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RFC 4037

Open Pluggable Edge Services (OPES) Callout Protocol (OCP) Core

Pages: 56
Proposed Standard
Part 3 of 3 – Pages 33 to 56
First   Prev   None

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11. 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. OCP extensions MUST NOT introduce order-dependent named parameters. No more than one named-parameter
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   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 message in valid format (see
   section 3.1), subject to the limitations of the recipient's
   resources.

   Unknown or unexpected message names, parameters, and payloads may be
   valid extensions.  For example, an "extra" named 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.

   Some message parameter values use uni identifiers to refer to various
   OCP states (see section 10.2 and Appendix B).  These identifiers are
   created, used, and destroyed by OCP agents via corresponding
   messages.  Except when creating a new identifier, an OCP agent MUST
   NOT send a uni identifier that corresponds to an inactive state
   (i.e., that was either never created or already destroyed).  Such
   identifiers invalidate the host OCP message (see section 5).  For
   example, the recipient must terminate the transaction when the xid
   parameter in a Data Use Mine (DUM) message refers to an unknown or
   already terminated OCP transaction.

11.1. Connection Start (CS)

CS: extends message; A Connection Start (CS) message indicates the start of an OCP connection. An OCP agent MUST send this message before it sends any other message on the connection. If the first message an OCP agent receives is not Connection Start (CS), the agent MUST terminate the connection with a Connection End (CE) message having 400 (failure) result status code. An OCP agent MUST send Connection Start (CS) message exactly once. An OCP agent MUST ignore repeated Connection Start (CS) messages. At any time, a callout server MAY refuse further processing on an OCP connection by sending a Connection End (CE) message with the status code 400 (failure). Note that the above requirement to send a CS message first still applies. With TCP/IP as transport, raw TCP connections (local and remote peer IP addresses with port numbers) identify an OCP connection. Other transports may provide OCP connection identifiers to distinguish logical connections that share the same transport. For example, a single BEEP [RFC3080] channel may be designated as a single OCP connection.
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11.2. Connection End (CE)

CE: extends message with { [result]; }; A Connection End (CE) Indicates the end of an OCP connection. The agent initiating closing or termination of a connection MUST send this message immediately prior to closing or termination. The recipient MUST free associated state, including transport state. Connection termination without a Connection End (CE) message indicates that the connection was prematurely closed, possibly without the closing-side agent's prior knowledge or intent. When an OCP agent detects a prematurely closed connection, the agent MUST act as if a Connection End (CE) message indicating a failure 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.

11.3. Service Group Created (SGC)

SGC: extends message with { my-sg-id services; }; A Service Group Created (SGC) message informs the recipient that a list of adaptation services has been associated with the given service group identifier ("my-sg-id"). Following this message, the sender can refer to the group by using the identifier. The recipient MUST maintain the association until a matching Service Group Destroyed (SGD) message is received or the corresponding OCP connection is closed. 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 Service Group Created (SGC) message does not create the requested association, it MUST immediately terminate the connection with a Connection End (CE) message indicating a failure.
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11.4. Service Group Destroyed (SGD)

SGD: extends message with { my-sg-id; }; A Service Group Destroyed (SGD) message instructs the recipient to forget about the service group associated with the specified identifier. The recipient MUST destroy the identified service group association.

11.5. Transaction Start (TS)

TS: extends message with { xid my-sg-id; }; Sent by an OPES processor, a Transaction Start (TS) message indicates the start of an OCP transaction. Upon receiving this message, the callout server MAY refuse further transaction processing by responding with a corresponding Transaction End (TE) 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 required "my-sg-id" identifier refers to a service group created with an a Service Group Created (SGC) message. The callout server MUST apply the list of services associated with "my-sg-id", in the specified order. This message introduces the transaction identifier (xid).

11.6. Transaction End (TE)

TE: extends message with { xid [result]; }; A Transaction End (TE) indicates the end of the identified OCP transaction. 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
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   example, unnecessary delays, rejection of new transactions, and even
   timeouts for agents that rely on this end-of-file condition to
   proceed.

   This message terminates the life of the transaction identifier (xid).

11.7. Application Message Start (AMS)

AMS: extends message with { xid; [Services: services]; }; An Application Message Start (AMS) message indicates the start of the original or adapted application message processing and dataflow. The recipient MAY refuse further processing by sending an Application Message End (AME) message indicating a failure. When an AMS message is sent by the OPES processor, the callout server usually sends an AMS message back, announcing the creation of an adapted version of the original application message. This announcement may be delayed. For example, the callout server may wait for more information from the OPES processor. When an AMS message is sent by the callout server, an optional "Services" parameter describes OPES services that the server MAY apply to the original application message. Usually, the "services" value matches what was asked by the OPES processor. The callout server SHOULD send a "Services" parameter if its value would differ from the list of services requested by the OPES processor. As the same service may be known under many names, the mismatch does not necessarily imply an error.

11.8. Application Message End (AME)

AME: extends message with { xid [result]; }; An Application Message End (AME) message indicates the end of the original or adapted application message processing and dataflow. The recipient should expect no more data for the corresponding application message. An Application Message End (AME) message ends any data preservation commitments and any other state associated with the corresponding application message.
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   An OCP agent MUST send an Application Message End (AME) message
   immediately after it makes a decision to stop processing of its
   application message.  Violating this requirement may cause, for
   example, unnecessary delays, rejection of new transactions, and even
   timeouts for agents that rely on this end-of-file condition to
   proceed.

11.9. Data Use Mine (DUM)

DUM: extends message with { xid my-offset; [As-is: org-offset]; [Kept: org-offset org-size ]; [Modp: modp]; } and payload; A Data Use Mine (DUM) message carries application data. It is the only OCP Core message with a documented payload. The sender MUST NOT make any gaps in data supplied by Data Use Mine (DUM) and Data Use Yours (DUY) messages (i.e., the my-offset of the next data message must be equal to the my-offset plus the payload size of the previous data message). Messages with gaps are invalid. The sender MUST send payload and MAY use empty payload (i.e., payload with zero size). A DUM message without payload is invalid. Empty payloads are useful for communicating meta-information about the data (e.g., modification predictions or preservation commitments) without sending data. An OPES processor MAY send a "Kept" parameter to indicate its current data preservation commitment (section 7) for original data. When an OPES processor sends a "Kept" parameter, the processor MUST keep a copy of the specified data (the preservation commitment starts or continues). The Kept offset parameter specifies the offset of the first octet of the preserved data. The Kept size parameter is the size of preserved data. Note that data preservation rules allow (i.e., do not prohibit) an OPES processor to decrease offset and to specify a data range not yet fully delivered to the callout server. OCP Core does not require any relationship between DUM payload and the "Kept" parameter. If the "Kept" parameter value violates data preservation rules but the recipient has not sent any Data Use Yours (DUY) messages for the given OCP transaction yet, then the recipient MUST NOT use any preserved data for the given transaction (i.e., must not sent any Data Use Yours (DUY) messages). If the "Kept" parameter value violates data preservation rules and the recipient has already sent Data Use Yours (DUY) messages, the DUM message is invalid, and the rules of section 5 apply. These requirements help preserve data integrity when "Kept" optimization is used by the OPES processor.
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   A callout server MUST send a "Modp" parameter if the server can
   provide a reliable value and has not already sent the same parameter
   value for the corresponding application message.  The definition of
   "reliable" is entirely up to the callout server.  The data
   modification prediction includes DUM payload.  That is, if the
   attached payload has been modified, the modp value cannot be 0%.

   A callout server SHOULD send an "As-is" parameter if the attached
   data is identical to a fragment at the specified offset in the
   original dataflow.  An "As-is" parameter specifying a data fragment
   that has not been sent to the callout server is invalid.  The
   recipient MUST ignore invalid "As-is" parameters.  Identical means
   that all adapted octets have the same numeric value as the
   corresponding original octets.  This parameter is meant to allow for
   partial data preservation optimizations without a preservation
   commitment.  The preserved data still crosses the connection with the
   callout server twice, but the OPES processor may be able to optimize
   its handling of the data.

   The OPES processor MUST NOT terminate its data preservation
   commitment (section 7) in reaction to receiving a Data Use Mine (DUM)
   message.

11.10. Data Use Yours (DUY)

DUY: extends message with { xid org-offset org-size; }; The callout server tells the OPES processor to use the "size" bytes of preserved original data, starting at the specified offset, as if that data chunk came from the callout server in a Data Use Mine (DUM) message. The OPES processor MUST NOT terminate its data preservation commitment (section 7) in reaction to receiving a Data Use Yours (DUY) message.

11.11. Data Preservation Interest (DPI)

DPI: extends message with { xid org-offset org-size; }; The Data Preservation Interest (DPI) message describes an original data chunk by using the first octet offset and size as parameters. The chunk is the only area of original data that the callout server may be interested in referring to in future Data Use Yours (DUY)
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   messages.  This data chunk is referred to as "reusable data".  The
   rest of the original data is referred to as "disposable data".  Thus,
   disposable data consists of octets below the specified offset and at
   or above the (offset + size) offset.

   After sending this message, the callout server MUST NOT send Data Use
   Yours (DUY) messages referring to disposable data chunk(s).  If an
   OPES processor is not preserving some reusable data, it MAY start
   preserving that data.  If an OPES processor preserves some disposable
   data, it MAY stop preserving that data.  If an OPES processor does
   not preserve some disposable data, it MAY NOT start preserving that
   data.

   A callout server MUST NOT indicate reusable data areas that overlap
   with disposable data areas indicated in previous Data Preservation
   Interest (DPI) messages.  In other words, reusable data must not
   grow, and disposable data must not shrink.  If a callout server
   violates this rule, the Data Preservation Interest (DPI) message is
   invalid (see section 5).

   The Data Preservation Interest (DPI) message cannot force the OPES
   processor to preserve data.  In this context, the term reusable
   stands for callout server interest in reusing the data in the future,
   given the OPES processor cooperation.

   For example, an offset value of zero and the size value of 2147483647
   indicate that the server may want to reuse all the original data.
   The size value of zero indicates that the server is not going to send
   any more Data Use Yours (DUY) messages.

11.12. Want Stop Receiving Data (DWSR)

DWSR: extends message with { xid org-size; }; The Want Stop Receiving Data (DWSR) message informs OPES processor that the callout server wants to stop receiving original data any time after receiving at least an org-size amount of an application message prefix. That is, the server is asking the processor to terminate original dataflow prematurely (see section 8.1) after sending at least org-size octets. An OPES processor receiving a Want Stop Receiving Data (DWSR) message SHOULD terminate original dataflow by sending an Application Message End (AME) message with a 206 (partial) status code.
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   An OPES processor MUST NOT terminate its data preservation commitment
   (section 7) in reaction to receiving a Want Stop Receiving Data
   (DWSR) message.  Just like with any other message, an OPES processor
   may use information supplied by Want Stop Receiving Data (DWSR) to
   decide on future preservation commitments.

11.13. Want Stop Sending Data (DWSS)

DWSS: extends message with { xid; }; The Want Stop Sending Data (DWSS) message informs the OPES processor that the callout server wants to stop sending adapted data as soon as possible; the server is asking the processor for permission to terminate adapted dataflow prematurely (see section 8.2). The OPES processor can grant this permission by using a Stop Sending Data (DSS) message. Once the DWSS message is sent, the callout server MUST NOT prematurely terminate adapted dataflow until the server receives a DSS message from the OPES processor. If the server violates this rule, the OPES processor MUST act as if no DWSS message were received. The latter implies that the OCP transaction is terminated by the processor, with an error. An OPES processor receiving a DWSS message SHOULD respond with a Stop Sending Data (DSS) message, provided the processor would not violate DSS message requirements by doing so. The processor SHOULD respond immediately once DSS message requirements can be satisfied.

11.14. Stop Sending Data (DSS)

DSS: extends message with { xid; }; The Stop Sending Data (DSS) message instructs the callout server to terminate adapted dataflow prematurely by sending an Application Message End (AME) message with a 206 (partial) status code. A callout server is expected to solicit the Stop Sending Data (DSS) message by sending a Want Stop Sending Data (DWSS) message (see section 8.2). A callout server receiving a solicited Stop Sending Data (DSS) message for a yet-unterminated adapted dataflow MUST immediately terminate dataflow by sending an Application Message End (AME) message with a 206 (partial) status code. If the callout server
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   already terminated adapted dataflow, the callout server MUST ignore
   the Stop Sending Data (DSS) message.  A callout server receiving an
   unsolicited DSS message for a yet-unterminated adapted dataflow MUST
   either treat that message as invalid or as solicited (i.e., the
   server cannot simply ignore unsolicited DSS messages).

   The OPES processor sending a Stop Sending Data (DSS) message MUST be
   able to reconstruct the adapted application message correctly after
   the callout server terminates dataflow.  This requirement implies
   that the processor must have access to any original data sent to the
   callout after the Stop Sending Data (DSS) message, if there is any.
   Consequently, the OPES processor either has to send no data at all or
   has to keep a copy of it.

   If a callout server receives a DSS message and, in violation of the
   above rules, waits for more original data before sending an
   Application Message End (AME) response, a deadlock may occur: The
   OPES processor may wait for the Application Message End (AME) message
   to send more original data.

11.15. Want Data Paused (DWP)

DWP: extends message with { xid your-offset; }; The Want Data Paused (DWP) message indicates the sender's temporary lack of interest in receiving data starting with the specified offset. This disinterest implies nothing about sender's intent to send data. The "your-offset" parameter refers to dataflow originating at the OCP agent receiving the parameter. If, at the time the Want Data Paused (DWP) message is received, the recipient has already sent data at the specified offset, the message recipient MUST stop sending data immediately. Otherwise, the recipient MUST stop sending data immediately after it sends the specified offset. Once the recipient stops sending more data, it MUST immediately send a Paused My Data (DPM) message and MUST NOT send more data until it receives a Want More Data (DWM) message. As are most OCP Core mechanisms, data pausing is asynchronous. The sender of the Want Data Paused (DWP) message MUST NOT rely on the data being paused exactly at the specified offset or at all.
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11.16. Paused My Data (DPM)

DPM: extends message with { xid; }; The Paused My Data (DPM) message indicates the sender's commitment to send no more data until the sender receives a Want More Data (DWM) message. The recipient of the Paused My Data (DPM) message MAY expect the data delivery being paused. If the recipient receives data despite this expectation, it MAY abort the corresponding transaction with a Transaction End (TE) message indicating a failure.

11.17. Want More Data (DWM)

DWM: extends message with { xid; [Size-request: your-size]; }; The Want More Data (DWM) message indicates the sender's need for more data. Message parameters always refer to dataflow originating at the other OCP agent. When sent by an OPES processor, your-size is adp-size; when sent by a callout server, your-size is org-size. The "Size-request" parameter refers to dataflow originating at the OCP agent receiving the parameter. If a "Size-request" parameter is present, its value is the suggested minimum data size. It is meant to allow the recipient to deliver data in fewer chunks. The recipient MAY ignore the "Size-request" parameter. An absent "Size-request" parameter implies "any size". The message also cancels the Paused My Data (DPM) message effect. If the recipient was not sending any data because of its DPM message, the recipient MAY resume sending data. Note, however, that the Want More Data (DWM) message can be sent regardless of whether the dataflow in question has been paused. The "Size-request" parameter makes this message a useful stand-alone optimization.
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11.18. Negotiation Offer (NO)

NO: extends message with { features; [SG: my-sg-id]; [Offer-Pending: boolean]; }; A Negotiation Offer (NO) message solicits a selection of a single "best" feature out of a supplied list, using a Negotiation Response (NR) message. The sender is expected to list preferred features first when it is possible. The recipient MAY ignore sender preferences. If the list of features is empty, the negotiation is bound to fail but remains valid. Both the OPES processor and the 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. 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, the server 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 a Connection End (CE) message indicating a failure. An optional "Offer-Pending" parameter is used for Negotiation Phase maintenance (section 6.1). The option's value defaults to "false". 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
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   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 it is 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.

   As with other protocol elements, OCP Core extensions may document
   additional negotiation restrictions.  For example, specification of a
   transport security feature may prohibit the use of the SG parameter
   in negotiation offers, to avoid situations where encryption is
   enabled for only a portion of overlapping transactions on the same
   transport connection.

11.19. Negotiation Response (NR)

NR: extends message with { [feature]; [SG: my-sg-id]; [Rejects: features]; [Unknowns: features]; [Offer-Pending: boolean]; }; A Negotiation Response (NR) message conveys recipient's reaction to a Negotiation Offer (NO) request. An accepted offer (a.k.a., positive response) is indicated by the presence of an anonymous "feature" parameter, containing the selected feature. If the selected feature does not match any of the offered features, the offering agent MUST consider negotiation failed and MAY terminate the connection with a Connection End (CE) message indicating a failure. A rejected offer (negative response) is indicated by omitting the anonymous "feature" parameter. The successfully negotiated feature becomes effective immediately. The sender of a positive response MUST consider the corresponding feature enabled immediately after the response is sent; the recipient of a positive response MUST consider the corresponding feature enabled immediately after the response is received. Note that the scope of the negotiated feature application may be limited to a specified service group. The negotiation phase state does not affect enabling of the feature.
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   If negotiation offer contains an SG parameter, the responder MUST
   include that parameter in the Negotiation Response (NR) message.  The
   recipient of an NR message without the expected SG parameter MUST
   treat negotiation response as invalid.

   If the negotiation offer lacks an SG parameter, the responder MUST
   NOT include that parameter in the Negotiation Response (NR) message.
   The recipient of an NR message with an unexpected SG parameter MUST
   treat the negotiation response as invalid.

   An optional "Offer-Pending" parameter is used for Negotiation Phase
   maintenance (section 6.1).  The option's value defaults to "false".

   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) 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.

11.20. Ability Query (AQ)

AQ: extends message with { feature; }; An Ability Query (AQ) message solicits an immediate Ability Answer (AA) response. The recipient MUST respond immediately with an AA message. This is a read-only, non-modifying interface. The recipient MUST NOT enable or disable any features due to an AQ request. OCP extensions documenting a feature MAY extend AQ messages to supply additional information about the feature or the query itself. The primary intended purpose of the ability inquiry interface is debugging and troubleshooting and not automated fine-tuning of agent behavior and configuration. The latter may be better achieved by the OCP negotiation mechanism (section 6).

11.21. Ability Answer (AA)

AA: extends message with { boolean; };
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   An Ability Answer (AA) message expresses the sender's support for a
   feature requested via an Ability Query (AQ) message.  The sender MUST
   set the value of the anonymous boolean parameter to the truthfulness
   of the following statement: "At the time of this answer generation,
   the sender supports the feature in question".  The meaning of
   "support" and additional details are feature specific.  OCP
   extensions documenting a feature MUST document the definition of
   "support" in the scope of the above statement and MAY extend AA
   messages to supply additional information about the feature or the
   answer itself.

11.22. Progress Query (PQ)

PQ: extends message with { [xid]; }; A Progress Query (PQ) message solicits an immediate Progress Answer (PA) response. The recipient MUST immediately respond to a PQ request, even if the transaction identifier is invalid from the recipient's point of view.

11.23. Progress Answer (PA)

PA: extends message with { [xid]; [Org-Data: org-size]; }; A PA message carries the sender's state. The "Org-Data" size is the total original data size received or sent by the agent so far for the identified application message (an agent can be either sending or receiving original data, so there is no ambiguity). When referring to received data, progress information does not imply that the data has otherwise been processed in some way. The progress inquiry interface is useful for several purposes, including keeping idle OCP connections "alive", gauging the agent processing speed, verifying the agent's progress, and debugging OCP communications. Verifying progress, for example, may be essential to implement timeouts for callout servers that do not send any adapted data until the entire original application message is received and processed. A recipient of a PA message MUST NOT assume that the sender is not working on any transaction or application message not identified in the PA message. A PA message does not carry information about multiple transactions or application messages.
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   If an agent is working on the transaction identified in the Progress
   Query (PQ) request, the agent MUST send the corresponding transaction
   ID (xid) when answering the PQ with a PA message.  Otherwise, the
   agent MUST NOT send the transaction ID.  If an agent is working on
   the original application message for the specified transaction, the
   agent MUST send the Org-Data parameter.  If the agent has already
   sent or received the Application Message End (AME) message for the
   original dataflow, the agent MUST NOT send the Org-data parameter.

   Informally, the PA message relays the sender's progress with the
   transaction and original dataflow identified by the Progress Query
   (PQ) message, provided the transaction identifier is still valid at
   the time of the answer.  Absent information in the answer indicates
   invalid, unknown, or closed transaction and/or original dataflow from
   the query recipient's point of view.

11.24. Progress Report (PR)

PR: extends message with { [xid]; [Org-Data: org-size]; }; A Progress Report (PR) message carries the sender's state. The message semantics and associated requirements are identical to those of a Progress Answer (PA) message except that the PR message, is sent unsolicited. The sender MAY report progress at any time. The sender MAY report progress unrelated to any transaction or original application message or related to any valid (current) transaction or original dataflow. Unsolicited progress reports are especially useful for OCP extensions dealing with "slow" callout services that introduce significant delays for the final application message recipient. The report may contain progress information that will make that final recipient more delay tolerant.

12. IAB Considerations

OPES treatment of IETF Internet Architecture Board (IAB) considerations [RFC3238] are documented in [RFC3914].

13. Security Considerations

This section examines security considerations for OCP. OPES threats are documented in [RFC3837]
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   OCP relays application messages that may contain sensitive
   information.  Appropriate transport encryption can be negotiated to
   prevent information leakage or modification (see section 6), but OCP
   agents may support unencrypted transport by default.  These
   configurations will expose application messages to third-party
   recording and modification, even if OPES proxies 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 gain 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 Service
   Group Created (SGC) message instructs the recipient to maintain an
   association between a service group identifier and a list of
   services.

   Implementations that cannot correctly handle resource exhaustion
   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) messages.

   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 Service Group Created (SGC) 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) messages.
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   concurrent flows: OCP Core does not place an upper limit on the
      number of concurrent adapted flows that an OPES processor may be
      instructed to maintain via Application Message Start (AMS)
      messages.

14. IANA Considerations

The IANA maintains a list of OCP features, including application profiles (section 10.11). For each feature, its uri parameter value is registered along with the extension parameters (if there are any). Registered feature syntax and semantics are documented with PETDM notation (section 9). The IESG is responsible for assigning a designated expert to review each standards-track registration prior to IANA assignment. The OPES working group mailing list may be used to solicit commentary for both standards-track and non-standards-track features. Standards-track OCP Core extensions SHOULD use http://www.iana.org/assignments/opes/ocp/ prefix for feature uri parameters. It is suggested that the IANA populate resources identified by such "uri" parameters with corresponding feature registrations. It is also suggested that the IANA maintain an index of all registered OCP features at the http://www.iana.org/assignments/opes/ocp/ URL or on a page linked from that URL. This specification defines no OCP features for IANA registration.

15. Compliance

This specification defines compliance for the following compliance subjects: OPES processors (OCP client implementations), callout servers (OCP server implementations), and OCP extensions. An OCP agent (a processor or callout server) may also be referred to as the "sender" or "recipient" of an OCP message. A compliance subject is compliant if it satisfies all applicable "MUST" and "SHOULD" requirements. By definition, to satisfy a "MUST" requirement means to act as prescribed by the requirement; to satisfy a "SHOULD" requirement means either to act as prescribed by the requirement or to 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 that all "SHOULD" violations are deliberate. In other words, "SHOULD" means "MUST satisfy or MUST have a reason to violate". It is expected that compliance claims be accompanied by a
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   list of unsupported SHOULDs (if any), in an appropriate format,
   explaining why the preferred behavior was not chosen.

   Only normative parts of this specification affect compliance.
   Normative parts are those parts explicitly marked with the word
   "normative", definitions, and phrases containing unquoted capitalized
   keywords from [RFC2119].  Consequently, examples and illustrations
   are not normative.

15.1. Extending OCP Core

OCP extensions MUST NOT change the OCP Core message format, as defined by ABNF and accompanying normative rules in Section 3.1. This requirement is intended to allow OCP message viewers, validators, and "intermediary" software to at least isolate and decompose any OCP message, even a message with semantics unknown to them (i.e., extended). OCP extensions are allowed to change normative OCP Core requirements for OPES processors and callout servers. However, OCP extensions SHOULD NOT make these changes and MUST require on a "MUST"-level that these changes are negotiated prior to taking effect. Informally, this specification defines compliant OCP agent behavior until changes to this specification (if any) are successfully negotiated. For example, if an RTSP profile for OCP requires support for offsets exceeding 2147483647 octets, the profile specification can document appropriate OCP changes while requiring that RTSP adaptation agents negotiate "large offsets" support before using large offsets. This negotiation can be bundled with negotiating another feature (e.g., negotiating an RTSP profile may imply support for "large offsets"). As implied by the above rules, OCP extensions may dynamically alter the negotiation mechanism itself, but such an alternation would have to be negotiated first, using the negotiation mechanism defined by this specification. For example, successfully negotiating a feature might change the default "Offer-Pending" value from false to true.
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Appendix A. Message Summary

This appendix is not normative. The table below summarizes key OCP message properties. For each message, the table provides the following information: name: Message name as seen on the wire. title: Human-friendly message title. P: Whether this specification documents message semantics as sent by an OPES processor. S: Whether this specification documents message semantics as sent by a callout server. tie: Related messages such as associated request, response message, or associated state message. +-------+----------------------------+-------+-------+--------------+ | name | title | P | S | tie | +-------+----------------------------+-------+-------+--------------+ | CS | Connection Start | X | X | CE | | CE | Connection End | X | X | CS | | SGC | Service Group Created | X | X | SGD TS | | SGD | Service Group Destroyed | X | X | SGC | | TS | Transaction Start | X | | TE SGC | | TE | Transaction End | X | X | TS | | AMS | Application Message Start | X | X | AME | | AME | Application Message End | X | X | AMS DSS | | DUM | Data Use Mine | X | X | DUY DWP | | DUY | Data Use Yours | | X | DUM DPI | | DPI | Data Preservation Interest | | X | DUY | | DWSS | Want Stop Sending Data | | X | DWSR DSS | | DWSR | Want Stop Receiving Data | | X | DWSS | | DSS | Stop Sending Data | X | | DWSS | | DWP | Want Data Paused | X | X | DPM | | DPM | Paused My Data | X | X | DWP DWM | | DWM | Want More Data | X | X | DPM | | NO | Negotiation Offer | X | X | NR SGC | | NR | Negotiation Response | X | X | NO | | PQ | Progress Query | X | X | PA | | PA | Progress Answer | X | X | PQ PR | | PR | Progress Report | X | X | PA | | AQ | Ability Query | X | X | AA | | AA | Ability Answer | X | X | AQ | +-------+----------------------------+-------+-------+--------------+
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Appendix B. State Summary

This appendix is not normative. The table below summarizes OCP states. Some states are maintained across multiple transactions and application messages. Some correspond to a single request/response dialog; the asynchronous nature of most OCP message exchanges requires OCP agents to process other messages while waiting for a response to a request and, hence, while maintaining the state of the dialog. For each state, the table provides the following information: state: Short state label. birth: Messages creating this state. death: Messages destroying this state. ID: Associated identifier, if any. +-------------------------------+-------------+-------------+-------+ | state | birth | death | ID | +-------------------------------+-------------+-------------+-------+ | connection | CS | CE | | | service group | SGC | SGD | sg-id | | transaction | TS | TE | xid | | application message and | AMS | AME | | | dataflow | | | | | premature org-dataflow | DWSR | AME | | | termination | | | | | premature adp-dataflow | DWSS | DSS AME | | | termination | | | | | paused dataflow | DPM | DWM | | | preservation commitment | DUM | DPI AME | | | negotiation | NO | NR | | | progress inquiry | PQ | PA | | | ability inquiry | PQ | PA | | +-------------------------------+-------------+-------------+-------+
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Appendix C. Acknowledgements

The author gratefully acknowledges the contributions of Abbie Barbir (Nortel Networks), Oskar Batuner (Independent Consultant), Larry Masinter (Adobe), Karel Mittig (France Telecom R&D), Markus Hofmann (Bell Labs), Hilarie Orman (The Purple Streak), Reinaldo Penno (Nortel Networks), and Martin Stecher (Webwasher), as well as an anonymous OPES working group participant. Special thanks to Marshall Rose for his xml2rfc tool.

16. References

16.1. 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. [RFC3835] Barbir, A., Penno, R., Chen, R., Hofmann, M., and H. Orman, "An Architecture for Open Pluggable Edge Services (OPES)", RFC 3835, August 2004.

16.2. Informative References

[RFC3836] Beck, A., Hofmann, M., Orman, H., Penno, R., and A. Terzis, "Requirements for Open Pluggable Edge Services (OPES) Callout Protocols", RFC 3836, August 2004. [RFC3837] Barbir, A., Batuner, O., Srinivas, B., Hofmann, M., and H. Orman, "Security Threats and Risks for Open Pluggable Edge Services (OPES)", RFC 3837, August 2004. [RFC3752] Barbir, A., Burger, E., Chen, R., McHenry, S., Orman, H., and R. Penno, "Open Pluggable Edge Services (OPES) Use Cases and Deployment Scenarios", RFC 3752, April 2004. [RFC3838] Barbir, A., Batuner, O., Beck, A., Chan, T., and H. Orman, "Policy, Authorization, and Enforcement Requirements of the Open Pluggable Edge Services (OPES)", RFC 3838, August 2004.
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   [RFC3897]    Barbir, A., "Open Pluggable Edge Services (OPES)
                Entities and End Points Communication", RFC 3897,
                September 2004.

   [OPES-RULES] Beck, A. and A. Rousskov, "P: Message Processing
                Language", Work in Progress, October 2003.

   [RFC3914]    Barbir, A. and A. Rousskov, "Open Pluggable Edge
                Services (OPES) Treatment of IAB Considerations", RFC
                3914, October 2004.

   [OPES-HTTP]  Rousskov, A. and M. Stecher, "HTTP adaptation with
                OPES", Work in Progress, January 2004.

   [RFC2616]    Fielding,  R., Gettys, J., Mogul, J., Frystyk, 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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