1 <!-- $Header: /home/cvsroot/yaz/doc/asn.xml,v 1.2 2001-07-19 12:46:57 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 type of
247 data. You can the access the data directly through the union. When
248 constructing data for encoding, you set the union pointer to point to
249 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 <literal>octet-aligned</literal>
259 branch of the EXTERNAL CHOICE. The ASN-module will <emphasis>not</emphasis>
260 automatically decode these records. To help you decode the records in
261 the application, the function
265 Z_ext_typeent *z_ext_gettypebyref(oid_value ref);
269 Can be used to retrieve information about the known, external data
270 types. The function return a pointer to a static area, or NULL, if no
271 match for the given direct reference is found. The
272 <literal>Z_ext_typeent</literal>
277 typedef struct Z_ext_typeent
279 oid_value dref; /* the direct-reference OID value. */
280 int what; /* discriminator value for the external CHOICE */
281 Odr_fun fun; /* decoder function */
286 The <literal>what</literal> member contains the <literal>Z_External</literal>
287 union discriminator value for the given type: For the SUTRS record
288 syntax, the value would be <literal>Z_External_sutrs</literal>.
289 The <literal>fun</literal> member contains a pointer to the
290 function which encodes/decodes the given type. Again, for the SUTRS
291 record syntax, the value of <literal>fun</literal> would be
292 <literal>z_SUTRS</literal> (a function pointer).
296 If you receive an EXTERNAL which contains an octet-string value that
297 you suspect of being an ASN.1-structured data value, you can use
298 <literal>z_ext_gettypebyref</literal> to look for the provided
300 If the return value is different from NULL, you can use the provided
301 function to decode the BER string (see section <link linkend="odr-use">
306 If you want to <emphasis>send</emphasis> EXTERNALs containing
307 ASN.1-structured values in the occtet-aligned branch of the CHOICE, this
308 is possible too. However, on the encoding phase, it requires a somewhat
309 involved juggling around of the various buffers involved.
312 If you need to add new, externally defined data types, you must update
313 the struct above, in the source file <filename>prt-ext.h</filename>, as
314 well as the encoder/decoder in the file <filename>prt-ext.c</filename>.
315 When changing the latter, remember to update both the <literal>arm</literal>
316 arrary and the list <literal>type_table</literal>, which drives the CHOICE
317 biasing that is necessary to tell the different, structured types apart
323 Eventually, the EXTERNAL processing will most likely
324 automatically insert the correct OIDs or indirect-refs. First,
325 however, we need to determine how application-context management
326 (specifically the presentation-context-list) should fit into the
332 <sect1><title>PDU Contents Table</title>
335 We include, for reference, a listing of the fields of each top-level
336 PDU, as well as their default settings.
340 <table frame="top"><title>Default settings for Z39.50 PDU's</title>
342 <colspec colname="field"></colspec>
343 <colspec colname="type"></colspec>
344 <colspec colname="value"></colspec>
349 <entry>Default Value</entry>
354 <entry namest="field" nameend="field">Z_InitRequest</entry>
358 referenceId</entry><entry>Z_ReferenceId</entry><entry>NULL
362 protocolVersion</entry><entry>Odr_bitmask</entry><entry>Empty bitmask
366 options</entry><entry>Odr_bitmask</entry><entry>Empty bitmask
370 preferredMessageSize</entry><entry>int</entry><entry>30*1024
374 maximumRecordSize</entry><entry>int</entry><entry>30*1024
378 idAuthentication</entry><entry>Z_IdAuthentication</entry><entry>NULL
382 implementationId</entry><entry>char*</entry><entry>"YAZ (id=81)"
386 implementationName</entry><entry>char*</entry><entry>"Index Data/YAZ"
390 implementationVersion</entry><entry>char*</entry><entry>YAZ_VERSION
394 userInformationField</entry><entry>Z_UserInformation</entry><entry>NULL
398 otherInfo</entry><entry>Z_OtherInformation</entry><entry>NULL
408 Field Type Default value
410 referenceId Z_ReferenceId NULL
411 protocolVersion Odr_bitmask Empty bitmask
412 options Odr_bitmask Empty bitmask
413 preferredMessageSize int 30*1024
414 maximumRecordSize int 30*1024
416 implementationId char* "YAZ (id=81)"
417 implementationName char* "Index Data/YAZ"
418 implementationVersion char* YAZ_VERSION
419 userInformationField Z_UserInformat.. NULL
420 otherInfo Z_OtherInformation NULL
426 Field Type Default value
428 referenceId Z_ReferenceId NULL
429 smallSetUpperBound int 0
430 largeSetLowerBound int 1
431 mediumSetPresentNumber int 0
432 replaceIndicator bool_t TRUE
433 resultSetName char* "default"
434 num_databaseNames int 0
435 databaseNames char** NULL
436 smallSetElementSetNames Z_ElementSetNames NULL
437 mediumSetElementSetNames Z_ElementSetNames NULL
438 preferredRecordSyntax Odr_oid NULL
440 additionalSearchInfo Z_OtherInformation NULL
441 otherInfo Z_OtherInformation NULL
447 Field Type Default value
449 referenceId Z_ReferenceId NULL
451 numberOfRecordsReturned int 0
452 nextResultSetPosition int 0
453 searchStatus bool_t TRUE
454 resultSetStatus int NULL
455 presentStatus int NULL
456 records Z_Records NULL
457 additionalSearchInfo Z_OtherInformation NULL
458 otherInfo Z_OtherInformation NULL
464 Field Type Default value
466 referenceId Z_ReferenceId NULL
467 resultSetId char* "default"
468 resultSetStartPoint int 1
469 numberOfRecordsRequested int 10
471 additionalRanges Z_Range NULL
472 recordComposition Z_RecordComposition NULL
473 preferredRecordSyntax Odr_oid NULL
474 maxSegmentCount int NULL
475 maxRecordSize int NULL
476 maxSegmentSize int NULL
477 otherInfo Z_OtherInformation NULL
483 Field Type Default value
485 referenceId Z_ReferenceId NULL
486 numberOfRecordsReturned int 0
487 nextResultSetPosition int 0
488 presentStatus int Z_PRES_SUCCESS
489 records Z_Records NULL
490 otherInfo Z_OtherInformation NULL
494 Z_DeleteResultSetRequest
495 ------------------------
496 Field Type Default value
498 referenceId Z_ReferenceId NULL
499 deleteFunction int Z_DeleteRequest_list
501 resultSetList char** NULL
502 otherInfo Z_OtherInformation NULL
506 Z_DeleteResultSetResponse
507 -------------------------
508 Field Type Default value
510 referenceId Z_ReferenceId NULL
511 deleteOperationStatus int Z_DeleteStatus_success
513 deleteListStatuses Z_ListStatus** NULL
514 numberNotDeleted int NULL
515 num_bulkStatuses int 0
516 bulkStatuses Z_ListStatus NULL
517 deleteMessage char* NULL
518 otherInfo Z_OtherInformation NULL
524 Field Type Default value
526 referenceId Z_ReferenceId NULL
527 num_databaseNames int 0
528 databaseNames char** NULL
529 attributeSet Odr_oid NULL
530 termListAndStartPoint Z_AttributesPlus... NULL
532 numberOfTermsRequested int 20
533 preferredPositionInResponse int NULL
534 otherInfo Z_OtherInformation NULL
540 Field Type Default value
542 referenceId Z_ReferenceId NULL
544 scanStatus int Z_Scan_success
545 numberOfEntriesReturned int 0
546 positionOfTerm int NULL
547 entries Z_ListEntris NULL
548 attributeSet Odr_oid NULL
549 otherInfo Z_OtherInformation NULL
553 Z_TriggerResourceControlRequest
554 -------------------------------
555 Field Type Default value
557 referenceId Z_ReferenceId NULL
558 requestedAction int Z_TriggerResourceCtrl_resou..
559 prefResourceReportFormat Odr_oid NULL
560 resultSetWanted bool_t NULL
561 otherInfo Z_OtherInformation NULL
565 Z_ResourceControlRequest
566 ------------------------
567 Field Type Default value
569 referenceId Z_ReferenceId NULL
570 suspendedFlag bool_t NULL
571 resourceReport Z_External NULL
572 partialResultsAvailable int NULL
573 responseRequired bool_t FALSE
574 triggeredRequestFlag bool_t NULL
575 otherInfo Z_OtherInformation NULL
579 Z_ResourceControlResponse
580 -------------------------
581 Field Type Default value
583 referenceId Z_ReferenceId NULL
584 continueFlag bool_t TRUE
585 resultSetWanted bool_t NULL
586 otherInfo Z_OtherInformation NULL
590 Z_AccessControlRequest
591 ----------------------
592 Field Type Default value
594 referenceId Z_ReferenceId NULL
595 which enum Z_AccessRequest_simpleForm;
597 otherInfo Z_OtherInformation NULL
601 Z_AccessControlResponse
602 -----------------------
603 Field Type Default value
605 referenceId Z_ReferenceId NULL
606 which enum Z_AccessResponse_simpleForm
608 diagnostic Z_DiagRec NULL
609 otherInfo Z_OtherInformation NULL
615 Field Type Default value
617 referenceId Z_ReferenceId NULL
618 numberOfRecordsReturned int value=0
619 num_segmentRecords int 0
620 segmentRecords Z_NamePlusRecord NULL
621 otherInfo Z_OtherInformation NULL
627 Field Type Default value
629 referenceId Z_ReferenceId NULL
630 closeReason int Z_Close_finished
631 diagnosticInformation char* NULL
632 resourceReportFormat Odr_oid NULL
633 resourceFormat Z_External NULL
634 otherInfo Z_OtherInformation NULL