2 ## Copyright (c) 2000, Index Data.
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5 ## its documentation, in whole or in part, for any purpose, is hereby granted,
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18 ## WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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28 package Net::Z3950::SimpleServer;
31 use vars qw($VERSION @ISA @EXPORT @EXPORT_OK);
38 @ISA = qw(Exporter AutoLoader DynaLoader);
39 # Items to export into callers namespace by default. Note: do not export
40 # names by default without a very good reason. Use EXPORT_OK instead.
41 # Do not simply export all your public functions/methods/constants.
47 bootstrap Net::Z3950::SimpleServer $VERSION;
49 # Preloaded methods go here.
55 my $args = shift || croak "SimpleServer::new: Usage new(argument hash)";
59 carp "SimpleServer.pm: WARNING: Multithreaded server unsupported";
63 $self->{INIT} = $args->{INIT};
64 $self->{SEARCH} = $args->{SEARCH} || croak "SimpleServer.pm: ERROR: Unspecified search handler";
65 $self->{FETCH} = $args->{FETCH} || croak "SimpleServer.pm: ERROR: Unspecified fetch handler";
66 $self->{CLOSE} = $args->{CLOSE};
67 $self->{PRESENT} = $args->{PRESENT};
78 if (defined($self->{INIT})) {
79 set_init_handler($self->{INIT});
81 set_search_handler($self->{SEARCH});
82 set_fetch_handler($self->{FETCH});
83 if (defined($self->{CLOSE})) {
84 set_close_handler($self->{CLOSE});
86 if (defined($self->{PRESENT})) {
87 set_present_handler($self->{PRESENT});
94 # Autoload methods go after =cut, and are processed by the autosplit program.
98 # Below is the stub of documentation for your module. You better edit it!
102 Net::Z3950::SimpleServer - Simple Perl API for building Z39.50 servers.
106 use Net::Z3950::SimpleServer;
108 sub my_search_handler {
111 my $set_id = $args->{SETNAME};
112 my @database_list = @{ $args->{DATABASES} };
113 my $query = $args->{QUERY};
115 ## Perform the query on the specified set of databases
116 ## and return the number of hits:
118 $args->{HITS} = $hits;
121 sub my_fetch_handler { # Get a record for the user
124 my $set_id = $args->{SETNAME};
126 my $record = fetch_a_record($args->{OFFSET);
128 $args->{RECORD} = $record;
129 if (number_of_hits() == $args->{OFFSET}) { ## Last record in set?
137 ## Register custom event handlers:
139 my $handle = Net::Z3950::SimpleServer->new({
140 INIT => \&my_init_handler,
141 CLOSE => \&my_close_handler,
142 SEARCH => \&my_search_handler,
143 FETCH => \&my_fetch_handler
147 $handle->launch_server("ztest.pl", @ARGV);
151 The SimpleServer module is a tool for constructing Z39.50 "Information
152 Retrieval" servers in Perl. The module is easy to use, but it
153 does help to have an understanding of the Z39.50 query
154 structure and the construction of structured retrieval records.
156 Z39.50 is a network protocol for searching remote databases and
157 retrieving the results in the form of structured "records". It is widely
158 used in libraries around the world, as well as in the US Federal Government.
159 In addition, it is generally useful whenever you wish to integrate a number
160 of different database systems around a shared, asbtract data model.
162 The model of the module is simple: It implements a "generic" Z39.50
163 server, which invokes callback functions supplied by you to search
164 for content in your database. You can use any tools available in
165 Perl to supply the content, including modules like DBI and
168 The server will take care of managing the network connections for
169 you, and it will spawn a new process (or thread, in some
170 environments) whenever a new connection is received.
172 The programmer can specify subroutines to take care of the following type
178 - Fetching of records
179 - Closing down connection
181 Note that only the Search and Fetch handler functions are required.
182 The module can supply default responses to the other on its own.
184 After the launching of the server, all control is given away from
185 the Perl script to the server. The server calls the registered
186 subroutines to field incoming requests from Z39.50 clients.
188 A reference to an anonymous hash is passed to each handle. Some of
189 the entries of these hashes are to be considered input and others
192 The Perl programmer specifies the event handles for the server by
193 means of the the SimpleServer object constructor
195 my $handle = Net::Z3950::SimpleServer->new({
196 INIT => \&my_init_handler,
197 CLOSE => \&my_close_handler,
198 SEARCH => \&my_search_handler,
199 PRESENT => \&my_present_handler,
200 FETCH => \&my_fetch_handler });
202 After the custom event handles are declared, the server is launched
203 by means of the method
205 $handle->launch_server("MyServer.pl", @ARGV);
207 Notice, the first argument should be the name of your server
208 script (for logging purposes), while the rest of the arguments
209 are documented in the YAZ toolkit manual: The section on
210 application invocation: <http://www.indexdata.dk/yaz/yaz-7.php>
214 The init handler is called whenever a Z39.50 client is attempting
215 to logon to the server. The exchange of parameters between the
216 server and the handler is carried out via an anonymous hash reached
221 The argument hash passed to the init handler has the form
224 ## Response parameters:
226 IMP_NAME => "", ## Z39.50 Implementation name
227 IMP_VER => "", ## Z39.50 Implementation version
228 ERR_CODE => 0, ## Error code, cnf. Z39.50 manual
229 HANDLE => undef ## Handler of Perl data structure
232 The HANDLE member can be used to store any scalar value which will then
233 be provided as input to all subsequent calls (ie. for searching, record
234 retrieval, etc.). A common use of the handle is to store a reference to
235 a hash which may then be used to store session-specific parameters.
236 If you have any session-specific information (such as a list of
237 result sets or a handle to a back-end search engine of some sort),
238 it is always best to store them in a private session structure -
239 rather than leaving them in global variables in your script.
241 The Implementation name and version are only really used by Z39.50
242 client developers to see what kind of server they're dealing with.
243 Filling these in is optional.
245 The ERR_CODE should be left at 0 (the default value) if you wish to
246 accept the connection. Any other value is interpreted as a failure
247 and the client will be shown the door.
249 =head2 Search handler
251 Similarly, the search handler is called with a reference to an anony-
252 mous hash. The structure is the following:
255 ## Request parameters:
257 HANDLE => ref, ## Your session reference.
258 SETNAME => "id", ## ID of the result set
259 REPL_SET => 0, ## Replace set if already existing?
260 DATABASES => ["xxx"], ## Reference to a list of data-
262 QUERY => "query", ## The query expression
264 ## Response parameters:
266 ERR_CODE => 0, ## Error code (0=Succesful search)
267 ERR_STR => "", ## Error string
268 HITS => 0 ## Number of matches
271 Note that a search which finds 0 hits is considered successful in
272 Z39.50 terms - you should only set the ERR_CODE to a non-zero value
273 if there was a problem processing the request. The Z39.50 standard
274 provides a comprehensive list of standard diagnostic codes, and you
275 should use these whenever possible.
277 The QUERY is a tree-structure of terms combined by operators, the
278 terms being qualified by lists of attributes. The query is presented
279 to the search function in the Prefix Query Format (PQF) which is
280 used in many applications based on the YAZ toolkit. The full grammar
281 is described in the YAZ manual.
283 The following are all examples of valid queries in the PQF.
289 @or "dylan" "zimmerman"
293 @or @and bob dylan @set Result-1
295 @and @attr 1=1 "bob dylan" @attr 1=4 "slow train coming"
297 @attrset @attr 4=1 @attr 1=4 "self portrait"
299 You will need to write a recursive function or something similar to
300 parse incoming query expressions, and this is usually where a lot of
301 the work in writing a database-backend happens. Fortunately, you don't
302 need to support anymore functionality than you want to. For instance,
303 it is perfectly legal to not accept boolean operators, but you SHOULD
304 try to return good error codes if you run into something you can't or
307 =head2 Present handler
309 The presence of a present handler in a SimpleServer front-end is optional.
310 Each time a client wishes to retrieve records, the present service is
311 called. The present service allows the origin to request a certain number
312 of records retrieved from a given result set.
313 When the present handler is called, the front-end server should prepare a
314 result set for fetching. In practice, this means to get access to the
315 data from the backend database and store the data in a temporary fashion
316 for fast and efficient fetching. The present handler does *not* fetch
317 anything. This task is taken care of by the fetch handler, which will be
318 called the correct number of times by the YAZ library. More about this
320 If no present handler is implemented in the front-end, the YAZ toolkit
321 will take care of a minimum of preparations itself. This default present
322 handler is sufficient in many situations, where only a small amount of
323 records are expected to be retrieved. If on the other hand, large result
324 sets are likely to occur, the implementation of a reasonable present
325 handler can gain performance significantly.
327 The informations exchanged between client and present handle are:
330 ## Client/server request:
332 HANDLE => ref, ## Reference to datastructure
333 SETNAME => "id", ## Result set ID
334 START => xxx, ## Start position
335 COMP => "", ## Desired record composition
336 NUMBER => yyy, ## Number of requested records
339 ## Respons parameters:
341 HITS => zzz, ## Number of returned records
342 ERR_CODE => 0, ## Error code
343 ERR_STR => "" ## Error message
349 The fetch handler is asked to retrieve a SINGLE record from a given
350 result set (the front-end server will automatically call the fetch
351 handler as many times as required).
353 The parameters exchanged between the server and the fetch handler are
356 ## Client/server request:
358 HANDLE => ref ## Reference to data structure
359 SETNAME => "id" ## ID of the requested result set
360 OFFSET => nnn ## Record offset number
361 REQ_FORM => "n.m.k.l"## Client requested format OID
362 COMP => "xyz" ## Formatting instructions
366 RECORD => "" ## Record string
367 BASENAME => "" ## Origin of returned record
368 LAST => 0 ## Last record in set?
369 ERR_CODE => 0 ## Error code
370 ERR_STR => "" ## Error string
371 SUR_FLAG => 0 ## Surrogate diagnostic flag
372 REP_FORM => "n.m.k.l"## Provided format OID
375 The REP_FORM value has by default the REQ_FORM value but can be set to
376 something different if the handler desires. The BASENAME value should
377 contain the name of the database from where the returned record originates.
378 The ERR_CODE and ERR_STR works the same way they do in the search
379 handler. If there is an error condition, the SUR_FLAG is used to
380 indicate whether the error condition pertains to the record currently
381 being retrieved, or whether it pertains to the operation as a whole
382 (eg. the client has specified a result set which does not exist.)
384 If you need to return USMARC records, you might want to have a look at
385 the MARC module on CPAN, if you don't already have a way of generating
388 NOTE: The record offset is 1-indexed - 1 is the offset of the first
393 The argument hash recieved by the close handler has one element only:
397 HANDLE => ref ## Reference to data structure
400 What ever data structure the HANDLE value points at goes out of scope
401 after this call. If you need to close down a connection to your server
402 or something similar, this is the place to do it.
406 Anders Sønderberg (sondberg@indexdata.dk) and Sebastian Hammer
407 (quinn@indexdata.dk).
413 Any Perl module which is useful for accessing the database of your