HTTP/1.1, part 4: Conditional RequestsDay Software23 Corporate Plaza DR, Suite 280Newport BeachCA92660USA+1-949-706-5300+1-949-706-5305fielding@gbiv.comhttp://roy.gbiv.com/One Laptop per Child21 Oak Knoll RoadCarlisleMA01741USAjg@laptop.orghttp://www.laptop.org/Hewlett-Packard CompanyHP Labs, Large Scale Systems Group1501 Page Mill Road, MS 1177Palo AltoCA94304USAJeffMogul@acm.orgMicrosoft Corporation1 Microsoft WayRedmondWA98052USAhenrikn@microsoft.comAdobe Systems, Incorporated345 Park AveSan JoseCA95110USALMM@acm.orghttp://larry.masinter.net/Microsoft Corporation1 Microsoft WayRedmondWA98052paulle@microsoft.comWorld Wide Web ConsortiumMIT Computer Science and Artificial Intelligence LaboratoryThe Stata Center, Building 3232 Vassar StreetCambridgeMA02139USAtimbl@w3.orghttp://www.w3.org/People/Berners-Lee/World Wide Web ConsortiumW3C / ERCIM2004, rte des LuciolesSophia-AntipolisAM06902Franceylafon@w3.orghttp://www.raubacapeu.net/people/yves/greenbytes GmbHHafenweg 16MuensterNW48155Germany+49 251 2807760+49 251 2807761julian.reschke@greenbytes.dehttp://greenbytes.de/tech/webdav/HTTPbis Working Group
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World Wide Web global information
initiative since 1990. This document is Part 4 of the seven-part specification
that defines the protocol referred to as "HTTP/1.1" and, taken together,
obsoletes RFC 2616. Part 4 defines request header fields for
indicating conditional requests and the rules for constructing responses
to those requests.
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
and related documents (including fancy diffs) can be found at
.
The changes in this draft are summarized in .
This document defines HTTP/1.1 response metadata for indicating potential
changes to payload content, including modification time stamps and opaque
entity-tags, and the HTTP conditional request mechanisms that allow
preconditions to be placed on a request method. Conditional GET requests
allow for efficient cache updates. Other conditional request methods are
used to protect against overwriting or misunderstanding the state of a
resource that has been changed unbeknownst to the requesting client.
This document is currently disorganized in order to minimize the changes
between drafts and enable reviewers to see the smaller errata changes.
The next draft will reorganize the sections to better reflect the content.
In particular, the sections on resource metadata will be discussed first
and then followed by each conditional request-header, concluding with a
definition of precedence and the expectation of ordering strong validator
checks before weak validator checks. It is likely that more content from
will migrate to this part, where appropriate.
The current mess reflects how widely dispersed these topics and associated
requirements had become in .
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 .
An implementation is not compliant if it fails to satisfy one or more
of the MUST or REQUIRED level requirements for the protocols it
implements. An implementation that satisfies all the MUST or REQUIRED
level and all the SHOULD level requirements for its protocols is said
to be "unconditionally compliant"; one that satisfies all the MUST
level requirements but not all the SHOULD level requirements for its
protocols is said to be "conditionally compliant."
This specification uses the ABNF syntax defined in Section 1.2 of (which
extends the syntax defined in with a list rule).
shows the collected ABNF, with the list
rule expanded.
The following core rules are included by
reference, as defined in , Appendix B.1:
ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
OCTET (any 8-bit sequence of data), SP (space),
VCHAR (any visible USASCII character),
and WSP (whitespace).
The core rules below are defined in Section 1.2.2 of :
OWS =
]]>
The ABNF rules below are defined in other parts:
]]>
Entity tags are used for comparing two or more entities from the same
requested resource. HTTP/1.1 uses entity tags in the ETag (),
If-Match (), If-None-Match (), and
If-Range (Section 5.3 of ) header fields. The definition of how they
are used and compared as cache validators is in . An
entity tag consists of an opaque quoted string, possibly prefixed by
a weakness indicator.
A "strong entity tag" MAY be shared by two entities of a resource
only if they are equivalent by octet equality.
A "weak entity tag," indicated by the "W/" prefix, MAY be shared by
two entities of a resource only if the entities are equivalent and
could be substituted for each other with no significant change in
semantics. A weak entity tag can only be used for weak comparison.
An entity tag MUST be unique across all versions of all entities
associated with a particular resource. A given entity tag value MAY
be used for entities obtained by requests on different URIs. The use
of the same entity tag value in conjunction with entities obtained by
requests on different URIs does not imply the equivalence of those
entities.
If the client has performed a conditional GET request and access is
allowed, but the document has not been modified, the server SHOULD
respond with this status code. The 304 response MUST NOT contain a
message-body, and thus is always terminated by the first empty line
after the header fields.
The response MUST include the following header fields:
Date, unless its omission is required by Section 8.3.1 of .
If a clockless origin server obeys these rules, and proxies and
clients add their own Date to any response received without one (as
already specified by Section 8.3 of , caches will operate
correctly.ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request.Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same
variant.
If the conditional GET used a strong cache validator (see ),
the response SHOULD NOT include other entity-headers.
Otherwise (i.e., the conditional GET used a weak validator), the
response MUST NOT include other entity-headers; this prevents
inconsistencies between cached entity-bodies and updated headers.
If a 304 response indicates an entity not currently cached, then the
cache MUST disregard the response and repeat the request without the
conditional.
If a cache uses a received 304 response to update a cache entry, the
cache MUST update the entry to reflect any new field values given in
the response.
The precondition given in one or more of the request-header fields
evaluated to false when it was tested on the server. This response
code allows the client to place preconditions on the current resource
metainformation (header field data) and thus prevent the requested
method from being applied to a resource other than the one intended.
Since both origin servers and caches will compare two validators to
decide if they represent the same or different entities, one normally
would expect that if the entity (the entity-body or any entity-headers)
changes in any way, then the associated validator would
change as well. If this is true, then we call this validator a
"strong validator."
However, there might be cases when a server prefers to change the
validator only on semantically significant changes, and not when
insignificant aspects of the entity change. A validator that does not
always change when the resource changes is a "weak validator."
Entity tags are normally "strong validators," but the protocol
provides a mechanism to tag an entity tag as "weak." One can think of
a strong validator as one that changes whenever the bits of an entity
changes, while a weak value changes whenever the meaning of an entity
changes. Alternatively, one can think of a strong validator as part
of an identifier for a specific entity, while a weak validator is
part of an identifier for a set of semantically equivalent entities.
Note: One example of a strong validator is an integer that is
incremented in stable storage every time an entity is changed.
An entity's modification time, if represented with one-second
resolution, could be a weak validator, since it is possible that
the resource might be modified twice during a single second.
Support for weak validators is optional. However, weak validators
allow for more efficient caching of equivalent objects; for
example, a hit counter on a site is probably good enough if it is
updated every few days or weeks, and any value during that period
is likely "good enough" to be equivalent.
A "use" of a validator is either when a client generates a request
and includes the validator in a validating header field, or when a
server compares two validators.
Strong validators are usable in any context. Weak validators are only
usable in contexts that do not depend on exact equality of an entity.
For example, either kind is usable for a conditional GET of a full
entity. However, only a strong validator is usable for a sub-range
retrieval, since otherwise the client might end up with an internally
inconsistent entity.
Clients MUST NOT use weak validators in range requests ().
The only function that HTTP/1.1 defines on validators is
comparison. There are two validator comparison functions, depending
on whether the comparison context allows the use of weak validators
or not:
The strong comparison function: in order to be considered equal,
both opaque-tags MUST be identical character-by-character, and both
MUST NOT be weak.The weak comparison function: in order to be considered equal, both
opaque-tags MUST be identical character-by-character.
The example below shows the results for a set of entity tag pairs,
and both the weak and strong comparison function results:
ETag 1ETag 2Strong ComparisonWeak ComparisonW/"1"W/"1"no matchmatchW/"1"W/"2"no matchno matchW/"1""1"no matchmatch"1""1"matchmatch
An entity tag is strong unless it is explicitly tagged as weak.
gives the syntax for entity tags.
A Last-Modified time, when used as a validator in a request, is
implicitly weak unless it is possible to deduce that it is strong,
using the following rules:
The validator is being compared by an origin server to the
actual current validator for the entity and,That origin server reliably knows that the associated entity did
not change twice during the second covered by the presented
validator.
or
The validator is about to be used by a client in an If-Modified-Since
or If-Unmodified-Since header, because the client
has a cache entry for the associated entity, andThat cache entry includes a Date value, which gives the time
when the origin server sent the original response, andThe presented Last-Modified time is at least 60 seconds before
the Date value.
or
The validator is being compared by an intermediate cache to the
validator stored in its cache entry for the entity, andThat cache entry includes a Date value, which gives the time
when the origin server sent the original response, andThe presented Last-Modified time is at least 60 seconds before
the Date value.
This method relies on the fact that if two different responses were
sent by the origin server during the same second, but both had the
same Last-Modified time, then at least one of those responses would
have a Date value equal to its Last-Modified time. The arbitrary 60-second
limit guards against the possibility that the Date and Last-Modified
values are generated from different clocks, or at somewhat
different times during the preparation of the response. An
implementation MAY use a value larger than 60 seconds, if it is
believed that 60 seconds is too short.
If a client wishes to perform a sub-range retrieval on a value for
which it has only a Last-Modified time and no opaque validator, it
MAY do this only if the Last-Modified time is strong in the sense
described here.
A cache or origin server receiving a conditional range request
() MUST use the strong comparison function to
evaluate the condition.
These rules allow HTTP/1.1 caches and clients to safely perform sub-range
retrievals on values that have been obtained from HTTP/1.0
servers.
We adopt a set of rules and recommendations for origin servers,
clients, and caches regarding when various validator types ought to
be used, and for what purposes.
HTTP/1.1 origin servers:
SHOULD send an entity tag validator unless it is not feasible to
generate one.MAY send a weak entity tag instead of a strong entity tag, if
performance considerations support the use of weak entity tags,
or if it is unfeasible to send a strong entity tag.SHOULD send a Last-Modified value if it is feasible to send one,
unless the risk of a breakdown in semantic transparency that
could result from using this date in an If-Modified-Since header
would lead to serious problems.
In other words, the preferred behavior for an HTTP/1.1 origin server
is to send both a strong entity tag and a Last-Modified value.
In order to be legal, a strong entity tag MUST change whenever the
associated entity changes in any way. A weak entity tag SHOULD
change whenever the associated entity changes in a semantically
significant way.
Note: in order to provide semantically transparent caching, an
origin server must avoid reusing a specific strong entity tag
value for two different entities, or reusing a specific weak
entity tag value for two semantically different entities. Cache
entries might persist for arbitrarily long periods, regardless of
expiration times, so it might be inappropriate to expect that a
cache will never again attempt to validate an entry using a
validator that it obtained at some point in the past.
HTTP/1.1 clients:
If an entity tag has been provided by the origin server, MUST
use that entity tag in any cache-conditional request (using If-Match
or If-None-Match).If only a Last-Modified value has been provided by the origin
server, SHOULD use that value in non-subrange cache-conditional
requests (using If-Modified-Since).If only a Last-Modified value has been provided by an HTTP/1.0
origin server, MAY use that value in subrange cache-conditional
requests (using If-Unmodified-Since:). The user agent SHOULD
provide a way to disable this, in case of difficulty.If both an entity tag and a Last-Modified value have been
provided by the origin server, SHOULD use both validators in
cache-conditional requests. This allows both HTTP/1.0 and
HTTP/1.1 caches to respond appropriately.
An HTTP/1.1 origin server, upon receiving a conditional request that
includes both a Last-Modified date (e.g., in an If-Modified-Since or
If-Unmodified-Since header field) and one or more entity tags (e.g.,
in an If-Match, If-None-Match, or If-Range header field) as cache
validators, MUST NOT return a response status of 304 (Not Modified)
unless doing so is consistent with all of the conditional header
fields in the request.
An HTTP/1.1 caching proxy, upon receiving a conditional request that
includes both a Last-Modified date and one or more entity tags as
cache validators, MUST NOT return a locally cached response to the
client unless that cached response is consistent with all of the
conditional header fields in the request.
Note: The general principle behind these rules is that HTTP/1.1
servers and clients should transmit as much non-redundant
information as is available in their responses and requests.
HTTP/1.1 systems receiving this information will make the most
conservative assumptions about the validators they receive.
HTTP/1.0 clients and caches will ignore entity tags. Generally,
last-modified values received or used by these systems will
support transparent and efficient caching, and so HTTP/1.1 origin
servers should provide Last-Modified values. In those rare cases
where the use of a Last-Modified value as a validator by an
HTTP/1.0 system could result in a serious problem, then HTTP/1.1
origin servers should not provide one.
This section defines the syntax and semantics of HTTP/1.1 header fields
related to conditional requests.
For entity-header fields, both sender and recipient refer to either the
client or the server, depending on who sends and who receives the entity.
The response-header field "ETag" provides the current value of the
entity tag (see ) for the requested variant.
The headers used with entity
tags are described in Sections
and of this document,
and in Section 5.3 of . The entity tag
MAY be used for comparison with other entities from the same resource
(see ).
Examples:
The ETag response-header field value, an entity tag, provides for an
"opaque" cache validator. This might allow more reliable validation
in situations where it is inconvenient to store modification dates,
where the one-second resolution of HTTP date values is not
sufficient, or where the origin server wishes to avoid certain
paradoxes that might arise from the use of modification dates.
The principle behind entity tags is that only the service author
knows the semantics of a resource well enough to select an
appropriate cache validation mechanism, and the specification of any
validator comparison function more complex than byte-equality would
open up a can of worms. Thus, comparisons of any other headers
(except Last-Modified, for compatibility with HTTP/1.0) are never
used for purposes of validating a cache entry.
The request-header field "If-Match" is used with a method to make it
conditional. A client that has one or more entities previously
obtained from the resource can verify that one of those entities is
current by including a list of their associated entity tags in the
If-Match header field. Entity tags are defined in . The
purpose of this feature is to allow efficient updates of cached
information with a minimum amount of transaction overhead. It is also
used, on updating requests, to prevent inadvertent modification of
the wrong version of a resource. As a special case, the value "*"
matches any current entity of the resource.
If any of the entity tags match the entity tag of the entity that
would have been returned in the response to a similar GET request
(without the If-Match header) on that resource, or if "*" is given
and any current entity exists for that resource, then the server MAY
perform the requested method as if the If-Match header field did not
exist.
A server MUST use the strong comparison function (see )
to compare the entity tags in If-Match.
If none of the entity tags match, or if "*" is given and no current
entity exists, the server MUST NOT perform the requested method, and
MUST return a 412 (Precondition Failed) response. This behavior is
most useful when the client wants to prevent an updating method, such
as PUT, from modifying a resource that has changed since the client
last retrieved it.
If the request would, without the If-Match header field, result in
anything other than a 2xx or 412 status, then the If-Match header
MUST be ignored.
The meaning of "If-Match: *" is that the method SHOULD be performed
if the representation selected by the origin server (or by a cache,
possibly using the Vary mechanism, see Section 3.5 of ) exists, and
MUST NOT be performed if the representation does not exist.
A request intended to update a resource (e.g., a PUT) MAY include an
If-Match header field to signal that the request method MUST NOT be
applied if the entity corresponding to the If-Match value (a single
entity tag) is no longer a representation of that resource. This
allows the user to indicate that they do not wish the request to be
successful if the resource has been changed without their knowledge.
Examples:
The result of a request having both an If-Match header field and
either an If-None-Match or an If-Modified-Since header fields is
undefined by this specification.
The request-header field "If-Modified-Since" is used with a method to
make it conditional: if the requested variant has not been modified
since the time specified in this field, an entity will not be
returned from the server; instead, a 304 (Not Modified) response will
be returned without any message-body.
An example of the field is:
A GET method with an If-Modified-Since header and no Range header
requests that the identified entity be transferred only if it has
been modified since the date given by the If-Modified-Since header.
The algorithm for determining this includes the following cases:
If the request would normally result in anything other than a
200 (OK) status, or if the passed If-Modified-Since date is
invalid, the response is exactly the same as for a normal GET.
A date which is later than the server's current time is
invalid.If the variant has been modified since the If-Modified-Since
date, the response is exactly the same as for a normal GET.If the variant has not been modified since a valid If-Modified-Since
date, the server SHOULD return a 304 (Not
Modified) response.
The purpose of this feature is to allow efficient updates of cached
information with a minimum amount of transaction overhead.
Note: The Range request-header field modifies the meaning of If-Modified-Since;
see Section 5.4 of for full details.
Note: If-Modified-Since times are interpreted by the server, whose
clock might not be synchronized with the client.
Note: When handling an If-Modified-Since header field, some
servers will use an exact date comparison function, rather than a
less-than function, for deciding whether to send a 304 (Not
Modified) response. To get best results when sending an If-Modified-Since
header field for cache validation, clients are
advised to use the exact date string received in a previous Last-Modified
header field whenever possible.
Note: If a client uses an arbitrary date in the If-Modified-Since
header instead of a date taken from the Last-Modified header for
the same request, the client should be aware of the fact that this
date is interpreted in the server's understanding of time. The
client should consider unsynchronized clocks and rounding problems
due to the different encodings of time between the client and
server. This includes the possibility of race conditions if the
document has changed between the time it was first requested and
the If-Modified-Since date of a subsequent request, and the
possibility of clock-skew-related problems if the If-Modified-Since
date is derived from the client's clock without correction
to the server's clock. Corrections for different time bases
between client and server are at best approximate due to network
latency.
The result of a request having both an If-Modified-Since header field
and either an If-Match or an If-Unmodified-Since header fields is
undefined by this specification.
The request-header field "If-None-Match" is used with a method to make
it conditional. A client that has one or more entities previously
obtained from the resource can verify that none of those entities is
current by including a list of their associated entity tags in the
If-None-Match header field. The purpose of this feature is to allow
efficient updates of cached information with a minimum amount of
transaction overhead. It is also used to prevent a method (e.g. PUT)
from inadvertently modifying an existing resource when the client
believes that the resource does not exist.
As a special case, the value "*" matches any current entity of the
resource.
If any of the entity tags match the entity tag of the entity that
would have been returned in the response to a similar GET request
(without the If-None-Match header) on that resource, or if "*" is
given and any current entity exists for that resource, then the
server MUST NOT perform the requested method, unless required to do
so because the resource's modification date fails to match that
supplied in an If-Modified-Since header field in the request.
Instead, if the request method was GET or HEAD, the server SHOULD
respond with a 304 (Not Modified) response, including the cache-related
header fields (particularly ETag) of one of the entities that
matched. For all other request methods, the server MUST respond with
a status of 412 (Precondition Failed).
See for rules on how to
determine if two entity tags match.
If none of the entity tags match, then the server MAY perform the
requested method as if the If-None-Match header field did not exist,
but MUST also ignore any If-Modified-Since header field(s) in the
request. That is, if no entity tags match, then the server MUST NOT
return a 304 (Not Modified) response.
If the request would, without the If-None-Match header field, result
in anything other than a 2xx or 304 status, then the If-None-Match
header MUST be ignored. (See for a discussion of
server behavior when both If-Modified-Since and If-None-Match appear
in the same request.)
The meaning of "If-None-Match: *" is that the method MUST NOT be
performed if the representation selected by the origin server (or by
a cache, possibly using the Vary mechanism, see Section 3.5 of )
exists, and SHOULD be performed if the representation does not exist.
This feature is intended to be useful in preventing races between PUT
operations.
Examples:
The result of a request having both an If-None-Match header field and
either an If-Match or an If-Unmodified-Since header fields is
undefined by this specification.
The request-header field "If-Unmodified-Since" is used with a method to
make it conditional. If the requested resource has not been modified
since the time specified in this field, the server SHOULD perform the
requested operation as if the If-Unmodified-Since header were not
present.
If the requested variant has been modified since the specified time,
the server MUST NOT perform the requested operation, and MUST return
a 412 (Precondition Failed).
An example of the field is:
If the request normally (i.e., without the If-Unmodified-Since
header) would result in anything other than a 2xx or 412 status, the
If-Unmodified-Since header SHOULD be ignored.
If the specified date is invalid, the header is ignored.
The result of a request having both an If-Unmodified-Since header
field and either an If-None-Match or an If-Modified-Since header
fields is undefined by this specification.
The entity-header field "Last-Modified" indicates the date and time at
which the origin server believes the variant was last modified.
An example of its use is
The exact meaning of this header field depends on the implementation
of the origin server and the nature of the original resource. For
files, it may be just the file system last-modified time. For
entities with dynamically included parts, it may be the most recent
of the set of last-modify times for its component parts. For database
gateways, it may be the last-update time stamp of the record. For
virtual objects, it may be the last time the internal state changed.
An origin server MUST NOT send a Last-Modified date which is later
than the server's time of message origination. In such cases, where
the resource's last modification would indicate some time in the
future, the server MUST replace that date with the message
origination date.
An origin server SHOULD obtain the Last-Modified value of the entity
as close as possible to the time that it generates the Date value of
its response. This allows a recipient to make an accurate assessment
of the entity's modification time, especially if the entity changes
near the time that the response is generated.
HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.
The Last-Modified entity-header field value is often used as a cache
validator. In simple terms, a cache entry is considered to be valid
if the entity has not been modified since the Last-Modified value.
The Message Header Registry located at should be updated
with the permanent registrations below (see ):
Header Field NameProtocolStatusReferenceETaghttpstandardIf-MatchhttpstandardIf-Modified-SincehttpstandardIf-None-MatchhttpstandardIf-Unmodified-SincehttpstandardLast-Modifiedhttpstandard
The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
No additional security considerations have been identified beyond
those applicable to HTTP in general .
HTTP/1.1, part 1: URIs, Connections, and Message ParsingDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 5: Range Requests and Partial ResponsesDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 6: CachingDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deKey words for use in RFCs to Indicate Requirement LevelsHarvard Universitysob@harvard.eduAugmented BNF for Syntax Specifications: ABNFBrandenburg InternetWorking675 Spruce Dr.SunnyvaleCA94086US+1.408.246.8253dcrocker@bbiw.netTHUS plc.1/2 Berkeley Square99 Berkely StreetGlasgowG3 7HRUKpaul.overell@thus.netHypertext Transfer Protocol -- HTTP/1.1University of California, Irvinefielding@ics.uci.eduW3Cjg@w3.orgCompaq Computer Corporationmogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgXerox Corporationmasinter@parc.xerox.comMicrosoft Corporationpaulle@microsoft.comW3Ctimbl@w3.orgRegistration Procedures for Message Header FieldsNine by NineGK-IETF@ninebynine.orgBEA Systemsmnot@pobox.comHP LabsJeffMogul@acm.org
Allow weak entity tags in all requests except range requests (Sections
and
).
If-Match = "If-Match:" OWS If-Match-v
If-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
entity-tag ] ) )
If-Modified-Since = "If-Modified-Since:" OWS If-Modified-Since-v
If-Modified-Since-v = HTTP-date
If-None-Match = "If-None-Match:" OWS If-None-Match-v
If-None-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
entity-tag ] ) )
If-Unmodified-Since = "If-Unmodified-Since:" OWS
If-Unmodified-Since-v
If-Unmodified-Since-v = HTTP-date
Last-Modified = "Last-Modified:" OWS Last-Modified-v
Last-Modified-v = HTTP-date
OWS =
entity-tag = [ weak ] opaque-tag
opaque-tag = quoted-string
quoted-string =
weak = "W/"
]]>ABNF diagnostics:
Extracted relevant partitions from .
Closed issues:
:
"Normative and Informative references"
Other changes:
Move definitions of 304 and 412 condition codes from Part2.
Ongoing work on ABNF conversion ():
Add explicit references to BNF syntax and rules imported from other parts of the specification.
Closed issues:
:
"Weak ETags on non-GET requests"
Ongoing work on IANA Message Header Registration ():
Reference RFC 3984, and update header registrations for headers defined
in this document.
Closed issues:
:
"Examples for ETag matching"
:
"'entity value' undefined"
:
"bogus 2068 Date header reference"
Ongoing work on ABNF conversion ():
Use "/" instead of "|" for alternatives.
Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
Rewrite ABNFs to spell out whitespace rules, factor out
header value format definitions.
Final work on ABNF conversion ():
Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.