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.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
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.
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RFC 2936 HTTP MIME Type Handler Detection September 2000
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.
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RFC 2936 HTTP MIME Type Handler Detection September 2000
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 "". The following is a simple example of
conditional execution of parts of a web page based on JavaScript MIME
type handler detection.
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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].
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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 | |
| +---|
| 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 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.
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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", RFC 2706, October 1999.
[HTTP] Berners-Lee, T., Fielding, R. and H. Frystyk, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, 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", RFC 2616, June 1999.
[IOTP] Burdett, D., "Internet Open Trading Protocol - IOTP Version
1.0", RFC 2801, April 2000.
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[MIME] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, 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",
RFC 2048, November 1996.
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RFC 2936 HTTP MIME Type Handler Detection September 2000
[SET] "Secure Electronic Transaction (SET) Specification, Version
1.0", May 31, 1997, available from .
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,
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RFC 2936 HTTP MIME Type Handler Detection September 2000
Appendix A: Browser Version Sniffer Code
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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RFC 2936 HTTP MIME Type Handler Detection September 2000
Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Eastlake, et al. Informational [Page 13]
RFC, FYI, BCP