< draft-ietf-httpbis-content-disp-02.txt   draft-ietf-httpbis-content-disp-06.txt >
HTTPbis Working Group J. Reschke HTTPbis Working Group J. Reschke
Internet-Draft greenbytes Internet-Draft greenbytes
Updates: 2616 (if approved) September 22, 2010 Updates: 2616 (if approved) February 26, 2011
Intended status: Standards Track Intended status: Standards Track
Expires: March 26, 2011 Expires: August 30, 2011
Use of the Content-Disposition Header Field in the Use of the Content-Disposition Header Field in the
Hypertext Transfer Protocol (HTTP) Hypertext Transfer Protocol (HTTP)
draft-ietf-httpbis-content-disp-02 draft-ietf-httpbis-content-disp-06
Abstract Abstract
HTTP/1.1 defines the Content-Disposition response header field, but RFC 2616 defines the Content-Disposition response header field, but
points out that it is not part of the HTTP/1.1 Standard. This points out that it is not part of the HTTP/1.1 Standard. This
specification takes over the definition and registration of Content- specification takes over the definition and registration of Content-
Disposition, as used in HTTP, and clarifies internationalization Disposition, as used in HTTP, and clarifies internationalization
aspects. aspects.
Editorial Note (To be removed by RFC Editor before publication) Editorial Note (To be removed by RFC Editor before publication)
This specification is expected to replace the definition of Content- This specification is expected to replace the definition of Content-
Disposition in the HTTP/1.1 specification, as currently revised by Disposition in the HTTP/1.1 specification, as currently revised by
the IETF HTTPbis working group. See also the IETF HTTPbis working group. See also
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/123>. <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/123>.
Discussion of this draft should take place on the HTTPBIS working Discussion of this draft should take place on the HTTPBIS working
group mailing list (ietf-http-wg@w3.org). The current issues list is group mailing list (ietf-http-wg@w3.org). The current issues list is
at <http://trac.tools.ietf.org/wg/httpbis/trac/ at <http://trac.tools.ietf.org/wg/httpbis/trac/
query?component=content-disp> and related documents (including fancy query?component=content-disp> and related documents (including fancy
diffs) can be found at <http://tools.ietf.org/wg/httpbis/>. diffs) can be found at <http://tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix D.6. The changes in this draft are summarized in Appendix E.10.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 26, 2011. This Internet-Draft will expire on August 30, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
3. Header Field Definition . . . . . . . . . . . . . . . . . . . 4 3. Conformance and Error Handling . . . . . . . . . . . . . . . . 4
3.1. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Header Field Definition . . . . . . . . . . . . . . . . . . . 5
3.2. Disposition Type . . . . . . . . . . . . . . . . . . . . . 5 4.1. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Disposition Parameter: 'Filename' . . . . . . . . . . . . 5 4.2. Disposition Type . . . . . . . . . . . . . . . . . . . . . 6
3.4. Disposition Parameter: Extensions . . . . . . . . . . . . 6 4.3. Disposition Parameter: 'Filename' . . . . . . . . . . . . 6
3.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 6 4.4. Disposition Parameter: Extensions . . . . . . . . . . . . 7
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 7
5. Internationalization Considerations . . . . . . . . . . . . . 8 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Internationalization Considerations . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7.1. Registry for Disposition Values and Parameter . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.2. Header Field Registration . . . . . . . . . . . . . . . . 8 8.1. Registry for Disposition Values and Parameter . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 8.2. Header Field Registration . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Changes from the RFC 2616 Definition . . . . . . . . 10 Appendix A. Changes from the RFC 2616 Definition . . . . . . . . 10
Appendix B. Differences compared to RFC 2183 . . . . . . . . . . 10 Appendix B. Differences compared to RFC 2183 . . . . . . . . . . 11
Appendix C. Alternative Approaches to Internationalization . . . 10 Appendix C. Alternative Approaches to Internationalization . . . 11
C.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 11 C.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 11
C.2. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 11 C.2. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 12
C.3. Encoding Sniffing . . . . . . . . . . . . . . . . . . . . 11 C.3. Encoding Sniffing . . . . . . . . . . . . . . . . . . . . 12
C.4. Implementations (to be removed by RFC Editor before C.4. Implementations (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . . . 11 publication) . . . . . . . . . . . . . . . . . . . . . . . 12
Appendix D. Change Log (to be removed by RFC Editor before Appendix D. Advice on Generating Content-Disposition Header
publication) . . . . . . . . . . . . . . . . . . . . 12 Fields . . . . . . . . . . . . . . . . . . . . . . . 13
D.1. Since draft-reschke-rfc2183-in-http-00 . . . . . . . . . . 12 Appendix E. Change Log (to be removed by RFC Editor before
D.2. Since draft-reschke-rfc2183-in-http-01 . . . . . . . . . . 12 publication) . . . . . . . . . . . . . . . . . . . . 14
D.3. Since draft-reschke-rfc2183-in-http-02 . . . . . . . . . . 12 E.1. Since draft-reschke-rfc2183-in-http-00 . . . . . . . . . . 14
D.4. Since draft-reschke-rfc2183-in-http-03 . . . . . . . . . . 12 E.2. Since draft-reschke-rfc2183-in-http-01 . . . . . . . . . . 14
D.5. Since draft-ietf-httpbis-content-disp-00 . . . . . . . . . 12 E.3. Since draft-reschke-rfc2183-in-http-02 . . . . . . . . . . 14
D.6. Since draft-ietf-httpbis-content-disp-01 . . . . . . . . . 13 E.4. Since draft-reschke-rfc2183-in-http-03 . . . . . . . . . . 15
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 E.5. Since draft-ietf-httpbis-content-disp-00 . . . . . . . . . 15
E.6. Since draft-ietf-httpbis-content-disp-01 . . . . . . . . . 15
E.7. Since draft-ietf-httpbis-content-disp-02 . . . . . . . . . 15
E.8. Since draft-ietf-httpbis-content-disp-03 . . . . . . . . . 15
E.9. Since draft-ietf-httpbis-content-disp-04 . . . . . . . . . 16
E.10. Since draft-ietf-httpbis-content-disp-05 . . . . . . . . . 16
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
HTTP/1.1 defines the Content-Disposition response header field in RFC 2616 defines the Content-Disposition response header field in
Section 19.5.1 of [RFC2616], but points out that it is not part of Section 19.5.1 of [RFC2616], but points out that it is not part of
the HTTP/1.1 Standard (Section 15.5): the HTTP/1.1 Standard (Section 15.5):
Content-Disposition is not part of the HTTP standard, but since it Content-Disposition is not part of the HTTP standard, but since it
is widely implemented, we are documenting its use and risks for is widely implemented, we are documenting its use and risks for
implementers. implementers.
This specification takes over the definition and registration of This specification takes over the definition and registration of
Content-Disposition, as used in HTTP. Based on interoperability Content-Disposition, as used in HTTP. Based on interoperability
testing with existing User Agents, it fully defines a profile of the testing with existing User Agents, it fully defines a profile of the
features defined in the Multipurpose Internet Mail Extensions (MIME) features defined in the Multipurpose Internet Mail Extensions (MIME)
variant ([RFC2183]) of the header field, and also clarifies variant ([RFC2183]) of the header field, and also clarifies
internationalization aspects. internationalization aspects.
Note: this document does not apply to Content-Disposition header
fields appearing in payload bodies transmitted over HTTP, such as
when using the media type "multipart/form-data" ([RFC2388]).
2. Notational Conventions 2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
This specification uses the augmented BNF notation defined in Section This specification uses the augmented BNF notation defined in Section
2.1 of [RFC2616], including its rules for linear whitespace (LWS). 2.1 of [RFC2616], including its rules for implied linear whitespace
(LWS).
3. Header Field Definition 3. Conformance and Error Handling
This specification defines conformance criteria for both senders
(usually, HTTP origin servers) and recipients (usually, HTTP user
agents) of the Content-Disposition header field. An implementation
is considered conformant if it complies with all of the requirements
associated with its role.
This specification also defines certain forms of the header field-
value to be invalid, using both ABNF and prose requirements, but it
does not define special handling of these invalid field-values.
Senders MUST NOT generate Content-Disposition header fields that are
invalid.
Recipients MAY take steps to recover a usable field-value from an
invalid header field, but SHOULD NOT reject the message outright,
unless this is explicitly desirable behaviour (e.g., the
implementation is a validator). As such, the default handling of
invalid fields is to ignore them.
4. Header Field Definition
The Content-Disposition response header field is used to convey The Content-Disposition response header field is used to convey
additional information about how to process the response payload, and additional information about how to process the response payload, and
also can be used to attach additional metadata, such as the filename also can be used to attach additional metadata, such as the filename
to use when saving the response payload locally. to use when saving the response payload locally.
3.1. Grammar 4.1. Grammar
content-disposition = "Content-Disposition" ":" content-disposition = "Content-Disposition" ":"
disposition-type *( ";" disposition-parm ) disposition-type *( ";" disposition-parm )
disposition-type = "inline" | "attachment" | disp-ext-type disposition-type = "inline" | "attachment" | disp-ext-type
; case-insensitive ; case-insensitive
disp-ext-type = token disp-ext-type = token
disposition-parm = filename-parm | disp-ext-parm disposition-parm = filename-parm | disp-ext-parm
filename-parm = "filename" "=" value filename-parm = "filename" "=" value
| "filename*" "=" ext-value | "filename*" "=" ext-value
disp-ext-parm = token "=" value disp-ext-parm = token "=" value
| ext-token "=" ext-value | ext-token "=" ext-value
ext-token = <the characters in token, followed by "*"> ext-token = <the characters in token, followed by "*">
Defined in [RFC2616]: Defined in [RFC2616]:
token = <token, defined in [RFC2616], Section 2.2> token = <token, defined in [RFC2616], Section 2.2>
quoted-string = <quoted-string, defined in [RFC2616], Section 2.2>
value = <value, defined in [RFC2616], Section 3.6> value = <value, defined in [RFC2616], Section 3.6>
; token | quoted-string
Defined in [RFC5987]: Defined in [RFC5987]:
ext-value = <ext-value, defined in [RFC5987], Section 3.2> ext-value = <ext-value, defined in [RFC5987], Section 3.2>
3.2. Disposition Type Header field values with multiple instances of the same parameter
name are invalid.
Note that due to the rules for implied linear whitespace (Section 2.1
of [RFC2616]), OPTIONAL whitespace can appear between words (token or
quoted-string) and separator characters.
Furthermore note that the format used for ext-value allows specifying
a natural language; this is of limited use for filenames and is
likely to be ignored by recipients.
4.2. Disposition Type
If the disposition type matches "attachment" (case-insensitively), If the disposition type matches "attachment" (case-insensitively),
this indicates that the user agent should prompt the user to save the this indicates that the recipient should prompt the user to save the
response locally, rather than process it normally (as per its media response locally, rather than process it normally (as per its media
type). type).
On the other hand, if it matches "inline" (case-insensitively), this On the other hand, if it matches "inline" (case-insensitively), this
implies default processing. implies default processing. Therefore, the disposition type "inline"
is only useful when it is augmented with additional parameters, such
as the filename (see below).
Unknown or unhandled disposition types SHOULD be handled the same way Unknown or unhandled disposition types SHOULD be handled by
as "attachment" (see also [RFC2183], Section 2.8). recipients the same way as "attachment" (see also [RFC2183], Section
2.8).
3.3. Disposition Parameter: 'Filename' 4.3. Disposition Parameter: 'Filename'
The parameters "filename" and "filename*", to be matched case- The parameters "filename" and "filename*", to be matched case-
insensitively, provide information on how to construct a filename for insensitively, provide information on how to construct a filename for
storing the message payload. storing the message payload.
Depending on the disposition type, this information might be used Depending on the disposition type, this information might be used
right away (in the "save as..." interaction caused for the right away (in the "save as..." interaction caused for the
"attachment" disposition type), or later on (for instance, when the "attachment" disposition type), or later on (for instance, when the
user decides to save the contents of the current page being user decides to save the contents of the current page being
displayed). displayed).
skipping to change at page 6, line 19 skipping to change at page 6, line 48
"filename*" uses the encoding defined in [RFC5987], allowing the use "filename*" uses the encoding defined in [RFC5987], allowing the use
of characters not present in the ISO-8859-1 character set of characters not present in the ISO-8859-1 character set
([ISO-8859-1]). ([ISO-8859-1]).
Many user agent implementations predating this specification do not Many user agent implementations predating this specification do not
understand the "filename*" parameter. Therefore, when both understand the "filename*" parameter. Therefore, when both
"filename" and "filename*" are present in a single header field "filename" and "filename*" are present in a single header field
value, recipients SHOULD pick "filename*" and ignore "filename". value, recipients SHOULD pick "filename*" and ignore "filename".
This way, senders can avoid special-casing specific user agents by This way, senders can avoid special-casing specific user agents by
sending both the more expressive "filename*" parameter, and the sending both the more expressive "filename*" parameter, and the
"filename" parameter as fallback for legacy recipients (see Section 4 "filename" parameter as fallback for legacy recipients (see Section 5
for an example). for an example).
It is essential that user agents treat the specified filename as It is essential that recipients treat the specified filename as
advisory only, thus be very careful in extracting the desired advisory only, thus be very careful in extracting the desired
information. In particular: information. In particular:
o When the value contains path separator characters, all but the o When the value contains path separator characters ("\" or "/"),
last segment SHOULD be ignored. This prevents unintentional recipients SHOULD ignore all but the last path segment. This
overwriting of well-known file system location (such as "/etc/ prevents unintentional overwriting of well-known file system
passwd"). locations (such as "/etc/passwd").
o Many platforms do not use Internet Media Types ([RFC2046]) to hold o Many platforms do not use Internet Media Types ([RFC2046]) to hold
type information in the file system, but rely on filename type information in the file system, but rely on filename
extensions instead. Trusting the server-provided file extension extensions instead. Trusting the server-provided file extension
could introduce a privilege escalation when the saved file is could introduce a privilege escalation when the saved file is
later opened (consider ".exe"). Thus, recipients need to ensure later opened (consider ".exe"). Thus, recipients need to ensure
that a file extension is used that is safe, optimally matching the that a file extension is used that is safe, optimally matching the
media type of the received payload. media type of the received payload.
o Recipients are advised to strip or replace character sequences
that are known to cause confusion both in user interfaces and in
filenames, such as control characters and leading and trailing
whitespace.
o Other aspects recipients need to be aware of are names that have a o Other aspects recipients need to be aware of are names that have a
special meaning in the file system or in shell commands, such as special meaning in the file system or in shell commands, such as
"." and "..", "~", "|", and also device names. "." and "..", "~", "|", and also device names.
3.4. Disposition Parameter: Extensions Note: Many user agents do not properly handle the escape character
"\" when using the quoted-string form. Furthermore, some user
agents erroneously try to perform unescaping of "percent" escapes
(see Appendix C.2), and thus might misinterpret filenames
containing the percent character followed by two hex digits.
To enable future extensions, unknown parameters SHOULD be ignored 4.4. Disposition Parameter: Extensions
(see also [RFC2183], Section 2.8).
3.5. Extensibility To enable future extensions, recipients SHOULD ignore unrecognized
parameters (see also [RFC2183], Section 2.8).
4.5. Extensibility
Note that Section 9 of [RFC2183] defines IANA registries both for Note that Section 9 of [RFC2183] defines IANA registries both for
disposition types and disposition parameters. This registry is disposition types and disposition parameters. This registry is
shared by different protocols using Content-Disposition, such as MIME shared by different protocols using Content-Disposition, such as MIME
and HTTP. Therefore, not all registered values may make sense in the and HTTP. Therefore, not all registered values may make sense in the
context of HTTP. context of HTTP.
4. Examples 5. Examples
Direct UA to show "save as" dialog, with a filename of Direct UA to show "save as" dialog, with a filename of
"example.html": "example.html":
Content-Disposition: Attachment; filename=example.html Content-Disposition: Attachment; filename=example.html
Direct UA to behave as if the Content-Disposition header field wasn't Direct UA to behave as if the Content-Disposition header field wasn't
present, but to remember the filename "example.html" for a subsequent present, but to remember the filename "an example.html" for a
save operation: subsequent save operation:
Content-Disposition: INLINE; FILENAME= "example.html"
Direct UA to show "save as" dialog, with a filename of "an example":
Content-Disposition: Attachment; Filename*=UTF-8'en'an%20example Content-Disposition: INLINE; FILENAME= "an example.html"
Note that this example uses the extended encoding defined in Note: this uses the quoted-string form so that the space character
[RFC5987] to specify that the natural language of the filename is can be included.
English, and also to encode the space character which is not allowed
in the token production.
Direct UA to show "save as" dialog, with a filename containing the Direct UA to show "save as" dialog, with a filename containing the
Unicode character U+20AC (EURO SIGN): Unicode character U+20AC (EURO SIGN):
Content-Disposition: attachment; Content-Disposition: attachment;
filename*= UTF-8''%e2%82%ac%20rates filename*= UTF-8''%e2%82%ac%20rates
Here, the encoding defined in [RFC5987] is also used to encode the Here, the encoding defined in [RFC5987] is also used to encode the
non-ISO-8859-1 character. non-ISO-8859-1 character.
Same as above, but adding the "filename" parameter for compatibility Same as above, but adding the "filename" parameter for compatibility
with user agents not implementing RFC 5987: with user agents not implementing RFC 5987:
Content-Disposition: attachment; Content-Disposition: attachment;
filename="EURO rates"; filename="EURO rates";
filename*=utf-8''%e2%82%ac%20rates filename*=utf-8''%e2%82%ac%20rates
Note: as of September 2010, those user agents that do not support the Note: those user agents that do not support the RFC 5987 encoding
RFC 5987 encoding ignore "filename*" when it occurs after "filename". ignore "filename*" when it occurs after "filename".
Unfortunately, some user agents that do support RFC 5987 do pick the
"filename" rather than the "filename*" parameter when it occurs
first; it is expected that this situation is going to improve soon.
5. Internationalization Considerations 6. Internationalization Considerations
The "filename*" parameter (Section 3.3), using the encoding defined The "filename*" parameter (Section 4.3), using the encoding defined
in [RFC5987], allows the server to transmit characters outside the in [RFC5987], allows the server to transmit characters outside the
ISO-8859-1 character set, and also to optionally specify the language ISO-8859-1 character set, and also to optionally specify the language
in use. in use.
Future parameters might also require internationalization, in which Future parameters might also require internationalization, in which
case the same encoding can be used. case the same encoding can be used.
6. Security Considerations 7. Security Considerations
Using server-supplied information for constructing local filenames Using server-supplied information for constructing local filenames
introduces many risks. These are summarized in Section 3.3. introduces many risks. These are summarized in Section 4.3.
Furthermore, implementers also ought to be aware of the Security Furthermore, implementers also ought to be aware of the Security
Considerations applying to HTTP (see Section 15 of [RFC2616]), and Considerations applying to HTTP (see Section 15 of [RFC2616]), and
also the parameter encoding defined in [RFC5987] (see Section 5). also the parameter encoding defined in [RFC5987] (see Section 5).
7. IANA Considerations 8. IANA Considerations
7.1. Registry for Disposition Values and Parameter 8.1. Registry for Disposition Values and Parameter
This specification does not introduce any changes to the registration This specification does not introduce any changes to the registration
procedures for disposition values and parameters that are defined in procedures for disposition values and parameters that are defined in
Section 9 of [RFC2183]. Section 9 of [RFC2183].
7.2. Header Field Registration 8.2. Header Field Registration
This document updates the definition of the Content-Disposition HTTP This document updates the definition of the Content-Disposition HTTP
header field in the permanent HTTP header field registry (see header field in the permanent HTTP header field registry (see
[RFC3864]). [RFC3864]).
Header field name: Content-Disposition Header field name: Content-Disposition
Applicable protocol: http Applicable protocol: http
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document: this specification (Section 3) Specification document: this specification (Section 4)
8. Acknowledgements 9. Acknowledgements
Thanks to Rolf Eike Beer, Bjoern Hoehrmann, Alfred Hoenes, Roar Thanks to Adam Barth, Rolf Eike Beer, Bjoern Hoehrmann, Alfred
Lauritzsen, Henrik Nordstrom, and Mark Nottingham for their valuable Hoenes, Roar Lauritzsen, Henrik Nordstrom, and Mark Nottingham for
feedback. their valuable feedback.
9. References 10. References
9.1. Normative References 10.1. Normative References
[ISO-8859-1] International Organization for Standardization, [ISO-8859-1] International Organization for Standardization,
"Information technology -- 8-bit single-byte coded "Information technology -- 8-bit single-byte coded
graphic character sets -- Part 1: Latin alphabet No. graphic character sets -- Part 1: Latin alphabet No.
1", ISO/IEC 8859-1:1998, 1998. 1", ISO/IEC 8859-1:1998, 1998.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC5987] Reschke, J., "Character Set and Language Encoding for [RFC5987] Reschke, J., "Character Set and Language Encoding for
Hypertext Transfer Protocol (HTTP) Header Field Hypertext Transfer Protocol (HTTP) Header Field
Parameters", RFC 5987, August 2010. Parameters", RFC 5987, August 2010.
9.2. Informative References 10.2. Informative References
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types", Mail Extensions (MIME) Part Two: Media Types",
RFC 2046, November 1996. RFC 2046, November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
Extensions) Part Three: Message Header Extensions for Extensions) Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996. Non-ASCII Text", RFC 2047, November 1996.
[RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating
Presentation Information in Internet Messages: The Presentation Information in Internet Messages: The
Content-Disposition Header Field", RFC 2183, Content-Disposition Header Field", RFC 2183,
August 1997. August 1997.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and
Encoded Word Extensions: Character Sets, Languages, and Encoded Word Extensions: Character Sets, Languages, and
Continuations", RFC 2231, November 1997. Continuations", RFC 2231, November 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC2388] Masinter, L., "Returning Values from Forms: multipart/
10646", STD 63, RFC 3629, November 2003. form-data", RFC 2388, August 1998.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004. RFC 3864, September 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax", "Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005. STD 66, RFC 3986, January 2005.
Appendix A. Changes from the RFC 2616 Definition Appendix A. Changes from the RFC 2616 Definition
Compared to Section 19.5.1 of [RFC2616], the following normative Compared to Section 19.5.1 of [RFC2616], the following normative
changes reflecting actual implementations have been made: changes reflecting actual implementations have been made:
o According to RFC 2616, the disposition type "attachment" only o According to RFC 2616, the disposition type "attachment" only
applies to content of type "application/octet-stream". This applies to content of type "application/octet-stream". This
restriction has been removed, because user agents in practice do restriction has been removed, because recipients in practice do
not check the content type, and it also discourages properly not check the content type, and it also discourages properly
declaring the media type. declaring the media type.
o RFC 2616 only allows "quoted-string" for the filename parameter. o RFC 2616 only allows "quoted-string" for the filename parameter.
This would be an exceptional parameter syntax, and also doesn't This would be an exceptional parameter syntax, and also doesn't
reflect actual use. reflect actual use.
o The definition for the disposition type "inline" ([RFC2183], o The definition for the disposition type "inline" ([RFC2183],
Section 2.1) has been re-added with a suggestion for its Section 2.1) has been re-added with a suggestion for its
processing. processing.
o This specification requires support for the extended parameter o This specification requires support for the extended parameter
encoding defined in [RFC5987]. encoding defined in [RFC5987].
Appendix B. Differences compared to RFC 2183 Appendix B. Differences compared to RFC 2183
Section 2 of [RFC2183] defines several additional disposition Section 2 of [RFC2183] defines several additional disposition
parameters: "creation-date", "modification-date", "quoted-date-time", parameters: "creation-date", "modification-date", "quoted-date-time",
and "size". These do not appear to be implemented by any user agent, and "size". The majority of user agents does not implement these,
thus have been omitted from this specification. thus they have been omitted from this specification.
Appendix C. Alternative Approaches to Internationalization Appendix C. Alternative Approaches to Internationalization
By default, HTTP header field parameters cannot carry characters By default, HTTP header field parameters cannot carry characters
outside the ISO-8859-1 ([ISO-8859-1]) character encoding (see outside the ISO-8859-1 ([ISO-8859-1]) character encoding (see
[RFC2616], Section 2.2). For the "filename" parameter, this of [RFC2616], Section 2.2). For the "filename" parameter, this of
course is an unacceptable restriction. course is an unacceptable restriction.
Unfortunately, user agent implementers have not managed to come up Unfortunately, user agent implementers have not managed to come up
with an interoperable approach, although the IETF Standards Track with an interoperable approach, although the IETF Standards Track
skipping to change at page 11, line 26 skipping to change at page 12, line 16
Type or Content-Disposition field, or in any structured field body Type or Content-Disposition field, or in any structured field body
except within a 'comment' or 'phrase'. except within a 'comment' or 'phrase'.
In practice, some user agents implement the encoding, some do not In practice, some user agents implement the encoding, some do not
(exposing the encoded string to the user), and some get confused by (exposing the encoded string to the user), and some get confused by
it. it.
C.2. Percent Encoding C.2. Percent Encoding
Some user agents accept percent encoded ([RFC3986], Section 2.1) Some user agents accept percent encoded ([RFC3986], Section 2.1)
sequences of characters encoded using the UTF-8 ([RFC3629]) character sequences of characters. The character encoding being used for
encoding. decoding depends on various factors, including the encoding of the
referring page, the user agent's locale, its configuration, and also
the actual value of the parameter.
In practice, this is hard to use because those user agents that do In practice, this is hard to use because those user agents that do
not support it will display the escaped character sequence to the not support it will display the escaped character sequence to the
user. user. For those user agents that do implement this it is difficult
to predict what character encoding they actually expect.
Furthermore, the first user agent to implement this did choose the
encoding based on local settings; thus making it very hard to use in
multi-lingual environments.
C.3. Encoding Sniffing C.3. Encoding Sniffing
Some user agents inspect the value (which defaults to ISO-8859-1) and Some user agents inspect the value (which defaults to ISO-8859-1 for
switch to UTF-8 when it seems to be more likely to be the correct the quoted-string form) and switch to UTF-8 when it seems to be more
interpretation. likely to be the correct interpretation.
As with the approaches above, this is not interoperable and As with the approaches above, this is not interoperable and
furthermore risks misinterpreting the actual value. furthermore risks misinterpreting the actual value.
C.4. Implementations (to be removed by RFC Editor before publication) C.4. Implementations (to be removed by RFC Editor before publication)
Unfortunately, as of September 2010, neither the encoding defined in Unfortunately, as of February 2011, neither the encoding defined in
RFCs 2231 and 5987, nor any of the alternate approaches discussed RFCs 2231 and 5987, nor any of the alternate approaches discussed
above was implemented interoperably. Thus, this specification above was implemented interoperably. Thus, this specification
recommends the approach defined in RFC 5987, which at least has the recommends the approach defined in RFC 5987, which at least has the
advantage of actually being specified properly. advantage of actually being specified properly.
The table below shows the implementation support for the various The table below shows the implementation support for the various
approaches: approaches:
+---------------+------------+--------+--------------+--------------+ +---------------+------------+--------+--------------+--------------+
| User Agent | RFC | RFC | Percent | Encoding | | User Agent | RFC | RFC | Percent | Encoding |
| | 2231/5987 | 2047 | Encoding | Sniffing | | | 2231/5987 | 2047 | Encoding | Sniffing |
+---------------+------------+--------+--------------+--------------+ +---------------+------------+--------+--------------+--------------+
| Chrome | no | yes | yes | yes | | Chrome | yes | yes | yes | yes |
| Firefox | yes (*) | yes | no | yes | | Firefox | yes (*) | yes | no | yes |
| Internet | no | no | yes | no | | Internet | yes (**) | no | yes | no |
| Explorer | | | | | | Explorer | | | | |
| Konqueror | yes | no | no | no | | Konqueror | yes | no | no | no |
| Opera | yes (*) | no | no | no | | Opera | yes | no | no | no |
| Safari | no | no | no | yes | | Safari | no | no | no | yes |
+---------------+------------+--------+--------------+--------------+ +---------------+------------+--------+--------------+--------------+
(*) Does not implement the fallback behavior to "filename" described (*) Does not implement the fallback behavior to "filename" described
in Section 3.3. in Section 4.3; a fix is planned for Firefox 5.
Appendix D. Change Log (to be removed by RFC Editor before publication) (**) Starting with IE9RC, but only implements UTF-8.
D.1. Since draft-reschke-rfc2183-in-http-00 Appendix D. Advice on Generating Content-Disposition Header Fields
To successfully interoperate with existing and future user agents,
senders of the Content-Disposition header field are advised to:
o Include a "filename" parameter when US-ASCII is sufficiently
expressive.
o Use the 'token' form of the filename parameter only when it does
not contain disallowed characters (e.g., spaces); in such cases,
the quoted-string form should be used.
o Avoid including the percent character followed by two hexadecimal
characters (e.g., %A9) in the filename parameter, since some
existing implementations consider it to be an escape character,
while others will pass it through unchanged.
o Avoid including the "\" character in the quoted-string form of the
filename parameter, as escaping is not implemented by some user
agents, and can be considered as an illegal path character.
o Avoid using non-ASCII characters in the filename parameter.
Although most existing implementations will decode them as ISO-
8859-1, some will apply heuristics to detect UTF-8, and thus might
fail on certain names.
o Include a "filename*" parameter where the desired filename cannot
be expressed faithfully using the "filename" form. Note that
legacy user agents will not process this, and will fall back to
using the "filename" parameter's content.
o When a "filename*" parameter is sent, to also generate a
"filename" parameter as a fallback for user agents that do not
support the "filename*" form, if possible. This can be done by
substituting characters with US-ASCII sequences (e.g., Unicode
character point U+00E4 (LATIN SMALL LETTER A WITH DIARESIS) by
"ae"). Note that this may not be possible in some locales.
o When a "filename" parameter is included as a fallback (as per
above), "filename" should occur first, due to parsing problems in
some existing implementations. [[fallbackbug: Firefox is known to
pick the wrong parameter; a bug fix is scheduled for Firefox 5.
--jre]]
o Use UTF-8 as the encoding of the "filename*" parameter, when
present, because at least one existing implementation only
implements that encoding.
Note that this advice is based upon UA behaviour at the time of
writing, and might be superseded.
<http://purl.org/NET/http/content-disposition-tests> provides an
overview of current levels of support in various implementations.
Appendix E. Change Log (to be removed by RFC Editor before publication)
Note: the issues names in the change log entries for
draft-reschke-rfc2183-in-http refer to <http://greenbytes.de/tech/
webdav/draft-reschke-rfc2183-in-http-issues.html>.
E.1. Since draft-reschke-rfc2183-in-http-00
Adjust terminology ("header" -> "header field"). Update rfc2231-in- Adjust terminology ("header" -> "header field"). Update rfc2231-in-
http reference. http reference.
D.2. Since draft-reschke-rfc2183-in-http-01 E.2. Since draft-reschke-rfc2183-in-http-01
Update rfc2231-in-http reference. Actually define the "filename" Update rfc2231-in-http reference. Actually define the "filename"
parameter. Add internationalization considerations. Add examples parameter. Add internationalization considerations. Add examples
using the RFC 5987 encoding. Add overview over other approaches, using the RFC 5987 encoding. Add overview over other approaches,
plus a table reporting implementation status. Add and resolve issue plus a table reporting implementation status. Add and resolve issue
"nodep2183". Add issues "asciivsiso", "deplboth", "quoted", and "nodep2183". Add issues "asciivsiso", "deplboth", "quoted", and
"registry". "registry".
D.3. Since draft-reschke-rfc2183-in-http-02 E.3. Since draft-reschke-rfc2183-in-http-02
Add and close issue "docfallback". Close issues "asciivsiso", Add and close issue "docfallback". Close issues "asciivsiso",
"deplboth", "quoted", and "registry". "deplboth", "quoted", and "registry".
D.4. Since draft-reschke-rfc2183-in-http-03 E.4. Since draft-reschke-rfc2183-in-http-03
Updated to be a Working Draft of the IETF HTTPbis Working Group. Updated to be a Working Draft of the IETF HTTPbis Working Group.
D.5. Since draft-ietf-httpbis-content-disp-00 E.5. Since draft-ietf-httpbis-content-disp-00
Closed issues: Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/242>: "handling of o <http://tools.ietf.org/wg/httpbis/trac/ticket/242>: "handling of
unknown disposition types" unknown disposition types"
Slightly updated the notes about the proposed fallback behavior. Slightly updated the notes about the proposed fallback behavior.
D.6. Since draft-ietf-httpbis-content-disp-01 E.6. Since draft-ietf-httpbis-content-disp-01
None yet. Various editorial improvements.
E.7. Since draft-ietf-httpbis-content-disp-02
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/244>: "state that
repeating parameters are invalid"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/245>: "warn about
%xx in filenames being misinterpreted"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/246>: "mention
control chars when talking about postprecessing the filename
parameter"
Update Appendix C.4; Opera 10.63 RC implements the recommended
fallback behavior.
E.8. Since draft-ietf-httpbis-content-disp-03
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/252>:
"'modification-date' *is* implemented in Konq 4.5"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/253>: "clarify what
LWS means for the Content-Disp grammar"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/258>: "Avoid passive
voice in message requirements"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/263>: "text about
historical percent-decoding unclear"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/264>: "add
explanation of language tagging"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/265>: "Clarify that
C-D spec does not apply to multipart upload"
E.9. Since draft-ietf-httpbis-content-disp-04
Updated implementation information (Chrome 9 implements RFC 5987, IE
9 RC implements it for UTF-8 only).
Clarify who requirements are on, add a section discussing conformance
and handling of invalid field values in general.
Closed issues:
o <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/243>: "avoid
stating ISO-8859-1 default for header param" (the default is still
mentioned, but it was clarified what it applies to).
o <http://tools.ietf.org/wg/httpbis/trac/ticket/272>: "Path
Separator Characters"
E.10. Since draft-ietf-httpbis-content-disp-05
Editorial changes: Fixed two typos where the new Conformance section
said "Content-Location" instead of "Content-Disposition". Cleaned up
terminology ("user agent", "recipient", "sender", "message body",
...). Stated what the escape character for quoted-string is.
Explained a use case for "inline" disposition type. Updated
implementation notes with respect to the fallback behavior.
Added appendix "Advice on Generating Content-Disposition Header
Fields".
Index Index
C C
Content-Disposition header 4 Content-Disposition header field 5
H H
Headers Header Fields
Content-Disposition 4 Content-Disposition 5
Author's Address Author's Address
Julian F. Reschke Julian F. Reschke
greenbytes GmbH greenbytes GmbH
Hafenweg 16 Hafenweg 16
Muenster, NW 48155 Muenster, NW 48155
Germany Germany
EMail: julian.reschke@greenbytes.de EMail: julian.reschke@greenbytes.de
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