1 package Net::Z3950::SimpleServer;
4 use vars qw($VERSION @ISA @EXPORT @EXPORT_OK);
11 @ISA = qw(Exporter AutoLoader DynaLoader);
12 # Items to export into callers namespace by default. Note: do not export
13 # names by default without a very good reason. Use EXPORT_OK instead.
14 # Do not simply export all your public functions/methods/constants.
20 bootstrap Net::Z3950::SimpleServer $VERSION;
22 # Preloaded methods go here.
28 my $args = shift || croak "SimpleServer::new: Usage new(argument hash)";
32 carp "SimpleServer.pm: WARNING: Multithreaded server unsupported";
36 $self->{INIT} = $args->{INIT};
37 $self->{SEARCH} = $args->{SEARCH} || croak "SimpleServer.pm: ERROR: Unspecified search handler";
38 $self->{FETCH} = $args->{FETCH} || croak "SimpleServer.pm: ERROR: Unspecified fetch handler";
39 $self->{CLOSE} = $args->{CLOSE};
50 if (defined($self->{INIT})) {
51 set_init_handler($self->{INIT});
53 set_search_handler($self->{SEARCH});
54 set_fetch_handler($self->{FETCH});
55 if (defined($self->{CLOSE})) {
56 set_close_handler($self->{CLOSE});
63 # Autoload methods go after =cut, and are processed by the autosplit program.
67 # Below is the stub of documentation for your module. You better edit it!
71 Zfront - Simple Perl API for building Z39.50 servers.
77 sub my_search_handler {
80 my $set_id = $args->{SETNAME};
81 my @database_list = @{ $args->{DATABASES} };
82 my $query = $args->{QUERY};
84 ## Perform the query on the specified set of databases
85 ## and return the number of hits:
87 $args->{HITS} = $hits;
90 sub my_fetch_handler { # Get a record for the user
93 my $set_id = $args->{SETNAME};
95 my $record = fetch_a_record($args->{OFFSET);
97 $args->{RECORD} = $record;
98 $args->{LEN} = length($record);
99 if (number_of_hits() == $args->{OFFSET}) { ## Last record in set?
107 ## Register custom event handlers:
109 Zfront::set_search_handler(\&my_search_handler);
110 Zfront::set_fetch_handler(\&my_fetch_handler);
114 Zfront::start_server("mytestserver", @ARGV);
118 The Zfront module is a tool for constructing Z39.50 "Information
119 Retrieval" servers in Perl. The module is easy to use, but it
120 does help to have an understanding of the Z39.50 query
121 structure and the construction of structured retrieval records.
123 Z39.50 is a network protocol for searching remote databases and
124 retrieving the results in the form of structured "records". It is widely
125 used in libraries around the world, as well as in the US Federal Government.
126 In addition, it is generally useful whenever you wish to integrate a number
127 of different database systems around a shared, asbtract data model.
129 The model of the module is simple: It implements a "generic" Z39.50
130 server, which invokes callback functions supplied by you to search
131 for content in your database. You can use any tools available in
132 Perl to supply the content, including modules like DBI and
135 The server will take care of managing the network connections for
136 you, and it will spawn a new process (or thread, in some
137 environments) whenever a new connection is received.
139 The programmer can specify subroutines to take care of the following type
144 - Fetching of records
145 - Closing down connection
147 Note that only the Search and Fetch handler functions are required.
148 The module can supply default responses to the other on its own.
150 After the launching of the server, all control is given away from
151 the Perl script to the server. The server calls the registered
152 subroutines to field incoming requests from Z39.50 clients.
154 A reference to an anonymous hash is passed to each handle. Some of
155 the entries of these hashes are to be considered input and others
158 The Perl programmer specifies the event handles for the server by
159 means of the subroutines
161 Zfront::set_init_handler(\&my_init_handler);
162 Zfront::set_search_handler(\&my_search_handler);
163 Zfront::set_fetch_handler(\&my_fetch_handler);
164 Zfront::set_close_handler(\&my_close_handler);
166 After each handle is declared, the server is launched by means of
169 Zfront::start_server($script_name, @ARGV);
171 Notice, the first argument should be the name of your server
172 script (for logging purposes), while the rest of the arguments
173 are documented in the YAZ toolkit manual: The section on
174 application invocation: <http://www.indexdata.dk/yaz/yaz-7.php>
178 The init handler is called whenever a Z39.50 client is attempting
179 to logon to the server. The exchange of parameters between the
180 server and the handler is carried out via an anonymous hash reached
185 The argument hash passed to the init handler has the form
188 ## Response parameters:
190 IMP_NAME => "" ## Z39.50 Implementation name
191 IMP_VER => "" ## Z39.50 Implementation version
192 ERR_CODE => 0 ## Error code, cnf. Z39.50 manual
193 HANDLE => undef ## Handler of Perl data structure
196 The HANDLE member can be used to store any scalar value which will then
197 be provided as input to all subsequent calls (ie. for searching, record
198 retrieval, etc.). A common use of the handle is to store a reference to
199 a hash which may then be used to store session-specific parameters.
200 If you have any session-specific information (such as a list of
201 result sets or a handle to a back-end search engine of some sort),
202 it is always best to store them in a private session structure -
203 rather than leaving them in global variables in your script.
205 The Implementation name and version are only really used by Z39.50
206 client developers to see what kind of server they're dealing with.
207 Filling these in is optional.
209 The ERR_CODE should be left at 0 (the default value) if you wish to
210 accept the connection. Any other value is interpreted as a failure
211 and the client will be shown the door.
213 =head2 Search handler
215 Similarly, the search handler is called with a reference to an anony-
216 mous hash. The structure is the following:
219 ## Request parameters:
221 HANDLE => ref ## Your session reference.
222 SETNAME => "id" ## ID of the result set
223 REPL_SET => 0 ## Replace set if already existing?
224 DATABASES => ["xxx"] ## Reference to a list of data-
226 QUERY => "query" ## The query expression
228 ## Response parameters:
230 ERR_CODE => 0 ## Error code (0=Succesful search)
231 ERR_STR => "" ## Error string
232 HITS => 0 ## Number of matches
235 Note that a search which finds 0 hits is considered successful in
236 Z39.50 terms - you should only set the ERR_CODE to a non-zero value
237 if there was a problem processing the request. The Z39.50 standard
238 provides a comprehensive list of standard diagnostic codes, and you
239 should use these whenever possible.
241 The QUERY is a tree-structure of terms combined by operators, the
242 terms being qualified by lists of attributes. The query is presented
243 to the search function in the Prefix Query Format (PQF) which is
244 used in many applications based on the YAZ toolkit. The full grammar
245 is described in the YAZ manual.
247 The following are all examples of valid queries in the PQF.
253 @or "dylan" "zimmerman"
257 @or @and bob dylan @set Result-1
259 @and @attr 1=1 "bob dylan" @attr 1=4 "slow train coming"
261 @attrset @attr 4=1 @attr 1=4 "self portrait"
263 You will need to write a recursive function or something similar to
264 parse incoming query expressions, and this is usually where a lot of
265 the work in writing a database-backend happens. Fortunately, you don't
266 need to support anymore functionality than you want to. For instance,
267 it is perfectly legal to not accept boolean operators, but you SHOULD
268 try to return good error codes if you run into something you can't or
273 The fetch handler is asked to retrieve a SINGLE record from a given
274 result set (the front-end server will automatically call the fetch
275 handler as many times as required).
277 The parameters exchanged between the server and the fetch handler are
280 ## Client/server request:
282 HANDLE => ref ## Reference to data structure
283 SETNAME => "id" ## ID of the requested result set
284 OFFSET => nnn ## Record offset number
285 REQ_FORM => "USMARC" ## Client requested record format
289 RECORD => "" ## Record string
290 LEN => 0 ## Length of record string
291 BASENAME => "" ## Origin of returned record
292 LAST => 0 ## Last record in set?
293 ERR_CODE => 0 ## Error code
294 ERR_STR => "" ## Error string
295 SUR_FLAG => 0 ## Surrogate diagnostic flag
296 REP_FORM => "USMARC" ## Provided record format
299 The REP_FORM value has by default the REQ_FORM value but can be set to
300 something different if the handler desires. The BASENAME value should
301 contain the name of the database from where the returned record originates.
302 The ERR_CODE and ERR_STR works the same way they do in the search
303 handler. If there is an error condition, the SUR_FLAG is used to
304 indicate whether the error condition pertains to the record currently
305 being retrieved, or whether it pertains to the operation as a whole
306 (eg. the client has specified a result set which does not exist.)
308 Record formats are currently carried as strings (eg. USMARC, TEXT_XML,
309 SUTRS), but this will probably change to proper OID strings in the
310 future (not to worry, though, the module will supply constant values
311 for the common OIDs). If you need to return USMARC records, you might
312 want to have a look at the MARC module on CPAN, if you don't already
313 have a way of generating these.
315 NOTE: The record offset is 1-indexed - 1 is the offset of the first
320 The argument hash recieved by the close handler has one element only:
324 HANDLE => ref ## Reference to data structure
327 What ever data structure the HANDLE value points at goes out of scope
328 after this call. If you need to close down a connection to your server
329 or something similar, this is the place to do it.
333 Anders Sønderberg (sondberg@indexdata.dk) and Sebastian Hammer
334 (quinn@indexdata.dk).
340 Any Perl module which is useful for accessing the database of your