As per Relevance of the word following, we have this rfc below:
Network Working Group P.
Request for Comments: 2756
Category: Experimental D.
January 2000
Hyper Text Caching Protocol (HTCP/0.0)
Status of this
This memo defines an Experimental Protocol for the
community. It does not specify an Internet standard of any kind
Discussion and suggestions for improvement are requested
Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (2000). All Rights Reserved
This document describes HTCP, a protocol for discovering HTTP
and cached data, managing sets of HTTP caches, and monitoring
activity. This is an experimental protocol, one among
proposals to perform these functions
1. Definitions, Rationale and
1.1. HTTP/1.1 (see [RFC2616]) permits the transfer of web
from "origin servers," possibly via "proxies" (which are
under some circumstances to "cache" such objects for
reuse) to "clients" which consume the object in some way, usually
displaying it as part of a "web page." HTTP/1.0 and later
"headers" to be included in a request and/or a response,
expanding upon the HTTP/0.9 (and earlier) behaviour of
only a URI in the request and offering only a body in the response
1.2. ICP (see [RFC2186]) permits caches to be queried as to
content, usually by other caches who are hoping to avoid an
fetch from a distant origin server. ICP was designed with HTTP/0.9
in mind, such that only the URI (without any headers) is used
describing cached content, and the possibility of multiple
bodies for the same URI had not yet been imagined
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
1.3. This document specifies a Hyper Text Caching Protocol (HTCP
which permits full request and response headers to be used in
management, and expands the domain of cache management to
monitoring a remote cache's additions and deletions,
immediate deletions, and sending hints about web objects such as
third party locations of cacheable objects or the
uncacheability or unavailability of web objects
2. HTCP
2.1. All multi-octet HTCP protocol elements are transmitted
network byte order. All RESERVED fields should be set to binary
by senders and left unexamined by receivers. Headers must
presented with the CRLF line termination, as in HTTP
2.2. Any hostnames specified should be compatible between sender
receiver, such that if a private naming scheme (such as HOSTS.TXT
NIS) is in use, names depending on such schemes will only be sent
HTCP neighbors who are known to participate in said schemes.
addresses (dotted quad IPv4, or colon-format IPv6) are universal,
are public DNS names. Use of private names or addresses will
special operational care
2.3. HTCP messages may be sent as UDP datagrams, or over
connections. UDP must be supported. HTCP agents must not
isolated from NETWORK failures and delays. An HTCP agent should
prepared to act in useful ways when no response is forthcoming,
when responses are delayed or reordered or damaged. TCP is
and is expected to be used only for protocol debugging. The IANA
assigned port 4827 as the standard TCP and UDP port number for HTCP
2.4. A set of configuration variables concerning
characteristics should be maintained for each agent which is
of initiating HTCP transactions, perhaps with a set of per-
global defaults. These variables are
Maximum number of unacknowledged transactions before a "failure"
imputed
Maximum interval without a response to some transaction before
"failure" is imputed
Minimum interval before trying a new transaction after a failure
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
2.5. An HTCP Message has the following general format
+---------------------+
| HEADER | tells message length and protocol
+---------------------+
| DATA | HTCP message (varies per major version number
+---------------------+
| AUTH | optional authentication for
+---------------------+
2.6. An HTCP/*.* HEADER has the following format
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | LENGTH |
+ + + + + + + + + + + + + + + + +
2: | LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | MAJOR | MINOR |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
LENGTH is the message length, inclusive of all header and
octets, including the LENGTH field itself. This field
be equal to the datagram payload size ("record length") if
datagram protocol is in use, and can include padding, i.e.,
not all octets of the message need be used in the DATA
AUTH sections
MAJOR is the major version number (0 for this specification).
DATA section of an HTCP message need not be upward
downward compatible between different major version numbers
MINOR is the minor version number (0 for this specification).
Feature levels and interpretation rules can vary depending
this field, in particular RESERVED fields can take on
(though optional) meaning in successive minor version
within the same major version number
2.6.1. It is expected that an HTCP initiator will know the
number of a prospective HTCP responder, or that the initiator
probe using declining values for MINOR and MAJOR (beginning with
highest locally supported value) and locally cache the probed
number of the responder
2.6.2. Higher MAJOR numbers are to be preferred, as are higher
numbers within a particular MAJOR number
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
2.7. An HTCP/0.* DATA has the following structure
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPCODE | RESPONSE | RESERVED |F1 |RR |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | TRANS-ID |
+ + + + + + + + + + + + + + + + +
6: | TRANS-ID |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
8: | |
/ OP-DATA /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
LENGTH is the number of octets of the message which are
for the DATA section, including the LENGTH field itself
This number can include padding, i.e., not all
reserved by LENGTH need be used in OP-DATA
OPCODE is the operation code of an HTCP transaction. An
transaction can consist of multiple HTCP messages, e.g.,
request (sent by the initiator), or a response (sent by
responder).
RESPONSE is a numeric code indicating the success or failure of
transaction. It should be set to zero (0) by
and ignored by responders. Each operation has its own
of response codes, which are described later. The
message has a set of response codes which are as follows
0 authentication wasn't used but is
1 authentication was used but
2 opcode not
3 major version not
4 minor version not supported (major version is ok
5 inappropriate, disallowed, or undesirable
The above response codes all indicate errors and all
for their visibility on MO=1 (as specified below).
RR is a flag indicating whether this message is a request (0)
or response (1).
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
F1 is overloaded such that it is used differently
requestors than by responders. If RR=0, then F1 is
as RD. If RR=1, then F1 is defined as MO
RD is a flag which if set to 1 means that a response
desired. Some OPCODEs require RD to be set to 1 to
meaningful
MO (em-oh) is a flag which indicates whether the RESPONSE
is to be interpreted as a response to the overall
(fixed fields in DATA or any field of AUTH) [MO=1] or as
response to fields in the OP-DATA [MO=0].
TRANS-ID is a 32-bit value which when combined with the initiator'
network address, uniquely identifies this HTCP transaction
Care should be taken not to reuse TRANS-ID's within
life-time of a UDP datagram
OP-DATA is opcode-dependent and is defined below, per opcode
2.8. An HTCP/0.0 AUTH has the following structure
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | SIG-TIME |
+ + + + + + + + + + + + + + + + +
4: | SIG-TIME |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: | SIG-EXPIRE |
+ + + + + + + + + + + + + + + + +
8: | SIG-EXPIRE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
10: | |
/ KEY-NAME /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
n: | |
/ SIGNATURE /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
LENGTH is the number of octets used by the AUTH, including
LENGTH field itself. If the optional AUTH is not
transmitted, this field should be set to 2 (two).
can include padding, which means that not all
reserved by LENGTH will necessarily be consumed
SIGNATURE
SIG-TIME is an unsigned binary count of the number of
since 00:00:00 1-Jan-70 UTC at the time the SIGNATURE
generated
SIG-EXPIRE is an unsigned binary count of the number of
since 00:00:00 1-Jan-70 UTC at the time the SIGNATURE
considered to have expired
KEY-NAME is a COUNTSTR [3.1] which specifies the name of a
secret. (Each HTCP implementation is expected to
configuration of several shared secrets, each of
will have a name.)
SIGNATURE is a COUNTSTR [3.1] which holds the HMAC-MD5 digest (
[RFC 2104]), with a B value of 64, of the
elements, each of which is digested in its "on the wire
format, including transmitted padding if any is
by a field's associated LENGTH
IP SRC ADDR [4 octets
IP SRC PORT [2 octets
IP DST ADDR [4 octets
IP DST PORT [2 octets
HTCP MAJOR version number [1 octet
HTCP MINOR version number [1 octet
SIG-TIME [4 octets
SIG-EXPIRE [4 octets
HTCP DATA [variable
KEY-NAME (the whole COUNTSTR [3.1]) [variable
2.8.1. Shared secrets should be cryptorandomly generated and
be at least a few hundred octets in size
3. Data
HTCP/0.* data types are defined as follows
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
3.1. COUNTSTR is a counted string whose format is
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | |
/ TEXT /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
LENGTH is the number of octets which will follow in TEXT.
field is *not* self-inclusive as is the case with other
LENGTH fields
TEXT is a stream of uninterpreted octets, usually ISO8859-1
"characters".
3.2. SPECIFIER is used with the TST and CLR request messages
defined below. Its format is
+---------------------+
| METHOD | :
+---------------------+
| URI | :
+---------------------+
| VERSION | :
+---------------------+
| REQ-HDRS | :
+---------------------+
METHOD (Since HTCP only returns headers, methods GET and HEAD
equivalent.)
URI (If the URI is a URL, it should always include a ":"
specifier, but in its absense, port 80 should be imputed
a receiver.)
VERSION is an entire HTTP version string such as" HTTP/1.1".
VERSION strings with prefixes other than "HTTP/" or
version numbers less than "1.1" are outside the domain
this specification
REQ-HDRS are those presented by an HTTP initiator. These
should include end-to-end but NOT hop-by-hop headers,
they can be canonicalized (aggregation of "Accept:"
permitted, for example.)
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
3.3. DETAIL is used with the TST response message, defined below
Its format is
+---------------------+
| RESP-HDRS | :
+---------------------+
| ENTITY-HDRS | :
+---------------------+
| CACHE-HDRS | :
+---------------------+
3.4. IDENTITY is used with the MON request and SET response message
defined below. Its format is
+---------------------+
| SPECIFIER |
+---------------------+
| DETAIL |
+---------------------+
4. Cache
HTCP/0.0 CACHE-HDRS consist of zero or more of the following headers
Cache-Vary: ...
The sender of this header has learned that content varies on a
of headers different from the set given in the object's Vary
header. Cache-Vary:, if present, overrides the object's Vary
header
Cache-Location: hostname>: ...
The sender of this header has learned of one or more proxy
who are holding a copy of this object. Probing these caches
HTCP may result in discovery of new, close-by (preferrable
current) HTCP neighbors
Cache-Policy: [no-cache] [no-share] [no-cache-cookie
The sender of this header has learned that the object's
policy has more detail than is given in its response headers
no-cache means that it is uncacheable (no reason given),
but may be shareable between
requestors
no-share means that it is unshareable (no reason given),
and per-requestor tunnelling is
required).
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
no-cache-cookie means that the content could change as a
of different, missing, or even random
being included in the request headers, and
caching is inadvisable
Cache-Flags: [incomplete
The sender of this header has modified the object's caching
locally, such that requesters may need to treat this
specially, i.e., not necessarily in accordance with the object'
actual policy
incomplete means that the response headers and/or entity
given in this response are not known to be complete
and may not be suitable for use as a cache key
Cache-Expiry:
The sender of this header has learned that this object should
considered to have expired at a time different than that
by its response headers. The format is the same as HTTP/1.1
Expires:.
Cache-MD5:
The sender of this header has computed an MD5 checksum for
object which is either different from that given in the object'
Content-MD5: header, or is being supplied since the object has
Content-MD5 header. The format is the same as HTTP/1.1 Content
MD5:.
Cache-to-Origin:
The sender of this header has measured the round trip time to
origin server (given as a hostname or literal address). The
is the average number of seconds, expressed as decimal ASCII
arbitrary precision and no exponent. is the number
RTT samples which have had input to this average. is
number of routers between the cache and the origin, expressed
decimal ASCII with arbitrary precision and no exponent, or 0
the cache doesn't know
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
6. HTCP
HTCP/0.* opcodes and their respective OP-DATA are defined below
6.1. NOP (OPCODE 0):
This is an HTCP-level "ping." Responders are encouraged to
NOP's with minimum delay since the requestor may be using the NOP
(round trip time) for configuration or mapping purposes.
RESPONSE code for a NOP is always zero (0). There is no OP-DATA
a NOP. NOP requests with RD=0 cause no processing to occur at all
6.2. TST (OPCODE 1):
Test for the presence of a specified content entity in a proxy cache
TST requests with RD=0 cause no processing to occur at all
TST requests have the following OP-DATA
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | |
/ SPECIFIER /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
RESPONSE codes for TST are as follows
0 entity is present in responder's
1 entity is not present in responder's
TST responses have the following OP-DATA, if RESPONSE is zero (0):
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | |
/ DETAIL /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Note: The response headers returned by a positive TST can be of
stale object. Requestors should be prepared to cope with
condition, either by using the responder as a source for
object (which could cause the responder to simply refresh it
or by choosing a different responder
Vixie & Wessels Experimental [Page 10]
RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
TST responses have the following OP-DATA, if RESPONSE is one (1):
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | |
/ CACHE-HDRS /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6.3. MON (OPCODE 2):
Monitor activity in a proxy cache's local object store (adds, deletes
replacements, etc). Since interleaving of HTCP transactions over
single pair of UDP endpoints is not supported, it is recommended that
unique UDP endpoint be allocated by the requestor for each
MON request. MON requests with RD=0 are equivalent to those with RD=1
and TIME=0; that is, they will cancel any outstanding MON transaction
MON requests have the following OP-DATA structure
+0 (MSB
+---+---+---+---+---+---+---+---+
0: | TIME |
+---+---+---+---+---+---+---+---+
TIME is the number of seconds of monitoring output desired by
initiator. Subsequent MON requests from the same
with the same TRANS-ID should update the time on a ongoing
transaction. This is called "overlapping renew."
RESPONSE codes for MON are as follows
0 accepted, OP-DATA is present and
1 refused (quota error -- too many MON's are active
MON responses have the following OP-DATA structure, if RESPONSE
zero (0):
+0 (MSB) +1 (LSB
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | TIME | ACTION | REASON |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | |
/ IDENTITY /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
TIME is the number of seconds remaining for this
transaction
ACTION is a numeric code indicating a cache population action
Codes are
0 an entity has been added to the
1 an entity in the cache has been
2 an entity in the cache has been
3 an entity in the cache has been
REASON is a numeric code indicating the reason for an ACTION
Codes are
0 some reason not covered by the other REASON
1 a proxy client fetched this
2 a proxy client fetched with caching
3 the proxy server prefetched this
4 the entity expired, per its
5 the entity was purged due to caching storage
6.4. SET (OPCODE 3):
Inform a cache of the identity of an object. This is a "push
transaction, whereby cooperating caches can share information such
updated Age/Date/Expires headers (which might result from an
"304 Not modified" HTTP response) or updated cache headers (
might result from the discovery of non-authoritative "vary
conditions or from learning of second or third party cache
for this entity. RD is honoured
SET requests have the following OP-DATA structure
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | |
/ IDENTITY /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
RESPONSE codes are as follows
0 identity accepted, thank
1 identity ignored, no reason given, thank
SET responses have no OP-DATA
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RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
6.5. CLR (OPCODE 4):
Tell a cache to completely forget about an entity. RD is honoured
CLR requests have the following OP-DATA structure
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | RESERVED | REASON |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | |
/ SPECIFIER /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
REASON is a numeric code indicating the reason why the
is asking that this entity be removed. The codes are
follows
0 some reason not better specified by another
1 the origin server told me that this entity does
RESPONSE codes are as follows
0 i had it, it's gone
1 i had it, i'm keeping it, no reason given
2 i didn't have
CLR responses have no OP-DATA
Clearing a URI without specifying response, entity, or cache
means to clear all entities using that URI
7. Security
If the optional AUTH element is not used, it is possible
unauthorized third parties to both view and modify a cache using
HTCP protocol
8.
Mattias Wingstedt of Idonex brought key insights to the
of this protocol. David Hankins helped clarify this document
Vixie & Wessels Experimental [Page 13]
RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
9.
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter
L., Leach, P. and T. Berners-Lee, "Hypertext
Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed
Hashing for Message Authentication", RFC 2104, February
1997.
[RFC2186] Wessels, D. and K. Claffy, "Internet Cache Protocol (ICP),
version 2", RFC 2186, September 1997.
10. Authors'
Paul
Internet Software
950 Charter
Redwood City, CA 94063
Phone: +1 650 779 7001
EMail: vixie@isc.
Duane
National Lab for Applied Network
USCD, 9500 Gilman
La Jolla, CA 92093
Phone: +1 303 497 1822
EMail: wessels@nlanr.
Vixie & Wessels Experimental [Page 14]
RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) January 2000
11. Full Copyright
Copyright (C) The Internet Society (2000). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Funding for the RFC Editor function is currently provided by
Internet Society
Vixie & Wessels Experimental [Page 15]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
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