Open Pluggable Edge Services A. Rousskov
Internet-Draft The Measurement Factory
Expires: April 26, 2004 October 27, 2003
OPES Callout Protocol Core
draft-ietf-opes-ocp-core-02
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document specifies Open Pluggable Edge Services (OPES) Callout
Protocol (OCP). OCP is an application-agnostic protocol that
facilitates exchange of application messages between an OPES
processor and a callout server, for the purpose of adaptation of
application messages at the callout server.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Overall Operation . . . . . . . . . . . . . . . . . . . . 7
2.1 Initialization . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Original Dataflow . . . . . . . . . . . . . . . . . . . . 7
2.3 Adapted Dataflow . . . . . . . . . . . . . . . . . . . . . 7
2.4 Termination . . . . . . . . . . . . . . . . . . . . . . . 8
2.5 Exchange Patterns . . . . . . . . . . . . . . . . . . . . 8
2.6 OCP Environment . . . . . . . . . . . . . . . . . . . . . 9
3. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Message Format . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Message Rendering . . . . . . . . . . . . . . . . . . . . 11
3.3 Message Examples . . . . . . . . . . . . . . . . . . . . . 12
3.4 Message Names . . . . . . . . . . . . . . . . . . . . . . 13
4. Transactions . . . . . . . . . . . . . . . . . . . . . . . 14
5. Invalid input . . . . . . . . . . . . . . . . . . . . . . 15
6. Negotiation . . . . . . . . . . . . . . . . . . . . . . . 16
7. Capability and State Inquiry . . . . . . . . . . . . . . . 18
8. 'Data Recycling' Optimization . . . . . . . . . . . . . . 19
9. 'Out Of The Loop' Optimization . . . . . . . . . . . . . . 21
10. Message Parameters . . . . . . . . . . . . . . . . . . . . 22
10.1 Type Declaration Mnemonic . . . . . . . . . . . . . . . . 22
10.2 Parameter Types . . . . . . . . . . . . . . . . . . . . . 23
10.2.1 Uri . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.2.2 Uni . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
10.2.3 Size . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
10.2.4 Boolean . . . . . . . . . . . . . . . . . . . . . . . . . 24
11. Parameter Definitions . . . . . . . . . . . . . . . . . . 25
11.1 xid . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.2 rid . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.3 service . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.4 services . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.5 sg-id . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.6 am-id . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.7 size-request . . . . . . . . . . . . . . . . . . . . . . . 26
11.8 offset . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.9 modp . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.10 result . . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.11 feature . . . . . . . . . . . . . . . . . . . . . . . . . 28
12. Message Definitions . . . . . . . . . . . . . . . . . . . 29
12.1 Connection Start (CS) . . . . . . . . . . . . . . . . . . 29
12.2 Connection End (CE) . . . . . . . . . . . . . . . . . . . 30
12.3 Create Service Group (SGC) . . . . . . . . . . . . . . . . 31
12.4 Destroy Service Group (SGD) . . . . . . . . . . . . . . . 32
12.5 Transaction Start (TS) . . . . . . . . . . . . . . . . . . 32
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12.6 Transaction End (TE) . . . . . . . . . . . . . . . . . . . 33
12.7 Application Message Start (AMS) . . . . . . . . . . . . . 33
12.8 Application Message End (AME) . . . . . . . . . . . . . . 34
12.9 Data Use Mine (DUM) . . . . . . . . . . . . . . . . . . . 34
12.10 Data Use Yours (DUY) . . . . . . . . . . . . . . . . . . . 36
12.11 Data Won't Send Yours (DWSY) . . . . . . . . . . . . . . . 36
12.12 Data Won't Look At Yours (DWLY) . . . . . . . . . . . . . 37
12.13 Data Want Out (DWO) . . . . . . . . . . . . . . . . . . . 38
12.14 Data Pause (data-pause) . . . . . . . . . . . . . . . . . 38
12.15 Data Paused (data-paused) . . . . . . . . . . . . . . . . 39
12.16 Data Need (data-need) . . . . . . . . . . . . . . . . . . 40
12.17 Data ACK (DACK) . . . . . . . . . . . . . . . . . . . . . 40
12.18 I Am Here (pong) . . . . . . . . . . . . . . . . . . . . . 41
12.19 Are You There? (ping) . . . . . . . . . . . . . . . . . . 42
12.20 Negotiation Offer (NO) . . . . . . . . . . . . . . . . . . 42
12.21 Negotiation Response (NR) . . . . . . . . . . . . . . . . 43
12.22 I Support (i-can) . . . . . . . . . . . . . . . . . . . . 44
12.23 Can You Support (can-you) . . . . . . . . . . . . . . . . 44
12.24 I Currently Use (i-do) . . . . . . . . . . . . . . . . . . 45
12.25 Do You Currently Use (do-you) . . . . . . . . . . . . . . 45
13. Application Protocol Requirements . . . . . . . . . . . . 46
14. IAB Considerations . . . . . . . . . . . . . . . . . . . . 47
15. Security Considerations . . . . . . . . . . . . . . . . . 48
16. Compliance . . . . . . . . . . . . . . . . . . . . . . . . 50
17. To-do . . . . . . . . . . . . . . . . . . . . . . . . . . 51
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 53
B. Change Log . . . . . . . . . . . . . . . . . . . . . . . . 54
Normative References . . . . . . . . . . . . . . . . . . . 61
Informative References . . . . . . . . . . . . . . . . . . 62
Author's Address . . . . . . . . . . . . . . . . . . . . . 62
Intellectual Property and Copyright Statements . . . . . . 63
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1. Introduction
The Open Pluggable Edge Services (OPES) architecture
[I-D.ietf-opes-architecture], enables cooperative application
services (OPES services) between a data provider, a data consumer,
and zero or more OPES processors. The application services under
consideration analyze and possibly transform application-level
messages exchanged between the data provider and the data consumer.
The OPES processor can delegate the responsibility of service
execution by communicating with remote callout servers. As described
in [I-D.ietf-opes-protocol-reqs], an OPES processor communicates with
and invokes services on a callout server by using a callout protocol.
This document specifies the core of such a protocol.
OCP Core specification documents general, application-independent
protocol mechanisms. A separate series of documents describe
application-specific aspects of OCP. For example, "HTTP adaptation
with OPES" [I-D.ietf-opes-http] describes, in part, how HTTP messages
and HTTP meta-information can be communicated over OCP.
1.1 Scope
As an application proxy, OPES processor proxies a single application
protocol or converts from one application protocol to another. At the
same time, OPES processor may be an OCP client, using OCP to
facilitate adaptation of proxied messages at callout servers. It is
therefore natural to assume that OPES processor takes application
messages being proxied, passes them over OCP to callout servers, and
then puts the adaptation results back on the wire. However, such an
assumption implies that OCP is applied directly to application
messages that OPES processor is proxing, which may not be the case.
OPES processor scope callout server scope
+-----------------+ +-----------------+
| pre-processing | OCP scope | |
| +- - - - - - - - - - - - - - - - - - -+ |
| iteration | <== ( application data ) ==> | adaptation |
| +- - - - - - - - - - - - - - - - - - -+ |
| post-processing | | |
+-----------------+ +-----------------+
Figure 1
OPES processor may preprocess (or postprocess) proxied application
messages before (or after) they are adapted at callout servers. For
example, a processor may take an HTTP response being proxied and pass
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it as is, along with metadata about the corresponding HTTP
connection. Another processor may take an HTTP response, extract its
body, and pass that body, along with the content-encoding metadata.
Moreover, to perform adaptation, OPES processor may execute several
callout services, iterating over several callout servers. Such
preprocessing, postprocessing, and iterations make it impossible to
rely on any specific relationship between application messages being
proxied and application messages being sent to a callout service.
Similarly, specific adaptation actions at the callout server are
outside of OCP Core scope.
This specification does not define or require any specific
relationship among application messages being proxied by the OPES
processor and application messages being exchanged with callout
servers via OCP. OPES processor usually provides some mapping among
these application messages, but processor's specific actions are
beyond OCP scope. In other words, this specification is not concerned
with the OPES processor role as an application proxy, or as an
iterator of callout services. The scope of OCP Core is communication
between a single OPES processor and a single callout server.
Furthermore, an OPES processor is at liberty to choose which proxied
application messages or information about them to send over OCP. All
proxied messages on all proxied connections (if connections are
defined for a given application protocol), everything on some
connections, selected proxied messages, or nothing might be sent over
OCP to callout servers. OPES processor and callout server state
related to proxied protocols can be relayed over OCP as application
message metadata.
1.2 Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. When used
with the normative meanings, these keywords will be all uppercase.
Occurrences of these words in lowercase comprise normal prose usage,
with no normative implications.
OPES processor works with messages from application protocols and may
relay information about those application messages to a callout
server. OCP is also an application protocol. Thus, protocol elements
like "message", "connection", or "transaction" exist in OCP and other
application protocols. In this specification, all references to
elements from application protocols other than OCP are used with an
explicit "application" qualifier. References without the
"application" qualifier, refer to OCP elements.
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OCP message: OCP message is a basic unit of communication between an
OPES processor and a callout server. Message is a sequence of
octets formatted according to syntax rules (Section 3.1). Message
semantics is defined in Section 12.
application message: An entity defined by OPES processor and callout
server negotiation. Usually, the negotiated definition would match
the definition from an application protocol (e.g., [RFC2616]
definition of an HTTP message, including headers, and body).
application message data: An opaque sequence of octets representing
complete or partial application message. OCP Core does not
distinguish application message structure (if any). Application
message data may be empty.
data: Same as application message data.
original Referring to application message flowing from the OPES
processor to a callout server.
adapted Referring to application message flowing from an OPES callout
server to the OPES processor.
adaptation: Any kind of access by a callout server, including
modification and copying. For example, translating or logging an
SMTP message is adaptation of that application message.
agent: Client or server for a given communication protocol. A proxy
is both a client and a server and, hence, also an agent. For
example, OPES processor and callout server are OCP agents.
immediate: Performing the specified action before reacting to new
incoming messages or sending any new messages unrelated to the
specified action.
OCP extension: A specification extending or adjusting this document
to cover an application protocol (a.k.a., application binding,
e.g., [I-D.ietf-opes-http]), new OCP functionality (e.g.,
transport encryption and authentication), and/or new OCP Core
version.
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2. Overall Operation
OPES processor may use OPES callout protocol (OCP) to communicate
with callout servers. Adaptation using callout services is sometimes
called a "bump in the wire" architecture.
2.1 Initialization
OPES processor establishes transport connections with callout servers
for the purpose of exchanging application messages with the callout
server(s) using OCP. After a transport-layer connection (usually TCP/
IP) is established, communicating OCP agents exchange Connection
Start (CS (Section 12.1)) messages. Next, OCP features can be
negotiated between the processor and the callout server (see Section
6). For example, OCP agents have to agree on transport encryption
and application message definition. When enough settings are
negotiated, OCP agents may start exchanging application messages.
2.2 Original Dataflow
When OPES processor wants to adapt an application message, the OPES
processor sends a Transaction Start (TS (Section 12.5)) message to
initiate an OCP transaction dedicated to that application message.
The processor then sends an Application Message Start (AMS (Section
12.7)) message to prepare the callout server for application data
that will follow. Once application message scope is established,
application data can be sent to the callout server, using Data Use
Mine (DUM (Section 12.9)) and related OCP message(s). All these
messages correspond to the original dataflow.
2.3 Adapted Dataflow
The callout server receives data and metadata sent by the OPES
processor (original data flow). The callout server analyses metadata
and adapts data as it comes in. The server usually builds its version
of metadata and responds to OPES processor with an
'app-message-start' message. Adapted application message data can be
sent next, using Data Use Mine (DUM (Section 12.9)) OCP message(s).
The application message is then announced to be "completed" or
"closed" using an Application Message End (AME (Section 12.8))
message. The transaction may be closed using a Transaction End (TE
(Section 12.6)) message as well. All these messages correspond to
adapted data flow.
+---------------+ +-------+
| OPES | == (original data flow) ==> |callout|
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| processor | <== (adapted data flow) === |server |
+---------------+ +-------+
Figure 2
Depending on the negotiated application message definition, it may be
possible or even required for callout server to respond with more
than one application message within the same transaction. In other
words, the callout server may adapt a single original application
message into multiple application messages. Each application message
sent by the callout server is individually identified by an "am-id"
parameter (Section 11.6) and can be sent independently from other
application messages within the same transaction (this allows for
logical- and transport-level interleaving of OCP messages related to
different application messages).
The OPES processor receives the application message sent by the
callout server. Other OPES processor actions specific to the
application message received are out of this specification scope.
2.4 Termination
Either OCP agent can terminate application message delivery,
transaction, or connection by sending an appropriate OCP message.
Usually, the callout server terminates application message delivery
and the transaction. Abnormal terminations at arbitrary times are
supported. The termination message includes a result description.
2.5 Exchange Patterns
In addition to messages carrying application data, OCP agents may
also exchange messages related to their configuration, state,
transport connections, application connections, etc. A callout server
may remove itself from the application message processing loop. A
single OPES processor can communicate with many callout servers and
vice versa. Though many OCP exchange patterns do not follow a classic
client-server model, it is possible to think of an OPES processor as
an ``OCP client'' and of a callout server as an ``OCP server''. The
OPES architecture document [I-D.ietf-opes-architecture] describes
configuration possibilities.
The following informal rules illustrate relationships between
transport connections, transactions, OCP messages, and application
messages:
o An OCP agent may communicate with multiple OCP agents.
Communication with multiple OCP agents is outside of this
specification scope.
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o An OPES processor may have multiple concurrent OCP connections to
a callout server. Communication over multiple OCP connections is
outside of this specification scope.
o A connection may carry multiple concurrent transactions. A
transaction is always associated with a single connection (i.e., a
transaction cannot span multiple concurrent connections).
o A connection may carry at most one message at a time, including
control messages and transaction-related messages. A message is
always associated with a single connection (i.e., a message cannot
span multiple concurrent connections).
o A transaction is a sequence of messages related to application of
a given set of callout services to a single application message.
A sequence of transaction messages from an OPES processor to a
callout server is called original flow. A sequence of transaction
messages from a callout server to an OPES processor is called
adapted flow. The two flows may overlap in time.
o A transaction is always associated with a single (original)
application message. Adapted flow may transfer information about
multiple (adapted) application messages.
o An application message (adapted or original) is transferred using
a sequence of OCP messages.
2.6 OCP Environment
OCP communication is assumed to usually take place over TCP/IP
connections on the Internet (though no default TCP port is assigned
to OCP). This does not preclude OCP from being implemented on top of
any other transport protocol, on any other network. OCP only
presumes a reliable connection-oriented transport; any protocol that
provides such guarantees can be used; the mapping of OCP message
structures onto the transport data units of the protocol in question
is outside the scope of this specification.
OCP is application agnostic but it is not suitable for all
applications. This specification documents known application scope
limitations in Section 13. OCP messages can carry
application-specific information as payload or application-specific
message parameters.
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3. Messages
As defined in Section 1.2, an OCP message is a basic unit of
communication between an OPES processor and a callout server. A
message is a sequence of octets formatted according to syntax rules
(Section 3.1). Message semantics is defined in Section 12. Messages
are transmitted on top of OCP transport.
OCP messages deal with transport and transaction management as well
as application data exchange between a single OPES processor and a
single callout server. Some messages can only be emitted by an OPES
processor; some only by a callout server; some can be emitted by both
OPES processor and callout server. Some messages require responses
(one could call such messages "requests"); some can only be used in
response to other messages ("responses"); some may be sent without
solicitation and/or may not require a response.
3.1 Message Format
An OCP message consists of a message name followed by optional
parameters and payload. The exact message syntax is defined by the
following Augmented Backus-Naur Form (ABNF) [RFC2234]:
message = name [SP anonym-parameters]
[CRLF named-parameters CRLF]
[CRLF payload CRLF]
";" CRLF
anonym-parameters = value *(SP value) ; space-separated
named-parameters = named-value *(CRLF named-value) ; CRLF-separated
list-items = value *("," value) ; comma-separated
payload = data
named-value = name ":" SP value
value = structure / list / atom
structure = "{" [anonym-parameters] [CRLF named-parameters CRLF] "}"
list = "(" [ list-items ] ")"
atom = bare-value / quoted-value
name = ALPHA *safe-OCTET
bare-value = 1*safe-OCTET
quoted-value = DQUOTE data DQUOTE
data = size ":" <n>OCTET ; n == size
safe-OCTET = ALPHA / DIGIT / "-" / "_"
size = dec-number ; 0-2147483647
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dec-number = 1*DIGIT ; no leading zeros or signs
Figure 3
Several normative rules accompany the above ABNF:
o There is no "implied linear space" (LWS) rule. LWS rules are
common to MIME-based grammars, but are not used here. The
whitespace syntax is restricted to what is explicitly allowed by
the above ABNF.
o All protocol elements are case sensitive unless specified
otherwise. In particular, message names and parameter names are
case sensitive.
o Sizes are interpreted as decimal values and cannot have leading
zeros.
o Sizes do not exceed 2147483647.
o The size attribute in a quoted-value encoding specifies the exact
number of OCTETs following the column (':') separator. If size
OCTETs are not followed by a quote ('"') character, the encoding
is syntactically invalid.
o Empty quoted-values are encoded as a 4-OCTET sequence "0:".
o Any bare-value MAY be encoded as a quoted-value. A quoted-value
MUST be interpreted after the encoding is removed. For example,
number 1234 can be encoded as four OCTETs 1234 or as eight OCTETs
"4:1234", yielding exactly the same meaning.
o By default, all values MUST be interpreted as having UTF-8
encoding. Note that ASCII is a UTF-8 subset, and that the syntax
prohibits non-ASCII characters outside of the "data" element.
(XXX: check that this is enough to satisfy i18n and whatever
internationalization requirements IETF has)
Messages violating formatting rules are, by definition, invalid. See
Section 5 for rules on processing invalid messages.
3.2 Message Rendering
OCP message samples in this specification and its application
bindings may not be typeset to depict minor syntactical details of
OCP message format. Specifically, SP and CRLF characters are not
shown explicitly. No rendering of an OCP message can be used to infer
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message format. The message format definition above is the only
normative source for all implementations.
On occasion, an OCP message line exceeds text width allowed by this
specification format. A backslash ("\"), a "soft linebreak" character
is used to emphasize a protocol-violating presentation-only
linebreak. Bare backslashes are prohibited by OCP syntax. Similarly,
a "\r\n" string is sometimes used to emphasize the presence of a CRLF
sequence, usually before OCP message payload. Normally, visible end
of line corresponds to the CRLF sequence on the wire.
The next section (Section 3.3) contains specific OCP message
examples, some of which illustrate the above rendering techniques.
3.3 Message Examples
OCP syntax provides for compact representation of short control
messages and required parameters while allowing for parameter
extensions. Below are examples of short control messages. The
required CRLF sequence at the end of each line is not shown
explicitly (see Section 3.2).
TS 1;
ping 123 2;
data-pause 22 1;
x-doit "5:xyzzy";
Figure 4
The above examples contain atomic anonymous parameter values such as
number and string constants. OCP messages sometimes use more
complicated parameters such as item lists or structures with named
values. As both messages below illustrate, structures and lists can
be nested:
i-can ({"28:http://iana.org/opes/ocp/TLS"});
i-can ({\
"38:http://iana.org/opes/ocp/HTTP/response"
Optional-Parts: (request-header)
},{\
"38:http://iana.org/opes/ocp/HTTP/response"
Optional-Parts: (request-header,request-body)
Transfer-Encodings: (chunked)
});
Figure 5
Optional parameters and extensions are possible using named
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parameters approach as illustrated by the following example. The
data-need (Section 12.16) message in the example has three anonymous
parameters and two named parameters (the last one being an
extension).
data-need 1 3 12345
size-request: 16384
x-need-info: "26:twenty six octet extension";
Figure 6
Finally, any message may have a payload part. For example, the Data
Use Mine (DUM (Section 12.9)) message below carries 8865 bytes of raw
data.
DUM 1 3 0 8865
modp: 75
\r\n
8865:<... 8865 octets of raw data ...>;
Figure 7
3.4 Message Names
Most OCP messages defined in this specification have short names,
formed by abbreviating or compressing a longer but human-friendlier
message title. Short names without a central registration system
(like this specification or IANA registry) are likely to cause
conflicts. Informal protocol extensions should avoid short names. To
emphasize what is already defined by message syntax, implementations
cannot assume that all message names are very short.
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4. Transactions
OCP transaction is a logical sequence of OCP messages processing a
single original application message. The result of the processing may
be zero or more application messages, adapted from the original. A
typical transaction consists of two message flows: a flow from the
OPES processor to the callout server (sending original application
message) and a flow from the callout server to the OPES processor
(sending adapted application messages). The number of application
messages produced by the callout server and whether the callout
server actually modifies original application message may depend on
the requested callout service and other factors. The OPES processor
or the callout server can terminate the transaction by sending a
corresponding message to the other side.
A OCP transaction starts with an explicit Transaction Start (TS
(Section 12.5)) message sent by the OPES processor. A transaction
ends with the first Transaction End (TE (Section 12.6)) message sent
or received, explicit or implied, which can be sent by either side.
Zero or more OCP messages associated with the transaction can be
exchanged in between. The figure below illustrates possible message
sequence (prefix "P" stands for OCP Client, OPES processor; prefix
"S" stands for OCP callout server). Some message details are omitted.
P: TS 10;
P: AMS 10 1;
... processor sending application data to the callout server
S: AMS 10 2;
... callout server sending application data to the processor
... processor sending application data to the callout server
P: AME 10 1 result;
S: AME 10 2 result;
P: TE 10 result;
Figure 8
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5. Invalid input
This specification contains many criteria for valid OCP messages and
their parts, including syntax rules, semantics requirements, and
relationship to agents state. "Invalid input" in this context means
messages or message parts that violate at least one of the normative
rules of this specification. A message with an invalid part is, by
definition, invalid.
Unless explicitly allowed otherwise, OCP agents MUST terminate the
transaction if they receive an invalid message with transaction scope
and MUST terminate the connection if they receive an invalid message
with a connection scope. Such terminations MUST carry the result
status code of 400 and MAY carry termination cause information in
result status reason (see Section 11.10).
OCP usually deals with optional but invasive application message
manipulations where correctness ought to be valued above robustness.
For example, a failure to insert or remove certain optional web page
content is usually far less disturbing than corrupting the host page
while performing that insertion or removal. Most OPES adaptations are
high-level in nature, which makes it impossible to automatically
assess correctness of operations, especially if "robustness guesses"
are involved.
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6. Negotiation
The negotiation mechanism allows OCP client and server to agree on
mutually acceptable set of features, including optional and
application-specific behavior as well as OCP extensions. For example,
transport encryption, data format, and support for a new message can
be negotiated. Negotiation implies intent for a behavioral change. A
related mechanism allowing an agent to query capabilities of its
counterpart without changing counterpart's behavior is described in
Section 7.
Most negotiations require at least one round trip time delay. In rare
cases when other side's response is not required immediately,
negotiation delay can be eliminated.
Two core negotiation primitives are supported: negotiation offer and
negotiation response. A Negotiation Offer (NO (Section 12.20))
message allows an agent to specify a set of features from which the
responder has to select exactly one feature it prefers. The selection
is sent using a Negotiation Response (NR (Section 12.21)) message.
If the response is positive both sides assume that the selected
feature is in effect. If the response is negative, no behavioral
changes are assumed. In either case, further offers may follow.
Negotiating OCP agents have to take into account prior negotiated
(i.e., already enabled) features. OCP agents MUST NOT make and MUST
reject offers that would lead to a conflict with already negotiated
features. For example, an agent cannot offer an HTTP application
profile for a connection that already has SMTP application profile
enabled because there would be no way to resolve the conflict for a
given transaction. Similarly, once TLSv1 connection encryption is
negotiated, an agent must not offer and must reject offers for SSLv2
connection encryption.
Negotiation Offer (NO (Section 12.20)) messages may be sent by either
agent. Feature specifications MAY restrict initiator role to one of
the agents. For example, negotiation of transport security feature
[XXX] is initiated exclusively by OPES processors to avoid situations
where both agents wait for each other to make an offer.
Since either agent may make an offer, two "concurrent" offers may be
made at the same time, by the two communicating agents. Unmanaged
concurrent offers may lead to a negotiation deadlock. By giving OPES
processor a priority, offer handling rules (Section 12.20) ensure
that only one offer per transport connection is honored at a time,
and the other concurrent offers are ignored by both agents.
Violation of negotiation rules leads to OCP connection termination.
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This design reduces the number of negotiation scenarios resulting in
a deadlock when one of the agents is not compliant.
(XXX: add examples)
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7. Capability and State Inquiry
This section describes OCP interface for querying the capability or
state of an agent. A related mechanism allowing agents to negotiate
features is described in Section 6.
OCP supports two inquiry primitives: capability inquiry and state
inquiry. Capability inquiry (see Section 12.23) is concerned about
supported, but not necessarily active, features. A response to such a
query (see Section 12.22) may contain ranges of supported feature
parameters. State inquiry (Section 12.25) focuses on the current
state of enabled and active features. A response to a state inquiry
(Section 12.24) contains feature parameters specific to agent's
current state at the time the inquiry is received.
For example, a capability inquiry may reveal that an agent supports
two transport security mechanisms while a state inquiry may show a
specific security profile being enabled at the time of the inquiry.
The primary purpose of these inquiries is debugging and
troubleshooting rather than automated fine-tuning of cooperating
agent behavior and configurations. The latter is directly supported
by OCP negotiation mechanism.
(XXX: do we need this OPTIONS-like feature at all?)
(XXX: add examples)
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8. 'Data Recycling' Optimization
Many adaptations do not require any data modifications (e.g., message
logging or blocking). Some adaptations modify only a small portion of
application message content (e.g., ad filtering or insertion). Yet,
in many cases the callout service needs to see complete data. By
default, unmodified data would first travel from the OPES processor
to the callout server and then back. The "data recycling"
optimization in OCP helps to eliminate the return trip if both OCP
agents cooperate. This optimization is optional.
To avoid sending unmodified data back, a callout service has to know
that the OPES processor has a copy of the data. Since data sizes can
be very large and the callout service may not know in advance whether
it will be able to utilize the processor copy, it is not possible to
require the processor to keep a copy of the entire original data.
Instead, it is expected that a processor may keep some portion of the
data, depending on processor settings and state.
When processor commits to keeping a data chunk, it announces its
decision and the chunk parameters via a Kept parameter of a Data Use
Mine (DUM (Section 12.9)) message. The callout server MAY "use" the
chunk by sending a Data Use Yours (DUY (Section 12.10)) message
referring to the preserved chunk. That OCP message does not have
payload and, hence, the return trip is eliminated.
Since the mapping between original and adapted data is not known to
the processor, the processor MUST keep the chunk until the end of the
corresponding transaction, unless the callout server explicitly tells
processor that the chunk is not needed. As implied by the above
requirement, the processor cannot assume that a data chunk is no
longer needed just because the callout server sent a Data Use Yours
(DUY (Section 12.10)) message or adapted data with, say, the same
offset as the preserved chunk.
Both agents may benefit from data reuse. An OPES processor has to
allocate storage to support this optimization while a callout server
does not. On the other hand, it is the callout server that is
responsible for relieving the processor from data preservation
commitments. There is no simple way to resolve this conflict of
interest on a protocol level. Some OPES processors may allocate a
relatively small buffer for data preservation purposes and start
discarding data when the buffer gets full. Such technique would
benefit callout services that can quickly decide whether they need
the data. Another processor strategy would be to size the buffer
based on historical data reuse statistics. To improve chances of
beneficial cooperation, callout servers are strongly encouraged to
immediately notify OPES processors of unwanted data. The callout
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server that is not going to send a Data Use Yours (DUY (Section
12.10)) messages (for a specific data ranges or at all), SHOULD
immediately inform the OPES processor of that fact with corresponding
Data Won't Send Yours (DWSY (Section 12.11)) message(s) or other
mechanisms.
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9. 'Out Of The Loop' Optimization
Many services are applicable to a small percentage of application
messages and yet have to see the beginning of every application
message to decide on applicability (e.g., services that adapt based
on declared or guessed MIME type). Many services adapt application
message "headers" or "prefix" only and are not interested in the
remaining parts of an application message (e.g., URL blocking and ad
insertion services). 'Getting Out Of The Loop' optimization allows a
callout server to get out of application message processing loop when
the server is confident that it does not need to see remaining data.
Two conditions are necessary for the callout server to get out of the
loop nicely:
No adaptation need: The callout server must finish its primary work.
It should sent all adapted data to the processor and should
require no more original data from the processor. Since
adaptations and adaptation needs might not depend on original
data, only the server can evaluate this condition.
No copying need: The OPES processor must receive back all unpreserved
data chunks that were sent to the callout server for adaptation.
Note that data chunks that are not preserved and are not returned
by the callout service would be lost. Since the server may not
have seen all the original data sent, only the processor can
evaluate this condition.
Since no single agent can determine both conditions, the agents have
to cooperate. The callout server has to tell the processor when the
first condition is true. This is done via a Data Want Out (DWO
(Section 12.13)) message (XXX: mention that it is not a "I Wont
Adopt Anymore" message). The processor has to tell the service that
there are no pending unpreserved data chunks. This is done by
terminating the application message delivery using an Application
Message End (AME (Section 12.8)) message with a 206 "Get Out" result.
Between the above two conditions or messages, the callout server
returns all original data unmodified back to the OPES processor,
draining pending (uncopied) data queue (if any).
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10. Message Parameters
This section defines parameter value types that are used for message
definitions (Section 12).
10.1 Type Declaration Mnemonic
A parameter value type is a named set of syntax and semantics rules.
This section defines a simple, formal declaration mnemonic for types,
labeled TDM. TDM is meant to facilitate type declaration in this
specification and its extensions. OCP extensions MUST use TDM when
declaring new value types.
Atom, list, and structure constructs are three available base types.
Their syntax and semantics rules are defined in Section 3.1. New
types can be declared using TDM to extend base types semantics but
not syntax. The following templates are used to extend semantics of
types. The new semantics rules are meant to be attached to each
declaration using prose text. Things in angle brackets are template
placeholders to be substituted with actual type names or parameter
name tokens; square brackets surround optional structure members.
Declaring a new atomic type
<new-type-name>: extends atom;
Declaring a new list with old-type-name items. Unless explicitly
noted otherwise, empty lists are valid.
<new-type-name>: extends list of <old-type-name>;
Declaring a new structure with a few anonymous members and named
members. Neither group have to exist. Note that it is always possible
for extensions to add more members to old structures without
affecting type semantics because unrecognized members are ignored by
compliant implementations.
<new-type-name>: extends structure with {
<old-type-nameA> <old-type-nameB> [<old-type-nameC>] ...;
<member-name1>: <old-type-name1>;
<member-name2>: <old-type-name2>;
[<member-name3>: <old-type-name3>];
...
};
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Extending a non-base type with more semantics details. The "with
{...}" part can only be used when old-type-name is a structure-based
type; in this case, new anonymous members are appended to the
anonymous members of the old structure, and new named members are
merged with named members of the old structure.
<new-type-name>: extends <old-type-name> with {
<old-type-nameA> <old-type-nameB> [<old-type-nameC>] ...;
<member-name1>: <old-type-name1>;
<member-name2>: <old-type-name2>;
[<member-name3>: <old-type-name3>];
...
};
All extended types may be used as a replacement of the types they
extend. For example, a Negotiation Offer (NO (Section 12.20)) message
defined below uses a parameter of type Features. Features, also
defined below, is a list of Feature items. A Feature is a
structure-based type. An OCP extension (e.g., an HTTP application
binding) may extend the Feature type and use a value of that extended
type in a negotiation offer. Recipients that are aware of the
extension will recognize added members in Services items and
negotiate accordingly. Others will ignore them. Declaring a parameter
type freezes that parameter base syntax, but allows for fine-tuning
its semantics in extensions.
All OCP Core parameter types are declared using TDM. See below for
examples.
10.2 Parameter Types
This sections defines common parameter types using TDM. Before using
a parameter value, an agent MUST check whether it has the expected
type (i.e., whether it meets each rule from the type definition). A
rule violation means that the parameter is invalid. See Section 5
for rules on processing invalid input.
OCP extensions MAY define their own types. If they do, OCP extensions
MUST define types with exactly one base format, and MUST specify type
of every new parameter they introduce.
10.2.1 Uri
uri: extends atom;
Uri (universal resource identifier) is an atom formatted according to
URI rules in [RFC2396].
Often, a uri parameter is used as a unique (within a given scope)
identifier. Many uri parameters are URLs. Unless noted otherwise, URL
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identifiers do not imply existence of a serviceable resource at the
location they specify. For example, an HTTP request for "http://
ietf.org/opes/ocp/raw/tcp" URL (XXX: identifying an OCP transport
profile) may result in a 404 (Not Found) response.
10.2.2 Uni
uni: extends atom;
Uni (universal numeric identifier) is an atom formatted as dec-number
and with a value in the [0, 2147483647] inclusive range.
Often, a uni parameter is used as a unique (within a given scope)
identifier.
10.2.3 Size
size: extends atom;
Size is an atom formatted as dec-number and with a value in the [0,
2147483647] inclusive range.
OCP cannot handle application messages that exceed 2147483647 OCTETs
in size or require larger sizes as a part of OCP marshaling process.
However, since the definition of an application message is up to OCP
agents, it is possible to work around this limitation at a processing
level above OCP.
10.2.4 Boolean
boolean: extends atom;
Boolean type is an atom formatted as dec-number and with a value in
the [0, 1] inclusive range. A value of zero ("0") is interpreted as
"false". A value of one ("1") is interpreted as "true".
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11. Parameter Definitions
11.1 xid
xid: extends uni;
"Xid", an OCP transaction identifier, has "uni" type. "Xid" uniquely
identifies an OCP transaction originated by a given OPES processor.
11.2 rid
xid: extends uni;
"Rid", an OCP request identifier, has "uni" type. "Rid" uniquely
identifies an OCP request message on a connection. Request
identifiers are used to match certain requests and responses.
11.3 service
service: extends structure with {
uri;
};
"Service" is an "{id}" structure, where the id member is an OPES
service identifier of type "Uri". Services may have service-dependent
parameters. A document defining the service identifier for use with
OCP MUST also define service-dependent parameters as additional
"service" structure members, if any. For example, a "service" value
may look like this:
{"28:http://ietf.org/opes/ocp/tls" "8:blowfish"}
11.4 services
services: extends list of service;
"Services" is a list of "service" values. Unless noted otherwise, the
order of the values is the requested or actual service application
order.
This parameter MAY appear in any message from the callout server that
has an "am-id" parameter. If this parameter appears in a message from
the callout server that carries or refers to application data, its
value indicates the services actually applied to that data. If this
parameter appears in a message from the callout server that neither
carries nor refers to application data, its value indicates the
services that MAY be applied to that application message in the
future. (XXX: say where it cannot appear?)(XXX: make it symmetric
with processor)
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11.5 sg-id
sg-id: extends uni;
"Sg-id", a service group identifier, is of type "uni". "Sg-id"
uniquely identifies a group of services on an OCP connection.
11.6 am-id
am-id: extends uni;
"Am-id", an application message identifier, is of type "uni". "Am-id"
uniquely identifies an application message within an OCP transaction.
11.7 size-request
size-request: extends size;
"Size-request" is of type "Size". The sender uses "size-request" to
specify the number of data or metadata OCTETs it desires to receive.
11.8 offset
offset: extends size;
"Offset" is of type "Size". "Offset" describes payload start position
relative to the application message data or metadata. The offset of
the first application byte has a value of zero.
11.9 modp
offset: extends percent;
Future data modification prediction in percents. A modp value of 0
(zero) means the sender predicts that there will be no data
modifications. A value of 100 means the sender is predicts that there
will be data modifications. The value excludes data in the current
OCP message, if any. The prediction applies to a single application
message. This parameter can be used with any OCP message that has
am-id parameter.
11.10 result
result: extends structure with {
atom [string];
};
OCP processing result. Result is a structure with two documented
members: a required Uni status code and an optional string containing
informative textual information, not intended for automated
processing. For example,
{ 200 "2:OK" }
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This specification defines the following status codes:
Result Status Codes
+--------+--------------+-------------------------------------------+
| code | text | semantics |
+--------+--------------+-------------------------------------------+
| 200 | OK | Overall success. This specification does |
| | | not contain any general actions for 200 |
| | | status code recipients. |
| | | |
| 206 | partial data | Partial success. When sent by an OPES |
| | | processor, the remaining original data is |
| | | not going to be sent due to the callout |
| | | server disinterest expressed via a Data |
| | | Won't Look At Yours (DWLY) or a Data Want |
| | | Out (DWO) message. When sent by a callout |
| | | server, the remaining adapted application |
| | | data is identical to the remaining |
| | | original data flow and should come |
| | | directly from the OPES processor that |
| | | already committed to "Out Of The Loop" |
| | | optimization by sending a corresponding |
| | | AME message after receiving a Data Want |
| | | Out (DWO) message. |
| | | |
| 400 | failure | An error, exception, or trouble. A |
| | | recipient of a 400 (failure) result of a |
| | | AME, TE, or CE message MUST destroy any |
| | | state or data associated with the |
| | | corresponding data flow, transaction, or |
| | | connection. For example, adapted version |
| | | of the application message data must be |
| | | purged from the processor cache if the |
| | | OPES processor receives an Application |
| | | Message End (AME) message with result |
| | | code of 400. |
+--------+--------------+-------------------------------------------+
Specific OCP messages may require code-specific actions.
Extending result semantics is possible by adding new "result"
structure members or negotiating additional result codes (e.g., as a
part of a negotiated profile). A recipient of an unknown (in
then-current context) result code MUST act as if code 400 (failure)
was received.
The recipient of a message without the actual result parameter, but
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with an optional formal result parameter MUST act as if code 200 (OK)
was received.
11.11 feature
feature: extends structure with {
uri;
};
A OCP feature identifier with optional feature parameters (sometimes
called attributes). Used to declare support and negotiate use of OCP
optional or extension features.
OCP Core does not defines any features.
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12. Message Definitions
This section describes specific OCP messages. Each message is given a
unique name and usually has a set of anonymous and/or named
parameters. The order of anonymous parameters is specified in the
message definitions below. No particular order for named parameters
is implied by this specification. No more than one named-parameter
with a given name can appear in the message; messages with multiple
equally-named parameters are semantically invalid.
A recipient MUST be able to parse any valid message (see Section
3.1), subject to recipient resources limitations. If resources are
exhausted or if a syntactically malformed message is received, the
recipient MUST treat the message as invalid and having OCP connection
scope (see Section 5). The recipient MAY distinguish resource
limitations from syntax errors in the result reason string.
Unknown or unexpected message names, parameters, and payloads may be
valid extensions. For example, an "extra" anonymous parameter may be
used for a given message, in addition to what is documented in the
message definition below. A recipient MUST ignore any valid but
unknown or unexpected name, parameter, member, or payload. Recipients
MAY report (e.g., log) unknown or unexpected elements, of course.
Some message parameter values are identifiers. These identifiers are
created, used, and destroyed by OCP agents via corresponding
messages. Except for messages that introduce new identifiers, all
sent identifiers MUST be known to the recipient (i.e., introduced and
not ended by previous messages). Except for messages that introduce
new identifier value, unknown identifiers invalidate the host OCP
message. The recipient of an unknown identifier value MUST treat the
message as invalid. For example, recipient must terminate a
transaction when Data Use Mine (DUM (Section 12.9)) message xid
parameter refers to an unknown transaction.
(XXX Message parameters in [square brackets] are OPTIONAL. Other
parameters are REQUIRED.)
12.1 Connection Start (CS)
name: CS
anonymous parameters: none
named parameters: none
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payload: no
senders: OPES processor only
A Connection Start (CS) message indicates the start of an OCP
communication from the OPES processor. An OPES processor MUST send
this message immediately after establishing a transport connection to
the callout server. If the first message a callout server receives is
not Connection Start (CS), the callout server MUST terminate the
connection with a Connection End (CE (Section 12.2)) message.
Upon receiving of this message, the callout server MUST either start
maintaining connection state or refuse further processing by
responding with a Connection End (CE (Section 12.2)) message. A
callout server MUST maintain the state until it detects the end of
the connection or until it terminates the connection itself.
A callout server MUST NOT send this message (XXX: why?). If the first
message received by an OPES processor is a Connection Start (CS
(Section 12.1)) message, the processor MUST terminate the connection
with a Connection End (CE (Section 12.2)) message.
An OPES processor MUST NOT resend this message. If a callout server
receives this message and it is not the first message on a
connection, then, the callout server MUST terminate the connection
with a Connection End (CE (Section 12.2)) message.
With TCP/IP as transport, raw TCP connections (local and remote peer
addresses) identify an OCP connection. Other transports may provide
OCP connection identifiers to distinguish connections that share the
same transport. For example, a single BEEP [RFC3080] channel may be
designated as a single OCP connection.
12.2 Connection End (CE)
name: CE
anonymous parameters: [result]
named parameters: [error]
payload: no
senders: both OPES processor and callout server
Connection End (CE) Indicates an end of a transport connection. The
agent initiating closing or termination of a connection MUST send
this message immediately prior to closing or termination. The
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recipient MUST free associated state, including transport state. The
destruction of the state ensures that messages outside of the old
connection are ignored.
Connection termination without a Connection End (CE) message
indicates that the connection was prematurely closed without the
closing-side agent prior knowledge or intent. When an agent detects a
prematurely closed connection, the agent MUST behave as if a
Connection End (CE) message indicating a fatal error was received.
A Connection End (CE) message implies the end of all transactions,
negotiations, and service groups opened or active on the connection
being ended.
12.3 Create Service Group (SGC)
name: SGC
anonymous parameters: sg-id services
named parameters: none
payload: no
senders: both OPES processor and callout server
An Create Service Group (SGC) message instructs the recipient to
associate a list of services with a given service group identifier
("sg-id"). The group can then be referred by the sender using the
identifier. The recipient MUST maintain the association until a
corresponding Destroy Service Group (SGD (Section 12.4)) message is
received or implied.
Service groups have a connection scope. Transaction management
messages do not affect existing service groups.
Maintaining service group associations requires resources (e.g.,
storage to keep the group identifier and a list of service IDs).
Thus, there is a finite number of associations an implementation can
maintain. Callout servers MUST be able to maintain at least one
association for each OCP connection they accept. If a recipient of a
Create Service Group (SGC) message does not create the requested
association, it MUST immediately terminate the connection with a
Connection End (CE (Section 12.2)) message.
(XXX: document that wrong sq-id lead to semantically invalid
messages)
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12.4 Destroy Service Group (SGD)
name: SGD
anonymous parameters: sg-id
named parameters: none
payload: no
senders: both OPES processor and callout server
A Destroy Service Group (SGD) message instructs the recipient to
forget about the service group associated with the specified "sg-id"
identifier. If "sg-id" refers to an existing group, the recipient
MUST destroy the association. Otherwise, the recipient MUST treat the
message as invalid.
12.5 Transaction Start (TS)
name: TS
anonymous parameters: xid sg-id
named parameters: none
payload: no
senders: OPES processor only
Indicates the start of an OCP transaction. A callout server MUST NOT
send this message. Upon receiving of this message, the callout server
MUST either start maintaining transaction state or refuse further
processing by responding with a 'xaction-end' message. A callout
server MUST maintain the state until it receives a message indicating
the end of the transaction or until it terminates the transaction
itself.
The "sg-id" parameter refers to a service group created with a Create
Service Group (SGC (Section 12.3)) message. If no group is associated
with "sg-id", the callout server MUST treat the message as invalid.
Otherwise, the callout server MUST use the list of services
associated with "sg-id".
This message introduces transaction identifier (xid).
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12.6 Transaction End (TE)
name: TE
anonymous parameters: xid, result
named parameters: [error]
payload: no
senders: both OPES processor and callout server
Indicates the end of the OCP transaction. The recipient MUST free
associated state. The destruction of the state ensures that future
messages referring to the same transaction, if any, will be ignored.
This message terminates the life of the transaction identifier (xid).
An OCP agent MUST send a Transaction End (TE) message immediately
after it makes a decision to send no more messages related to the
corresponding transaction. Violating this requirement may cause, for
example, unnecessary delays and even timeouts for OPES processors
that rely on this end-of-file condition to proceed.
12.7 Application Message Start (AMS)
name: AMS
anonymous parameters: xid, am-id
named parameters: none
payload: no
senders: both OPES processor and callout server
Indicates the start of processing of an application message. The
recipient MUST either start processing the application message (and
maintain its state) or refuse further processing with an
'app-message-end' message. The recipient MUST maintain the state
until it receives a message indicating the end of application message
processing or until it terminates the processing itself.
When 'app-message-start' message is sent to the callout server, the
callout server usually sends an app-message-start message back,
announcing the creation of an adapted version of the original
application message. Such response may be delayed. For example, the
callout server may wait for more information to come from the OPES
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processor.
When 'app-message-start' message is sent to the OPES processor, an
OPTIONAL "services" parameter describes callout services that the
server MAY apply to the application message. Usually, the "services"
value matches what was asked by the OPES processor.
This message introduces application message identifier (am-id).
12.8 Application Message End (AME)
name: AME
anonymous parameters: xid, am-id, result
named parameters: [error]
payload: no
senders: both OPES processor and callout server
Informs the recipient that there will be no more data for the
corresponding application message and indicates the end of
application message processing. The recipient MUST free associated
application message state. The destruction of the state ensures that
future messages referring to the same application message, if any,
will be ignored.
An Application Message End (AME) message ends any data preservation
commitments associated with the corresponding application message.
This message terminates the life of the application message
identifier (am-id).
An OCP agent MUST send an Application Message End (AME) message
immediately after it makes a decision to send no more data for the
corresponding application message. Violating this requirement may
cause, for example, unnecessary delays and even timeouts for callout
servers that rely on this end-of-file condition to proceed.
12.9 Data Use Mine (DUM)
name: DUM
anonymous parameters: xid, am-id, offset
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named parameters: [As-is: am-id offset], [Kept: offset], [modp],
[ack]
payload: yes
senders: both OPES processor and callout server
This is the only OCP message that may carry application data. There
MUST NOT be any gaps in data supplied by Data Use Mine (DUM) and Data
Use Yours (DUY) messages (i.e., the offset of the next data message
must be equal to the offset plus the payload size of the previous
data message) (XXX: we do not need offset then; should we keep it as
a validation mechanism?) (XXX: document what to do when this MUST is
violated). Zero payload size is permitted and is useful for
communicating predictions without sending data.
When an OPES processor sends a "Kept" parameter, the processor MUST
keep a copy of the attached data (the preservation commitment
starts). The offset parameter specifies the offset of the first OCTET
in the payload (XXX: relative to what? DUM messages may transmit
metadata that is not kept). The first "Kept" offset sent is zero. The
next "Kept" offset sent is the previous "Kept" offset sent plus the
size of the previous "Kept" payload, modulo 2^32. Recipients of
invalid "Kept" parameters, MUST either terminate the corresponding
transaction or MUST not use any "Kept" parameter during the
transaction, including those received before the invalid one. This
requirement helps preserve data integrity when "Kept" optimization is
used by the processor.
An "as-is" parameter, sent only by the callout server, MUST specify a
data fragment in the original data flow. The callout server informs
the processor that the attached data is identical to an original data
fragment the processor sent earlier. Identical means that all adapted
OCTETs have the same numeric value as the corresponding original
OCTETs. The "am-id" field MUST correspond to the original application
message identifier for the same transaction. If the parameter does
not specify any original data fragment, the parameter is invalid.
Invalid "as-is" parameters MUST be ignored.
The recipient of an "ack" parameter MUST respond with a 'data-ack'
message. Note that OCP Core does not require these acknowledgments to
successfully exchange data; they are supported for debugging and
similar important applications outside of the Core scope.
The Data Use Mine (DUM) message has no effect on data preservation
commitment (Section 8).
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12.10 Data Use Yours (DUY)
name: DUY
anonymous parameters: xid, am-id, kept-offset, kept-size
payload: no
senders: callout server only
Tells the OPES processor to use "kept-size" bytes of preserved data
starting at "kept-offset" offset, as if that data came from the
callout server in a Data Use Mine (DUM (Section 12.9)) message with
payload size equal to the "kept-size" parameter. The identified data
fragment MUST be under the preservation commitment. If the OPES
processor receives a Data Use Yours (DUY) message for data not under
preservation commitment, the message is invalid.
If a Data Use Yours (DUY) message is invalid, the OPES processor MUST
abort am-id message processing (XXX: document how processing should
be aborted).
A Data Use Yours (DUY) message has no effect on data preservation
commitment (Section 8).
12.11 Data Won't Send Yours (DWSY)
name: DWSY
anonymous parameters: xid, am-id, offset
payload: no
senders: callout server only
The Data Won't Send Yours (DWSY) message relieves OPES processor from
preservation commitment for data at or below the given offset. After
sending this message, the callout server MUST NOT send Data Use Yours
(DUY) messages referring to data at or below the given offset. An
OPES processor that preserves any data at or below the offset MAY
stop preserving that data. An OPES processor that does not preserve
data at or below the offset MAY NOT start preserving that data.
A callout server MAY send DWSY offsets lower than or equal to the
previously sent DWSY offsets. However, as the above rules imply,
such offsets would have no effect if processor already acted on a
previous DWSY message with an equal or higher offset. Informally, a
processor may maintain a single "not useful for preservation" size
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per transaction and that size would never decrease.
Note that the message may refer to portions of data that has not been
used via the Data Use Yours message, indicating that callout server
is not going to use some preserved data.
For example, an offset value of 2147483647 indicates that the server
is not going to send any more Data Use Yours (DUY) messages.
See the Data Won't Look At Yours (DWLY (Section 12.12)) message
description for requirements related to using both DWSY and DWLY
messages within one transaction.
12.12 Data Won't Look At Yours (DWLY)
name: DWLY
anonymous parameters: xid, am-id, offset
payload: no
senders: callout server only
The Data Won't Look At Yours (DWLY) message informs OPES processor
that the callout server is going to ignore and discard original data
starting with the specified offset. After sending this message, the
callout server MUST NOT send Data Use Yours (DUY) messages referring
to data at or above the given offset. An OPES processor that
preserves any data at or above the offset MAY stop preserving that
data. An OPES processor that does not preserve data at or above the
offset MAY NOT start preserving that data.
If the recipient of a DWLY message has sent all original data below
the given offset, the processor SHOULD terminate the original
application message delivery using a Application Message End (AME
(Section 12.8)) message with a 206 result status code.
A callout server MAY send DWLY offsets higher than or equal to the
previously sent DWLY offsets. However, as the above rules imply,
such offsets would have no effect if processor already acted on a
previous DWLY message with an equal or lower offset. Informally, a
processor may maintain a single "not useful for sending" offset per
transaction and that offset would never increase.
For example, an offset value of zero indicates that the server is
going to ignore all original data and generate an adapted application
message from scratch. The OPES processor should most likely not send
any data to the callout server in this case.
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A callout server MUST NOT use both Data Won't Look At Yours (DWLY)
and Data Won't Send Yours (DWSY) messages during the same
transaction. Doing so may make OPES processor 206 (partial content)
status code ambiguous. If an OPES processor receives both DWLY and
DWSY messages during the same transaction, the processor MUST
terminate the transaction with an error.
12.13 Data Want Out (DWO)
name: DWO
anonymous parameters: xid, am-id, offset
payload: no
senders: callout server only
The Data Want Out (DWO) message informs OPES processor that the
callout server wants to get out of the processing loop once the
original data at or above the specified offset is received (see
Section 9). The OPES processor MAY respond (not necessarily
immediately) with an Application Message End (AME) message with 206
result status code. If the callout server receives that 206 status
code response, the server MAY terminate adaptation by sending an
Application Message End (AME) message with 206 result status code and
getting out of the loop.
While waiting for the 206 status code response, the callout server
MAY continue original data modifications. The Data Want Out (DWO)
message indicates desire to get out of the loop, not a commitment to
stop data modifications and not a permission to stop forwarding
unmodified data.
A callout server MUST NOT use both Data Want Out (DWO) and Data Won't
Look At Yours (DWLY) messages during the same transaction. Doing so
may make OPES processor 206 (partial content) status code ambiguous.
If an OPES processor receives both DWO and DWLY messages during the
same transaction, the processor MUST terminate the transaction with
an error.
12.14 Data Pause (data-pause)
name: data-pause
anonymous parameters: xid am-id
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named parameters: none
payload: no
senders: callout server only
Sent by a callout server, the Data Pause (data-pause) message informs
the OPES processor that it must stop sending data to the callout
server until the callout server explicitly asks for more data using a
Data Need (data-need (Section 12.16)) message. Upon receiving a
data-pause message, the OPES processor SHOULD stop sending
application message data to the callout server. If the OPES
processor stops sending, it SHOULD send a corresponding Data Paused
(data-paused (Section 12.15)) message to the callout server. Until
the OPES processor receives the message, it may continue sending data
to the callout server, of course. Thus, when the callout server sends
this message, it MUST NOT mark the application message as "paused".
(XXX: should we use MUST or MAY instead of SHOULDs above?)
An OPES processor MUST NOT send this message. A callout server MUST
ignore this message.
12.15 Data Paused (data-paused)
name: data-paused
anonymous parameters: xid, am-id
named parameters: none
payload: no
senders: OPES processor only
Sent by an OPES processor, the Data Paused (data-paused) message
informs the callout server that there will be no more data for the
specified application message until the callout server explicitly
asks for data using a 'Data Need (data-need (Section 12.16))'
message. After sending a data-paused message, the OPES processor
MUST stop sending application message data to the callout server. At
that time, there may be still unprocessed data in the callout server
queue, of course. When the callout server receives the message, it
MAY mark the application message as "paused". If the callout server
receives data for a paused message (a violation of the above MUST),
the callout server MAY abort application message processing.
A callout server MUST NOT send this message. An OPES processor MUST
ignore this message.
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12.16 Data Need (data-need)
name: data-need
anonymous parameters: xid am-id offset
named parameters: [Size-request: size]
payload: no
senders: callout server only
Informs the OPES processor that the callout server needs more
application message data. The "offset" parameter indicates the amount
of data already received.
If a "Size-request" parameter is present, its value is the suggested
data size, and it MAY be ignored by the OPES processor. An absent
"Size-request" parameter implies "any size". The callout server MUST
clear the "paused" state of the application message processing just
before sending this message.
The OPES processor MUST ignore a data-need message if the OPES
processor already sent request data.
An OPES processor MUST NOT send Data Need (data-need) messages (XXX:
should we give an OPES processor the same abilities to pause/resume
message processing that a callout server has?)
12.17 Data ACK (DACK)
name: DACK
anonymous parameters: xid, am-id, offset, size
named parameters: [wont-forward]
payload: no
senders: callout server only
Informs the OPES processor that the corresponding data chunk has been
received by the callout server.
An optional "wont-forward" flag terminates preservation commitment
for the corresponding data, if any. The flag is defined for callout
server 'data-ack' messages only.
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Responding with Data ACK (DACK) messages to Data Use Mine (DUM
(Section 12.9)) messages with an "ack" flag is REQUIRED. Responding
with DACK messages to DUM messages without an "ack" flag is OPTIONAL.
Implementations SHOULD be able to support debugging mode where every
DUM message is acked. (XXX: should we require responses for Data Use
Yours messages as well?)
A 'data-ack' response SHOULD be sent as soon as possible. If the
callout server does not know immediately whether it will forward the
data, it MUST respond without a "wont-forward" flag. If, at any time,
the callout server decides that it will not forward the data, it
SHOULD send a 'data-ack' message with a "wont-forward" flag. Thus,
multiple 'data-ack' messages and unsolicited 'data-ack' messages are
allowed.
Sending of a DACK message means that a complete DUM message has been
received, but does not imply that the data has been processed in any
other way.
The data acknowledgment mechanism has several purposes: to allow OPES
processor to gauge the speed at which the callout server is receiving
data (for optimization purposes); to send back "wont-forward"
notifications; and to assist in debugging OCP communications.
12.18 I Am Here (pong)
name: pong
anonymous parameters: [xid [am-id]]
named parameters: none
payload: no
senders: both OPES processor and callout server
Parameterless form informs the recipient that the sender is still
maintaining the OCP connection. If "xid" or "am-id" identifier(s) are
used, the message informs the recipient that the sender is still
processing the corresponding transaction or an application message.
An 'i-am-here' message MAY be sent without solicitation.
An 'i-am-here' message MUST be sent in response to an 'are-you-there'
request. The response MUST have the same set of "xid" and "am-id"
parameters if those identifiers are still valid. The response MUST
NOT use invalid identifiers.
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12.19 Are You There? (ping)
name: ping
anonymous parameters: [xid [am-id]]
named parameters: none
payload: no
senders: both OPES processor and callout server
Solicits an immediate 'i-am-here' response. If the response does not
use the same set of "xid" and "am-id" parameters, the recipient MAY
assume that missing identifier(s) correspond to OCP transaction or
application message that was not maintained at the time the response
was generated.
The recipient MUST handle an 'are-you-there' request even if
transaction or application message identifiers are invalid from the
recipient point of view. Normally, messages with invalid identifiers
are ignored.
12.20 Negotiation Offer (NO)
name: NO
anonymous parameters: (list of features)
named parameters: [SG: sg-id]
payload: no
senders: both OPES processor and callout server
A Negotiation Offer (NO) message solicits a selection of a single
"best" feature out of a supplied list, using a Negotiation Response
(NR (Section 12.21)) message. The sender is expected to list
preferred features first when possible. The recipient MAY ignore
sender preferences. If the list of features is empty, the negotiation
is bound to fail but remains valid.
Both OPES processor and callout server are allowed to send
Negotiation Offer (NO) messages. The rules in this section ensure
that only one offer is honored if two offers are submitted
concurrently. An agent MUST NOT send a Negotiation Offer (NO) message
if it still expects a response to its previous offer on the same
connection.
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If an OPES processor receives a Negotiation Offer (NO) message while
its own offer is pending, the processor MUST disregard the server
offer. Otherwise, it MUST respond immediately.
If a callout server receives a Negotiation Offer (NO) message when
its own offer is pending, the server MUST disregard its own offer.
In either case, it MUST respond immediately.
If an agent receives a message sequence that violates any of the
above rules in this section, the agent MUST terminate the connection
with an error.
An optional "SG" parameter is used to narrow the scope of
negotiations to the specified service group. If SG is present, the
negotiated features are negotiated and enabled only for transactions
that use the specified service group ID. Connection-scoped features
are negotiated and enabled for all service groups. The presence of
scope does not imply automatic conflict resolution common to
programming languages; no conflicts are allowed. When negotiating
connection-scoped features, an agent MUST check for conflicts within
each existing service group. When negotiating group-scoped features,
an agent MUST check for conflicts with connection-scoped features
already negotiated. For example, it must not be possible to
negotiate a connection-scoped HTTP application profile if one service
group already has an SMTP application profile and vice versa.
OCP agents SHOULD NOT send offers with service groups used by pending
transactions. Unless explicitly noted otherwise in a feature
documentation, OCP agents MUST NOT apply any negotiations to pending
transactions. In other words, negotiated features take effect with
the new OCP transaction.
12.21 Negotiation Response (NR)
name: NR
anonymous parameters: [feature]
named parameters: [SG: sg-id], [Rejects], [Unknowns]
payload: no
senders: both OPES processor and callout server
A Negotiation Response (NR) message conveys recipient reaction to a
Negotiation Offer (NO (Section 12.20)) request. An accepted offer is
indicated by the presence of a "feature" parameter, containing the
selected feature. If the selected feature does not match any of the
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offered features, the offering agent MUST consider negotiation failed
and MAY terminate the connection.
A rejected offer is indicated by omitting the "feature" parameter.
If negotiation offer contains an SG parameter, the responder MUST
include that parameter in the Negotiation Response (NR) message. The
recipient of a NR message without the expected SG parameter MUST
treat negotiation response as invalid.
If negotiation offer lack an SG parameter, the responder MUST NOT
include that parameter in the Negotiation Response (NR) message. The
recipient of a NR message with an unexpected SG parameter MUST treat
negotiation response as invalid.
When accepting or rejecting an offer, the sender of the Negotiation
Response (NR) message MAY supply additional details via Rejects and
Unknowns parameters. The Rejects parameter can be used to list
features that were known to the Negotiation Offer (NO (Section
12.20)) recipient but could not be supported given negotiated state
that existed when NO message was received. The Unknowns parameter can
be used to list features that were unknown to the NO recipient.
12.22 I Support (i-can)
name: i-can
anonymous parameters: [feature]
named parameters: none
payload: no
senders: both OPES processor and callout server
An I Support (i-can) message is sent in response to a Can You Support
(can-you (Section 12.23)) question. If the sender supports feature
identifier, the sender MUST respond with a "feature" parameter, set
to match actually supported feature and its attributes, if any.
Otherwise, the sender MUST respond without a "feature" parameter.
Note that supported features attributes of the sender may differ from
those in the Can You Support (can-you (Section 12.23)) question,
indicating a partial match or a mismatch.
12.23 Can You Support (can-you)
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name: can-you
anonymous parameters: feature
named parameters: none
payload: no
senders: both OPES processor and callout server
Can You Support (can-you) message solicits a declaration of support
for the supplied feature, using an I Support (i-can (Section 12.22))
message. The recipient MUST respond immediately.
12.24 I Currently Use (i-do)
name: i-do
anonymous parameters: feature
named parameters: none
payload: no
senders: both OPES processor and callout server
12.25 Do You Currently Use (do-you)
name: do-you
anonymous parameters: feature
named parameters: none
payload: no
senders: both OPES processor and callout server
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13. Application Protocol Requirements
Not all application protocols can be adapted with OCP. Compiling a
complete list of known limitations is impossible since "application
protocol" is not a well defined term. However, listing known
limitations can help it determining OCP applicability. This section
is not a normative part of the OCP specification.
Application protocol messages must have byte boundaries. OCP can
only handle application messages with the number of bits divisible
by 8.
XXX
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14. IAB Considerations
OPES treatment of IETF Internet Architecture Board (IAB)
considerations [RFC3238] are documented in [XXX].
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15. Security Considerations
This section examines security considerations for OCP. OPES threats
are documented in [XXX-Threat-Doc].
OCP relays application messages that may contain sensitive
information. Appropriate transport encryption can be negotiated to
prevent information leakage or modification (see section XXX on
transport security profile negotiation), but OCP agents may support
unencrypted transport by default. Such default OCP agent
configurations will expose application messages to third party
recording and modification, even if OPES agents themselves are
secure.
OCP implementation bugs may lead to security vulnerabilities in OCP
agents, even if OCP traffic itself remains secure. For example, a
buffer overflow in a callout server caused by a malicious OPES
processor may grant that processor access to information from other
(100% secure) OCP connections, including connections with other OPES
processors.
Careless OCP implementations may rely on various OCP identifiers to
be unique across all OCP agents. A malicious agent can inject an OCP
message that matches identifiers used by other agents, in an attempt
to get access to sensitive data. OCP implementations must always
check an identifier for being "local" to the corresponding connection
before using that identifier.
OCP is a stateful protocol. Several OCP commands increase the amount
of state that the recipient has to maintain. For example, a Create
Service Group (SGC (Section 12.3)) message instructs the recipient to
maintain an association between a service group identifier and a list
of services.
Implementations that cannot handle resource exhaustion correctly
increase security risks. The following are known OCP-related
resources that may be exhausted during a compliant OCP message
exchange:
OCP message structures: OCP message syntax does not limit the nesting
depth of OCP message structures and does not place an upper limit
on the length (number of OCTETs) of most syntax elements.
concurrent connections: OCP does not place an upper limit on the
number of concurrent connections that a callout server may be
instructed to create via Connection Start (CS (Section 12.1))
messages.
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service groups: OCP does not place an upper limit on the number of
service group associations that a callout server may be instructed
to create via Create Service Group (SGC (Section 12.3)) messages.
concurrent transactions: OCP does not place an upper limit on the
number of concurrent transactions that a callout server may be
instructed to maintain via Transaction Start (TS (Section 12.5))
messages.
concurrent flows: OCP Core does not place an upper limit on the
number of concurrent adapted data flows that an OPES processor may
be instructed to maintain via Application Message Start (AMS
(Section 12.7)) messages.
Denial of service attacks using OCP may slow a callout server down,
affecting performance of many independent OPES processors and, hence,
user-perceived performance. (XXX: this has nothing to do with OCP and
should be deleted from these specs, right?)
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16. Compliance
This specification defines compliance for the following subjects:
OCP client implementations (OPES processors), OCP server
implementations (callout servers), OCP application profiles, and OCP
extensions. A subject is compliant if it satisfies all applicable
"MUST" and "SHOULD" level requirements. By definition, to satisfy a
"MUST" level requirement means to act as prescribed by the
requirement; to satisfy a "SHOULD" level requirement means to either
act as prescribed by the requirement or have a reason to act
differently. A requirement is applicable to the subject if it
instructs (addresses) the subject.
Informally, OCP compliance means that there are no known "MUST"
violations, and all "SHOULD" violations are conscious. In other
words, a "SHOULD" means "MUST satisfy or MUST have a reason to
violate". It is expected that compliance claims are accompanied by a
list of unsupported SHOULDs (if any), in an appropriate format,
explaining why preferred behavior was not chosen.
Only normative parts of this specification affect compliance.
Normative parts are: parts explicitly marked using the word
"normative", definitions, and phrases containing unquoted capitalized
keywords from [RFC2119]. Consequently, examples and illustrations are
not normative.
OCP extensions MAY change any normative requirement documented in
this specification, including OCP message format, except for the
following rule: Changes to normative parts of OCP Core MUST be
negotiated.
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17. To-do
L4+ binding: Mention that transport might be L4 or above
timeouts: document what messages cause what timers to be [re]set.
parameter scope: Document that parameter names have message scope. A
known parameter name in an unknown message does not identify a
known parameter.
name named-paramters: Document names for all named parameters.
modified: replace with as-is approach
dack: Make data acknowledgment mechanism symmetric. Both agents
should be able to request DACK messages. Should we make the
acknowledgment mechanism to work with any OCP message? Merge with
ping/pong mechanism?
flags: Document flag parameter syntax ("0/1" or present/absent).
loss: Should OPES processor be able to signal loss of data to the
callout server. The current wording assumes that offset is
incremented using sizes of actually received data fragments; if
the processor detects loss it cannot pass that information and can
only hope that the callout server will notice (by interpreting the
data) or will not care (the server may be application- and/or
loss-agnostic; e.g., a logging or billing server)
modp: Min and max values (0 and 100) should be "commitments" rather
than "probabilities".
transactions-end: Decide whether we need a 'transactions-end' message
to terminate multiple transactions efficiently. Is terminating a
connection good enough?
error: Do we need this flag or should we use result codes to relay
the same meaning?
abort negotiation: Should we let the other side affect the abort
decision on OPES level? Perhaps the callout server is doing some
logging or accounting and MUST see every byte received by the OPES
processor, even if the application message is aborted by the
processor. Should we add some kind of 'xaction-need-all' message?
Or should we assume that the dispatcher always knows callout
server needs and vice versa?
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proxying Can OCP be proxied above transport layer? Perhaps to
implement parts of a given service, transparently to the OPES
processor?
normative IDs: To be normative, OPES Internet-Drafts must be replaced
with corresponding RFCs when the latter are published.
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Appendix A. Acknowledgements
The author gratefully acknowledges the contributions of: Abbie Barbir
(Nortel Networks), Oskar Batuner (Independent Consultant), Karel
Mittig (France Telecom R&D), Markus Hofmann (Bell Labs), Hilarie
Orman (The Purple Streak), Reinaldo Penno (Nortel Networks), Martin
Stecher (Webwasher) as well as an anonymous OPES working group
participant.
Special thanks to Marshall Rose for his xml2rfc tool.
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Appendix B. Change Log
Internal WG revision control ID: $Id: ocp-core.xml,v 1.35 2003/10/27
11:40:33 rousskov Exp $
2003/10/26
* Started using TDM for Core value types.
* Added Data Want Out (DWO) message.
* Added Data Wont Look at Yours (DWLY) message.
* Renamed Wont-Use to more specific Wont-Send. Made Wont-Send
parameter into a Data Wont Send Yours (DWSY) message because it
controls original data flow and is not specific to a particular
adapted AM (there can be many). This change means that Data Use
Yours (DUY) messages are no longer terminating preservation
commitment by default. Thus, we lost a little in terms of
performance (unless processors look ahead for DWSYs) but gained
a lot of simplicity in terms of support for multiple adapted
application messages (SMTP case).
* Added 206 (partial data) status code definition.
* 206 status code should be used with AME, not TE.
* Replaced "global scope" with "connection scope" in negotiation
rules.
2003/10/25
* Clarified negotiation mechanism when it comes to negotiating
multiple [possibly conflicting] features.
* Clarified service group-scoped negotiations. Agents must watch
out for global conflicts when doing group-scoped negotiations
and vice-versa.
2003/10/24
* Added 'Out Of The Loop' Optimization section.
* Added 'Data Recycling' Optimization section.
* Added "Type Declaration Mnemonic" (TDM) to facilitate type
declarations here and in OCP extensions.
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2003/10/19
* Removed optional "sizep" parameter. HTTP needs
content-dependent parameter (AM-EL), and we do not know any
generic application for sizep that would be worth supporting in
Core.
2003/10/08
* Documented backslash (\) and CRLF (\r\n) OCP message rendering
tricks.
2003/10/07
* Added named structure members to message BNF. Used MIME-like
syntax already used for named parameters. Named members are
needed to represent optional structure members.
head-sid15
* Removed leftovers of data-have message name. Use Data Use Mine
instead (Karel Mittig).
* Anonymized named parameters and removed currently unused "rid"
parameter in ping and pong messages (Karel Mittig).
* Renamed DUM.please-ack to "DUM.ack" (Karel Mittig). More work
is needed to polish and simplify acknowledgment mechanism.
head-sid14
* Documented known resource-exhaustion security risks.
* Polished compliance definition. Avoid two levels of compliance.
head-sid13
* Added SG parameter to Negotiation Offer (NO) and Negotiation
Response (NR) messages to limit the result of negotiations to
the specified service group. Still need to document SG-related
logic in the Negotiation section.
* Removed "services" parameter from Transaction Start (TS)
message because we have to rely on service groups exclusively,
because only service groups can have negotiated application
profiles associated with them.
* Replaced data-id parameter with "Kept: kept-offset" and
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"Wont-Use: used-size" parameter. We probably need octet-based
granularity, and old data-id only offered fragment-based
granularity.
* Made AME and TE messages required.
* Documented result parameter syntax and two result codes: 200
(success) and 400 (failure).
* Added optional "result" parameter to CE.
head-sid12
* Fixed BNF to remove extra SP and "," in front of structure and
list values.
* Fixed the type of "id" field in a "service" structure.
* Documented "sg-id" parameter.
* Renamed "copied" to "data-id" so that it can be used by both
agents. An OPES processor uses named "Copied: data-id"
parameter and a callout server uses anonymous "data-id"
parameter (instead of previously documented "copy-am-offset").
* Removed "rid" parameter from Negotiation Offer (NO) message as
unused.
* Removed "size" parameter from messages with payload since
payload syntax includes an explicit size value.
* Renamed Data Have (DH) message to Data Use Mine (DUM) message
to preserve the symmetry with Data Use Yours (DUY) message and
to prepare for possible addition of Data Check Mine (DCM)
message.
* Finished phasing out the "modified" message parameter.
* Added an "As-is" named-parameter to mark adapted pieces of data
identical to the original.
* Replaced a huge "message nesting" figure with a set of short
specific rules illustrating the same concept. Added a new
"Exchange Patterns" subsection to accommodate the rules and
related matters. The figure was not clear enough. Hopefully,
the rules are.
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head-sid10
* Removed the concept of OCP connection as a group of messages
sharing the same group of callout services. Now there is no
difference between OCP connection and transport connection.
* Added a concept of a Service Group, which is a list of services
with an identifier, for now. A given Service Group is
referenced by the creating/destroying side only, to prevent
destruction synchronization.
* Removed Connection Services (CSvc) message.
* Removed connection priority until proven generally useful. Can
be implemented as an extension.
head-sid9
* Added Negotiation and Capability Inquiry sections.
* Deleted data-end message because AME (Application Message End)
already does the same thing and because there is no data-start
message.
* Deleted meta-* messages. Data-* messages are now used for both
metadata and data since OCP does not know the difference, but
must provide the same exchange mechanism for both.
* Use a single message name (short or long, depending on the
message) instead of using full and abbreviated versions and
trying to enforce abbreviations on the wire. Be more consistent
in creating short message names.
* Resurrected OCP scope figure based on popular demand.
* Applied Martin Stecher comments dated 2003/05/30.
head-sid8
* Added structure and list values to ABNF syntax.
* Messages with multiple equally-named parameters are
semantically invalid.
* Added types for message parameters.
* Started replacing complicated, error-prone, and probably mostly
useless "modified" parameter with a clear and simple "as-is"
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parameter.
* Converted parameter descriptions from list items to
subsections.
* OCP syntax requires one or two character lookups to determine
the next message part. Fixed a comment for implementors saying
that one lookup is always sufficient.
head-sid7
* Mentioned TCP/IP/Internet as assumed transport/network, with
any other reliable connection-oriented transport/network usable
as well. We do not document how OCP messages are mapped to TCP
but it should be obvious. See Overall Operation section.
* Applied Martin Stecher's corrections to OCP message syntax and
definitions of messages.
* Restricted full message name use to documentation, debuggers,
and such. The differences in abbreviated and full name usage
still need more consideration and polishing.
* IAB Considerations section now refers to the future opes-iab
draft.
head-sid6
* Added OCP message syntax. Reformatted message descriptions to
match new syntax concepts.
* Started adding meta-have message to exchange metadata details.
Removed negotiation messages for now (posted new messages to
the list for a discussion).
* Added Security Considerations section (based on Abbie Barbir's
original text).
head-sid4
* Changed document labels to reflect future "WG draft" status.
* Added Acknowledgments section.
* Added "Core" to the title since we expect application specific
drafts to follow and because this document, even when complete,
cannot specify a "working" protocol without
application-specific parts. This change is still debatable.
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* Added reference to required future application-specific specs
in the Introduction.
* Moved all rant about irrelevance of application protocols
proxied by an OPES processor to the "Application proxies and
OCP scope" section. Removed "processor input" and "processor
output" terms. No reason to define a new term when its only
purpose is to document irrelevance?
* Moved "OCP message" definition to the terminology section.
* Clarified "application message" definition based on recent WG
discussions and suggestions. There seems to be consensus that
"application message" is whatever OPES processor and callout
server define or agree on, but OCP needs some minimal structure
(content + metadata)
* Synced data and metadata definitions with the new "application
message" definition.
* Simplified "Overall Operation" section since it no longer need
to talk about irrelevance of application protocols proxied by
an OPES processor.
* Illustrated nesting/relationship of key OCP concepts
(application message, OCP message, transaction, connection,
transport connection, etc.). The figure needs more work.
* Listed all from-processor and from-server OCP messages in one
place, with references to message definitions.
* Added "services" message parameter, assuming that more than one
service may be requested/executed with one transaction.
* Gave callout server ability to report what services were
actually applied (see "services" parameter definition).
head-sid3
* clarified application message definition and OCP boundaries by
introducing three kinds of "applications": processor input,
processor output, and OCP application
* made "Overall Operation" a top-level section since it got long
and has its own subsections now; lots of editorial changes in
this sections, new figures
* added illustrations of OCP messages, transactions, and
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connections
head-sid2
* introduced a notion of meta-data to both simplify OCP and make
OCP agnostic to application meta-data; previous approach
essentially assumed existence of a few common properties like
protocol name or application message source/destination while
not allowing any other properties to be exchanged between OCP
agents); specific meta-data format/contents is not important to
OCP but OCP will help agents to negotiate that format/contents
* removed wording implying that OCP adapts application messages;
OCP only used to exchange data and meta-data (which facilitates
adaptation)
* changed most of the definitions; added definitions for
meta-data, original/adapted flows, and others
* split 'data-pause' message into 'data-pause' request by the
callout server and 'data-paused' notification by the OPES
processor; fixed "paused" state management
* added motivation for data acking mechanism
* replaced "am-proto", "am-kind", "am-source", and
"am-destination" parameters with "meta-data"
* replaced SERVER and CLIENT placeholders with "callout server"
and "OPES processor"
* added editing marks
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Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[I-D.ietf-opes-architecture]
Barbir, A., "An Architecture for Open Pluggable Edge
Services (OPES)", draft-ietf-opes-architecture-04 (work in
progress), December 2002.
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Informative References
[I-D.ietf-opes-protocol-reqs]
Beck, A., "Requirements for OPES Callout Protocols",
draft-ietf-opes-protocol-reqs-03 (work in progress),
December 2002.
[I-D.ietf-opes-scenarios]
Barbir, A., "OPES Use Cases and Deployment Scenarios",
draft-ietf-opes-scenarios-01 (work in progress), August
2002.
[I-D.ietf-opes-http]
Rousskov, A. and M. Stecher, "HTTP adaptation with OPES",
draft-ietf-opes-http-00 (work in progress), August 2003.
[I-D.ietf-fax-esmtp-conneg]
Toyoda, K. and D. Crocker, "SMTP Service Extension for Fax
Content Negotiation", draft-ietf-fax-esmtp-conneg-08 (work
in progress), June 2003.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3080] Rose, M., "The Blocks Extensible Exchange Protocol Core",
RFC 3080, March 2001.
[RFC3238] Floyd, S. and L. Daigle, "IAB Architectural and Policy
Considerations for Open Pluggable Edge Services", RFC
3238, January 2002.
Author's Address
Alex Rousskov
The Measurement Factory
EMail: rousskov@measurement-factory.com
URI: http://www.measurement-factory.com/
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Rousskov Expires April 26, 2004 [Page 64]
