1 <!-- $Id: frontend.xml,v 1.12 2002-05-30 20:57:38 adam Exp $ -->
2 <chapter id="server"><title>Generic server</title>
3 <sect1><title>Introduction</title>
6 If you aren't into documentation, a good way to learn how the
7 back end interface works is to look at the <filename>backend.h</filename>
8 file. Then, look at the small dummy-server in
9 <filename>ztest/ztest.c</filename>. The <filename>backend.h</filename>
10 file also makes a good reference, once you've chewed your way through
11 the prose of this file.
15 If you have a database system that you would like to make available by
16 means of Z39.50, &yaz; basically offers your two options. You
17 can use the APIs provided by the &asn;, &odr;, and &comstack;
19 create and decode PDUs, and exchange them with a client.
20 Using this low-level interface gives you access to all fields and
21 options of the protocol, and you can construct your server as close
22 to your existing database as you like.
23 It is also a fairly involved process, requiring
24 you to set up an event-handling mechanism, protocol state machine,
25 etc. To simplify server implementation, we have implemented a compact
26 and simple, but reasonably full-functioned server-frontend that will
27 handle most of the protocol mechanics, while leaving you to
28 concentrate on your database interface.
33 The backend interface was designed in anticipation of a specific
34 integration task, while still attempting to achieve some degree of
35 generality. We realize fully that there are points where the
36 interface can be improved significantly. If you have specific
37 functions or parameters that you think could be useful, send us a
38 mail (or better, sign on to the mailing list referred to in the
39 top-level README file). We will try to fit good suggestions into future
40 releases, to the extent that it can be done without requiring
41 too many structural changes in existing applications.
46 <sect1 id="server.frontend"><title>The Database Frontend</title>
49 We refer to this software as a generic database frontend. Your
50 database system is the <emphasis>backend database</emphasis>, and the
51 interface between the two is called the <emphasis>backend API</emphasis>.
52 The backend API consists of a small number of function handlers and
53 structure definitions. You are required to provide the
54 <function>main()</function> routine for the server (which can be
55 quite simple), as well as a set of handlers to match each of the prototypes.
56 The interface functions that you write can use any mechanism you like
57 to communicate with your database system: You might link the whole
58 thing together with your database application and access it by
59 function calls; you might use IPC to talk to a database server
60 somewhere; or you might link with third-party software that handles
61 the communication for you (like a commercial database client library).
62 At any rate, the handlers will perform the tasks of:
80 Scanning the database index (optional - if you wish to implement SCAN).
84 Extended Services (optional).
88 Result-Set Delete (optional).
92 Result-Set Sort (optional).
98 (more functions will be added in time to support as much of
99 Z39.50-1995 as possible).
103 <sect1 id="server.backend"><title>The Backend API</title>
106 The header file that you need to use the interface are in the
107 <filename>include/yaz</filename> directory. It's called
108 <filename>backend.h</filename>. It will include other files from
109 the <filename>include/yaz</filename> directory, so you'll
110 probably want to use the -I option of your compiler to tell it
111 where to find the files. When you run
112 <literal>make</literal> in the top-level &yaz; directory,
113 everything you need to create your server is to link with the
114 <filename>lib/libyaz.la</filename> library.
118 <sect1 id="server.main"><title>Your main() Routine</title>
121 As mentioned, your <function>main()</function> routine can be quite brief.
122 If you want to initialize global parameters, or read global configuration
123 tables, this is the place to do it. At the end of the routine, you should
128 int statserv_main(int argc, char **argv,
129 bend_initresult *(*bend_init)(bend_initrequest *r),
130 void (*bend_close)(void *handle));
134 The third and fourth arguments are pointers to handlers. Handler
135 <function>bend_init</function> is called whenever the server receives
136 an Initialize Request, so it serves as a Z39.50 session initializer. The
137 <function>bend_close</function> handler is called when the session is
142 <function>statserv_main</function> will establish listening sockets
143 according to the parameters given. When connection requests are received,
144 the event handler will typically <function>fork()</function> and
145 create a sub-process to handle a new connection.
146 Alternatively the server may be setup to create threads for each
148 If you do use global variables and forking, you should be aware, then,
149 that these cannot be shared between associations, unless you explicitly
150 disable forking by command line parameters.
154 The server provides a mechanism for controlling some of its behavior
155 without using command-line options. The function
159 statserv_options_block *statserv_getcontrol(void);
163 will return a pointer to a <literal>struct statserv_options_block</literal>
164 describing the current default settings of the server. The structure
165 contains these elements:
169 <literal>int dynamic</literal></term><listitem><para>
170 A boolean value, which determines whether the server
171 will fork on each incoming request (TRUE), or not (FALSE). Default is
172 TRUE. This flag is only read by UNIX-based servers (WIN32 based servers
174 </para></listitem></varlistentry>
177 <literal>int threads</literal></term><listitem><para>
178 A boolean value, which determines whether the server
179 will create a thread on each incoming request (TRUE), or not (FALSE).
180 Default is FALSE. This flag is only read by UNIX-based servers
181 that offer POSIX Threads support.
182 WIN32-based servers always operate in threaded mode.
183 </para></listitem></varlistentry>
186 <literal>int inetd</literal></term><listitem><para>
187 A boolean value, which determines whether the server
188 will operates under a UNIX INET daemon (inetd). Default is FALSE.
189 </para></listitem></varlistentry>
192 <literal>int loglevel</literal></term><listitem><para>
193 Set this by ORing the constants defined in
194 <filename>include/yaz/yaz-log.h</filename>.
195 </para></listitem></varlistentry>
198 <literal>char logfile[ODR_MAXNAME+1]</literal></term>
199 <listitem><para>File for diagnostic output ("": stderr).
200 </para></listitem></varlistentry>
203 <literal>char apdufile[ODR_MAXNAME+1]</literal></term>
205 Name of file for logging incoming and outgoing APDUs
206 ("": don't log APDUs, "-":
207 <literal>stderr</literal>).
208 </para></listitem></varlistentry>
211 <literal>char default_listen[1024]</literal></term>
212 <listitem><para>Same form as the command-line specification of
213 listener address. "": no default listener address.
214 Default is to listen at "tcp:@:9999". You can only
215 specify one default listener address in this fashion.
216 </para></listitem></varlistentry>
219 <literal>enum oid_proto default_proto;</literal></term>
220 <listitem><para>Either <literal>PROTO_Z3950</literal> or
221 <literal>PROTO_SR</literal>.
222 Default is <literal>PROTO_Z39_50</literal>.
223 </para></listitem></varlistentry>
226 <literal>int idle_timeout;</literal></term>
227 <listitem><para>Maximum session idle-time, in minutes. Zero indicates
228 no (infinite) timeout. Default is 120 minutes.
229 </para></listitem></varlistentry>
232 <literal>int maxrecordsize;</literal></term>
233 <listitem><para>Maximum permissible record (message) size. Default
234 is 1Mb. This amount of memory will only be allocated if a
235 client requests a very large amount of records in one operation
237 Set it to a lower number if you are worried about resource
238 consumption on your host system.
239 </para></listitem></varlistentry>
242 <literal>char configname[ODR_MAXNAME+1]</literal></term>
243 <listitem><para>Passed to the backend when a new connection is received.
244 </para></listitem></varlistentry>
247 <literal>char setuid[ODR_MAXNAME+1]</literal></term>
248 <listitem><para>Set user id to the user specified, after binding
249 the listener addresses.
250 </para></listitem></varlistentry>
253 <literal>void (*bend_start)(struct statserv_options_block *p)</literal>
255 <listitem><para>Pointer to function which is called after the
256 command line options have been parsed - but before the server
258 For forked UNIX servers this handler is called in the mother
259 process; for threaded servers this handler is called in the
261 The default value of this pointer is NULL in which case it
262 isn't invoked by the frontend server.
263 When the server operates as an NT service this handler is called
264 whenever the service is started.
265 </para></listitem></varlistentry>
268 <literal>void (*bend_stop)(struct statserv_options_block *p)</literal>
270 <listitem><para>Pointer to function which is called whenever the server
271 has stopped listening for incoming connections. This function pointer
272 has a default value of NULL in which case it isn't called.
273 When the server operates as an NT service this handler is called
274 whenever the service is stopped.
275 </para></listitem></varlistentry>
278 <literal>void *handle</literal></term>
279 <listitem><para>User defined pointer (default value NULL).
280 This is a per-server handle that can be used to specify "user-data".
281 Do not confuse this with the session-handle as returned by bend_init.
282 </para></listitem></varlistentry>
288 The pointer returned by <literal>statserv_getcontrol</literal> points to
289 a static area. You are allowed to change the contents of the structure,
290 but the changes will not take effect before you call
294 void statserv_setcontrol(statserv_options_block *block);
299 that you should generally update this structure before calling
300 <function>statserv_main()</function>.
305 <sect1 id="server.backendfunctions"><title>The Backend Functions</title>
308 For each service of the protocol, the backend interface declares one or
309 two functions. You are required to provide implementations of the
310 functions representing the services that you wish to implement.
313 <sect2><title>Init</title>
316 bend_initresult (*bend_init)(bend_initrequest *r);
320 This handler is called once for each new connection request, after
321 a new process/thread has been created, and an Initialize Request has
322 been received from the client. The pointer to the
323 <function>bend_init</function> handler is passed in the call to
324 <function>statserv_start</function>.
327 Unlike previous versions of YAZ, the <function>bend_init</function> also
328 serves as a handler that defines the Z39.50 services that the backend
329 wish to support. Pointers to <emphasis>all</emphasis> service handlers,
330 including search - and fetch must be specified here in this handler.
333 The request - and result structures are defined as
337 typedef struct bend_initrequest
339 Z_IdAuthentication *auth;
340 ODR stream; /* encoding stream */
341 ODR print; /* printing stream */
342 Z_ReferenceId *referenceId;/* reference ID */
343 char *peer_name; /* dns host of peer (client) */
345 char *implementation_id;
346 char *implementation_name;
347 char *implementation_version;
348 int (*bend_sort) (void *handle, bend_sort_rr *rr);
349 int (*bend_search) (void *handle, bend_search_rr *rr);
350 int (*bend_fetch) (void *handle, bend_fetch_rr *rr);
351 int (*bend_present) (void *handle, bend_present_rr *rr);
352 int (*bend_esrequest) (void *handle, bend_esrequest_rr *rr);
353 int (*bend_delete)(void *handle, bend_delete_rr *rr);
354 int (*bend_scan)(void *handle, bend_scan_rr *rr);
355 int (*bend_segment)(void *handle, bend_segment_rr *rr);
358 typedef struct bend_initresult
360 int errcode; /* 0==OK */
361 char *errstring; /* system error string or NULL */
362 void *handle; /* private handle to the backend module */
367 In general, the server frontend expects that the
368 <literal>bend_*result</literal> pointer that you return is valid at
369 least until the next call to a <literal>bend_* function</literal>.
370 This applies to all of the functions described herein. The parameter
371 structure passed to you in the call belongs to the server frontend, and
372 you should not make assumptions about its contents after the current
373 function call has completed. In other words, if you want to retain any
374 of the contents of a request structure, you should copy them.
378 The <literal>errcode</literal> should be zero if the initialization of
379 the backend went well. Any other value will be interpreted as an error.
380 The <literal>errstring</literal> isn't used in the current version, but
381 one option would be to stick it in the initResponse as a VisibleString.
382 The <literal>handle</literal> is the most important parameter. It should
383 be set to some value that uniquely identifies the current session to
384 the backend implementation. It is used by the frontend server in any
385 future calls to a backend function.
386 The typical use is to set it to point to a dynamically allocated state
387 structure that is private to your backend module.
391 The <literal>auth</literal> member holds the authentication information
392 part of the Z39.50 Initialize Request. Interpret this if your serves
393 requires authentication.
397 The members <literal>peer_name</literal>,
398 <literal>implementation_id</literal>,
399 <literal>implementation_name</literal> and
400 <literal>implementation_version</literal> holds DNS of client, ID of implementor, name
401 of client (Z39.50) implementation - and version.
405 The <literal>bend_</literal> - members are set to NULL when
406 <function>bend_init</function> is called. Modify the pointers by
407 setting them to point to backend functions.
412 <sect2><title>Search and retrieve</title>
414 <para>We now describe the handlers that are required to support search -
415 and retrieve. You must support two functions - one for search - and one
416 for fetch (retrieval of one record). If desirable you can provide a
417 third handler which is called when a present request is received which
418 allows you to optimize retrieval of multiple-records.
422 int (*bend_search) (void *handle, bend_search_rr *rr);
425 char *setname; /* name to give to this set */
426 int replace_set; /* replace set, if it already exists */
427 int num_bases; /* number of databases in list */
428 char **basenames; /* databases to search */
429 Z_ReferenceId *referenceId;/* reference ID */
430 Z_Query *query; /* query structure */
431 ODR stream; /* encode stream */
432 ODR decode; /* decode stream */
433 ODR print; /* print stream */
435 bend_request request;
436 bend_association association;
438 int hits; /* number of hits */
439 int errcode; /* 0==OK */
440 char *errstring; /* system error string or NULL */
446 The <function>bend_search</function> handler is a fairly close
447 approximation of a protocol Search Request - and Response PDUs
448 The <literal>setname</literal> is the resultSetName from the protocol.
449 You are required to establish a mapping between the set name and whatever
450 your backend database likes to use.
451 Similarly, the <literal>replace_set</literal> is a boolean value
452 corresponding to the resultSetIndicator field in the protocol.
453 <literal>num_bases/basenames</literal> is a length of/array of character
454 pointers to the database names provided by the client.
455 The <literal>query</literal> is the full query structure as defined in
456 the protocol ASN.1 specification.
457 It can be either of the possible query types, and it's up to you to
458 determine if you can handle the provided query type.
459 Rather than reproduce the C interface here, we'll refer you to the
460 structure definitions in the file
461 <filename>include/yaz/z-core.h</filename>. If you want to look at the
462 attributeSetId OID of the RPN query, you can either match it against
463 your own internal tables, or you can use the
464 <literal>oid_getentbyoid</literal> function provided by &yaz;.
468 The structure contains a number of hits, and an
469 <literal>errcode/errstring</literal> pair. If an error occurs
470 during the search, or if you're unhappy with the request, you should
471 set the errcode to a value from the BIB-1 diagnostic set. The value
472 will then be returned to the user in a nonsurrogate diagnostic record
473 in the response. The <literal>errstring</literal>, if provided, will
474 go in the addinfo field. Look at the protocol definition for the
475 defined error codes, and the suggested uses of the addinfo field.
480 int (*bend_fetch) (void *handle, bend_fetch_rr *rr);
482 typedef struct bend_fetch_rr {
483 char *setname; /* set name */
484 int number; /* record number */
485 Z_ReferenceId *referenceId;/* reference ID */
486 oid_value request_format; /* One of the CLASS_RECSYN members */
487 int *request_format_raw; /* same as above (raw OID) */
488 Z_RecordComposition *comp; /* Formatting instructions */
489 ODR stream; /* encoding stream - memory source if req */
490 ODR print; /* printing stream */
492 char *basename; /* name of database that provided record */
493 int len; /* length of record or -1 if structured */
494 char *record; /* record */
495 int last_in_set; /* is it? */
496 oid_value output_format; /* format */
497 int *output_format_raw; /* used instead of above if not-null */
498 int errcode; /* 0==success */
499 char *errstring; /* system error string or NULL */
500 int surrogate_flag; /* surrogate diagnostic */
505 The frontend server calls the <function>bend_fetch</function> handler
506 when it needs database records to fulfill a Search Request or a Present
508 The <literal>setname</literal> is simply the name of the result set
509 that holds the reference to the desired record.
510 The <literal>number</literal> is the offset into the set (with 1
511 being the first record in the set). The <literal>format</literal> field
512 is the record format requested by the client (See section
513 <link linkend="oid">Object Identifiers</link>). The value
514 <literal>VAL_NONE</literal> indicates that the client did not
515 request a specific format. The <literal>stream</literal> argument
516 is an &odr; stream which should be used for
517 allocating space for structured data records.
518 The stream will be reset when all records have been assembled, and
519 the response package has been transmitted.
520 For unstructured data, the backend is responsible for maintaining a
521 static or dynamic buffer for the record between calls.
525 In the structure, the <literal>basename</literal> is the name of the
526 database that holds the
527 record. <literal>len</literal> is the length of the record returned, in
528 bytes, and <literal>record</literal> is a pointer to the record.
529 <literal>Last_in_set</literal> should be nonzero only if the record
530 returned is the last one in the given result set.
531 <literal>errcode</literal> and <literal>errstring</literal>, if
532 given, will be interpreted as a global error pertaining to the
533 set, and will be returned in a non-surrogate-diagnostic.
534 If you wish to return the error as a surrogate-diagnostic
535 (local error) you can do this by setting
536 <literal>surrogate_flag</literal> to 1 also.
540 If the <literal>len</literal> field has the value -1, then
541 <literal>record</literal> is assumed to point to a constructed data
542 type. The <literal>format</literal> field will be used to determine
543 which encoder should be used to serialize the data.
548 If your backend generates structured records, it should use
549 <function>odr_malloc()</function> on the provided stream for allocating
550 data: This allows the frontend server to keep track of the record sizes.
555 The <literal>format</literal> field is mapped to an object identifier
556 in the direct reference of the resulting EXTERNAL representation
562 The current version of &yaz; only supports the direct reference mode.
567 int (*bend_present) (void *handle, bend_present_rr *rr);
570 char *setname; /* set name */
572 int number; /* record number */
573 oid_value format; /* One of the CLASS_RECSYN members */
574 Z_ReferenceId *referenceId;/* reference ID */
575 Z_RecordComposition *comp; /* Formatting instructions */
576 ODR stream; /* encoding stream */
577 ODR print; /* printing stream */
578 bend_request request;
579 bend_association association;
581 int hits; /* number of hits */
582 int errcode; /* 0==OK */
583 char *errstring; /* system error string or NULL */
588 The <function>bend_present</function> handler is called when
589 the server receives a Present Request. The <literal>setname</literal>,
590 <literal>start</literal> and <literal>number</literal> is the
591 name of the result set - start position - and number of records to
592 be retrieved respectively. <literal>format</literal> and
593 <literal>comp</literal> is the preferred transfer syntax and element
594 specifications of the present request.
597 Note that this is handler serves as a supplement for
598 <function>bend_fetch</function> and need not to be defined in order to
599 support search - and retrieve.
604 <sect2><title>Delete</title>
607 For back-ends that supports delete of a result set only one handler
612 int (*bend_delete)(void *handle, bend_delete_rr *rr);
614 typedef struct bend_delete_rr {
618 Z_ReferenceId *referenceId;
619 int delete_status; /* status for the whole operation */
620 int *statuses; /* status each set - indexed as setnames */
628 The delete set function definition is rather primitive, mostly because
629 we have had no practical need for it as of yet. If someone wants
630 to provide a full delete service, we'd be happy to add the
631 extra parameters that are required. Are there clients out there
632 that will actually delete sets they no longer need?
638 <sect2><title>scan</title>
641 For servers that wish to offer the scan service one handler
646 int (*bend_delete)(void *handle, bend_delete_rr *rr);
649 BEND_SCAN_SUCCESS, /* ok */
650 BEND_SCAN_PARTIAL /* not all entries could be found */
653 typedef struct bend_scan_rr {
654 int num_bases; /* number of elements in database list */
655 char **basenames; /* databases to search */
656 oid_value attributeset;
657 Z_ReferenceId *referenceId; /* reference ID */
658 Z_AttributesPlusTerm *term;
659 ODR stream; /* encoding stream - memory source if required */
660 ODR print; /* printing stream */
662 int *step_size; /* step size */
663 int term_position; /* desired index of term in result list/returned */
664 int num_entries; /* number of entries requested/returned */
666 struct scan_entry *entries;
667 bend_scan_status status;
675 <sect1 id="server.invocation"><title>Application Invocation</title>
678 The finished application has the following
679 invocation syntax (by way of <function>statserv_main()</function>):
683 <replaceable>appname</replaceable> [-szSiTu -a <replaceable>apdufile</replaceable> -l <replaceable>logfile</replaceable> -v <replaceable>loglevel</replaceable> -c <replaceable>config</replaceable>]
684 [listener ...]
692 <varlistentry><term><literal>-a </literal>
693 <replaceable>file</replaceable></term>
695 Specify a file for dumping PDUs (for diagnostic purposes).
696 The special name "-" sends output to
697 <literal>stderr</literal>.
698 </para></listitem></varlistentry>
700 <varlistentry><term><literal>-S</literal></term>
702 Don't fork or make threads on connection requests. This is good for
703 debugging, but not recommended for real operation: Although the
704 server is asynchronous and non-blocking, it can be nice to keep
705 a software malfunction (okay then, a crash) from affecting all
707 </para></listitem></varlistentry>
709 <varlistentry><term><literal>-T</literal></term>
711 Operate the server in threaded mode. The server creates a thread
712 for each connection rather than a fork a process. Only available
713 on UNIX systems that offers POSIX threads.
714 </para></listitem></varlistentry>
716 <varlistentry><term><literal>-s</literal></term>
718 Use the SR protocol (obsolete).
719 </para></listitem></varlistentry>
721 <varlistentry><term><literal>-z</literal></term>
723 Use the Z39.50 protocol (default). These two options complement
724 each other. You can use both multiple times on the same command
725 line, between listener-specifications (see below). This way, you
726 can set up the server to listen for connections in both protocols
727 concurrently, on different local ports.
728 </para></listitem></varlistentry>
730 <varlistentry><term><literal>-l </literal>
731 <replaceable>file</replaceable></term>
732 <listitem><para>The logfile.
733 </para></listitem></varlistentry>
735 <varlistentry><term><literal>-c </literal>
736 <replaceable>config</replaceable></term>
737 <listitem><para>A user option that serves as a specifier for some
738 sort of configuration, e.g. a filename.
739 The argument to this option is transferred to member
740 <literal>configname</literal>of the
741 <literal>statserv_options_block</literal>.
742 </para></listitem></varlistentry>
744 <varlistentry><term><literal>-v </literal>
745 <replaceable>level</replaceable></term>
747 The log level. Use a comma-separated list of members of the set
748 {fatal,debug,warn,log,all,none}.
749 </para></listitem></varlistentry>
751 <varlistentry><term><literal>-u </literal>
752 <replaceable>userid</replaceable></term>
754 Set user ID. Sets the real UID of the server process to that of the
755 given user. It's useful if you aren't comfortable with having the
756 server run as root, but you need to start it as such to bind a
758 </para></listitem></varlistentry>
760 <varlistentry><term><literal>-w </literal>
761 <replaceable>dir</replaceable></term>
764 </para></listitem></varlistentry>
766 <varlistentry><term><literal>-i</literal></term>
768 Use this to make the the server run from the
769 <application>inetd</application> server (UNIX only).
770 </para></listitem></varlistentry>
772 <varlistentry><term><literal>-install</literal></term>
774 Use this to install the server as an NT service (Windows 2000/NT only).
775 Control the server by going to the Services in the Control Panel.
776 </para></listitem></varlistentry>
778 <varlistentry><term><literal>-remove</literal></term>
780 Use this to remove the server from the NT services (Windows 2000/NT only).
781 </para></listitem></varlistentry>
783 <varlistentry><term><literal>-t </literal>
784 <replaceable>minutes</replaceable></term>
786 Idle session timeout, in minutes.
787 </para></listitem></varlistentry>
789 <varlistentry><term><literal>-k </literal>
790 <replaceable>size</replaceable></term>
792 Maximum record size/message size, in kilobytes.
793 </para></listitem></varlistentry>
799 A listener specification consists of a transport mode followed by a
800 colon (:) followed by a listener address. The transport mode is
801 either <literal>tcp</literal> or <literal>ssl</literal>.
805 For TCP and SSL, an address has the form
809 hostname | IP-number [: portnumber]
813 The port number defaults to 210 (standard Z39.50 port).
823 ssl:ssl.enterprise.com:3000
827 In both cases, the special hostname "@" is mapped to
828 the address <literal>INADDR_ANY</literal>, which causes the
829 server to listen on any local interface.
835 <!-- Keep this comment at the end of the file
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844 sgml-parent-document: "yaz.xml"
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