[yaz-moved-to-github.git] / doc / frontend.xml

<!-- $Id: frontend.xml,v 1.5 2001-08-13 09:42:54 adam Exp $ -->
 <chapter><title id="server">Making an IR Server for Your Database</title>
  <sect1><title>Introduction</title>

   <para>
    If you aren't into documentation, a good way to learn how the
    back end interface works is to look at the <filename>backend.h</filename>
    file. Then, look at the small dummy-server in
    <filename>ztest/ztest.c</filename>. Finally, you can have a look at
    the <filename>seshigh.c</filename> file, which is where most of the
    logic of the frontend server is located. The <filename>backend.h</filename>
    file also makes a good reference, once you've chewed your way through
    the prose of this file.
   </para>

   <para>
    If you have a database system that you would like to make available by
    means of Z39.50, &yaz; basically offers your two options. You
    can use the APIs provided by the &asn;, &odr;, and &comstack;
    modules to
    create and decode PDUs, and exchange them with a client.
    Using this low-level interface gives you access to all fields and
    options of the protocol, and you can construct your server as close
    to your existing database as you like.
    It is also a fairly involved process, requiring
    you to set up an event-handling mechanism, protocol state machine,
    etc. To simplify server implementation, we have implemented a compact
    and simple, but reasonably full-functioned server-frontend that will
    handle most of the protocol mechanics, while leaving you to
    concentrate on your database interface.
   </para>

   <note>
    <para>
     The backend interface was designed in anticipation of a specific
     integration task, while still attempting to achieve some degree of
     generality. We realize fully that there are points where the
     interface can be improved significantly. If you have specific
     functions or parameters that you think could be useful, send us a
     mail (or better, sign on to the mailing list referred to in the
     top-level README file). We will try to fit good suggestions into future
     releases, to the extent that it can be done without requiring
     too many structural changes in existing applications.
    </para>
   </note>
  </sect1>
  
  <sect1><title>The Database Frontend</title>

   <para>
    We refer to this software as a generic database frontend. Your
    database system is the <emphasis>backend database</emphasis>, and the
    interface between the two is called the <emphasis>backend API</emphasis>.
    The backend API consists of a small number of function handlers and
    structure definitions. You are required to provide the
    <function>main()</function> routine for the server (which can be
    quite simple), as well as a set of handlers to match each of the prototypes.
    The interface functions that you write can use any mechanism you like
    to communicate with your database system: You might link the whole
    thing together with your database application and access it by
    function calls; you might use IPC to talk to a database server
    somewhere; or you might link with third-party software that handles
    the communication for you (like a commercial database client library).
    At any rate, the handlers will perform the tasks of:
   </para>

   <itemizedlist>

    <listitem><para>
      Initialization.
     </para></listitem>

    <listitem><para>
      Searching.
     </para></listitem>

    <listitem><para>
      Fetching records.
     </para></listitem>

    <listitem><para>
      Scanning the database index (optional - if you wish to implement SCAN).
     </para></listitem>

    <listitem><para>
      Extended Services (optional).
     </para></listitem>
    
    <listitem><para>
      Result-Set Delete (optional).
     </para></listitem>

    <listitem><para>
      Result-Set Sort (optional).
     </para></listitem>
    
   </itemizedlist>

   <para>
    (more functions will be added in time to support as much of
    Z39.50-1995 as possible).
   </para>

  </sect1>
  <sect1><title>The Backend API</title>

   <para>
    The headers files that you need to use the interface are in the
    <filename>include/yaz</filename> directory. They are called
    <filename>statserv.h</filename> and <filename>backend.h</filename>. They
    will include other files from the <filename>include/yaz</filename>
    directory, so you'll probably want to use the -I option of your
    compiler to tell it where to find the files. When you run
    <literal>make</literal> in the top-level &yaz; directory,
    everything you need to create your server is put the
    <filename>lib/libyaz.a</filename> library.
   </para>
  </sect1>

  <sect1><title>Your main() Routine</title>

   <para>
    As mentioned, your <function>main()</function> routine can be quite brief.
    If you want to initialize global parameters, or read global configuration
    tables, this is the place to do it. At the end of the routine, you should
    call the function
   </para>

   <synopsis>
int statserv_main(int argc, char **argv,
                  bend_initresult *(*bend_init)(bend_initrequest *r),
                  void (*bend_close)(void *handle));
   </synopsis>

   <para>
    The third and fourth arguments are pointers to handlers. Handler
    <function>bend_init</function> is called whenever the server receives
    an Initialize Request, so it serves as a Z39.50 session initializer. The
    <function>bend_close</function> handler is called when the session is
    closed.
   </para>

   <para>
    <function>statserv_main</function> will establish listening sockets
    according to the parameters given. When connection requests are received,
    the event handler will typically <function>fork()</function> and
    create a sub-process to handle a new connection.
    Alternatively the server may be setup to create threads for each
    connection.
    If you do use global variables and forking, you should be aware, then,
    that these cannot be shared between associations, unless you explicitly
    disable forking by command line parameters. 
   </para>
   
   <para>
    The server provides a mechanism for controlling some of its behavior
    without using command-line options. The function
   </para>

   <synopsis>
statserv_options_block *statserv_getcontrol(void);
   </synopsis>

   <para>
    will return a pointer to a <literal>struct statserv_options_block</literal>
    describing the current default settings of the server. The structure
    contains these elements:
    
    <variablelist>
     <varlistentry><term>
       <literal>int dynamic</literal></term><listitem><para>
        A boolean value, which determines whether the server
        will fork on each incoming request (TRUE), or not (FALSE). Default is
        TRUE. This flag is only read by UNIX-based servers (WIN32 based servers
        doesn't fork).
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>int threads</literal></term><listitem><para>
        A boolean value, which determines whether the server
        will create a thread on each incoming request (TRUE), or not (FALSE).
        Default is FALSE. This flag is only read by UNIX-based servers
        that offer POSIX Threads support.
        WIN32-based servers always operate in threaded mode.
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>int inetd</literal></term><listitem><para>
        A boolean value, which determines whether the server
        will operates under a UNIX INET daemon (inetd). Default is FALSE.
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>int loglevel</literal></term><listitem><para>
        Set this by ORing the constants defined in
        <filename>include/yaz/yaz-log.h</filename>.
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>char logfile&lsqb;ODR_MAXNAME+1&rsqb;</literal></term>
      <listitem><para>File for diagnostic output (&quot;&quot;: stderr).
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>char apdufile&lsqb;ODR_MAXNAME+1&rsqb;</literal></term>
      <listitem><para>
        Name of file for logging incoming and outgoing APDUs
        (&quot;&quot;: don't log APDUs, &quot;-&quot;:
        <literal>stderr</literal>).
       </para></listitem></varlistentry>

     <varlistentry><term>
      <literal>char default_listen&lsqb;1024&rsqb;</literal></term>
      <listitem><para>Same form as the command-line specification of
        listener address. &quot;&quot;: no default listener address.
        Default is to listen at &quot;tcp:@:9999&quot;. You can only
        specify one default listener address in this fashion.
       </para></listitem></varlistentry>

     <varlistentry><term>
      <literal>enum oid_proto default_proto;</literal></term>
      <listitem><para>Either <literal>PROTO_SR</literal> or
        <literal>PROTO_Z3950</literal>.
        Default is <literal>PROTO_Z39_50</literal>.
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>int idle_timeout;</literal></term>
      <listitem><para>Maximum session idletime, in minutes. Zero indicates
        no (infinite) timeout. Default is 120 minutes.
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>int maxrecordsize;</literal></term>
      <listitem><para>Maximum permissible record (message) size. Default
        is 1Mb. This amount of memory will only be allocated if a
        client requests a very large amount of records in one operation
        (or a big record).
        Set it to a lower number if you are worried about resource
        consumption on your host system.
       </para></listitem></varlistentry>

     <varlistentry><term>
       <literal>char configname&lsqb;ODR_MAXNAME+1&rsqb;</literal></term>
      <listitem><para>Passed to the backend when a new connection is received.
       </para></listitem></varlistentry>

     <varlistentry><term>
       <literal>char setuid&lsqb;ODR_MAXNAME+1&rsqb;</literal></term>
      <listitem><para>Set user id to the user specified, after binding
        the listener addresses.
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>void (*bend_start)(struct statserv_options_block *p)</literal>
      </term>
      <listitem><para>Pointer to function which is called after the
        command line options have been parsed - but before the server
        starts listening.
        For forked UNIX servers this handler is called in the mother
        process; for threaded servers this handler is called in the
        main thread.
        The default value of this pointer is NULL in which case it
        isn't invoked by the frontend server.
        When the server operates as an NT service this handler is called
        whenever the service is started. 
       </para></listitem></varlistentry>
     
     <varlistentry><term>
       <literal>void (*bend_stop)(struct statserv_options_block *p)</literal>
      </term>
      <listitem><para>Pointer to function which is called whenever the server
        has stopped listening for incoming connections. This function pointer
        has a default value of NULL in which case it isn't called.
        When the server operates as an NT service this handler is called
        whenever the service is stopped.
       </para></listitem></varlistentry>

     <varlistentry><term>
       <literal>void *handle</literal></term>
      <listitem><para>User defined pointer (default value NULL).
        This is a per-server handle that can be used to specify "user-data".
        Do not confuse this with the session-handle as returned by bend_init.
       </para></listitem></varlistentry>

    </variablelist>
   </para>

   <para>
    The pointer returned by <literal>statserv_getcontrol</literal> points to
    a static area. You are allowed to change the contents of the structure,
    but the changes will not take effect before you call
   </para>
   
   <synopsis>
void statserv_setcontrol(statserv_options_block *block);
   </synopsis>

   <note>
    <para>
     that you should generally update this structure before calling
     <function>statserv_main()</function>.
    </para>
   </note>
  </sect1>

  <sect1><title>The Backend Functions</title>

   <para>
    For each service of the protocol, the backend interface declares one or
    two functions. You are required to provide implementations of the
    functions representing the services that you wish to implement.
   </para>

   <sect2><title>Init</title>

    <synopsis>
bend_initresult (*bend_init)(bend_initrequest *r);
    </synopsis>

    <para>
     This handler is called once for each new connection request, after
     a new process/thread has been created, and an Initialize Request has
     been received from the client. The pointer to the
     <function>bend_init</function> handler is passed in the call to
     <function>statserv_start</function>.
    </para>
    <para>
     Unlike previous versions of YAZ, the <function>bend_init</function> also
     serves as a handler that defines the Z39.50 services that the backend
     wish to support. Pointers to <emphasis>all</emphasis> service handlers,
     including search - and fetch must be specified here in this handler.
    </para>
    <para>
     The request  - and result structures are defined as
    </para>

    <synopsis>
typedef struct bend_initrequest
{
    Z_IdAuthentication *auth;
    ODR stream;                /* encoding stream */
    ODR print;                 /* printing stream */
    Z_ReferenceId *referenceId;/* reference ID */
    char *peer_name;           /* dns host of peer (client) */

    char *implementation_name;
    char *implementation_version;
    int (*bend_sort) (void *handle, bend_sort_rr *rr);
    int (*bend_search) (void *handle, bend_search_rr *rr);
    int (*bend_fetch) (void *handle, bend_fetch_rr *rr);
    int (*bend_present) (void *handle, bend_present_rr *rr);
    int (*bend_esrequest) (void *handle, bend_esrequest_rr *rr);
    int (*bend_delete)(void *handle, bend_delete_rr *rr);
    int (*bend_scan)(void *handle, bend_scan_rr *rr);
    int (*bend_segment)(void *handle, bend_segment_rr *rr);
} bend_initrequest;

typedef struct bend_initresult
{
    int errcode;       /* 0==OK */
    char *errstring;   /* system error string or NULL */
    void *handle;      /* private handle to the backend module */
} bend_initresult;
    </synopsis>

    <para>
     In general, the server frontend expects that the
     <literal>bend_*result</literal> pointer that you return is valid at
     least until the next call to a <literal>bend_* function</literal>.
     This applies to all of the functions described herein. The parameter
     structure passed to you in the call belongs to the server frontend, and
     you should not make assumptions about its contents after the current
     function call has completed. In other words, if you want to retain any
     of the contents of a request structure, you should copy them.
    </para>

    <para>
     The <literal>errcode</literal> should be zero if the initialization of
     the backend went well. Any other value will be interpreted as an error.
     The <literal>errstring</literal> isn't used in the current version, but
     one option would be to stick it in the initResponse as a VisibleString.
     The <literal>handle</literal> is the most important parameter. It should
     be set to some value that uniquely identifies the current session to
     the backend implementation. It is used by the frontend server in any
     future calls to a backend function.
     The typical use is to set it to point to a dynamically allocated state
     structure that is private to your backend module.
    </para>

    <para>
     The <literal>auth</literal> member holds the authentication information
     part of the Z39.50 Initialize Request. Interpret this if your serves
     requires authentication. 
    </para>

    <para>
     The members <literal>peer_name</literal>,
     <literal>implementation_name</literal> and
     <literal>implementation_version</literal> holds DNS of client, name
     of client (Z39.50) implementation - and version.
    </para>

    <para>
     The <literal>bend_</literal> - members are set to NULL when
     <function>bend_init</function> is called. Modify the pointers by
     setting them to point to backend functions.
    </para>

   </sect2>

   <sect2><title>Search and retrieve</title>

    <para>We now describe the handlers that are required to support search -
     and retrieve. You must support two functions - one for search - and one
     for fetch (retrieval of one record). If desirable you can provide a
     third handler which is called when a present request is received which
     allows you to optimize retrieval of multiple-records.
    </para>

    <synopsis>
int (*bend_search) (void *handle, bend_search_rr *rr);

typedef struct {
    char *setname;             /* name to give to this set */
    int replace_set;           /* replace set, if it already exists */
    int num_bases;             /* number of databases in list */
    char **basenames;          /* databases to search */
    Z_ReferenceId *referenceId;/* reference ID */
    Z_Query *query;            /* query structure */
    ODR stream;                /* encode stream */
    ODR decode;                /* decode stream */
    ODR print;                 /* print stream */

    bend_request request;
    bend_association association;
    int *fd;
    int hits;                  /* number of hits */
    int errcode;               /* 0==OK */
    char *errstring;           /* system error string or NULL */
} bend_search_rr;

    </synopsis>

    <para>
     The <function>bend_search</function> handler is a fairly close
     approximation of a protocol Search Request - and Response PDUs
     The <literal>setname</literal> is the resultSetName from the protocol.
     You are required to establish a mapping between the set name and whatever
     your backend database likes to use.
     Similarly, the <literal>replace_set</literal> is a boolean value
     corresponding to the resultSetIndicator field in the protocol.
     <literal>num_bases/basenames</literal> is a length of/array of character
     pointers to the database names provided by the client.
     The <literal>query</literal> is the full query structure as defined in
     the protocol ASN.1 specification.
     It can be either of the possible query types, and it's up to you to
     determine if you can handle the provided query type.
     Rather than reproduce the C interface here, we'll refer you to the
     structure definitions in the file
     <filename>include/yaz/z-core.h</filename>. If you want to look at the
     attributeSetId OID of the RPN query, you can either match it against
     your own internal tables, or you can use the
     <literal>oid_getentbyoid</literal> function provided by &yaz;.
    </para>

    <para>
     The structure contains a number of hits, and an
     <literal>errcode/errstring</literal> pair. If an error occurs
     during the search, or if you're unhappy with the request, you should
     set the errcode to a value from the BIB-1 diagnostic set. The value
     will then be returned to the user in a nonsurrogate diagnostic record
     in the response. The <literal>errstring</literal>, if provided, will
     go in the addinfo field. Look at the protocol definition for the
     defined error codes, and the suggested uses of the addinfo field.
    </para>


    <synopsis>
int (*bend_fetch) (void *handle, bend_fetch_rr *rr);

typedef struct bend_fetch_rr {
    char *setname;             /* set name */
    int number;                /* record number */
    Z_ReferenceId *referenceId;/* reference ID */
    oid_value request_format;  /* One of the CLASS_RECSYN members */
    int *request_format_raw;   /* same as above (raw OID) */
    Z_RecordComposition *comp; /* Formatting instructions */
    ODR stream;                /* encoding stream - memory source if req */
    ODR print;                 /* printing stream */

    char *basename;            /* name of database that provided record */
    int len;                   /* length of record or -1 if structured */
    char *record;              /* record */
    int last_in_set;           /* is it?  */
    oid_value output_format;   /* format */
    int *output_format_raw;    /* used instead of above if not-null */
    int errcode;               /* 0==success */
    char *errstring;           /* system error string or NULL */
    int surrogate_flag;        /* surrogate diagnostic */
} bend_fetch_rr;
    </synopsis>

    <para>
     The frontend server calls the <function>bend_fetch</function> handler
     when it needs database records to fulfill a Search Request or a Present
     Request.
     The <literal>setname</literal> is simply the name of the result set
     that holds the reference to the desired record.
     The <literal>number</literal> is the offset into the set (with 1
     being the first record in the set). The <literal>format</literal> field
     is the record format requested by the client (See section
     <link linkend="oid">Object Identifiers</link>). The value
     <literal>VAL_NONE</literal> indicates that the client did not
     request a specific format. The <literal>stream</literal> argument
     is an &odr; stream which should be used for
     allocating space for structured data records.
     The stream will be reset when all records have been assembled, and
     the response package has been transmitted.
     For unstructured data, the backend is responsible for maintaining a
     static or dynamic buffer for the record between calls.
    </para>

    <para>
     In the structure, the <literal>basename</literal> is the name of the
     database that holds the
     record. <literal>len</literal> is the length of the record returned, in
     bytes, and <literal>record</literal> is a pointer to the record.
     <literal>Last_in_set</literal> should be nonzero only if the record
     returned is the last one in the given result set.
     <literal>errcode</literal> and <literal>errstring</literal>, if
     given, will be interpreted as a global error pertaining to the
     set, and will be returned in a non-surrogate-diagnostic.
     If you wish to return the error as a surrogate-diagnostic
     (local error) you can do this by setting
     <literal>surrogate_flag</literal> to 1 also.
    </para>

    <para>
     If the <literal>len</literal> field has the value -1, then
     <literal>record</literal> is assumed to point to a constructed data
     type. The <literal>format</literal> field will be used to determine
     which encoder should be used to serialize the data.
    </para>

    <note>
     <para>
      If your backend generates structured records, it should use
      <function>odr_malloc()</function> on the provided stream for allocating
      data: This allows the frontend server to keep track of the record sizes.
     </para>
    </note>

    <para>
     The <literal>format</literal> field is mapped to an object identifier
     in the direct reference of the resulting EXTERNAL representation
     of the record.
    </para>

    <note>
     <para>
      The current version of &yaz; only supports the direct reference mode.
     </para>
    </note>

    <synopsis>
int (*bend_present) (void *handle, bend_present_rr *rr);

typedef struct {
    char *setname;             /* set name */
    int start;
    int number;                /* record number */
    oid_value format;          /* One of the CLASS_RECSYN members */
    Z_ReferenceId *referenceId;/* reference ID */
    Z_RecordComposition *comp; /* Formatting instructions */
    ODR stream;                /* encoding stream */
    ODR print;                 /* printing stream */
    bend_request request;
    bend_association association;

    int hits;                  /* number of hits */
    int errcode;               /* 0==OK */
    char *errstring;           /* system error string or NULL */
} bend_present_rr;
    </synopsis>

    <para>
     The <function>bend_present</function> handler is called when
     the server receives a Present Request. The <literal>setname</literal>,
     <literal>start</literal> and <literal>number</literal> is the
     name of the result set - start position - and number of records to
     be retrieved respectively. <literal>format</literal> and
     <literal>comp</literal> is the preferred transfer syntax and element
     specifications of the present request.
    </para>
    <para>
     Note that this is handler serves as a supplement for
     <function>bend_fetch</function> and need not to be defined in order to
     support search - and retrieve. 
    </para>

   </sect2>

   <sect2><title>Delete</title>

    <para>
     For back-ends that supports delete of a result set only one handler
     must be defined.
    </para>

    <synopsis>
int (*bend_delete)(void *handle, bend_delete_rr *rr);

typedef struct bend_delete_rr {
    int function;
    int num_setnames;
    char **setnames;
    Z_ReferenceId *referenceId;
    int delete_status;      /* status for the whole operation */
    int *statuses;          /* status each set - indexed as setnames */
    ODR stream;
    ODR print; 
} bend_delete_rr;
    </synopsis>

    <note>
     <para>
      The delete set function definition is rather primitive, mostly because
      we have had no practical need for it as of yet. If someone wants
      to provide a full delete service, we'd be happy to add the
      extra parameters that are required. Are there clients out there
      that will actually delete sets they no longer need?
     </para>
    </note>

   </sect2>

   <sect2><title>scan</title>

    <para>
     For servers that wish to offer the scan service one handler
     must be defined.
    </para>

    <synopsis>
int (*bend_delete)(void *handle, bend_delete_rr *rr);

typedef enum {
    BEND_SCAN_SUCCESS,  /* ok */
    BEND_SCAN_PARTIAL   /* not all entries could be found */
} bend_scan_status;

typedef struct bend_scan_rr {
    int num_bases;      /* number of elements in databaselist */
    char **basenames;   /* databases to search */
    oid_value attributeset;
    Z_ReferenceId *referenceId; /* reference ID */
    Z_AttributesPlusTerm *term;
    ODR stream;         /* encoding stream - memory source if required */
    ODR print;          /* printing stream */

    int *step_size;     /* step size */
    int term_position;  /* desired index of term in result list/returned */
    int num_entries;    /* number of entries requested/returned */

    struct scan_entry *entries;
    bend_scan_status status;
    int errcode;
    char *errstring;
} bend_scan_rr;
    </synopsis>
   </sect2>
  </sect1>

  <sect1><title>Application Invocation</title>

   <para>
    The finished application has the following
    invocation syntax (by way of <function>statserv_main()</function>):
   </para>

   <synopsis>
    <replaceable>appname</replaceable> &lsqb;-szSiTu -a <replaceable>apdufile</replaceable> -l <replaceable>logfile</replaceable> -v <replaceable>loglevel</replaceable> -c <replaceable>config</replaceable>&rsqb;
    &lsqb;listener ...&rsqb;
   </synopsis>

   <para>
    The options are

    <variablelist>

     <varlistentry><term>-a <replaceable>file</replaceable></term>
      <listitem><para>
        Specify a file for dumping PDUs (for diagnostic purposes).
        The special name &quot;-&quot; sends output to
        <literal>stderr</literal>.
       </para></listitem></varlistentry>

     <varlistentry><term>-S</term>
      <listitem><para>
        Don't fork or make threads on connection requests. This is good for
        debugging, but not recommended for real operation: Although the
        server is asynchronous and non-blocking, it can be nice to keep
        a software malfunction (okay then, a crash) from affecting all
        current users.
       </para></listitem></varlistentry>

     <varlistentry><term>-T</term>
      <listitem><para>
        Operate the server in threaded mode. The server creates a thread
        for each connection rather than a fork a process. Only available
        on UNIX systems that offers POSIX threads.
       </para></listitem></varlistentry>

     <varlistentry><term>-s</term>
      <listitem><para>
        Use the SR protocol (obsolete).
       </para></listitem></varlistentry>

     <varlistentry><term>-z</term>
      <listitem><para>
        Use the Z39.50 protocol (default). These two options complement
        each other. You can use both multiple times on the same command
        line, between listener-specifications (see below). This way, you
        can set up the server to listen for connections in both protocols
        concurrently, on different local ports.
       </para></listitem></varlistentry>

     <varlistentry><term>-l <replaceable>file</replaceable></term>
      <listitem><para>The logfile.
       </para></listitem></varlistentry>

     <varlistentry><term>-c <replaceable>config</replaceable></term>
      <listitem><para>A user option that serves as a specifier for some
        sort of configuration, e.g. a filename.
        The argument to this option is transferred to member
        <literal>configname</literal>of the
        <literal>statserv_options_block</literal>.
       </para></listitem></varlistentry>

     <varlistentry><term>-v <replaceable>level</replaceable></term>
      <listitem><para>
        The log level. Use a comma-separated list of members of the set
        {fatal,debug,warn,log,all,none}.
       </para></listitem></varlistentry>

     <varlistentry><term>-u <replaceable>userid</replaceable></term>
      <listitem><para>
        Set user ID. Sets the real UID of the server process to that of the
        given user. It's useful if you aren't comfortable with having the
        server run as root, but you need to start it as such to bind a
        privileged port.
       </para></listitem></varlistentry>

     <varlistentry><term>-w <replaceable>dir</replaceable></term>
      <listitem><para>
        Working directory.
       </para></listitem></varlistentry>

     <varlistentry><term>-i</term>
      <listitem><para>
        Use this when running from the <application>inetd</application> server.
       </para></listitem></varlistentry>

     <varlistentry><term>-t <replaceable>minutes</replaceable></term>
      <listitem><para>
        Idle session timeout, in minutes.
       </para></listitem></varlistentry>

     <varlistentry><term>-k <replaceable>size</replaceable></term>
      <listitem><para>
        Maximum record size/message size, in kilobytes.
       </para></listitem></varlistentry>

    </variablelist>
   </para>

   <para>
    A listener specification consists of a transport mode followed by a
    colon (:) followed by a listener address. The transport mode is
    either <literal>osi</literal> or <literal>tcp</literal>.
   </para>

   <para>
    For TCP, an address has the form
   </para>

   <synopsis>
    hostname | IP-number &lsqb;: portnumber&rsqb;
   </synopsis>

   <para>
    The port number defaults to 210 (standard Z39.50 port).
   </para>

   <para>
    For osi, the address form is
   </para>

   <synopsis>
    &lsqb;t-selector /&rsqb; hostname | IP-number &lsqb;: portnumber&rsqb;
   </synopsis>

   <para>
    The transport selector is given as a string of hex digits (with an even
    number of digits). The default port number is 102 (RFC1006 port).
   </para>

   <para>
    Examples
   </para>

   <screen>
    tcp:dranet.dra.com

    osi:0402/dbserver.osiworld.com:3000
   </screen>

   <para>
    In both cases, the special hostname &quot;@&quot; is mapped to
    the address INADDR_ANY, which causes the server to listen on any local
    interface. To start the server listening on the registered ports for
    Z39.50 and SR over OSI/RFC1006, and to drop root privileges once the
    ports are bound, execute the server like this (from a root shell):
   </para>

   <screen>
    my-server -u daemon tcp:@ -s osi:@
   </screen>

   <para>
    You can replace <literal>daemon</literal> with another user, eg. your
    own account, or a dedicated IR server account.
    <literal>my-server</literal> should be the name of your
    server application. You can test the procedure with the
    <application>yaz-ztest</application> application.
   </para>

  </sect1>
 </chapter>

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