draft-ietf-httpbis-content-disp-06.txt   draft-ietf-httpbis-content-disp-latest.txt 
HTTPbis Working Group J. Reschke HTTPbis Working Group J. Reschke
Internet-Draft greenbytes Internet-Draft greenbytes
Updates: 2616 (if approved) February 26, 2011 Updates: 2616 (if approved) June 2011
Intended status: Standards Track Intended status: Standards Track
Expires: August 30, 2011 Expires: December 3, 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-06 draft-ietf-httpbis-content-disp-latest
Abstract Abstract
RFC 2616 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)
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://trac.tools.ietf.org/wg/httpbis/trac/ticket/123>.
Discussion of this draft should take place on the HTTPBIS working
group mailing list (ietf-http-wg@w3.org). The current issues list is
at <http://trac.tools.ietf.org/wg/httpbis/trac/
query?component=content-disp> and related documents (including fancy
diffs) can be found at <http://tools.ietf.org/wg/httpbis/>.
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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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 August 30, 2011.
This Internet-Draft will expire on December 3, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Conformance and Error Handling . . . . . . . . . . . . . . . . 4 3. Conformance and Error Handling . . . . . . . . . . . . . . . . 3
4. Header Field Definition . . . . . . . . . . . . . . . . . . . 5 4. Header Field Definition . . . . . . . . . . . . . . . . . . . 4
4.1. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Disposition Type . . . . . . . . . . . . . . . . . . . . . 6 4.2. Disposition Type . . . . . . . . . . . . . . . . . . . . . 5
4.3. Disposition Parameter: 'Filename' . . . . . . . . . . . . 6 4.3. Disposition Parameter: 'Filename' . . . . . . . . . . . . 5
4.4. Disposition Parameter: Extensions . . . . . . . . . . . . 7 4.4. Disposition Parameter: Extensions . . . . . . . . . . . . 6
4.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 7 4.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 6
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Internationalization Considerations . . . . . . . . . . . . . 8 6. Internationalization Considerations . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. Registry for Disposition Values and Parameter . . . . . . 9 8.1. Registry for Disposition Values and Parameters . . . . . . 8
8.2. Header Field Registration . . . . . . . . . . . . . . . . 9 8.2. Header Field Registration . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . . 10 10.2. Informative References . . . . . . . . . . . . . . . . . . 9
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 . . . . . . . . . . 11 Appendix B. Differences Compared to RFC 2183 . . . . . . . . . . 10
Appendix C. Alternative Approaches to Internationalization . . . 11 Appendix C. Alternative Approaches to Internationalization . . . 10
C.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 11 C.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 11
C.2. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 12 C.2. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 11
C.3. Encoding Sniffing . . . . . . . . . . . . . . . . . . . . 12 C.3. Encoding Sniffing . . . . . . . . . . . . . . . . . . . . 11
C.4. Implementations (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . . . 12
Appendix D. Advice on Generating Content-Disposition Header Appendix D. Advice on Generating Content-Disposition Header
Fields . . . . . . . . . . . . . . . . . . . . . . . 13 Fields . . . . . . . . . . . . . . . . . . . . . . . 11
Appendix E. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 14
E.1. Since draft-reschke-rfc2183-in-http-00 . . . . . . . . . . 14
E.2. Since draft-reschke-rfc2183-in-http-01 . . . . . . . . . . 14
E.3. Since draft-reschke-rfc2183-in-http-02 . . . . . . . . . . 14
E.4. Since draft-reschke-rfc2183-in-http-03 . . . . . . . . . . 15
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
RFC 2616 defines the Content-Disposition response header field in RFC 2616 defines the Content-Disposition response header field
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 (UAs), it fully defines a profile
features defined in the Multipurpose Internet Mail Extensions (MIME) of the features defined in the Multipurpose Internet Mail Extensions
variant ([RFC2183]) of the header field, and also clarifies (MIME) variant ([RFC2183]) of the header field, and also clarifies
internationalization aspects. internationalization aspects.
Note: this document does not apply to Content-Disposition header Note: This document does not apply to Content-Disposition header
fields appearing in payload bodies transmitted over HTTP, such as fields appearing in payload bodies transmitted over HTTP, such as
when using the media type "multipart/form-data" ([RFC2388]). 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 (ABNF) notation defined in
2.1 of [RFC2616], including its rules for implied linear whitespace Section 2.1 of [RFC2616], including its rules for implied linear
(LWS). whitespace (LWS).
3. Conformance and Error Handling 3. Conformance and Error Handling
This specification defines conformance criteria for both senders This specification defines conformance criteria for both senders
(usually, HTTP origin servers) and recipients (usually, HTTP user (usually, HTTP origin servers) and recipients (usually, HTTP user
agents) of the Content-Disposition header field. An implementation agents) of the Content-Disposition header field. An implementation
is considered conformant if it complies with all of the requirements is considered conformant if it complies with all of the requirements
associated with its role. associated with its role.
This specification also defines certain forms of the header field- This specification also defines certain forms of the header field
value to be invalid, using both ABNF and prose requirements, but it value to be invalid, using both ABNF and prose requirements
does not define special handling of these invalid field-values. (Section 4), but it does not define special handling of these invalid
field values.
Senders MUST NOT generate Content-Disposition header fields that are Senders MUST NOT generate Content-Disposition header fields that are
invalid. invalid.
Recipients MAY take steps to recover a usable field-value from an Recipients MAY take steps to recover a usable field value from an
invalid header field, but SHOULD NOT reject the message outright, invalid header field, but SHOULD NOT reject the message outright,
unless this is explicitly desirable behaviour (e.g., the unless this is explicitly desirable behavior (e.g., the
implementation is a validator). As such, the default handling of implementation is a validator). As such, the default handling of
invalid fields is to ignore them. invalid fields is to ignore them.
4. Header Field Definition 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.
skipping to change at page 5, line 44 skipping to change at page 4, line 45
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> 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 ; 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>
Header field values with multiple instances of the same parameter Content-Disposition header field values with multiple instances of
name are invalid. the same parameter name are invalid.
Note that due to the rules for implied linear whitespace (Section 2.1 Note that due to the rules for implied linear whitespace (Section 2.1
of [RFC2616]), OPTIONAL whitespace can appear between words (token or of [RFC2616]), OPTIONAL whitespace can appear between words (token or
quoted-string) and separator characters. quoted-string) and separator characters.
Furthermore note that the format used for ext-value allows specifying Furthermore, note that the format used for ext-value allows
a natural language; this is of limited use for filenames and is specifying a natural language (e.g., "en"); this is of limited use
likely to be ignored by recipients. for filenames and is likely to be ignored by recipients.
4.2. Disposition Type 4.2. Disposition Type
If the disposition type matches "attachment" (case-insensitively), If the disposition type matches "attachment" (case-insensitively),
this indicates that the recipient 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. Therefore, the disposition type "inline" implies default processing. Therefore, the disposition type "inline"
skipping to change at page 6, line 52 skipping to change at page 5, line 52
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 5 "filename" parameter as fallback for legacy recipients (see Section 5
for an example). for an example).
It is essential that recipients 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, and thus be very careful in extracting the desired
information. In particular: information. In particular:
o When the value contains path separator characters ("\" or "/"), o Recipients MUST NOT be able to write into any location other than
recipients SHOULD ignore all but the last path segment. This one to which they are specifically entitled. To illustrate the
prevents unintentional overwriting of well-known file system problem, consider the consequences of being able to overwrite
locations (such as "/etc/passwd"). well-known system locations (such as "/etc/passwd"). One strategy
to achieve this is to never trust folder name information in the
filename parameter, for instance by stripping all but the last
path segment and only considering the actual filename (where 'path
segments' are the components of the field value delimited by the
path separator characters "\" and "/").
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 that make use of
that a file extension is used that is safe, optimally matching the file extensions to determine the media type MUST ensure that a
media type of the received payload. file extension is used that is safe, optimally matching the media
type of the received payload.
o Recipients are advised to strip or replace character sequences o Recipients SHOULD strip or replace character sequences that are
that are known to cause confusion both in user interfaces and in known to cause confusion both in user interfaces and in filenames,
filenames, such as control characters and leading and trailing such as control characters and leading and trailing whitespace.
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. Recipients SHOULD
ignore or substitute names like these.
Note: Many user agents do not properly handle the escape character Note: Many user agents do not properly handle the escape character
"\" when using the quoted-string form. Furthermore, some user "\" when using the quoted-string form. Furthermore, some user
agents erroneously try to perform unescaping of "percent" escapes agents erroneously try to perform unescaping of "percent" escapes
(see Appendix C.2), and thus might misinterpret filenames (see Appendix C.2), and thus might misinterpret filenames
containing the percent character followed by two hex digits. containing the percent character followed by two hex digits.
4.4. Disposition Parameter: Extensions 4.4. Disposition Parameter: Extensions
To enable future extensions, recipients SHOULD ignore unrecognized To enable future extensions, recipients SHOULD ignore unrecognized
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4.5. Extensibility 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.
5. Examples 5. Examples
Direct UA to show "save as" dialog, with a filename of Direct the 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 the UA to behave as if the Content-Disposition header field
present, but to remember the filename "an example.html" for a wasn't present, but to remember the filename "an example.html" for a
subsequent save operation: subsequent save operation:
Content-Disposition: INLINE; FILENAME= "an example.html" Content-Disposition: INLINE; FILENAME= "an example.html"
Note: this uses the quoted-string form so that the space character Note: This uses the quoted-string form so that the space character
can be included. can be included.
Direct UA to show "save as" dialog, with a filename containing the Direct the UA to show "save as" dialog, with a filename containing
Unicode character U+20AC (EURO SIGN): the 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 This example is the same as the one above, but adding the "filename"
with user agents not implementing RFC 5987: parameter for compatibility 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: those user agents that do not support the RFC 5987 encoding Note: Those user agents that do not support the RFC 5987 encoding
ignore "filename*" when it occurs after "filename". ignore "filename*" when it occurs after "filename".
6. Internationalization Considerations 6. Internationalization Considerations
The "filename*" parameter (Section 4.3), 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.
7. 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 4.3. introduces many risks. These are summarized in Section 4.3.
Furthermore, implementers also ought to be aware of the Security Furthermore, implementers 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).
8. IANA Considerations 8. IANA Considerations
8.1. Registry for Disposition Values and Parameter 8.1. Registry for Disposition Values and Parameters
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].
8.2. 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]).
skipping to change at page 9, line 38 skipping to change at page 8, line 38
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 4) Specification document: this specification (Section 4)
Related information: none
9. Acknowledgements 9. Acknowledgements
Thanks to Adam Barth, Rolf Eike Beer, Bjoern Hoehrmann, Alfred Thanks to Adam Barth, Rolf Eike Beer, Stewart Bryant, Bjoern
Hoenes, Roar Lauritzsen, Henrik Nordstrom, and Mark Nottingham for Hoehrmann, Alfred Hoenes, Roar Lauritzsen, Alexey Melnikov, Henrik
their valuable feedback. Nordstrom, and Mark Nottingham for their valuable feedback.
10. References 10. References
10.1. 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
1", ISO/IEC 8859-1:1998, 1998. No. 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
skipping to change at page 10, line 26 skipping to change at page 9, line 27
10.2. 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, Ed.,
Presentation Information in Internet Messages: The "Communicating Presentation Information in Internet
Content-Disposition Header Field", RFC 2183, Messages: The Content-Disposition Header Field",
August 1997. RFC 2183, 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.
[RFC2388] Masinter, L., "Returning Values from Forms: multipart/ [RFC2388] Masinter, L., "Returning Values from Forms: multipart/
form-data", RFC 2388, August 1998. 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.
[US-ASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
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 recipients 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.
skipping to change at page 11, line 19 skipping to change at page 10, line 27
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". The majority of user agents does not implement these, and "size". The majority of user agents do not implement these;
thus they 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
specifies exactly one solution ([RFC2231], clarified and profiled for specifies exactly one solution ([RFC2231], clarified and profiled for
HTTP in [RFC5987]). HTTP in [RFC5987]).
For completeness, the sections below describe the various approaches For completeness, the sections below describe the various approaches
that have been tried, and explains how they are inferior to the RFC that have been tried, and explain how they are inferior to the
5987 encoding used in this specification. RFC 5987 encoding used in this specification.
C.1. RFC 2047 Encoding C.1. RFC 2047 Encoding
RFC 2047 defines an encoding mechanism for header fields, but this RFC 2047 defines an encoding mechanism for header fields, but this
encoding is not supposed to be used for header field parameters - see encoding is not supposed to be used for header field parameters --
Section 5 of [RFC2047]: see Section 5 of [RFC2047]:
An 'encoded-word' MUST NOT appear within a 'quoted-string'. An 'encoded-word' MUST NOT appear within a 'quoted-string'.
... ...
An 'encoded-word' MUST NOT be used in parameter of a MIME Content- An 'encoded-word' MUST NOT be used in parameter of a MIME Content-
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. The character encoding being used for sequences of characters. The character encoding being used for
decoding depends on various factors, including the encoding of the decoding depends on various factors, including the encoding of the
referring page, the user agent's locale, its configuration, and also referring page, the user agent's locale, its configuration, and also
the actual value of the parameter. 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. For those user agents that do implement this it is difficult user. For those user agents that do implement this, it is difficult
to predict what character encoding they actually expect. to predict what character encoding they actually expect.
C.3. Encoding Sniffing C.3. Encoding Sniffing
Some user agents inspect the value (which defaults to ISO-8859-1 for Some user agents inspect the value (which defaults to ISO-8859-1 for
the quoted-string form) and switch to UTF-8 when it seems to be more the quoted-string form) and switch to UTF-8 when it seems to be more
likely to be the correct 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)
Unfortunately, as of February 2011, neither the encoding defined in
RFCs 2231 and 5987, nor any of the alternate approaches discussed
above was implemented interoperably. Thus, this specification
recommends the approach defined in RFC 5987, which at least has the
advantage of actually being specified properly.
The table below shows the implementation support for the various
approaches:
+---------------+------------+--------+--------------+--------------+
| User Agent | RFC | RFC | Percent | Encoding |
| | 2231/5987 | 2047 | Encoding | Sniffing |
+---------------+------------+--------+--------------+--------------+
| Chrome | yes | yes | yes | yes |
| Firefox | yes (*) | yes | no | yes |
| Internet | yes (**) | no | yes | no |
| Explorer | | | | |
| Konqueror | yes | no | no | no |
| Opera | yes | no | no | no |
| Safari | no | no | no | yes |
+---------------+------------+--------+--------------+--------------+
(*) Does not implement the fallback behavior to "filename" described
in Section 4.3; a fix is planned for Firefox 5.
(**) Starting with IE9RC, but only implements UTF-8.
Appendix D. Advice on Generating Content-Disposition Header Fields Appendix D. Advice on Generating Content-Disposition Header Fields
To successfully interoperate with existing and future user agents, To successfully interoperate with existing and future user agents,
senders of the Content-Disposition header field are advised to: senders of the Content-Disposition header field are advised to:
o Include a "filename" parameter when US-ASCII is sufficiently o Include a "filename" parameter when US-ASCII ([US-ASCII]) is
expressive. sufficiently expressive.
o Use the 'token' form of the filename parameter only when it does o Use the 'token' form of the filename parameter only when it does
not contain disallowed characters (e.g., spaces); in such cases, not contain disallowed characters (e.g., spaces); in such cases,
the quoted-string form should be used. the quoted-string form should be used.
o Avoid including the percent character followed by two hexadecimal o Avoid including the percent character followed by two hexadecimal
characters (e.g., %A9) in the filename parameter, since some characters (e.g., %A9) in the filename parameter, since some
existing implementations consider it to be an escape character, existing implementations consider it to be an escape character,
while others will pass it through unchanged. while others will pass it through unchanged.
o Avoid including the "\" character in the quoted-string form of the o Avoid including the "\" character in the quoted-string form of the
filename parameter, as escaping is not implemented by some user filename parameter, as escaping is not implemented by some user
agents, and can be considered as an illegal path character. agents, and "\" can be considered an illegal path character.
o Avoid using non-ASCII characters in the filename parameter. o Avoid using non-ASCII characters in the filename parameter.
Although most existing implementations will decode them as ISO- Although most existing implementations will decode them as
8859-1, some will apply heuristics to detect UTF-8, and thus might ISO-8859-1, some will apply heuristics to detect UTF-8, and thus
fail on certain names. might fail on certain names.
o Include a "filename*" parameter where the desired filename cannot o Include a "filename*" parameter where the desired filename cannot
be expressed faithfully using the "filename" form. Note that be expressed faithfully using the "filename" form. Note that
legacy user agents will not process this, and will fall back to legacy user agents will not process this, and will fall back to
using the "filename" parameter's content. using the "filename" parameter's content.
o When a "filename*" parameter is sent, to also generate a o When a "filename*" parameter is sent, to also generate a
"filename" parameter as a fallback for user agents that do not "filename" parameter as a fallback for user agents that do not
support the "filename*" form, if possible. This can be done by support the "filename*" form, if possible. This can be done by
substituting characters with US-ASCII sequences (e.g., Unicode substituting characters with US-ASCII sequences (e.g., Unicode
character point U+00E4 (LATIN SMALL LETTER A WITH DIARESIS) by character point U+00E4 (LATIN SMALL LETTER A WITH DIARESIS) by
"ae"). Note that this may not be possible in some locales. "ae"). Note that this may not be possible in some locales.
o When a "filename" parameter is included as a fallback (as per o When a "filename" parameter is included as a fallback (as per
above), "filename" should occur first, due to parsing problems in above), "filename" should occur first, due to parsing problems in
some existing implementations. [[fallbackbug: Firefox is known to some existing implementations.
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 o Use UTF-8 as the encoding of the "filename*" parameter, when
present, because at least one existing implementation only present, because at least one existing implementation only
implements that encoding. implements that encoding.
Note that this advice is based upon UA behaviour at the time of Note that this advice is based upon UA behavior at the time of
writing, and might be superseded. writing, and might be superseded. At the time of publication of this
<http://purl.org/NET/http/content-disposition-tests> provides an document, <http://purl.org/NET/http/content-disposition-tests>
overview of current levels of support in various implementations. 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-
http reference.
E.2. Since draft-reschke-rfc2183-in-http-01
Update rfc2231-in-http reference. Actually define the "filename"
parameter. Add internationalization considerations. Add examples
using the RFC 5987 encoding. Add overview over other approaches,
plus a table reporting implementation status. Add and resolve issue
"nodep2183". Add issues "asciivsiso", "deplboth", "quoted", and
"registry".
E.3. Since draft-reschke-rfc2183-in-http-02
Add and close issue "docfallback". Close issues "asciivsiso",
"deplboth", "quoted", and "registry".
E.4. Since draft-reschke-rfc2183-in-http-03
Updated to be a Working Draft of the IETF HTTPbis Working Group.
E.5. Since draft-ietf-httpbis-content-disp-00
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/242>: "handling of
unknown disposition types"
Slightly updated the notes about the proposed fallback behavior.
E.6. Since draft-ietf-httpbis-content-disp-01
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
C
Content-Disposition header field 5
H
Header Fields
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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