Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)

Status of this Memo

This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79.¶

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.¶

This Internet-Draft will expire on April 19, 2010.¶

Copyright Notice

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document.¶

Abstract

HTTP/1.1 defines the Content-Disposition Response Header, but points out that it is not part of the HTTP/1.1 Standard. This specification takes over the definition and registration of Content-Disposition, as used in HTTP, and clarifies internationalization considerations.¶

Editorial Note (To be removed by RFC Editor before publication)

This specification is expected to replace the definition of Content-Disposition in the HTTP/1.1 specification, as currently revised by the IETF HTTPbis working group. See also <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/123>.¶

Distribution of this document is unlimited. Although this is not a work item of the HTTPbis Working Group, comments should be sent to the Hypertext Transfer Protocol (HTTP) mailing list at ietf-http-wg@w3.org, which may be joined by sending a message with subject "subscribe" to ietf-http-wg-request@w3.org.¶

Discussions of the HTTPbis Working Group are archived at <http://lists.w3.org/Archives/Public/ietf-http-wg/>.¶

XML versions, latest edits and the issues list for this document are available from <http://greenbytes.de/tech/webdav/#draft-reschke-rfc2183-in-http>. A collection of test cases is available at <http://greenbytes.de/tech/tc2231/>.¶

1. Introduction

HTTP/1.1 defines the Content-Disposition response header in Section 19.5.1 of [RFC2616], but points out that is not part of the HTTP/1.1 Standard (Section 15.5):¶

Content-Disposition is not part of the HTTP standard, but since it is widely implemented, we are documenting its use and risks for implementors.¶

This specification takes over the definition and registration of Content-Disposition, as used in HTTP. Based on interoperability testing with existing User Agents, it defines a profile of the features defined in the MIME variant ([RFC2183]) of the header, and also clarifies internationalization considerations.¶

2. Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶

This specification uses the augmented BNF notation defined in Section 2.1 of [RFC2616], including its rules for linear whitespace (LWS).¶

3. Header Definition

3.1. Grammar

  content-disposition = "Content-Disposition" ":"
                         disposition-type *( ";" disposition-parm )

  disposition-type    = "inline" | "attachment" | disp-ext-type
                      ; case-insensitive
  disp-ext-type       = token

  disposition-parm    = filename-parm | disp-ext-parm

  filename-parm       = "filename" "=" value
                      | "filename*" "=" ext-value
  
  disp-ext-parm       = token "=" value
                      | ext-token "=" ext-value
  ext-token           = <the characters in token, followed by "*">

Defined in [RFC2616]:

  token       = <token, defined in [RFC2616], Section 2.2>
  value       = <value, defined in [RFC2616], Section 3.6>

Defined in [draft-reschke-rfc2231-in-http]:

  ext-value   = <ext-value, defined in [draft-reschke-rfc2231-in-http], Section 3.2>

3.2. Disposition Type

If the disposition type matches "attachment" (case-insensitively), the implied suggestion is that the user agent should not display the response, but directly enter a "save response as..." dialog.¶

On the other hand, if it matches "inline", this implies regular processing. Note that this type may be used when it is desirable to transport filename information for the case of a subsequent, user-initiated, save operation.¶

Other disposition types SHOULD be handled the same way as "attachment" ([RFC2183], Section 2.8).¶

3.3. Disposition Parameter: 'Filename'

[rfc.comment.1: Talk about expected behavior, mention security considerations.] ¶

3.4. Disposition Parameter: Extensions

Parameters other then "filename" SHOULD be ignored ([RFC2183], Section 2.8).¶

4. Examples

Direct UA to show "save as" dialog, with a filename of "foo.html":

Content-Disposition: Attachment; filename=foo.html

Direct UA to behave as if the Content-Disposition header wasn't present, but to remember the filename "foo.html" for a subsequent save operation:

Content-Disposition: INLINE; FILENAME= "foo.html"

5. Security Considerations

[csec: Both refer to 2183, and also mention: long filenames, dot and dotdot, absolute paths, mismatches between media type and extension] ¶

6. IANA Considerations

6.1. Registry for Disposition Values and Parameter

Section 9 of [RFC2183] defines the registration procedure for new disposition values and parameters.¶

7. Acknowledgements

[rfc.comment.2: TBD.] ¶

8. References

8.1. Normative References

[draft-reschke-rfc2231-in-http]: Reschke, J., “Applicability of RFC 2231 Encoding to Hypertext Transfer Protocol (HTTP) Headers”, Internet-Draft draft-reschke-rfc2231-in-http-05 (work in progress), October 2009.
[RFC2119]: Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, March 1997.
[RFC2183]: Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field”, RFC 2183, August 1997.
[RFC2616]: 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.

8.2. Informative References

[RFC3864]: Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields”, BCP 90, RFC 3864, September 2004.

Appendix A. Changes from the RFC 2616 Definition

Compared to Section 19.5.1 of [RFC2616], the following normative changes reflecting actual implementations have been made: ¶

According to RFC 2616, the disposition type "attachment" only applies to content of type "application/octet-stream". This restriction has been removed, because user agents in practice do not check the content type, and it also discourages properly declaring the media type.
The definition for the disposition type "inline" ([RFC2183], Section 2.1) has been re-added with a suggestion for its processing.
This specification requires support for the extended parameter encoding defined in [draft-reschke-rfc2231-in-http].

C
- Content-Disposition header 3, 6.2
D
- draft-reschke-rfc2231-in-http 3.1, 3.1, 8.1, A
  - Section 3.2 3.1
H
- Headers
  - Content-Disposition 3, 6.2
R
- RFC2119 2, 8.1
- RFC2183 1, 3.2, 3.4, 6.1, 8.1, A, B
  - Section 2 B
  - Section 2.1 A
  - Section 2.8 3.2, 3.4
  - Section 9 6.1
- RFC2616 1, 1, 2, 3.1, 3.1, 3.1, 8.1, A
  - Section 2.1 2
  - Section 2.2 3.1
  - Section 3.6 3.1
  - Section 15.5 1
  - Section 19.5.1 1, A
- RFC3864 6.2, 8.2

Author's Address

Julian F. Reschke
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/