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NAME

       bpextensions - interface for adding extensions to Bundle Protocol

SYNOPSIS

           #include "bpextensions.c"

DESCRIPTION

       ION's interface for extending the Bundle Protocol enables the definition of external
       functions that insert extension blocks into outbound bundles (either before or after the
       payload block), parse and record extension blocks in inbound bundles, and modify extension
       blocks at key points in bundle processing.  All extension-block handling is statically
       linked into ION at build time, but the addition of an extension never requires that any
       standard ION source code be modified.

       Standard structures for recording extension blocks -- both in transient storage [memory]
       during bundle acquisition (AcqExtBlock) and in persistent storage [the ION database]
       during subsequent bundle processing (ExtensionBlock) -- are defined in the bpP.h header
       file.  In each case, the extension block structure comprises a block type code, block
       processing flags, possibly a list of EID references, an array of bytes (the serialized
       form of the block, for transmission), the length of that array, optionally an extension-
       specific opaque object whose structure is designed to characterize the block in a manner
       that's convenient for the extension processing functions, and the size of that object.

       The definition of each extension is asserted in an ExtensionDef structure, also as defined
       in the bpP.h header file.  Each ExtensionDef must supply:

           The name of the extension.  (Used in some diagnostic messages.)

           The extension's block type code.

           An indication as to whether the local node is to insert this extension block before
           (0) or after (1) the payload block when new bundles are locally sourced.

           A pointer to an offer function.

           A pointer to a release function.

           A pointer to an accept function.

           A pointer to a check function.

           A pointer to a record function.

           A pointer to a clear function.

           A pointer to a copy function.

           A pointer to a function to be called when forwarding a bundle containing this sort of
           block.

           A pointer to a function to be called when taking custody of a bundle containing this
           sort of block.

           A pointer to a function to be called when enqueuing for transmission a bundle
           containing this sort of block.

           A pointer to a function to be called when a convergence-layer adapter dequeues a
           bundle containing this sort of block, before serializing it.

           A pointer to a function to be called immediately before a convergence-layer adapter
           transmits a bundle containing this sort of block, after the bundle has been
           serialized.

       All extension definitions must be coded into an array of ExtensionDef structures named
       extensions.  The order of appearance of extension definitions in the extensions array
       determines the order in which extension blocks will be inserted into locally sourced
       bundles.

       The standard extensions array -- which is empty -- is in the noextensions.c prototype
       source file.  The procedure for extending the Bundle Protocol in ION is as follows:

       1.  Specify -DBP_EXTENDED in the Makefile's compiler command line when building the
       libbpP.c library module.

       2.  Create a copy of the prototype extensions file, named "bpextensions.c", in a directory
       that is made visible to the Makefile's libbpP.c compilation command line (by a -I
       parameter).

       3.  In the "external function declarations" area of "bpextensions.c", add "extern"
       function declarations identifying the functions that will implement your extension (or
       extensions).

       4.  Add one or more ExtensionDef structure initialization lines to the extensions array,
       referencing those declared functions.

       5.  Develop the implementations of those functions in one or more new source code files.

       6.  Add the object file or files for the new extension implementation source file (or
       files) to the Makefile's command line for linking libbpP.so.

       The function pointers supplied in each ExtensionDef must conform to the following
       specifications.  NOTE that any function that modifies the bytes member of an
       ExtensionBlock or AckExtBlock must set the corresponding length to the new length of the
       bytes array, if changed.

       int (*BpExtBlkOfferFn)(ExtensionBlock *blk, Bundle *bundle)
           Populates all fields of the indicated ExtensionBlock structure for inclusion in the
           indicated outbound bundle.  This function is automatically called when a new bundle is
           locally sourced or upon acquisition of a remotely sourced bundle that does not contain
           an extension block of this type.  The values of the extension block are typically
           expected to be a function of the state of the bundle, but this is extension-specific.
           If it is not appropriate to offer an extension block of this type as part of this
           bundle, then the size, length, object, and bytes members of blk must all be set to
           zero.  If it is appropriate to offer such a block but no internal object representing
           the state of the block is needed, the object and size members of blk must be set to
           zero.  The type, blkProcFlags, and dataLength members of blk must be populated by the
           implementation of the "offer" function, but the length and bytes members are typically
           populated by calling the BP library function serializeExtBlk(), which must be passed
           the block to be serialized (with type, blkProcFlags and dataLength already set), a
           Lyst of EID references (two list elements -- offsets -- per EID reference, if
           applicable; otherwise NULL), and a pointer to the extension-specific block data.  The
           block's bytes array and object (if present) must occupy space allocated from the ION
           database heap.  Return zero on success, -1 on any system failure.

       void (*BpExtBlkReleaseFn)(ExtensionBlock *blk)
           Releases all ION database space occupied by the object member of blk.  This function
           is automatically called when a bundle is destroyed.  Note that incorrect
           implementation of this function may result in a database space leak.

       int (*BpExtBlkRecordFn)(ExtensionBlock *blk, AcqExtBlock *acqblk)
           Copies the object member of acqblk to ION database heap space and places the address
           of that non-volatile object in the object member of blk; also sets size in blk.  This
           function is automatically called when an acquired bundle is accepted for forwarding
           and/or delivery.  Return zero on success, -1 on any system failure.

       int (*BpExtBlkCopyFn)(ExtensionBlock *newblk, ExtensionBlock *oldblk)
           Copies the object member of oldblk to ION database heap space and places the address
           of that new non-volatile object in the object member of newblk, also sets size in
           newblk.  This function is automatically called when two copies of a bundle are needed,
           e.g., in the event that it must both be delivered to a local client and also fowarded
           to another node.  Return zero on success, -1 on any system failure.

       int (*BpExtBlkProcessFn)(ExtensionBlock *blk, Bundle *bundle, void *context)
           Performs some extension-specific transformation of the data encapsulated in blk based
           on the state of bundle.  The transformation to be performed will typically vary
           depending on whether the identified function is the one that is automatically invoked
           upon forwarding the bundle, upon taking custody of the bundle, upon enqueuing the
           bundle for transmission, upon removing the bundle from the transmission queue, or upon
           transmitting the serialized bundle.  The context argument may supply useful
           supplemental information; in particular, the context provided to the ON_DEQUEUE
           function will comprise the name of the protocol for the duct from which the bundle has
           been dequeued, together with the EID of the neighboring node endpoint to which the
           bundle will be directly transmitted when serialized.  The block-specific data in blk
           is located within bytes immediately after the header of the extension block; the
           length of the block's header is the difference between length and dataLength.
           Whenever the block's blkProcFlags, EID extensions, and/or block-specific data are
           altered, the serializeExtBlk() function should be called again to recalculate the size
           of the extension block and rebuild the bytes array.  Return zero on success, -1 on any
           system failure.

       int (*BpAcqExtBlkAcquireFn)(AcqExtBlock *acqblk, AcqWorkArea *work)
           Populates the indicated AcqExtBlock structure with size and object for retention as
           part of the indicated inbound bundle.  (The type, blkProcFlags, EID references (if
           any), dataLength, length, and bytes values of the structure are pre-populated with
           data as extracted from the serialized bundle.)  This function is automatically called
           when an extension block of this type is encountered in the course of parsing and
           acquiring a bundle for local delivery and/or forwarding.  If no internal object
           representing the state of the block is needed, the object member of acqblk must be set
           to NULL and the size member must be set to zero.  If an object is needed for this
           block, it must occupy space that is allocated from ION working memory using MTAKE and
           its size must be indicated in blk.  Return zero if the block is malformed (this will
           cause the bundle to be discarded), 1 if the block is successfully parsed, -1 on any
           system failure.

       int (*BpAcqExtBlkCheckFn)(AcqExtBlock *acqblk, AcqWorkArea *work)
           Examines the bundle in work to determine whether or not it is authentic, in the
           context of the indicated extension block.  Return 1 if the block is determined to be
           inauthentic (this will cause the bundle to be discarded), zero if no inauthenticity is
           detected, -1 on any system failure.

       void (*BpAcqExtBlkClearFn)(AcqExtBlock *acqblk)
           Uses MRELEASE to release all ION working memory occupied by the object member of
           acqblk.  This function is automatically called when acquisition of a bundle is
           completed, whether or not the bundle is accepted.  Note that incorrect implementation
           of this function may result in a working memory leak.

   UTILITY FUNCTIONS FOR EXTENSION PROCESSING
       void discardExtensionBlock(AcqExtBlock *blk)
           Deletes this block from the bundle acquisition work area prior to the recording of the
           bundle in the ION database.

       void scratchExtensionBlock(ExtensionBlock *blk)
           Deletes this block from the bundle after the bundle has been recorded in the ION
           database.

       Object findExtensionBlock(Bundle *bundle, unsigned int type, unsigned int listIdx)
           On success, returns the address of the ExtensionBlock in bundle for the indicated type
           and listIdx.  If no such extension block exists, returns zero.

       int serializeExtBlk(ExtensionBlock *blk, Lyst eidReferences, char *blockData)
           Constructs an RFC5050-conformant serialized representation of this extension block in
           blk->bytes.  Returns 0 on success, -1 on an unrecoverable system error.

       void suppressExtensionBlock(ExtensionBlock *blk)
           Causes blk to be omitted when the bundle to which it is attached is serialized for
           transmission.  This suppression remains in effect until it is reversed by
           restoreExtensionBlock();

       void restoreExtensionBlock(ExtensionBlock *blk)
           Reverses the effect of suppressExtensionBlock(), enabling the block to be included
           when the bundle to which it is attached is serialized.

SEE ALSO

       bp(3)