1 <!-- $Id: zoom.xml,v 1.13 2001-11-22 09:45:31 adam Exp $ -->
2 <chapter id="zoom"><title>Building clients with ZOOM</title>
5 &zoom; is an acronym for 'Z39.50 Object-Orientation Model' and is
6 an initiative started by Mike Taylor (Mike is from the UK, which
7 explains the peculiar name of the model). The goal of &zoom; is to
8 provide a common Z39.50 client API not bound to a particular
9 programming language or toolkit.
12 The lack of a simple Z39.50 client API for &yaz; has become more
13 and more apparent over time. So when the first &zoom; specification
15 an implementation for &yaz; was quickly developed. For the first time, it is
16 now as easy (or easier!) to develop clients than servers with &yaz;. This
17 chapter describes the &zoom; C binding. Before going futher, please
18 reconsider whether C is the right programming language for the job.
19 There are other language bindings available for &yaz;, and still
21 are in active development. See the
22 <ulink url="http://zoom.z3950.org/">ZOOM website</ulink> for
27 In order to fully understand this chapter you should read and
28 try the example programs <literal>zoomtst1.c</literal>,
29 <literal>zoomtst2.c</literal>, .. in the <literal>zoom</literal>
34 The C language misses many features found in object oriented languages
35 such as C++, Java, etc. For example, you'll have to manually,
36 destroy all objects you create, even though you may think of them as
37 temporary. Most objects has a <literal>_create</literal> - and a
38 <literal>_destroy</literal> variant.
39 All objects are in fact pointers to internal stuff, but you don't see
40 that because of typedefs. All destroy methods should gracefully ignore a
41 <literal>NULL</literal> pointer.
44 In each of the sections below you'll find a sub section called
45 protocol behavior, that descries how the API maps to the Z39.50
48 <sect1 id="zoom.connections"><title>Connections</title>
50 <para>The Connection object is a session with a target.
53 #include <yaz/zoom.h>
55 ZOOM_connection ZOOM_connection_new (const char *host, int portnum);
57 ZOOM_connection ZOOM_connection_create (ZOOM_options options);
59 void ZOOM_connection_connect(ZOOM_connection c, const char *host,
61 void ZOOM_connection_destroy (ZOOM_connection c);
64 Connection objects are created with either function
65 <function>ZOOM_connection_new</function> or
66 <function>ZOOM_connection_create</function>.
67 The former creates and automatically attempts to establish a network
68 connection with the target. The latter doesn't establish
69 a connection immediately, thus allowing you to specify options
70 before establishing network connection using the function
71 <function>ZOOM_connection_connect</function>.
72 If the portnumber, <literal>portnum</literal>, is zero, the
73 <literal>host</literal> is consulted for a port specification.
74 If no port is given, 210 is used. A colon denotes the beginning of
75 a port number in the host string. If the host string includes a
76 slash, the following part specifies a database for the connection.
79 Connection objects should be destroyed using the function
80 <function>ZOOM_connection_destroy</function>.
83 void ZOOM_connection_option_set (ZOOM_connection c,
87 const char *ZOOM_connection_option_get (ZOOM_connection c,
91 The <function>ZOOM_connection_option_set</function> allows you to
92 set an option given by <parameter>key</parameter> to the value
93 <parameter>value</parameter> for the connection.
94 Function <function>ZOOM_connection_option_get</function> returns
95 the value for an option given by <parameter>key</parameter>.
97 <table frame="sides" colsep="1"><title>ZOOM Connection Options</title>
99 <colspec colwidth="4*" colname="name"></colspec>
100 <colspec colwidth="7*" colname="description"></colspec>
101 <colspec colwidth="3*" colname="default"></colspec>
104 <entry>Option</entry>
105 <entry>Description</entry>
106 <entry>Default</entry>
111 implementationName</entry><entry>Name of Your client
112 </entry><entry>none</entry></row>
114 user</entry><entry>Authentication user name
115 </entry><entry>none</entry></row>
117 group</entry><entry>Authentication group name
118 </entry><entry>none</entry></row>
120 pass</entry><entry>Authentication password
121 </entry><entry>none</entry></row>
123 host</entry><entry>Target host. This setting is "read-only".
124 It's automatically set internally when connecting to a target.
125 </entry><entry>none</entry></row>
127 proxy</entry><entry>Proxy host
128 </entry><entry>none</entry></row>
130 async</entry><entry>If true (1) the connection operates in
131 asynchronous operation which means that all calls are non-blocking
133 <link linkend="zoom.events"><function>ZOOM_event</function></link>.
134 </entry><entry>0</entry></row>
136 maximumRecordSize</entry><entry> Maximum size of single record.
137 </entry><entry>1 MB</entry></row>
139 preferredMessageSize</entry><entry> Maximum size of multiple records.
140 </entry><entry>1 MB</entry></row>
145 int ZOOM_connection_error (ZOOM_connection c, const char **cp,
146 const char **addinfo);
149 Use <function>ZOOM_connection_error</function> to check for
150 errors for the last operation(s) performed. The function returns
151 zero if no errors occurred; non-zero otherwise indicating the error.
152 Pointers <parameter>cp</parameter> and <parameter>addinfo</parameter>
153 holds messages for the error and additional-info if passed as
154 non-<literal>NULL</literal>.
156 <sect2><title>Protocol behavior</title>
158 The calls <function>ZOOM_connection_new</function> and
159 <function>ZOOM_connection_connect</function> establises a TCP/IP
160 connection and sends an Initialize Request to the target if
161 possible. In addition, the calls waits for an Initialize Response
162 from the target and the result is inspected (OK or rejected).
165 If <literal>proxy</literal> is set then the client will establish
166 a TCP/IP connection with the peer as specified by the
167 <literal>proxy</literal> host and the hostname as part of the
168 connect calls will be set as part of the Initialize Request.
169 The proxy server will then "forward" the PDU's transparently
170 to the target behind the proxy.
173 For the authentication parameters, if option <literal>user</literal>
174 is set and both options <literal>group</literal> and
175 <literal>pass</literal> are unset, then Open style
176 authentication is used (Version 2/3) in which case the username
177 is usually followed by a slash, then by a password.
178 If either <literal>group</literal>
179 or <literal>pass</literal> is set then idPass authentication
180 (Version 3 only) is used. If none of the options are set, no
181 authentication parameters are set as part of the Initialize Request
185 When option <literal>async</literal> is 1, it really means that
186 all network operations are postponed (and queued) until the
187 function <literal>ZOOM_event</literal> is invoked. When doing so
188 it doesn't make sense to check for errors after
189 <literal>ZOOM_connection_new</literal> is called since that
190 operation "connecting - and init" is still incomplete and the
191 API cannot tell the outcome (yet).
195 <sect1 id="zoom.query"><title>Queries</title>
197 Query objects represents queries.
200 ZOOM_query ZOOM_query_create(void);
202 void ZOOM_query_destroy(ZOOM_query q);
204 int ZOOM_query_prefix(ZOOM_query q, const char *str);
206 int ZOOM_query_sortby(ZOOM_query q, const char *criteria);
209 Create query objects using <function>ZOOM_query_create</function>
210 and destroy them by calling <function>ZOOM_query_destroy</function>.
211 RPN-queries can be specified in <link linkend="PQF">PQF</link>
212 notation by using the
213 function <function>ZOOM_query_prefix</function>. More
214 query types will be added later, such as
215 <link linkend="CCL">CCL</link> to RPN-mapping, native CCL query,
216 etc. In addition to a search, a sort criteria may be set. Function
217 <function>ZOOM_query_sortby</function> specifies a
218 sort criteria using the same string notation for sort as offered by
219 the <link linkend="sortspec">YAZ client</link>.
221 <sect2><title>Protocol behavior</title>
223 The query object is just an interface for the member Query
224 in the SearchRequest. The sortby-function is an interface to the
225 sortSequence member of the SortRequest.
229 <sect1 id="zoom.resultsets"><title>Result sets</title>
231 The result set object is a container for records returned from
235 ZOOM_resultset ZOOM_connection_search(ZOOM_connection,
238 ZOOM_resultset ZOOM_connection_search_pqf(ZOOM_connection c,
241 void ZOOM_resultset_destroy(ZOOM_resultset r);
244 Function <function>ZOOM_connection_search</function> creates
245 a result set given a connection and query.
246 Destroy a result set by calling
247 <function>ZOOM_resultset_destroy</function>.
248 Simple clients may using PQF only may use function
249 <function>ZOOM_connection_search_pqf</function> in which case
250 creating query objects is not necessary.
253 void ZOOM_resultset_option_set (ZOOM_resultset r,
257 const char *ZOOM_resultset_option_get (ZOOM_resultset r,
260 size_t ZOOM_resultset_size (ZOOM_resultset r);
263 Functions <function>ZOOM_resultset_options_set</function> and
264 <function>ZOOM_resultset_get</function> sets and gets an option
265 for a result set similar to <function>ZOOM_connection_option_get</function>
266 and <function>ZOOM_connection_option_set</function>.
269 The number of hits also called result-count is returned by
270 function <function>ZOOM_resultset_size</function>.
272 <table frame="top"><title>ZOOM Result set Options</title>
274 <colspec colwidth="4*" colname="name"></colspec>
275 <colspec colwidth="7*" colname="description"></colspec>
276 <colspec colwidth="2*" colname="default"></colspec>
279 <entry>Option</entry>
280 <entry>Description</entry>
281 <entry>Default</entry>
286 piggyback</entry><entry>True (1) if piggyback should be
287 used in searches; false (0) if not.
288 </entry><entry>1</entry></row>
290 start</entry><entry>Offset of first record to be
291 retrieved from target. First record has offset 0 unlike the
292 protocol specifications where first record has position 1.
293 </entry><entry>0</entry></row>
295 count</entry><entry>Number of records to be retrieved.
296 </entry><entry>0</entry></row>
298 elementSetName</entry><entry>Element-Set name of records.
299 Most targets should honor element set name <literal>B</literal>
300 and <literal>F</literal> for brief and full respectively.
301 </entry><entry>none</entry></row>
303 preferredRecordSyntax</entry><entry>Preferred Syntax, such as
304 <literal>USMARC</literal>, <literal>SUTRS</literal>, etc.
305 </entry><entry>none</entry></row>
307 smallSetUpperBound</entry><entry>If hits is less than or equal to this
308 value, then target will return all records using small element set name
309 </entry><entry>0</entry></row>
311 largeSetLowerBound</entry><entry>If hits is greator than this
312 value, the target will return no records.
313 </entry><entry>1</entry></row>
315 mediumSetPresentNumber</entry><entry>This value represents
316 the number of records to be returned as part of a search when when
317 hits is less than or equal to large set lower bound and if hits
318 is greator than small set upper bound.
319 </entry><entry>0</entry></row>
321 smallSetElementSetName</entry><entry>
322 The element set name to be used for small result sets.
323 </entry><entry>none</entry></row>
325 mediumSetElementSetName</entry><entry>
326 The element set name to be for medium-sized result sets.
327 </entry><entry>none</entry></row>
329 databaseName</entry><entry>One or more database names
330 separated by character plus (<literal>+</literal>).
331 </entry><entry>Default</entry></row>
333 setname</entry><entry>Name of Result Set (Result Set ID).
334 If this option isn't set, the ZOOM module will automatically
335 allocate a result set name.
336 </entry><entry>default</entry></row>
341 <title>Protocol behavior</title>
343 The creation of a result set involves at least a SearchRequest
344 - SearchResponse protocol handshake. Following that, if a sort
345 critieria was specified as part of the query, a sortRequest -
346 SortResponse handshake takes place. Note that it is necessary to
347 perform sorting before any retrieval takes place, so no records will
348 be returned from the target as part of the SearchResponse because these
349 would be unsorted. Hence, piggyback is disabled when sort critieria
350 is set. Following Search - and a Possible sort, Retrieval takes
351 place - as one or more Present Requests - Present Response being
355 The API allows for two different modes for retrieval. A high level
356 mode which is somewhat more powerful and a low level one.
357 The low level is "enabled" when the settings
358 <literal>smallSetUpperBound</literal>,
359 <literal>mediumSetPresentNumber</literal> and
360 <literal>largeSetLowerBound</literal> are set. The low level mode
361 thus allows you to precisely set how records are returned as part
362 of a search response as offered by the Z39.50 protocol.
363 Since the client may be retrieving records as part of the
364 search response, this mode doesn't work well if sorting is used.
367 The high-level mode allows you to fetch a range of records from
368 the result set with a given start offset. When you use this mode
369 the client will automatically use piggyback if that is possible
370 with the target and perform one or more present requests as needed.
371 Even if the target returns fewer records as part of a present response
372 because of a record size limit, etc. the client will repeat sending
373 present requests. As an example, if option <literal>start</literal>
374 is 0 (default) and <literal>count</literal> is 4, and
375 <literal>piggyback</literal> is 1 (default) and no sorting critieria
376 is specified, then the client will attempt to retrieve the 4
377 records as part the search response (using piggyback). On the other
378 hand, if either <literal>start</literal> is positive or if
379 a sorting criteria is set, or if <literal>piggyback</literal>
380 is 0, then the client will not perform piggyback but send Present
384 If either of the options <literal>mediumSetElementSetName</literal> and
385 <literal>smallSetElementSetName</literal> are unset, the value
386 of option <literal>elementSetName</literal> is used for piggyback
387 searches. This means that for the high-level mode you only have
388 to specify one elementSetName option rather than three.
392 <sect1 id="zoom.records"><title>Records</title>
394 A record object is a retrival record on the client side -
395 created from result sets.
398 void ZOOM_resultset_records (ZOOM_resultset r,
400 size_t start, size_t count);
401 ZOOM_record ZOOM_resultset_record (ZOOM_resultset s, size_t pos);
403 void *ZOOM_record_get (ZOOM_record rec, const char *type,
406 ZOOM_record ZOOM_record_clone (ZOOM_record rec);
408 void ZOOM_record_destroy (ZOOM_record rec);
411 References to temporary records are returned by functions
412 <function>ZOOM_resultset_records</function> or
413 <function>ZOOM_resultset_record</function>.
416 If a persistent reference to a record is desired
417 <function>ZOOM_record_clone</function> should be used.
418 It returns a record reference that should be destroyed
419 by a call to <function>ZOOM_record_destroy</function>.
422 A single record is returned by function
423 <function>ZOOM_resultset_record</function> that takes a
424 position as argument. First record has position zero.
425 If no record could be obtained <literal>NULL</literal> is returned.
428 Function <function>ZOOM_resultset_records</function> retrieves
429 a number of records from a result set. Parameter <literal>start</literal>
430 and <literal>count</literal> specifies the range of records to
431 be returned. Upon completion array
432 <literal>recs[0], ..recs[count-1]</literal>
433 holds record objects for the records. The array of records
434 <literal>recs</literal> should be allocated prior the call
435 <function>ZOOM_resultset_records</function>. Note that for those
436 records that couldn't be retrieved from the target
437 <literal>recs[ ..]</literal> is set to <literal>NULL</literal>.
439 <para id="zoom.record.get">
440 In order to extract information about a single record,
441 <function>ZOOM_record_get</function> is provided. The
442 function returns a pointer to certain record information. The
443 nature (type) of the pointer depends on the parameter,
444 <function>type</function>.
445 In addition, for certain types, the length
446 <literal>len</literal> passed will be set to the size in bytes of
447 the returned information.
449 <varlistentry><term><literal>database</literal></term>
450 <listitem><para>Database of record is returned
451 as a C null-terminated string. Return type <literal>char *</literal>.
454 <varlistentry><term><literal>syntax</literal></term>
455 <listitem><para>The transfer syntax (OID) of the record is returned
456 as a C null-terminated string. Return type <literal>char *</literal>.
459 <varlistentry><term><literal>render</literal></term>
460 <listitem><para>The record is returned in a display friendly
461 format. Upon completion buffer is returned
462 (type <literal>char *</literal>) and length is stored in
463 <literal>*len</literal>.
466 <varlistentry><term><literal>raw</literal></term>
467 <listitem><para>The record is returned in the internal
468 YAZ specific format. The raw data is returned as type
469 <literal>Z_External *</literal> which is just the type for
470 the member <literal>retrievalRecord</literal> in
471 type <literal>NamePlusRecord</literal>.
476 <sect2><title>Protocol behavior</title>
478 The functions <function>ZOOM_resultset_record</function> and
479 <function>ZOOM_resultset_records</function> inspects the client-side
480 record cache. Records not found in cache are fetched using
482 The functions may block (and perform network I/O) - even though option
483 <literal>async</literal> is 1, because they return records objects.
484 (and there's no way to return records objects without retrieving them!).
487 There is a trick, however, in the usage of function
488 <function>ZOOM_resultset_records</function> that allows for
489 delayed retrieval (and makes it non-blocking). By passing
490 a null pointer for <parameter>recs</parameter> you're indicating
491 you're not interested in getting records objects
492 <emphasis>now</emphasis>.
496 <sect1 id="zoom.options"><title>Options</title>
498 Most &zoom; objects provide a way to specify options to change behavior.
499 From an implementation point of view a set of options is just like
500 an associative array / hash array, etc.
503 ZOOM_options ZOOM_options_create (void);
505 ZOOM_options ZOOM_options_create_with_parent (ZOOM_options parent);
507 void ZOOM_options_destroy (ZOOM_options opt);
510 const char *ZOOM_options_get (ZOOM_options opt, const char *name);
512 void ZOOM_options_set (ZOOM_options opt, const char *name,
516 typedef const char *(*ZOOM_options_callback)
517 (void *handle, const char *name);
519 ZOOM_options_callback
520 ZOOM_options_set_callback (ZOOM_options opt,
521 ZOOM_options_callback c,
525 <sect1 id="zoom.events"><title>Events</title>
527 If you're developing non-blocking applications, you have to deal
531 int ZOOM_event (int no, ZOOM_connection *cs);
534 The <function>ZOOM_event</function> executes pending events for
535 a number of connections. Supply the number of connections in
536 <literal>no</literal> and an array of connections in
537 <literal>cs</literal> (<literal>cs[0] ... cs[no-1]</literal>).
538 A pending event could be a sending a search, receiving a response,
540 When an event has occured for one of the connections, this function
541 returns a positive integer <literal>n</literal> denoting that an event
542 occurred for connection <literal>cs[n-1]</literal>.
543 When no events are pending for the connections, a value of zero is
545 To ensure that all outstanding requests are performed call this function
546 repeatedly until zero is returned.
551 <!-- Keep this comment at the end of the file
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