1 <!-- $Id: zoom.xml,v 1.10 2001-11-15 21:58:50 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 Z3950_connection Z3950_connection_new (const char *host, int portnum);
57 Z3950_connection Z3950_connection_create (Z3950_options options);
59 void Z3950_connection_connect(Z3950_connection c, const char *host,
61 void Z3950_connection_destroy (Z3950_connection c);
64 Connection objects are created with either function
65 <function>Z3950_connection_new</function> or
66 <function>Z3950_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>Z3950_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>Z3950_connection_destroy</function>.
83 void Z3950_connection_option_set (Z3950_connection c,
87 const char *Z3950_connection_option_get (Z3950_connection c,
90 const char *Z3950_connection_host (Z3950_connection c);
93 The <function>Z3950_connection_option_set</function> allows you to
94 set an option given by <parameter>key</parameter> to the value
95 <parameter>value</parameter> for the connection.
96 Function <function>Z3950_connection_option_get</function> returns
97 the value for an option given by <parameter>key</parameter>.
99 <table frame="top"><title>ZOOM Connection Options</title>
101 <colspec colwidth="4*" colname="name"></colspec>
102 <colspec colwidth="7*" colname="description"></colspec>
103 <colspec colwidth="3*" colname="default"></colspec>
106 <entry>Option</entry>
107 <entry>Description</entry>
108 <entry>Default</entry>
113 implementationName</entry><entry>Name of Your client
114 </entry><entry>none</entry></row>
116 user</entry><entry>Authentication user name
117 </entry><entry>none</entry></row>
119 group</entry><entry>Authentication group name
120 </entry><entry>none</entry></row>
122 pass</entry><entry>Authentication password
123 </entry><entry>none</entry></row>
125 proxy</entry><entry>Proxy host
126 </entry><entry>none</entry></row>
128 async</entry><entry>If true (1) the connection operates in
129 asynchronous operation which means that all calls are non-blocking
131 <link linkend="zoom.events"><function>Z3950_event</function></link>.
132 </entry><entry>0</entry></row>
134 maximumRecordSize</entry><entry> Maximum size of single record.
135 </entry><entry>1 MB</entry></row>
137 preferredMessageSize</entry><entry> Maximum size of multiple records.
138 </entry><entry>1 MB</entry></row>
143 Function <function>Z3950_connection_host</function> returns
144 the host for the connection as specified in a call to
145 <function>Z3950_connection_new</function> or
146 <function>Z3950_connection_connect</function>.
147 This function returns <literal>NULL</literal> if host isn't
148 set for the connection.
151 int Z3950_connection_error (Z3950_connection c, const char **cp,
152 const char **addinfo);
155 Use <function>Z3950_connection_error</function> to check for
156 errors for the last operation(s) performed. The function returns
157 zero if no errors occurred; non-zero otherwise indicating the error.
158 Pointers <parameter>cp</parameter> and <parameter>addinfo</parameter>
159 holds messages for the error and additional-info if passed as
160 non-<literal>NULL</literal>.
162 <sect2><title>Protocol behavior</title>
164 The calls <function>Z3950_connection_new</function> and
165 <function>Z3950_connection_connect</function> establises a TCP/IP
166 connection and sends an Initialize Request to the target if
167 possible. In addition, the calls waits for an Initialize Response
168 from the target and the result is inspected (OK or rejected).
171 If <literal>proxy</literal> is set then the client will establish
172 a TCP/IP connection with the peer as specified by the
173 <literal>proxy</literal> host and the hostname as part of the
174 connect calls will be set as part of the Initialize Request.
175 The proxy server will then "forward" the PDU's transparently
176 to the target behind the proxy.
179 For the authentication parameters, if option <literal>user</literal>
180 is set and both options <literal>group</literal> and
181 <literal>pass</literal> are unset, then Open style
182 authentication is used (Version 2/3) in which case the username
183 is usually followed by a slash, then by a password.
184 If either <literal>group</literal>
185 or <literal>pass</literal> is set then idPass authentication
186 (Version 3 only) is used. If none of the options are set, no
187 authentication parameters are set as part of the Initialize Request
191 When option <literal>async</literal> is 1, it really means that
192 all network operations are postponed (and queued) until the
193 function <literal>Z3950_event</literal> is invoked. When doing so
194 it doesn't make sense to check for errors after
195 <literal>Z3950_connection_new</literal> is called since that
196 operation "connecting - and init" is still incomplete and the
197 API cannot tell the outcome (yet).
201 <sect1 id="zoom.query"><title>Queries</title>
203 Query objects represents queries.
206 Z3950_query Z3950_query_create(void);
208 void Z3950_query_destroy(Z3950_query q);
210 int Z3950_query_prefix(Z3950_query q, const char *str);
212 int Z3950_query_sortby(Z3950_query q, const char *criteria);
215 Create query objects using <function>Z3950_query_create</function>
216 and destroy them by calling <function>Z3950_query_destroy</function>.
217 RPN-queries can be specified in <link linkend="PQF">PQF</link>
218 notation by using the
219 function <function>Z3950_query_prefix</function>. More
220 query types will be added later, such as
221 <link linkend="CCL">CCL</link> to RPN-mapping, native CCL query,
222 etc. In addition to a search, a sort criteria may be set. Function
223 <function>Z3950_query_sortby</function> specifies a
224 sort criteria using the same string notation for sort as offered by
225 the <link linkend="sortspec">YAZ client</link>.
227 <sect2><title>Protocol behavior</title>
229 The query object is just an interface for the member Query
230 in the SearchRequest. The sortby-function is an interface to the
231 sortSequence member of the SortRequest.
235 <sect1 id="zoom.resultsets"><title>Result sets</title>
237 The result set object is a container for records returned from
241 Z3950_resultset Z3950_connection_search(Z3950_connection,
244 Z3950_resultset Z3950_connection_search_pqf(Z3950_connection c,
247 void Z3950_resultset_destroy(Z3950_resultset r);
250 Function <function>Z3950_connection_search</function> creates
251 a result set given a connection and query.
252 Destroy a result set by calling
253 <function>Z3950_resultset_destroy</function>.
254 Simple clients may using PQF only may use function
255 <function>Z3950_connection_search_pqf</function> in which case
256 creating query objects is not necessary.
259 void Z3950_resultset_option_set (Z3950_resultset r,
263 const char *Z3950_resultset_option_get (Z3950_resultset r,
266 size_t Z3950_resultset_size (Z3950_resultset r);
269 Functions <function>Z3950_resultset_options_set</function> and
270 <function>Z3950_resultset_get</function> sets and gets an option
271 for a result set similar to <function>Z3950_connection_option_get</function>
272 and <function>Z3950_connection_option_set</function>.
275 The number of hits also called result-count is returned by
276 function <function>Z3950_resultset_size</function>.
278 <table frame="top"><title>ZOOM Result set Options</title>
280 <colspec colwidth="4*" colname="name"></colspec>
281 <colspec colwidth="7*" colname="description"></colspec>
282 <colspec colwidth="2*" colname="default"></colspec>
285 <entry>Option</entry>
286 <entry>Description</entry>
287 <entry>Default</entry>
292 piggyback</entry><entry>True (1) if piggyback should be
293 used in searches; false (0) if not.
294 </entry><entry>1</entry></row>
296 start</entry><entry>Offset of first record to be
297 retrieved from target. First record has offset 0 unlike the
298 protocol specifications where first record has position 1.
299 </entry><entry>0</entry></row>
301 count</entry><entry>Number of records to be retrieved.
302 </entry><entry>0</entry></row>
304 elementSetName</entry><entry>Element-Set name of records.
305 Most targets should honor element set name <literal>B</literal>
306 and <literal>F</literal> for brief and full respectively.
307 </entry><entry>none</entry></row>
309 preferredRecordSyntax</entry><entry>Preferred Syntax, such as
310 <literal>USMARC</literal>, <literal>SUTRS</literal>, etc.
311 </entry><entry>none</entry></row>
313 smallSetUpperBound</entry><entry>If hits is less than or equal to this
314 value, then target will return all records using small element set name
315 </entry><entry>0</entry></row>
317 largeSetLowerBound</entry><entry>If hits is greator than this
318 value, the target will return no records.
319 </entry><entry>1</entry></row>
321 mediumSetPresentNumber</entry><entry>This value represents
322 the number of records to be returned as part of a search when when
323 hits is less than or equal to large set lower bound and if hits
324 is greator than small set upper bound.
325 </entry><entry>0</entry></row>
327 smallSetElementSetName</entry><entry>
328 The element set name to be used for small result sets.
329 </entry><entry>none</entry></row>
331 mediumSetElementSetName</entry><entry>
332 The element set name to be for medium-sized result sets.
333 </entry><entry>none</entry></row>
335 databaseName</entry><entry>One or more database names
336 separated by character plus (<literal>+</literal>).
337 </entry><entry>Default</entry></row>
342 <title>Protocol behavior</title>
344 The creation of a result set involves at least a SearchRequest
345 - SearchResponse protocol handshake. Following that, if a sort
346 critieria was specified as part of the query, a sortRequest -
347 SortResponse handshake takes place. Note that it is necessary to
348 perform sorting before any retrieval takes place, so no records will
349 be returned from the target as part of the SearchResponse because these
350 would be unsorted. Hence, piggyback is disabled when sort critieria
351 is set. Following Search - and a Possible sort, Retrieval takes
352 place - as one or more Present Requests - Present Response being
356 The API allows for two different modes for retrieval. A high level
357 mode which is somewhat more powerful and a low level one.
358 The low level is "enabled" when the settings
359 <literal>smallSetUpperBound</literal>,
360 <literal>mediumSetPresentNumber</literal> and
361 <literal>largeSetLowerBound</literal> are set. The low level mode
362 thus allows you to precisely set how records are returned as part
363 of a search response as offered by the Z39.50 protocol.
364 Since the client may be retrieving records as part of the
365 search response, this mode doesn't work well if sorting is used.
368 The high-level mode allows you to fetch a range of records from
369 the result set with a given start offset. When you use this mode
370 the client will automatically use piggyback if that is possible
371 with the target and perform one or more present requests as needed.
372 Even if the target returns fewer records as part of a present response
373 because of a record size limit, etc. the client will repeat sending
374 present requests. As an example, if option <literal>start</literal>
375 is 0 (default) and <literal>count</literal> is 4, and
376 <literal>piggyback</literal> is 1 (default) and no sorting critieria
377 is specified, then the client will attempt to retrieve the 4
378 records as part the search response (using piggyback). On the other
379 hand, if either <literal>start</literal> is positive or if
380 a sorting criteria is set, or if <literal>piggyback</literal>
381 is 0, then the client will not perform piggyback but send Present
385 If either of the options <literal>mediumSetElementSetName</literal> and
386 <literal>smallSetElementSetName</literal> are unset, the value
387 of option <literal>elementSetName</literal> is used for piggyback
388 searches. This means that for the high-level mode you only have
389 to specify one elementSetName option rather than three.
393 <sect1 id="zoom.records"><title>Records</title>
395 A record object is a retrival record on the client side -
396 created from result sets.
399 void Z3950_resultset_records (Z3950_resultset r,
401 size_t start, size_t count);
402 Z3950_record Z3950_resultset_record (Z3950_resultset s, size_t pos);
404 void *Z3950_record_get (Z3950_record rec, const char *type,
407 Z3950_record Z3950_record_dup (Z3950_record rec);
409 void Z3950_record_destroy (Z3950_record rec);
412 References to temporary records are returned by functions
413 <function>Z3950_resultset_records</function> or
414 <function>Z3950_resultset_record</function>.
417 If a persistent pointer to a record is desired
418 <function>Z3950_record_dup</function> should be used.
419 It returns a record reference that at any
420 later stage should be destroyed by
421 <function>Z3950_record_destroy</function>.
424 A single record is returned by function
425 <function>Z3950_resultset_record</function> that takes a
426 position as argument. First record has position zero.
427 If no record could be obtained <literal>NULL</literal> is returned.
430 Function <function>Z3950_resultset_records</function> retrieves
431 a number of records from a result set. Parameter <literal>start</literal>
432 and <literal>count</literal> specifies the range of records to
433 be returned. Upon completion array
434 <literal>recs[0], ..recs[count-1]</literal>
435 holds record objects for the records. The array of records
436 <literal>recs</literal> should be allocate prior to calling
437 <function>Z3950_resultset_records</function>. Note that for those
438 records that couldn't be retrieved from the target
439 <literal>recs[ ..]</literal> is set to <literal>NULL</literal>.
441 <para id="zoom.record.get">
442 In order to extract information about a single record,
443 <function>Z3950_record_get</function> is provided. The
444 function returns a pointer to certain record information. The
445 nature (type) of the pointer depends on the <function>type</function>
446 given. In addition for certain types, the length
447 <literal>len</literal> passed will be set to the size in bytes of
448 the returned information.
450 <varlistentry><term><literal>database</literal></term>
451 <listitem><para>Database of record is returned
452 as a C null-terminated string. Return type <literal>char *</literal>.
455 <varlistentry><term><literal>syntax</literal></term>
456 <listitem><para>The transfer syntax (OID) of the record is returned
457 as a C null-terminated string. Return type <literal>char *</literal>.
460 <varlistentry><term><literal>render</literal></term>
461 <listitem><para>The record is returned in a display friendly
462 format. Upon completion buffer is returned
463 (type <literal>char *</literal>) and length is stored in
464 <literal>*len</literal>.
467 <varlistentry><term><literal>raw</literal></term>
468 <listitem><para>The record is returned in the internal
469 YAZ specific format. The raw data is returned as type
470 <literal>Z_External *</literal> which is just the type for
471 the member <literal>retrievalRecord</literal> in
472 type <literal>NamePlusRecord</literal>.
477 <sect2><title>Protocol behavior</title>
479 The functions <function>Z3950_resultset_record</function> and
480 <function>Z3950_resultset_records</function> inspects the client-side
481 record cache. If the records(s) were not found, i.e. not yet retrieved
482 from, they are fetched using Present Requests.
486 <sect1 id="zoom.options"><title>Options</title>
488 Most &zoom; objects provide a way to specify options to default behavior.
489 From an implementation point of view a set of options is just like
490 an associate array / hash array, etc.
493 Z3950_options Z3950_options_create (void);
495 Z3950_options Z3950_options_create_with_parent (Z3950_options parent);
497 void Z3950_options_destroy (Z3950_options opt);
500 const char *Z3950_options_get (Z3950_options opt, const char *name);
502 void Z3950_options_set (Z3950_options opt, const char *name,
506 typedef const char *(*Z3950_options_callback)
507 (void *handle, const char *name);
509 Z3950_options_callback
510 Z3950_options_set_callback (Z3950_options opt,
511 Z3950_options_callback c,
515 <sect1 id="zoom.events"><title>Events</title>
517 If you're developing non-blocking applications, you have to deal
521 int Z3950_event (int no, Z3950_connection *cs);
524 The <function>Z3950_event</function> executes pending events for
525 a number of connections. Supply the number of connections in
526 <literal>no</literal> and an array of connections in
527 <literal>cs</literal> (<literal>cs[0] ... cs[no-1]</literal>).
528 A pending event could be a sending a search, receiving a response,
530 When an event has a occured for one of the connections, this function
531 returns a positive integer <literal>n</literal> denoting that an event
532 occurred for connection <literal>cs[n-1]</literal>.
533 When no events are pending for the connections, a value of zero is
535 To ensure that all outstanding requests are performed call this function
536 repeatedly until zero is returned.
541 <!-- Keep this comment at the end of the file
546 sgml-minimize-attributes:nil
547 sgml-always-quote-attributes:t
550 sgml-parent-document: "yaz.xml"
551 sgml-local-catalogs: nil
552 sgml-namecase-general:t