie5up = (is_ie && !is_ie3 && !is_ie4);

// KNOWN BUG: On AOL4, returns false if IE3 is embedded browser

// or if this is the first browser window opened. Thus the

// variables is_aol, is_aol3, and is_aol4 aren't 100% reliable.

var is_aol = (agt.indexOf("aol") != -1);

var is_aol3 = (is_aol && is_ie3);

var is_aol4 = (is_aol && is_ie4);

var is_opera = (agt.indexOf("opera") != -1);

var is_webtv = (agt.indexOf("webtv") != -1);

// *** JAVASCRIPT VERSION CHECK ***

var is_js;

if (is_nav2 is_ie3) is_js = 1.0

else if (is_nav3 is_opera) is_js = 1.1

else if ((is_nav4 && (is_minor <= 4.05)) is_ie4) is_js = 1.2

else if ((is_nav4 && (is_minor > 4.05)) is_ie5) is_js = 1.3

else if (is_nav5) is_js = 1.4

// 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.x capable. Always check for JS version compatibility

// with > or >=.

else if (is_nav && (is_major > 5)) is_js = 1.4

else if (is_ie && (is_major > 5)) is_js = 1.3

// HACK: no idea for other browsers;

// always check for JS version with > or >=

else is_js = 0.0;

// *** PLATFORM ***

var is_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.

var is_win95 = ((agt.indexOf("win95")!=-1)

(agt.indexOf("windows 95")!=-1));

// is this a 16 bit compiled version?

var is_win16 = ((agt.indexOf("win16")!=-1)

(agt.indexOf("16bit")!=-1)

(agt.indexOf("windows 3.1")!=-1)

(agt.indexOf("windows 16-bit")!=-1) );

var is_win31 = ((agt.indexOf("windows 3.1")!=-1)

(agt.indexOf("win16")!=-1)

(agt.indexOf("windows 16-bit")!=-1));

// 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".

var is_win98 = ((agt.indexOf("win98")!=-1)

(agt.indexOf("Windows 98")!=-1));

var is_winnt = ((agt.indexOf("winnt")!=-1)

(agt.indexOf("windows nt")!=-1));

var is_win32 = (is_win95 is_winnt is_win98

((is_major >= 4) &&

(navigator.platform == "Win32"))

(agt.indexOf("win32")!=-1)

(agt.indexOf("32bit")!=-1));

var is_os2 = ((agt.indexOf("os/2")!=-1)

(navigator.appVersion.indexOf("OS/2")!=-1)

(agt.indexOf("ibm-webexplorer")!=-1));

var is_mac = (agt.indexOf("mac")!=-1);

var is_mac68k = (is_mac && ((agt.indexOf("68k")!=-1)

(agt.indexOf("68000")!=-1)));

var is_macppc = (is_mac && ((agt.indexOf("ppc")!=-1)

(agt.indexOf("powerpc")!=-1)));

var is_sun = (agt.indexOf("sunos")!=-1);

var is_sun4 = (agt.indexOf("sunos 4")!=-1);

var is_sun5 = (agt.indexOf("sunos 5")!=-1);

var is_suni86= (is_sun && (agt.indexOf("i86")!=-1));

var is_irix = (agt.indexOf("irix") !=-1); // SGI

var is_irix5 = (agt.indexOf("irix 5") !=-1);

var is_irix6 = ((agt.indexOf("irix 6") !=-1)

(agt.indexOf("irix6") !=-1));

var is_hpux = (agt.indexOf("hp-ux")!=-1);

var is_hpux9 = (is_hpux && (agt.indexOf("09.")!=-1));

var is_hpux10= (is_hpux && (agt.indexOf("10.")!=-1));

var is_aix = (agt.indexOf("aix") !=-1); // IBM

var is_aix1 = (agt.indexOf("aix 1") !=-1);

var is_aix2 = (agt.indexOf("aix 2") !=-1);

var is_aix3 = (agt.indexOf("aix 3") !=-1);

var is_aix4 = (agt.indexOf("aix 4") !=-1);

var is_linux = (agt.indexOf("inux")!=-1);

var is_sco = (agt.indexOf("sco")!=-1)

(agt.indexOf("unix_sv")!=-1);

var is_unixware = (agt.indexOf("unix_system_v")!=-1);

var is_mpras = (agt.indexOf("ncr")!=-1);

var is_reliant = (agt.indexOf("reliantunix")!=-1);

var is_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));

var is_sinix = (agt.indexOf("sinix")!=-1);

var is_freebsd = (agt.indexOf("freebsd")!=-1);

var is_bsd = (agt.indexOf("bsd")!=-1);

var is_unix = ((agt.indexOf("x11")!=-1) is_sun

is_irix is_hpux

is_sco is_unixware is_mpras is_reliant

is_dec is_sinix is_aix is_linux

is_bsd is_freebsd);

var is_vms = ((agt.indexOf("vax")!=-1)

(agt.indexOf("openvms")!=-1));

</SCRIPT>

Authors' Addresses

Donald E. Eastlake 3rd

Motorola

140 Forest Avenue

Hudson, MA 01749 USA

Phone: +1 978-562-2827(h)

+1 508-261-5434(w)

Fax: +1 508-261-4447(w)

EMail: Donald.Eastlake@motorola.com

Chris J. Smith

Royal Bank of Canada

277 Front Street West

Toronto, Ontario M5V 3A4 CANADA

Phone: +1 416-348-6090

Fax: +1 416-348-2210

EMail: chris.smith@royalbank.com

David M. Soroka

IBM

Raleigh, NC

Phone: +1 919-486-2684

Fax: +1 919-543-4653

EMail: dsoroka@us.ibm.com

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