1 <!-- $Id: asn.xml,v 1.4 2001-07-19 23:29:40 adam Exp $ -->
2 <chapter><title>The ASN Module</title>
3 <sect1><title>Introduction</title>
5 The &asn; module provides you with a set of C struct definitions for the
6 various PDUs of the protocol, as well as for the complex types
7 appearing within the PDUs. For the primitive data types, the C
8 representation often takes the form of an ordinary C language type,
9 such as <literal>int</literal>. For ASN.1 constructs that have no direct
10 representation in C, such as general octet strings and bit strings,
11 the &odr; module (see section <link linkend="odr">The ODR Module</link>)
12 provides auxiliary definitions.
15 <sect1><title>Preparing PDUs</title>
18 A structure representing a complex ASN.1 type doesn't in itself contain the
19 members of that type. Instead, the structure contains
20 <emphasis>pointers</emphasis> to the members of the type.
21 This is necessary, in part, to allow a mechanism for specifying which
22 of the optional structure (SEQUENCE) members are present, and which
23 are not. It follows that you will need to somehow provide space for
24 the individual members of the structure, and set the pointers to
28 The conversion routines don't care how you allocate and maintain your
29 C structures - they just follow the pointers that you provide.
30 Depending on the complexity of your application, and your personal
31 taste, there are at least three different approaches that you may take
32 when you allocate the structures.
36 You can use static or automatic local variables in the function that
37 prepares the PDU. This is a simple approach, and it provides the most
38 efficient form of memory management. While it works well for flat
39 PDUs like the InitReqest, it will generally not be sufficient for say,
40 the generation of an arbitrarily complex RPN query structure.
43 You can individually create the structure and its members using the
44 <function>malloc(2)</function> function. If you want to ensure that
45 the data is freed when it is no longer needed, you will have to
46 define a function that individually releases each member of a
47 structure before freeing the structure itself.
50 You can use the <function>odr_malloc()</function> function (see section
51 <link linkend="odr-use">Using ODR</link> for details). When you use
52 <function>odr_malloc()</function>, you can release all of the
53 allocated data in a single operation, independent of any pointers and
54 relations between the data. <function>odr_malloc()</function> is based on a
55 "nibble-memory"
56 scheme, in which large portions of memory are allocated, and then
57 gradually handed out with each call to <function>odr_malloc()</function>.
58 The next time you call <function>odr_reset()</function>, all of the
59 memory allocated since the last call is recycled for future use (actually,
60 it is placed on a free-list).
63 You can combine all of the methods described here. This will often be
64 the most practical approach. For instance, you might use
65 <function>odr_malloc()</function> to allocate an entire structure and
66 some of its elements, while you leave other elements pointing to global
67 or per-session default variables.
71 The &asn; module provides an important aid in creating new PDUs. For
72 each of the PDU types (say, <function>Z_InitRequest</function>), a
73 function is provided that allocates and initializes an instance of
74 that PDU type for you. In the case of the InitRequest, the function is
75 simply named <function>zget_InitRequest()</function>, and it sets up
76 reasonable default value for all of the mandatory members. The optional
77 members are generally initialized to null pointers. This last aspect
78 is very important: it ensures that if the PDU definitions are
79 extended after you finish your implementation (to accommodate
80 new versions of the protocol, say), you won't get into trouble with
81 uninitialized pointers in your structures. The functions use
82 <function>odr_malloc()</function> to
83 allocate the PDUs and its members, so you can free everything again with a
84 single call to <function>odr_reset()</function>. We strongly recommend
85 that you use the <literal>zget_*</literal>
86 functions whenever you are preparing a PDU (in a C++ API, the
87 <literal>zget_</literal>
88 functions would probably be promoted to constructors for the
92 The prototype for the individual PDU types generally look like this:
95 Z_<type> *zget_<type>(ODR o);
103 Z_InitRequest *zget_InitRequest(ODR o);
107 The &odr; handle should generally be your encoding stream, but it needn't be.
110 As well as the individual PDU functions, a function <function>
111 zget_APDU()</function> is
112 provided, which allocates a toplevel Z-APDU of the type requested:
116 Z_APDU *zget_APDU(ODR o, int which);
120 The <varname>which</varname> parameter is (of course) the discriminator
121 belonging to the <varname>Z_APDU</varname> <literal>CHOICE</literal> type.
122 All of the interface described here is provided by the &asn; module, and
123 you access it through the <filename>proto.h</filename> header file.
127 <sect1><title id="oid">Object Identifiers</title>
129 When you refer to object identifiers in your application, you need to
130 be aware that SR and Z39.50 use two different set of OIDs to refer to
131 the same objects. To handle this easily, &yaz; provides a utility module
132 to &asn; which provides an internal representation of the OIDs used in
133 both protocols. Each oid is described by a structure:
137 typedef struct oident
139 enum oid_proto proto;
140 enum oid_class class;
141 enum oid_value value;
142 int oidsuffix[OID_SIZE];
148 The <literal>proto</literal> field can be set to either
149 <literal>PROTO_SR</literal> or <literal>PROTO_Z3950</literal>.
150 The <literal>class</literal> might be, say,
151 <literal>CLASS_RECSYN</literal>, and the <literal>value</literal> might be
152 <literal>VAL_USMARC</literal> for the USMARC record format. Functions
156 int *oid_ent_to_oid(struct oident *ent, int *dst);
157 struct oident *oid_getentbyoid(int *o);
161 are provided to map between object identifiers and database entries.
162 If you store a member of the <literal>oid_proto</literal> type in
163 your association state information, it's a simple matter, at runtime,
164 to generate the correct OID when you need it. For decoding, you can
165 simply ignore the proto field, or if you're strict, you can verify
166 that your peer is using the OID family from the correct protocol.
167 The <literal>desc</literal> field is a short, human-readable name
168 for the PDU, useful mainly for diagnostic output.
173 The old function <function>oid_getoidbyent</function> still exists but is
174 not thread safe. Use <function>oid_ent_to_oid</function> instead
175 and pass an array of size <literal>OID_SIZE</literal>.
181 Plans are underway to merge the two protocols into a single
182 definition, with one set of object identifiers. When this happens, the
183 oid module will no longer be required to support protocol
184 independence, but it should still be useful as a simple OID database.
189 <sect1><title>EXTERNAL Data</title>
192 In order to achieve extensibility and adaptability to different
193 application domains, the new version of the protocol defines many
194 structures outside of the main ASN.1 specification, referencing them
195 through ASN.1 EXTERNAL constructs. To simplify the construction and access
196 to the externally referenced data, the &asn; module defines a
197 specialized version of the EXTERNAL construct, called
198 <literal>Z_External</literal>.It is defined thus:
202 typedef struct Z_External
204 Odr_oid *direct_reference;
205 int *indirect_reference;
210 Z_External_single = 0,
212 Z_External_arbitrary,
216 Z_External_explainRecord,
217 Z_External_resourceReport1,
218 Z_External_resourceReport2
226 Odr_any *single_ASN1_type;
227 Odr_oct *octet_aligned;
228 Odr_bitmask *arbitrary;
232 Z_ExplainRecord *explainRecord;
233 Z_ResourceReport1 *resourceReport1;
234 Z_ResourceReport2 *resourceReport2;
243 When decoding, the &asn; module will attempt to determine which
244 syntax describes the data by looking at the reference fields
245 (currently only the direct-reference). For ASN.1 structured data, you
246 need only consult the <literal>which</literal> field to determine the
247 type of data. You can the access the data directly through the union.
248 When constructing data for encoding, you set the union pointer to point
249 to the data, and set the <literal>which</literal> field accordingly.
250 Remember also to set the direct (or indirect) reference to the correct
251 OID for the data type.
252 For non-ASN.1 data such as MARC records, use the
253 <literal>octet_aligned</literal> arm of the union.
257 Some servers return ASN.1 structured data values (eg. database
258 records) as BER-encoded records placed in the
259 <literal>octet-aligned</literal> branch of the EXTERNAL CHOICE.
260 The ASN-module will <emphasis>not</emphasis> automatically decode
261 these records. To help you decode the records in the application, the
266 Z_ext_typeent *z_ext_gettypebyref(oid_value ref);
270 Can be used to retrieve information about the known, external data
271 types. The function return a pointer to a static area, or NULL, if no
272 match for the given direct reference is found. The
273 <literal>Z_ext_typeent</literal>
278 typedef struct Z_ext_typeent
280 oid_value dref; /* the direct-reference OID value. */
281 int what; /* discriminator value for the external CHOICE */
282 Odr_fun fun; /* decoder function */
287 The <literal>what</literal> member contains the
288 <literal>Z_External</literal> union discriminator value for the
289 given type: For the SUTRS record syntax, the value would be
290 <literal>Z_External_sutrs</literal>.
291 The <literal>fun</literal> member contains a pointer to the
292 function which encodes/decodes the given type. Again, for the SUTRS
293 record syntax, the value of <literal>fun</literal> would be
294 <literal>z_SUTRS</literal> (a function pointer).
298 If you receive an EXTERNAL which contains an octet-string value that
299 you suspect of being an ASN.1-structured data value, you can use
300 <literal>z_ext_gettypebyref</literal> to look for the provided
302 If the return value is different from NULL, you can use the provided
303 function to decode the BER string (see section <link linkend="odr-use">
308 If you want to <emphasis>send</emphasis> EXTERNALs containing
309 ASN.1-structured values in the occtet-aligned branch of the CHOICE, this
310 is possible too. However, on the encoding phase, it requires a somewhat
311 involved juggling around of the various buffers involved.
314 If you need to add new, externally defined data types, you must update
315 the struct above, in the source file <filename>prt-ext.h</filename>, as
316 well as the encoder/decoder in the file <filename>prt-ext.c</filename>.
317 When changing the latter, remember to update both the <literal>arm</literal>
318 arrary and the list <literal>type_table</literal>, which drives the CHOICE
319 biasing that is necessary to tell the different, structured types apart
325 Eventually, the EXTERNAL processing will most likely
326 automatically insert the correct OIDs or indirect-refs. First,
327 however, we need to determine how application-context management
328 (specifically the presentation-context-list) should fit into the
334 <sect1><title>PDU Contents Table</title>
337 We include, for reference, a listing of the fields of each top-level
338 PDU, as well as their default settings.
341 <table frame="top"><title>Default settings for PDU Initialize Request</title>
343 <colspec colname="field"></colspec>
344 <colspec colname="type"></colspec>
345 <colspec colname="value"></colspec>
350 <entry>Default Value</entry>
356 referenceId</entry><entry>Z_ReferenceId</entry><entry>NULL
360 protocolVersion</entry><entry>Odr_bitmask</entry><entry>Empty bitmask
364 options</entry><entry>Odr_bitmask</entry><entry>Empty bitmask
368 preferredMessageSize</entry><entry>int</entry><entry>30*1024
372 maximumRecordSize</entry><entry>int</entry><entry>30*1024
376 idAuthentication</entry><entry>Z_IdAuthentication</entry><entry>NULL
380 implementationId</entry><entry>char*</entry><entry>"YAZ (id=81)"
384 implementationName</entry><entry>char*</entry><entry>"Index Data/YAZ"
388 implementationVersion</entry><entry>char*</entry><entry>YAZ_VERSION
392 userInformationField</entry><entry>Z_UserInformation</entry><entry>NULL
396 otherInfo</entry><entry>Z_OtherInformation</entry><entry>NULL
403 <table frame="top"><title>Default settings for PDU Initialize Response</title>
405 <colspec colname="field"></colspec>
406 <colspec colname="type"></colspec>
407 <colspec colname="value"></colspec>
412 <entry>Default Value</entry>
418 referenceId</entry><entry>Z_ReferenceId</entry><entry>NULL
422 protocolVersion</entry><entry>Odr_bitmask</entry><entry>Empty bitmask
426 options</entry><entry>Odr_bitmask</entry><entry>Empty bitmask
430 preferredMessageSize</entry><entry>int</entry><entry>30*1024
434 maximumRecordSize</entry><entry>int</entry><entry>30*1024
438 result</entry><entry>bool_t</entry><entry>TRUE
442 implementationId</entry><entry>char*</entry><entry>"YAZ (id=81)"
446 implementationName</entry><entry>char*</entry><entry>"Index Data/YAZ"
450 implementationVersion</entry><entry>char*</entry><entry>YAZ_VERSION
454 userInformationField</entry><entry>Z_UserInformation</entry><entry>NULL
458 otherInfo</entry><entry>Z_OtherInformation</entry><entry>NULL
465 <table frame="top"><title>Default settings for PDU Search Request</title>
467 <colspec colname="field"></colspec>
468 <colspec colname="type"></colspec>
469 <colspec colname="value"></colspec>
474 <entry>Default Value</entry>
480 referenceId</entry><entry>Z_ReferenceId</entry><entry>NULL
484 smallSetUpperBound</entry><entry>int</entry><entry>0
488 largeSetLowerBound</entry><entry>int</entry><entry>1
492 mediumSetPresentNumber</entry><entry>int</entry><entry>0
496 replaceIndicator</entry><entry>bool_t</entry><entry>TRUE
500 resultSetName</entry><entry>char *</entry><entry>"default"
504 num_databaseNames</entry><entry>int</entry><entry>0
508 databaseNames</entry><entry>char **</entry><entry>NULL
512 smallSetElementSetNames</entry><entry>Z_ElementSetNames</entry><entry>NULL
516 mediumSetElementSetNames</entry><entry>Z_ElementSetNames</entry><entry>NULL
520 preferredRecordSyntax</entry><entry>Odr_oid</entry><entry>NULL
524 query</entry><entry>Z_Query</entry><entry>NULL
528 additionalSearchInfo</entry><entry>Z_OtherInformation</entry><entry>NULL
532 otherInfo</entry><entry>Z_OtherInformation</entry><entry>NULL
542 Field Type Default value
544 referenceId Z_ReferenceId NULL
546 numberOfRecordsReturned int 0
547 nextResultSetPosition int 0
548 searchStatus bool_t TRUE
549 resultSetStatus int NULL
550 presentStatus int NULL
551 records Z_Records NULL
552 additionalSearchInfo Z_OtherInformation NULL
553 otherInfo Z_OtherInformation NULL
559 Field Type Default value
561 referenceId Z_ReferenceId NULL
562 resultSetId char* "default"
563 resultSetStartPoint int 1
564 numberOfRecordsRequested int 10
566 additionalRanges Z_Range NULL
567 recordComposition Z_RecordComposition NULL
568 preferredRecordSyntax Odr_oid NULL
569 maxSegmentCount int NULL
570 maxRecordSize int NULL
571 maxSegmentSize int NULL
572 otherInfo Z_OtherInformation NULL
578 Field Type Default value
580 referenceId Z_ReferenceId NULL
581 numberOfRecordsReturned int 0
582 nextResultSetPosition int 0
583 presentStatus int Z_PRES_SUCCESS
584 records Z_Records NULL
585 otherInfo Z_OtherInformation NULL
589 Z_DeleteResultSetRequest
590 ------------------------
591 Field Type Default value
593 referenceId Z_ReferenceId NULL
594 deleteFunction int Z_DeleteRequest_list
596 resultSetList char** NULL
597 otherInfo Z_OtherInformation NULL
601 Z_DeleteResultSetResponse
602 -------------------------
603 Field Type Default value
605 referenceId Z_ReferenceId NULL
606 deleteOperationStatus int Z_DeleteStatus_success
608 deleteListStatuses Z_ListStatus** NULL
609 numberNotDeleted int NULL
610 num_bulkStatuses int 0
611 bulkStatuses Z_ListStatus NULL
612 deleteMessage char* NULL
613 otherInfo Z_OtherInformation NULL
619 Field Type Default value
621 referenceId Z_ReferenceId NULL
622 num_databaseNames int 0
623 databaseNames char** NULL
624 attributeSet Odr_oid NULL
625 termListAndStartPoint Z_AttributesPlus... NULL
627 numberOfTermsRequested int 20
628 preferredPositionInResponse int NULL
629 otherInfo Z_OtherInformation NULL
635 Field Type Default value
637 referenceId Z_ReferenceId NULL
639 scanStatus int Z_Scan_success
640 numberOfEntriesReturned int 0
641 positionOfTerm int NULL
642 entries Z_ListEntris NULL
643 attributeSet Odr_oid NULL
644 otherInfo Z_OtherInformation NULL
648 Z_TriggerResourceControlRequest
649 -------------------------------
650 Field Type Default value
652 referenceId Z_ReferenceId NULL
653 requestedAction int Z_TriggerResourceCtrl_resou..
654 prefResourceReportFormat Odr_oid NULL
655 resultSetWanted bool_t NULL
656 otherInfo Z_OtherInformation NULL
660 Z_ResourceControlRequest
661 ------------------------
662 Field Type Default value
664 referenceId Z_ReferenceId NULL
665 suspendedFlag bool_t NULL
666 resourceReport Z_External NULL
667 partialResultsAvailable int NULL
668 responseRequired bool_t FALSE
669 triggeredRequestFlag bool_t NULL
670 otherInfo Z_OtherInformation NULL
674 Z_ResourceControlResponse
675 -------------------------
676 Field Type Default value
678 referenceId Z_ReferenceId NULL
679 continueFlag bool_t TRUE
680 resultSetWanted bool_t NULL
681 otherInfo Z_OtherInformation NULL
685 Z_AccessControlRequest
686 ----------------------
687 Field Type Default value
689 referenceId Z_ReferenceId NULL
690 which enum Z_AccessRequest_simpleForm;
692 otherInfo Z_OtherInformation NULL
696 Z_AccessControlResponse
697 -----------------------
698 Field Type Default value
700 referenceId Z_ReferenceId NULL
701 which enum Z_AccessResponse_simpleForm
703 diagnostic Z_DiagRec NULL
704 otherInfo Z_OtherInformation NULL
710 Field Type Default value
712 referenceId Z_ReferenceId NULL
713 numberOfRecordsReturned int value=0
714 num_segmentRecords int 0
715 segmentRecords Z_NamePlusRecord NULL
716 otherInfo Z_OtherInformation NULL
722 Field Type Default value
724 referenceId Z_ReferenceId NULL
725 closeReason int Z_Close_finished
726 diagnosticInformation char* NULL
727 resourceReportFormat Odr_oid NULL
728 resourceFormat Z_External NULL
729 otherInfo Z_OtherInformation NULL
736 <!-- Keep this comment at the end of the file
741 sgml-minimize-attributes:nil
742 sgml-always-quote-attributes:t
745 sgml-parent-document: "yaz.xml"
746 sgml-local-catalogs: "../../docbook/docbook.cat"
747 sgml-namecase-general:t