The Z39.50 ASN.1 Module Introduction The &asn; module provides you with a set of C struct definitions for the various PDUs of the Z39.50 protocol, as well as for the complex types appearing within the PDUs. For the primitive data types, the C representation often takes the form of an ordinary C language type, such as Odr_int which is equivalent to an integral C integer. For ASN.1 constructs that have no direct representation in C, such as general octet strings and bit strings, the &odr; module (see section The ODR Module) provides auxiliary definitions. The &asn; module is located in sub directory z39.50. There you'll find C files that implements encoders and decoders for the Z39.50 types. You'll also find the protocol definitions: z3950v3.asn, esupdate.asn, and others. Preparing PDUs A structure representing a complex ASN.1 type doesn't in itself contain the members of that type. Instead, the structure contains pointers to the members of the type. This is necessary, in part, to allow a mechanism for specifying which of the optional structure (SEQUENCE) members are present, and which are not. It follows that you will need to somehow provide space for the individual members of the structure, and set the pointers to refer to the members. The conversion routines don't care how you allocate and maintain your C structures - they just follow the pointers that you provide. Depending on the complexity of your application, and your personal taste, there are at least three different approaches that you may take when you allocate the structures. You can use static or automatic local variables in the function that prepares the PDU. This is a simple approach, and it provides the most efficient form of memory management. While it works well for flat PDUs like the InitReqest, it will generally not be sufficient for say, the generation of an arbitrarily complex RPN query structure. You can individually create the structure and its members using the malloc(2) function. If you want to ensure that the data is freed when it is no longer needed, you will have to define a function that individually releases each member of a structure before freeing the structure itself. You can use the odr_malloc() function (see for details). When you use odr_malloc(), you can release all of the allocated data in a single operation, independent of any pointers and relations between the data. odr_malloc() is based on a "nibble-memory" scheme, in which large portions of memory are allocated, and then gradually handed out with each call to odr_malloc(). The next time you call odr_reset(), all of the memory allocated since the last call is recycled for future use (actually, it is placed on a free-list). You can combine all of the methods described here. This will often be the most practical approach. For instance, you might use odr_malloc() to allocate an entire structure and some of its elements, while you leave other elements pointing to global or per-session default variables. The &asn; module provides an important aid in creating new PDUs. For each of the PDU types (say, Z_InitRequest), a function is provided that allocates and initializes an instance of that PDU type for you. In the case of the InitRequest, the function is simply named zget_InitRequest(), and it sets up reasonable default value for all of the mandatory members. The optional members are generally initialized to null pointers. This last aspect is very important: it ensures that if the PDU definitions are extended after you finish your implementation (to accommodate new versions of the protocol, say), you won't get into trouble with uninitialized pointers in your structures. The functions use odr_malloc() to allocate the PDUs and its members, so you can free everything again with a single call to odr_reset(). We strongly recommend that you use the zget_* functions whenever you are preparing a PDU (in a C++ API, the zget_ functions would probably be promoted to constructors for the individual types). The prototype for the individual PDU types generally look like this: Z_<type> *zget_<type>(ODR o); eg.: Z_InitRequest *zget_InitRequest(ODR o); The &odr; handle should generally be your encoding stream, but it needn't be. As well as the individual PDU functions, a function zget_APDU() is provided, which allocates a top-level Z-APDU of the type requested: Z_APDU *zget_APDU(ODR o, int which); The which parameter is (of course) the discriminator belonging to the Z_APDU CHOICE type. All of the interface described here is provided by the &asn; module, and you access it through the proto.h header file. EXTERNAL Data In order to achieve extensibility and adaptability to different application domains, the new version of the protocol defines many structures outside of the main ASN.1 specification, referencing them through ASN.1 EXTERNAL constructs. To simplify the construction and access to the externally referenced data, the &asn; module defines a specialized version of the EXTERNAL construct, called Z_External.It is defined thus: typedef struct Z_External { Odr_oid *direct_reference; int *indirect_reference; char *descriptor; enum { /* Generic types */ Z_External_single = 0, Z_External_octet, Z_External_arbitrary, /* Specific types */ Z_External_SUTRS, Z_External_explainRecord, Z_External_resourceReport1, Z_External_resourceReport2 ... } which; union { /* Generic types */ Odr_any *single_ASN1_type; Odr_oct *octet_aligned; Odr_bitmask *arbitrary; /* Specific types */ Z_SUTRS *sutrs; Z_ExplainRecord *explainRecord; Z_ResourceReport1 *resourceReport1; Z_ResourceReport2 *resourceReport2; ... } u; } Z_External; When decoding, the &asn; module will attempt to determine which syntax describes the data by looking at the reference fields (currently only the direct-reference). For ASN.1 structured data, you need only consult the which field to determine the type of data. You can the access the data directly through the union. When constructing data for encoding, you set the union pointer to point to the data, and set the which field accordingly. Remember also to set the direct (or indirect) reference to the correct OID for the data type. For non-ASN.1 data such as MARC records, use the octet_aligned arm of the union. Some servers return ASN.1 structured data values (eg. database records) as BER-encoded records placed in the octet-aligned branch of the EXTERNAL CHOICE. The ASN-module will not automatically decode these records. To help you decode the records in the application, the function Z_ext_typeent *z_ext_gettypebyref(const oid *oid); Can be used to retrieve information about the known, external data types. The function return a pointer to a static area, or NULL, if no match for the given direct reference is found. The Z_ext_typeent is defined as: typedef struct Z_ext_typeent { int oid[OID_SIZE]; /* the direct-reference OID. */ int what; /* discriminator value for the external CHOICE */ Odr_fun fun; /* decoder function */ } Z_ext_typeent; The what member contains the Z_External union discriminator value for the given type: For the SUTRS record syntax, the value would be Z_External_sutrs. The fun member contains a pointer to the function which encodes/decodes the given type. Again, for the SUTRS record syntax, the value of fun would be z_SUTRS (a function pointer). If you receive an EXTERNAL which contains an octet-string value that you suspect of being an ASN.1-structured data value, you can use z_ext_gettypebyref to look for the provided direct-reference. If the return value is different from NULL, you can use the provided function to decode the BER string (see ). If you want to send EXTERNALs containing ASN.1-structured values in the occtet-aligned branch of the CHOICE, this is possible too. However, on the encoding phase, it requires a somewhat involved juggling around of the various buffers involved. If you need to add new, externally defined data types, you must update the struct above, in the source file prt-ext.h, as well as the encoder/decoder in the file prt-ext.c. When changing the latter, remember to update both the arm arrary and the list type_table, which drives the CHOICE biasing that is necessary to tell the different, structured types apart on decoding. Eventually, the EXTERNAL processing will most likely automatically insert the correct OIDs or indirect-refs. First, however, we need to determine how application-context management (specifically the presentation-context-list) should fit into the various modules. PDU Contents Table We include, for reference, a listing of the fields of each top-level PDU, as well as their default settings. Default settings for PDU Initialize Request Field Type Default Value referenceIdZ_ReferenceIdNULL protocolVersionOdr_bitmaskEmpty bitmask optionsOdr_bitmaskEmpty bitmask preferredMessageSizeOdr_int30*1024 maximumRecordSizeOdr_int30*1024 idAuthenticationZ_IdAuthenticationNULL implementationIdchar*"81" implementationNamechar*"YAZ" implementationVersionchar*YAZ_VERSION userInformationFieldZ_UserInformationNULL otherInfoZ_OtherInformationNULL
Default settings for PDU Initialize Response Field Type Default Value referenceIdZ_ReferenceIdNULL protocolVersionOdr_bitmaskEmpty bitmask optionsOdr_bitmaskEmpty bitmask preferredMessageSizeOdr_int30*1024 maximumRecordSizeOdr_int30*1024 resultOdr_boolTRUE implementationIdchar*"id)" implementationNamechar*"YAZ" implementationVersionchar*YAZ_VERSION userInformationFieldZ_UserInformationNULL otherInfoZ_OtherInformationNULL
Default settings for PDU Search Request Field Type Default Value referenceIdZ_ReferenceIdNULL smallSetUpperBoundOdr_int0 largeSetLowerBoundOdr_int1 mediumSetPresentNumberOdr_int0 replaceIndicatorOdr_boolTRUE resultSetNamechar *"default" num_databaseNamesOdr_int0 databaseNameschar **NULL smallSetElementSetNamesZ_ElementSetNames NULL mediumSetElementSetNamesZ_ElementSetNames NULL preferredRecordSyntaxOdr_oidNULL queryZ_QueryNULL additionalSearchInfoZ_OtherInformation NULL otherInfoZ_OtherInformationNULL
Default settings for PDU Search Response Field Type Default Value referenceIdZ_ReferenceIdNULL resultCountOdr_int0 numberOfRecordsReturnedOdr_int0 nextResultSetPositionOdr_int0 searchStatusOdr_boolTRUE resultSetStatusOdr_intNULL presentStatusOdr_intNULL recordsZ_RecordsNULL additionalSearchInfo Z_OtherInformationNULL otherInfoZ_OtherInformationNULL
Default settings for PDU Present Request Field Type Default Value referenceIdZ_ReferenceIdNULL resultSetIdchar*"default" resultSetStartPointOdr_int1 numberOfRecordsRequestedOdr_int10 num_rangesOdr_int0 additionalRangesZ_RangeNULL recordCompositionZ_RecordCompositionNULL preferredRecordSyntaxOdr_oidNULL maxSegmentCountOdr_intNULL maxRecordSizeOdr_intNULL maxSegmentSizeOdr_intNULL otherInfoZ_OtherInformationNULL
Default settings for PDU Present Response Field Type Default Value referenceIdZ_ReferenceIdNULL numberOfRecordsReturnedOdr_int0 nextResultSetPositionOdr_int0 presentStatusOdr_intZ_PresentStatus_success recordsZ_RecordsNULL otherInfoZ_OtherInformationNULL
Default settings for Delete Result Set Request Field Type Default Value referenceId Z_ReferenceIdNULL deleteFunctionOdr_intZ_DeleteResultSetRequest_list num_idsOdr_int0 resultSetListchar**NULL otherInfoZ_OtherInformationNULL
Default settings for Delete Result Set Response Field Type Default Value referenceIdZ_ReferenceIdNULL deleteOperationStatusOdr_int Z_DeleteStatus_success num_statusesOdr_int0 deleteListStatusesZ_ListStatus**NULL numberNotDeletedOdr_intNULL num_bulkStatusesOdr_int0 bulkStatusesZ_ListStatusNUL L deleteMessagechar*NULL otherInfoZ_OtherInformationNULL
Default settings for Scan Request Field Type Default Value referenceIdZ_ReferenceIdNULL num_databaseNamesOdr_int0 databaseNameschar**NULL attributeSetOdr_oidNULL termListAndStartPointZ_AttributesPlus... NULL stepSizeOdr_intNULL numberOfTermsRequestedOdr_int20 preferredPositionInResponseOdr_intNULL otherInfoZ_OtherInformationNULL
Default settings for Scan Response Field Type Default Value referenceIdZ_ReferenceIdNULL stepSizeOdr_intNULL scanStatusOdr_intZ_Scan_success numberOfEntriesReturnedOdr_int0 positionOfTermOdr_intNULL entriesZ_ListEntrisNULL attributeSetOdr_oidNULL otherInfoZ_OtherInformationNULL
Default settings for Trigger Resource Control Request Field Type Default Value referenceIdZ_ReferenceIdNULL requestedActionOdr_int Z_TriggerResourceCtrl_resou.. prefResourceReportFormatOdr_oidNULL resultSetWantedOdr_boolNULL otherInfoZ_OtherInformationNULL
Default settings for Resource Control Request Field Type Default Value referenceIdZ_ReferenceIdNULL suspendedFlagOdr_boolNULL resourceReportZ_ExternalNULL partialResultsAvailableOdr_intNULL responseRequiredOdr_boolFALSE triggeredRequestFlagOdr_boolNULL otherInfoZ_OtherInformationNULL
Default settings for Resource Control Response Field Type Default Value referenceIdZ_ReferenceIdNULL continueFlagbool_tTRUE resultSetWantedbool_tNULL otherInfoZ_OtherInformationNULL
Default settings for Access Control Request Field Type Default Value referenceIdZ_ReferenceIdNULL whichenumZ_AccessRequest_simpleForm; uunionNULL otherInfoZ_OtherInformationNULL
Default settings for Access Control Response Field Type Default Value referenceIdZ_ReferenceIdNULL whichenumZ_AccessResponse_simpleForm uunionNULL diagnosticZ_DiagRecNULL otherInfoZ_OtherInformationNULL
Default settings for Segment Field Type Default Value referenceIdZ_ReferenceIdNULL numberOfRecordsReturnedOdr_intvalue=0 num_segmentRecordsOdr_int0 segmentRecordsZ_NamePlusRecordNULL otherInfoZ_OtherInformationNULL
Default settings for Close Field Type Default Value referenceIdZ_ReferenceIdNULL closeReasonOdr_intZ_Close_finished diagnosticInformationchar*NULL resourceReportFormatOdr_oidNULL resourceFormatZ_ExternalNULL otherInfoZ_OtherInformationNULL