Generic Autonomic Signaling Protocol Application Program Interface (GRASP API)
draft-ietf-anima-grasp-api-01

Network Working Group                                       B. Carpenter
Internet-Draft                                         Univ. of Auckland
Intended status: Informational                               B. Liu, Ed.
Expires: September 4, 2018                           Huawei Technologies
                                                                 W. Wang
                                                                 X. Gong
                                                         BUPT University
                                                           March 3, 2018

   Generic Autonomic Signaling Protocol Application Program Interface
                              (GRASP API)
                     draft-ietf-anima-grasp-api-01

Abstract

   This document is a conceptual outline of an application programming
   interface (API) for the Generic Autonomic Signaling Protocol (GRASP).
   Such an API is needed for Autonomic Service Agents (ASA) calling the
   GRASP protocol module to exchange autonomic network messages with
   other ASAs.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 4, 2018.

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   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  GRASP API for ASA . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Design Principles . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Asynchronous Operations . . . . . . . . . . . . . . . . .   5
     2.3.  API definition  . . . . . . . . . . . . . . . . . . . . .   6
       2.3.1.  Parameters and data structures  . . . . . . . . . . .   6
       2.3.2.  Registration  . . . . . . . . . . . . . . . . . . . .   9
       2.3.3.  Discovery . . . . . . . . . . . . . . . . . . . . . .  11
       2.3.4.  Negotiation . . . . . . . . . . . . . . . . . . . . .  12
       2.3.5.  Synchronization and Flooding  . . . . . . . . . . . .  17
       2.3.6.  Invalid Message Function  . . . . . . . . . . . . . .  21
   3.  Example Logic Flows . . . . . . . . . . . . . . . . . . . . .  21
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Appendix A.  Error Codes  . . . . . . . . . . . . . . . . . . . .  23
   Appendix B.  Change log [RFC Editor: Please remove] . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   As defined in [I-D.ietf-anima-reference-model], the Autonomic Service
   Agent (ASA) is the atomic entity of an autonomic function, and it is
   instantiated on autonomic nodes.  When ASAs communicate with each
   other, they should use the Generic Autonomic Signaling Protocol
   (GRASP) [I-D.ietf-anima-grasp].

   As the following figure shows, a GRASP implementation could contain
   two major sub-layers.  The bottom is the GRASP base protocol module,
   which is only responsible for sending and receiving GRASP messages
   and maintaining shared data structures.  The upper layer contains
   some extended functions based upon GRASP basic protocol.  For
   example, [I-D.liu-anima-grasp-distribution] describes a possible
   extended function.

   It is desirable that ASAs can be designed as portable user-space
   programs using a portable API.  In many operating systems, the GRASP

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   module will therefore be split into two layers, one being a library
   that provides the API and the other being core code containing common
   components such as multicast handling and the discovery cache.  The
   details of this are system-dependent.  In particular, the GRASP
   library might need to communicate with the GRASP core via an inter-
   process communication (IPC) mechanism.

             +----+                              +----+
             |ASAs|                              |ASAs|
             +----+                              +----+
                |                                   |
                | GRASP Function API                |
                |                                   |
             +------------------+                   |GRASP API
             | GRASP Extended   |                   |
             | Function Modules |                   |
             +------------------+                   |
             +------------------------------------------+
             |                   GRASP Library          |
             |  GRASP Module - - - - - - - - - - - - - -|
             |                   GRASP Core             |
             +------------------------------------------+

   Both the GRASP library and the extended function modules should be
   available to the ASAs.  Thus, there need to be two sub-sets of API.
   However, since the extended functions are expected to be added in an
   incremental manner, it is inappropriate to define the function APIs
   in a single document.  This document only describes the base GRASP
   API.

   Note that a very simple autonomic node might contain only a single
   ASA in addition to the autonomic infrastructure components described
   in [I-D.ietf-anima-bootstrapping-keyinfra] and
   [I-D.ietf-anima-autonomic-control-plane].  Such a node might directly
   integrate GRASP in its autonomic code and therefore not require this
   API to be installed.

   This document gives a conceptual outline of the API.  It is not a
   formal specification for any particular programming language or
   operating system, and it is expected that details will be clarified
   in individual implementations.

2.  GRASP API for ASA

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2.1.  Design Principles

   The assumption of this document is that any Autonomic Service Agent
   (ASA) needs to call a GRASP module that handles protocol details
   (security, sending and listening for GRASP messages, waiting, caching
   discovery results, negotiation looping, sending and receiving
   sychronization data, etc.) but understands nothing about individual
   objectives.  The semantics of objectives are unknown to the GRASP
   module and are handled only by the ASAs.  Thus, this is a high level
   abstract API for use by ASAs.  Individual language bindings should be
   defined in separate documents.

   An assumption of this API is that ASAs may fall into various classes:

   o  ASAs that only use GRASP for discovery purposes.

   o  ASAs that use GRASP negotiation but only as an initiator (client).

   o  ASAs that use GRASP negotiation but only as a responder.

   o  ASAs that use GRASP negotiation as an initiator or responder.

   o  ASAs that use GRASP synchronization but only as an initiator
      (recipient).

   o  ASAs that use GRASP synchronization but only as a responder and/or
      flooder.

   o  ASAs that use GRASP synchronization as an initiator, responder
      and/or flooder.

   The API also assumes that one ASA may support multiple objectives.
   Nothing prevents an ASA from supporting some objectives for
   synchronization and others for negotiation.

   The API design assumes that the operating system and programming
   language provide a mechanism for simultaneous asynchronous
   operations.  This is discussed in detail in Section 2.2.

   This is a preliminary version.  A few gaps exist:

   o  Authorization of ASAs is out of scope.

   o  User-supplied explicit locators for an objective are not
      supported.

   o  The Rapid mode of GRASP is not supported.

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2.2.  Asynchronous Operations

   GRASP includes asynchronous operations and wait states.  Most ASAs
   will need to support several simultaneous operations; for example an
   ASA might need to negotiate one objective with a peer while
   discovering and synchronizing a different objective with a different
   peer.  Alternatively, an ASA which acts as a resource manager might
   need to run simultaneous negotiations for a given objective with
   multiple different peers.  Thus, both the GRASP core and most ASAs
   need to support asynchronous operations.  Depending on both the
   operating system and the programming language in use, there are two
   main techniques for such parallel operations: multi-threading, or a
   polling or 'event loop' structure.

   In multi-threading, the operating system and language will provide
   the necessary support for asynchronous operations, including creation
   of new threads, context switching between threads, queues, locks, and
   implicit wait states.  In this case, all API calls can be treated
   naturally as synchronous, even if they include wait states, blocking
   and queueing.  Simultaneous operations will each run in their own
   threads.

   In an event loop implementation, synchronous blocking calls are not
   acceptable.  Therefore all calls must be non-blocking, and the main
   loop will support multiple GRASP sessions in parallel by repeatedly
   checking each one for a change of state.  To facilitate this, the API
   implementation will provide non-blocking versions of all the
   functions that otherwise involve blocking and queueing.  In these
   calls, a 'noReply' code will be returned by each call instead of
   blocking, until such time as the event for which it is waiting (or a
   failure) has occurred.  Thus, for example, discover() would return
   "noReply" instead of waiting until discovery has succeeded or timed
   out.  The discover() call would be repeated in every cycle of the
   main loop until it completes.  A 'session_nonce' parameter (described
   below) is used to distinguish simultaneous GRASP sessions from each
   other, so that any number of sessions may proceed in parallel.

   The following calls involve waiting for a remote operation, so they
   could use this mechanism:

      discover()

      request_negotiate()

      negotiate_step()

      listen_negotiate()

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      synchronize()

   In all these calls, the 'session_nonce' is a read/write parameter.
   On the first call, it is set to a null value, and the API returns the
   'noReply' code and a non-null value.  This value must be used in all
   subsequent calls.  By this mechanism, multiple overlapping sessions
   can be distinguished, both in the ASA and in the GRASP core.

2.3.  API definition

2.3.1.  Parameters and data structures

   This section describes parameters and data structures uaed in
   multiple API calls.

2.3.1.1.  Errorcode

   All functions in the API have an unsigned 'errorcode' integer as
   their return value (the first returned value in languages that allow
   multiple returned parameters).  An errorcode of zero indicates
   success.  Any other value indicates failure of some kind.  The first
   three errorcodes have special importance:

   1.  Declined: used to indicate that the other end has sent a GRASP
       Negotiation End message (M_END) with a Decline option
       (O_DECLINE).

   2.  No reply: used in non-blocking calls to indicate that the other
       end has sent no reply so far (see Section 2.2).

   3.  Unspecified error: used when no more specific error code applies.

   Appendix A gives a full list of currently defined error codes, based
   on implementation experience.

2.3.1.2.  Timeout

   Wherever a 'timeout' parameter appears, it is an integer expressed in
   milliseconds.  If it is zero, the GRASP default timeout
   (GRASP_DEF_TIMEOUT, see [I-D.ietf-anima-grasp]) will apply.  If no
   response is received before the timeout expires, the call will fail
   unless otherwise noted.

2.3.1.3.  Objective

   An 'objective' parameter is a data structure with the following
   components:

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   o  name (UTF-8 string) - the objective's name

   o  neg (Boolean flag) - True if objective supports negotiation
      (default False)

   o  synch (Boolean flag) - True if objective supports synchronization
      (default False)

   o  dry (Boolean flag) - True if objective supports dry-run
      negotiation (default False)

      *  Note 1: All objectives are assumed to support discovery, so
         there is no Boolean for that.

      *  Note 2: Only one of 'synch' or 'neg' may be True.

      *  Note 3: 'dry' must not be True unless 'neg' is also True.

      *  Note 4: In a language such as C the preferred implementation
         may be to represent the Boolean flags as bits in a single byte.

   o  loop_count (integer) - Limit on negotiation steps etc. (default
      GRASP_DEF_LOOPCT, see [I-D.ietf-anima-grasp])

   o  value - a specific data structure expressing the value of the
      objective.  The format is language dependent, with the constraint
      that it can be validly represented in CBOR (default integer = 0).

      An essential requirement for all language mappings and all
      implementations is that, regardless of what other options exist
      for a language-specific represenation of the value, there is
      always an option to use a CBOR byte string as the value.  The API
      will then wrap this byte string in CBOR Tag 24 for transmission
      via GRASP, and unwrap it after reception.

      An example data structure definition for an objective in the C
      language is:

       typedef struct {
          char *name;
          uint8_t flags;            // flag bits as defined by GRASP
          int loop_count;
          int value_size;           // size of value
          uint8_t cbor_value[];     // CBOR bytestring of value
          } objective;

      An example data structure definition for an objective in the
      Python language is:

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    class objective:
       """A GRASP objective"""
       def __init__(self, name):
           self.name = name    #Unique name, string
           self.neg = False    #True if objective supports negotiation
           self.dry = False    #True if objective supports dry-run neg.
           self.synch = False  #True if objective supports synch
           self.loop_count = GRASP_DEF_LOOPCT  #Default starting value
           self.value = 0      #Place holder; any valid Python object

2.3.1.4.  ASA_locator

   An 'ASA_locator' parameter is a data structure with the following
   contents:

   o  locator - The actual locator, either an IP address or an ASCII
      string.

   o  ifi (integer) - The interface identifier index via which this was
      discovered - probably no use to a normal ASA

   o  expire (system dependent type) - The time on the local system
      clock when this locator will expire from the cache

   o  is_ipaddress (Boolean) - True if the locator is an IP address

   o  is_fqdn (Boolean) - True if the locator is an FQDN

   o  is_uri (Boolean) - True if the locator is a URI

   o  diverted (Boolean) - True if the locator was discovered via a
      Divert option

   o  protocol (integer) - Applicable transport protocol (IPPROTO_TCP or
      IPPROTO_UDP)

   o  port (integer) - Applicable port number

2.3.1.5.  Tagged_objective

   A 'tagged_objective' parameter is a data structure with the following
   contents:

   o  objective - An objective

   o  locator - The ASA_locator associated with the objective, or a null
      value.

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2.3.1.6.  Asa_nonce

   In most calls, an 'asa_nonce' parameter is required.  It is generated
   when an ASA registers with GRASP, and any call in which an invalid
   nonce is presented will fail.  It is an up to 32-bit opaque value
   (for example represented as a uint32_t, depending on the language).
   It should be unpredictable; a possible implementation is to use the
   same mechanism that GRASP uses to generate Session IDs
   [I-D.ietf-anima-grasp].  Another possible implementation is to hash
   the name of the ASA with a locally defined secret key.

2.3.1.7.  Session_nonce

   In some calls, a 'session_nonce' parameter is required.  This is an
   opaque data structure as far as the ASA is concerned, used to
   identify calls to the API as belonging to a specific GRASP session
   (see Section 2.2).  In fully threaded implementations this parameter
   might not be needed, but it is included to act as a session handle if
   necessary.  It will also allow GRASP to detect and ignore malicious
   calls or calls from timed-out sessions.  A possible implementation is
   to form the nonce from the underlying GRASP Session ID and the source
   address of the session.

2.3.2.  Registration

   These functions are used to register an ASA and the objectives that
   it supports with the GRASP module.  If an authorization model is
   added to GRASP, it would be added here.

   o  register_asa()

         Input parameter:

            name of the ASA (UTF-8 string)

         Return parameters:

            errorcode (integer)

            asa_nonce (integer) (if successful)

         This initialises state in the GRASP module for the calling
         entity (the ASA).  In the case of success, an 'asa_nonce' is
         returned which the ASA must present in all subsequent calls.
         In the case of failure, the ASA has not been authorized and
         cannot operate.

   o  deregister_asa()

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         Input parameters:

            asa_nonce (integer)

            name of the ASA (UTF-8 string)

         Return parameter:

            errorcode (integer)

         This removes all state in the GRASP module for the calling
         entity (the ASA), and deregisters any objectives it has
         registered.  Note that these actions must also happen
         automatically if an ASA crashes.

         Note - the ASA name is strictly speaking redundant in this
         call, but is present for clarity.

   o  register_objective()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

            ttl (integer - default GRASP_DEF_TIMEOUT)

            discoverable (Boolean - default False)

            overlap (Boolean - default False)

            local (Boolean - default False)

         Return parameter:

            errorcode (integer)

         This registers an objective that this ASA supports and may
         modify.  The 'objective' becomes a candidate for discovery.
         However, discovery responses should not be enabled until the
         ASA calls listen_negotiate() or listen_synchronize(), showing
         that it is able to act as a responder.  The ASA may negotiate
         the objective or send synchronization or flood data.
         Registration is not needed if the ASA only wants to receive
         synchronization or flood data for the objective concerned.

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         The 'ttl' parameter is the valid lifetime (time to live) in
         milliseconds of any discovery response for this objective.  The
         default value should be the GRASP default timeout
         (GRASP_DEF_TIMEOUT, see [I-D.ietf-anima-grasp]).

         If the optional parameter 'discoverable' is True, the objective
         is immediately discoverable.  This is intended for objectives
         that are only defined for GRASP discovery, and which do not
         support negotiation or synchronization.

         If the optional parameter 'overlap' is True, more than one ASA
         may register this objective in the same GRASP instance.

         If the optional parameter 'local' is True, discovery must
         return a link-local address.  This feature is for objectives
         that must be restricted to the local link.

         This call may be repeated for multiple objectives.

   o  deregister_objective()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

         Return parameter:

            errorcode (integer)

         The 'objective' must have been registered by the calling ASA;
         if not, this call fails.  Otherwise, it removes all state in
         the GRASP module for the given objective.

2.3.3.  Discovery

   o  discover()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

            timeout (integer)

            flush (Boolean - default False)

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         Return parameters:

            errorcode (integer)

            locator_list (structure)

         This returns a list of discovered 'ASA_locator's for the given
         objective.  If the optional parameter 'flush' is True, any
         locally cached locators for the objective are deleted first.
         Otherwise, they are returned immediately.  If not, GRASP
         discovery is performed, and all results obtained before the
         timeout expires are returned.  If no results are obtained, an
         empty list is returned after the timeout.  That is not an error
         condition.

         Threaded implementation: This should be called in a separate
         thread if asynchronous operation is required.

         Event loop implementation: An additional read/write
         'session_nonce' parameter is used.

2.3.4.  Negotiation

   o  request_negotiate()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

            peer (ASA_locator)

            timeout (integer)

         Return parameters:

            errorcode (integer)

            session_nonce (structure) (if successful)

            proffered_objective (structure) (if successful)

            reason (string) (if negotiation declined)

         This function opens a negotiation session.  The 'objective'
         parameter must include the requested value, and its loop count

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         should be set to a suitable value by the ASA.  If not, the
         GRASP default will apply.

         Note that a given negotiation session may or may not be a dry-
         run negotiation; the two modes must not be mixed in a single
         session.

         The 'peer' parameter is the target node; it must be an
         'ASA_locator' as returned by discover().  If the peer is null,
         GRASP discovery is performed first.

         If the 'errorcode' return parameter is 0, the negotiation has
         successfully started.  There are then two cases:

         1.  The 'session_nonce' parameter is null.  In this case the
             negotiation has succeeded (the peer has accepted the
             request).  The returned 'proffered_objective' contains the
             value accepted by the peer.

         2.  The 'session_nonce' parameter is not null.  In this case
             negotiation must continue.  The returned
             'proffered_objective' contains the first value proffered by
             the negotiation peer.  Note that this instance of the
             objective must be used in the subsequent negotiation call
             because it also contains the current loop count.  The
             'session_nonce' must be presented in all subsequent
             negotiation steps.

             This function must be followed by calls to 'negotiate_step'
             and/or 'negotiate_wait' and/or 'end_negotiate' until the
             negotiation ends. 'request_negotiate' may then be called
             again to start a new negotation.

         If the 'errorcode' parameter has the value 1 ('declined'), the
         negotiation has been declined by the peer (M_END and O_DECLINE
         features of GRASP).  The 'reason' string is then available for
         information and diagnostic use, but it may be a null string.
         For this and any other error code, an exponential backoff is
         recommended before any retry.

         Threaded implementation: This should be called in a separate
         thread if asynchronous operation is required.

         Event loop implementation: The 'session_nonce' parameter is
         used in read/write mode.

         Special note for the ACP infrastructure ASA: It is likely that
         this ASA will need to discover and negotiate with its peers in

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         each of its on-link neighbors.  It will therefore need to know
         not only the link-local IP address but also the physical
         interface and transport port for connecting to each neighbor.
         One implementation approach to this is to include these details
         in the 'session_nonce' data structure, which is opaque to
         normal ASAs.

   o  listen_negotiate()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

         Return parameters:

            errorcode (integer)

            session_nonce (structure) (if successful)

            requested_objective (structure) (if successful)

         This function instructs GRASP to listen for negotiation
         requests for the given 'objective'.  It also enables discovery
         responses for the objective.

         Threaded implementation: It will block waiting for an incoming
         request, so should be called in a separate thread if
         asynchronous operation is required.

         Event loop implementation: A read/write 'session_nonce'
         parameter is used.

         Unless there is an unexpected failure, this call only returns
         after an incoming negotiation request.  When it does so,
         'requested_objective' contains the first value requested by the
         negotiation peer.  Note that this instance of the objective
         must be used in the subsequent negotiation call because it also
         contains the current loop count.  The 'session_nonce' must be
         presented in all subsequent negotiation steps.

         This function must be followed by calls to 'negotiate_step'
         and/or 'negotiate_wait' and/or 'end_negotiate' until the
         negotiation ends. 'listen_negotiate' may then be called again
         to await a new negotation.

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         If an ASA is capable of handling multiple negotiations
         simultaneously, it may call 'listen_negotiate' simultaneously
         from multiple threads.  The API and GRASP implementation must
         support re-entrant use of the listening state and the
         negotiation calls.  Simultaneous sessions will be distinguished
         by the threads themselves, the GRASP Session IDs, and the
         underlying unicast transport sockets.

   o  stop_listen_negotiate()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

         Return parameter:

            errorcode (integer)

         Instructs GRASP to stop listening for negotiation requests for
         the given objective, i.e., cancels 'listen_negotiate'.

         Threaded implementation: Must be called from a different thread
         than 'listen_negotiate'.

         Event loop implementation: no special considerations.

   o  negotiate_step()

         Input parameters:

            asa_nonce (integer)

            session_nonce (structure)

            objective (structure)

            timeout (integer)

         Return parameters:

            Exactly as for 'request_negotiate'

         Executes the next negotation step with the peer.  The
         'objective' parameter contains the next value being proffered
         by the ASA in this step.

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         Threaded implementation: Called in the same thread as the
         preceding 'request_negotiate' or 'listen_negotiate', with the
         same value of 'session_nonce'.

         Event loop implementation: Must use the same value of
         'session_nonce' returned by the preceding 'request_negotiate'
         or 'listen_negotiate'.

   o  negotiate_wait()

         Input parameters:

            asa_nonce (integer)

            session_nonce (structure)

            timeout (integer)

         Return parameters:

            errorcode (integer)

         Delay negotiation session by 'timeout' milliseconds.

         Threaded implementation: Called in the same thread as the
         preceding 'request_negotiate' or 'listen_negotiate', with the
         same value of 'session_nonce'.

         Event loop implementation: Must use the same value of
         'session_nonce' returned by the preceding 'request_negotiate'
         or 'listen_negotiate'.

   o  end_negotiate()

         Input parameters:

            asa_nonce (integer)

            session_nonce (structure)

            reply (Boolean)

            reason (UTF-8 string)

         Return parameters:

            errorcode (integer)

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         End the negotiation session.

         'reply' = True for accept (successful negotiation), False for
         decline (failed negotiation).

         'reason' = optional string describing reason for decline.

         Threaded implementation: Called in the same thread as the
         preceding 'request_negotiate' or 'listen_negotiate', with the
         same value of 'session_nonce'.

         Event loop implementation: Must use the same value of
         'session_nonce' returned by the preceding 'request_negotiate'
         or 'listen_negotiate'.

2.3.5.  Synchronization and Flooding

   o  synchronize()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

            peer (ASA_locator)

            timeout (integer)

         Return parameters:

            errorcode (integer)

            objective (structure) (if successful)

         This call requests the synchronized value of the given
         'objective'.

         Since this is essentially a read operation, any ASA can do it.
         Therefore the API checks that the ASA is registered but the
         objective doesn't need to be registered by the calling ASA.

         If the objective was already flooded, the flooded value is
         returned immediately in the 'result' parameter.  In this case,
         the 'source' and 'timeout' are ignored.

         Otherwise, synchronization with a discovered ASA is performed.
         The 'peer' parameter is an 'ASA_locator' as returned by

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         discover().  If 'peer' is null, GRASP discovery is performed
         first.

         This call should be repeated whenever the latest value is
         needed.

         Threaded implementation: Call in a separate thread if
         asynchronous operation is required.

         Event loop implementation: An additional read/write
         'session_nonce' parameter is used.

         Since this is essentially a read operation, any ASA can use it.
         Therefore GRASP checks that the calling ASA is registered but
         the objective doesn't need to be registered by the calling ASA.

         In the case of failure, an exponential backoff is recommended
         before retrying.

   o  listen_synchronize()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

         Return parameters:

            errorcode (integer)

         This instructs GRASP to listen for synchronization requests for
         the given objective, and to respond with the value given in the
         'objective' parameter.  It also enables discovery responses for
         the objective.

         This call is non-blocking and may be repeated whenever the
         value changes.

   o  stop_listen_synchronize()

         Input parameters:

            asa_nonce (integer)

            objective (structure)

         Return parameters:

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            errorcode (integer)

         This call instructs GRASP to stop listening for synchronization
         requests for the given 'objective', i.e. it cancels a previous
         listen_synchronize.

   o  flood()

         Input parameters:

            asa_nonce (integer)

            ttl (integer)

            tagged_objective_list (structure)

         Return parameters:

            errorcode (integer)

         This call instructs GRASP to flood the given synchronization
         objective(s) and their value(s) and associated locator(s) to
         all GRASP nodes.

         The 'ttl' parameter is the valid lifetime (time to live) of the
         flooded data in milliseconds (0 = infinity)

         The 'tagged_objective_list' parameter is a list of one or more
         'tagged_objective' couplets.  The 'locator' parameter that tags
         each objective is normally null but may be a valid
         'ASA_locator'.  Infrastructure ASAs needing to flood an
         {address, protocol, port} 3-tuple with an objective create an
         ASA_locator object to do so.  If the IP address in that locator
         is the unspecified address ('::') it is replaced by the link-
         local address of the sending node in each copy of the flood
         multicast, which will be forced to have a loop count of 1.
         This feature is for objectives that must be restricted to the
         local link.

         The function checks that the ASA registered each objective.

         This call may be repeated whenever any value changes.

   o  get_flood()

         Input parameters:

            asa_nonce (integer)

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            objective (structure)

         Return parameters:

            errorcode (integer)

            tagged_objective_list (structure) (if successful)

         This call instructs GRASP to return the given synchronization
         objective if it has been flooded and its lifetime has not
         expired.

         Since this is essentially a read operation, any ASA can do it.
         Therefore the API checks that the ASA is registered but the
         objective doesn't need to be registered by the calling ASA.

         The 'tagged_objective_list' parameter is a list of
         'tagged_objective' couplets, each one being a copy of the
         flooded objective and a coresponding locator.  Thus if the same
         objective has been flooded by multiple ASAs, the recipient can
         distinguish the copies.

         Note that this call is for advanced ASAs.  In a simple case, an
         ASA can simply call synchronize() in order to get a valid
         flooded objective.

   o  expire_flood()

         Input parameters:

            asa_nonce (integer)

            tagged_objective (structure)

         Return parameters:

            errorcode (integer)

         This is a call that can only be used after a preceding call to
         get_flood() by an ASA that is capable of deciding that the
         flooded value is stale or invalid.  Use with care.

         The 'tagged_objective' parameter is the one to be expired.

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2.3.6.  Invalid Message Function

   o  send_invalid()

         Input parameters:

            asa_nonce (integer)

            session_nonce (structure)

            info (bytes)

         Return parameters:

            errorcode (integer)

         Sends a GRASP Invalid Message (M_INVALID) message, as described
         in [I-D.ietf-anima-grasp].  Should not be used if
         end_negotiate() would be sufficient.  Note that this message
         may be used in response to any unicast GRASP message that the
         receiver cannot interpret correctly.  In most cases this
         message will be generated internally by a GRASP implementation.

         'info' = optional diagnostic data.  May be raw bytes from the
         invalid message.

3.  Example Logic Flows

   TBD

   (Until this section is written, some Python examples can be found at
   <https://github.com/becarpenter/graspy>.)

4.  Security Considerations

   Security issues for the GRASP protocol are discussed in
   [I-D.ietf-anima-grasp].  Authorization of ASAs is a subject for
   future study.

   The 'asa_nonce' parameter is used in the API as a first line of
   defence against a malware process attempting to imitate a
   legitimately registered ASA.  The 'session_nonce' parameter is used
   in the API as a first line of defence against a malware process
   attempting to hijack a GRASP session.

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5.  IANA Considerations

   This document currently makes no request of the IANA.

   Open question: Do we need an IANA registry for the error codes?

6.  Acknowledgements

   Excellent suggestions were made by Michael Richardson and other
   participansts in the ANIMA WG.

7.  References

7.1.  Normative References

   [I-D.ietf-anima-grasp]
              Bormann, C., Carpenter, B., and B. Liu, "A Generic
              Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
              grasp-15 (work in progress), July 2017.

7.2.  Informative References

   [I-D.ietf-anima-autonomic-control-plane]
              Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
              Control Plane (ACP)", draft-ietf-anima-autonomic-control-
              plane-13 (work in progress), December 2017.

   [I-D.ietf-anima-bootstrapping-keyinfra]
              Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
              S., and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-11 (work in progress), February 2018.

   [I-D.ietf-anima-reference-model]
              Behringer, M., Carpenter, B., Eckert, T., Ciavaglia, L.,
              and J. Nobre, "A Reference Model for Autonomic
              Networking", draft-ietf-anima-reference-model-06 (work in
              progress), February 2018.

   [I-D.liu-anima-grasp-distribution]
              Liu, B., Jiang, S., Xiao, X., Hecker, A., and Z.
              Despotovic, "Information Distribution in Autonomic
              Networking", draft-liu-anima-grasp-distribution-05 (work
              in progress), February 2018.

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Appendix A.  Error Codes

   This Appendix lists the error codes defined so far, with suggested
   symbolic names and corresponding descriptive strings in English.  It
   is expected that complete API implementations will provide for
   localisation of these descriptive strings, and that additional error
   codes will be needed according to implementation details.

   ok               0 "OK"
   declined         1 "Declined"
   noReply          2 "No reply"
   unspec           3 "Unspecified error"
   ASAfull          4 "ASA registry full"
   dupASA           5 "Duplicate ASA name"
   noASA            6 "ASA not registered"
   notYourASA       7 "ASA registered but not by you"
   notBoth          8 "Objective cannot support both negotiation
                       and synchronization"
   notDry           9 "Dry-run allowed only with negotiation"
   notOverlap      10 "Overlap not supported by this implementation"
   objFull         11 "Objective registry full"
   objReg          12 "Objective already registered"
   notYourObj      13 "Objective not registered by this ASA"
   notObj          14 "Objective not found"
   notNeg          15 "Objective not negotiable"
   noSecurity      16 "No security"
   noDiscReply     17 "No reply to discovery"
   sockErrNegRq    18 "Socket error sending negotiation request"
   noSession       19 "No session"
   noSocket        20 "No socket"
   loopExhausted   21 "Loop count exhausted"
   sockErrNegStep  22 "Socket error sending negotiation step"
   noPeer          23 "No negotiation peer"
   CBORfail        24 "CBOR decode failure"
   invalidNeg      25 "Invalid Negotiate message"
   invalidEnd      26 "Invalid end message"
   noNegReply      27 "No reply to negotiation step"
   noValidStep     28 "No valid reply to negotiation step"
   sockErrWait     29 "Socket error sending wait message"
   sockErrEnd      30 "Socket error sending end message"
   IDclash         31 "Incoming request Session ID clash"
   notSynch        32 "Not a synchronization objective"
   notFloodDisc    33 "Not flooded and no reply to discovery"
   sockErrSynRq    34 "Socket error sending synch request"
   noListener      35 "No synch listener"
   noSynchReply    36 "No reply to synchronization request"
   noValidSynch    37 "No valid reply to synchronization request"
   invalidLoc      38 "Invalid locator"

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Appendix B.  Change log [RFC Editor: Please remove]

   draft-ietf-anima-grasp-api-01, 2018-03-03:

   Editorial updates

   draft-ietf-anima-grasp-api-00, 2017-12-23:

   WG adoption

   Editorial improvements.

   draft-liu-anima-grasp-api-06, 2017-11-24:

   Improved description of event-loop model.

   Changed intended status to Informational.

   Editorial improvements.

   draft-liu-anima-grasp-api-05, 2017-10-02:

   Added send_invalid()

   draft-liu-anima-grasp-api-04, 2017-06-30:

   Noted that simple nodes might not include the API.

   Minor clarifications.

   draft-liu-anima-grasp-api-03, 2017-02-13:

   Changed error return to integers.

   Required all implementations to accept objective values in CBOR.

   Added non-blocking alternatives.

   draft-liu-anima-grasp-api-02, 2016-12-17:

   Updated for draft-ietf-anima-grasp-09

   draft-liu-anima-grasp-api-02, 2016-09-30:

   Added items for draft-ietf-anima-grasp-07

   Editorial corrections

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   draft-liu-anima-grasp-api-01, 2016-06-24:

   Updated for draft-ietf-anima-grasp-05

   Editorial corrections

   draft-liu-anima-grasp-api-00, 2016-04-04:

   Initial version

Authors' Addresses

   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland  1142
   New Zealand

   Email: brian.e.carpenter@gmail.com

   Bing Liu (editor)
   Huawei Technologies
   Q22, Huawei Campus
   No.156 Beiqing Road
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: leo.liubing@huawei.com

   Wendong Wang
   BUPT University
   Beijing University of Posts & Telecom.
   No.10 Xitucheng Road
   Hai-Dian District, Beijing 100876
   P.R. China

   Email: wdwang@bupt.edu.cn

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   Xiangyang Gong
   BUPT University
   Beijing University of Posts & Telecom.
   No.10 Xitucheng Road
   Hai-Dian District, Beijing 100876
   P.R. China

   Email: xygong@bupt.edu.cn

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