Use of the Content-Disposition Header Field in the Hypertext Transfer Protocol (HTTP)
draft-reschke-rfc2183-in-http-00

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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/.

Table of Contents

1.  Introduction
2.  Notational Conventions
3.  Header Definition
    3.1.  Grammar
    3.2.  Disposition Type
    3.3.  Disposition Parameter: 'Filename'
    3.4.  Disposition Parameter: Extensions
4.  Examples
5.  Security Considerations
6.  IANA Considerations
    6.1.  Registry for Disposition Values and Parameter
    6.2.  Header Registration
7.  Acknowledgements
8.  References
    8.1.  Normative References
    8.2.  Informative References
Appendix A.  Changes from the RFC 2616 Definition
Appendix B.  Differences compared to RFC 2183
Appendix C.  Alternative Approaches to Filename Escaping
§  Index
§  Author's Address

1.  Introduction

HTTP/1.1 defines the Content-Disposition response header in Section 19.5.1 of [RFC2616] (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.), 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] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.)) 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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

This specification uses the augmented BNF notation defined in Section 2.1 of [RFC2616] (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.), 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] (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.):

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

Defined in [draft‑reschke‑rfc2231‑in‑http] (Reschke, J., “Applicability of RFC 2231 Encoding to Hypertext Transfer Protocol (HTTP) Headers,” October 2009.):

  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] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.), Section 2.8).

3.3.  Disposition Parameter: 'Filename'

[anchor3] (Talk about expected behavior, mention security considerations.)

3.4.  Disposition Parameter: Extensions

Parameters other then "filename" SHOULD be ignored ([RFC2183] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.), 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] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.) defines the registration procedure for new disposition values and parameters.

6.2.  Header Registration

This document updates the definition of the Content-Disposition HTTP header in the permanent HTTP header registry (see [RFC3864] (Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields,” September 2004.)).

Header field name:

Content-Disposition

Applicable protocol:

http

Status:

standard

Author/Change controller:

IETF

Specification document:

this specification (Section 3 (Header Definition))

7.  Acknowledgements

[anchor6] (TBD.)

8.  References

8.1. Normative References

8.2. Informative References

Appendix A.  Changes from the RFC 2616 Definition

Compared to Section 19.5.1 of [RFC2616] (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.), 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] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.), 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] (Reschke, J., “Applicability of RFC 2231 Encoding to Hypertext Transfer Protocol (HTTP) Headers,” October 2009.).

Appendix B.  Differences compared to RFC 2183

Section 2 of [RFC2183] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.) defines several additional disposition parameters: "creation-date", "modification-date", "quoted-date-time", and "size". These do not appear to be implemented by any user agent, thus have been ommitted from this specification.

Appendix C.  Alternative Approaches to Filename Escaping

[anchor10] (Mention: RFC 2047, IE, Safari)

Index

Author's Address