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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.
</p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="server.init"></a>5.1. Init</h3></div></div></div><pre class="synopsis">
bend_initresult (*bend_init)(bend_initrequest *r);
</pre><p>
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
<code class="function">bend_init</code> handler is passed in the call to
<code class="function">statserv_start</code>.
</p><p>
This handler is also called when operating in SRU mode - when
a connection has been made (even though SRU does not offer
this service).
</p><p>
Unlike previous versions of YAZ, the <code class="function">bend_init</code> also
serves as a handler that defines the Z39.50 services that the backend
wish to support. Pointers to <span class="emphasis"><em>all</em></span> service handlers,
including search - and fetch must be specified here in this handler.
</p><p>
The request - and result structures are defined as
</p><pre class="synopsis">
typedef struct bend_initrequest
{
/** \brief user/name/password to be read */
Z_IdAuthentication *auth;
/** \brief encoding stream (for results) */
ODR stream;
/** \brief printing stream */
ODR print;
/** \brief decoding stream (use stream for results) */
ODR decode;
/** \brief reference ID */
Z_ReferenceId *referenceId;
/** \brief peer address of client */
char *peer_name;
/** \brief character set and language negotiation
see include/yaz/z-charneg.h
*/
Z_CharSetandLanguageNegotiation *charneg_request;
/** \brief character negotiation response */
Z_External *charneg_response;
/** \brief character set (encoding) for query terms
This is NULL by default. It should be set to the native character
set that the backend assumes for query terms */
char *query_charset;
/** \brief whehter query_charset also applies to recors
Is 0 (No) by default. Set to 1 (yes) if records is in the same
character set as queries. If in doubt, use 0 (No).
*/
int records_in_same_charset;
char *implementation_id;
char *implementation_name;
char *implementation_version;
/** \brief Z39.50 sort handler */
int (*bend_sort)(void *handle, bend_sort_rr *rr);
/** \brief SRU/Z39.50 search handler */
int (*bend_search)(void *handle, bend_search_rr *rr);
/** \brief SRU/Z39.50 fetch handler */
int (*bend_fetch)(void *handle, bend_fetch_rr *rr);
/** \brief SRU/Z39.50 present handler */
int (*bend_present)(void *handle, bend_present_rr *rr);
/** \brief Z39.50 extended services handler */
int (*bend_esrequest) (void *handle, bend_esrequest_rr *rr);
/** \brief Z39.50 delete result set handler */
int (*bend_delete)(void *handle, bend_delete_rr *rr);
/** \brief Z39.50 scan handler */
int (*bend_scan)(void *handle, bend_scan_rr *rr);
/** \brief Z39.50 segment facility handler */
int (*bend_segment)(void *handle, bend_segment_rr *rr);
/** \brief SRU explain handler */
int (*bend_explain)(void *handle, bend_explain_rr *rr);
/** \brief SRU scan handler */
int (*bend_srw_scan)(void *handle, bend_scan_rr *rr);
/** \brief SRU record update handler */
int (*bend_srw_update)(void *handle, bend_update_rr *rr);
/** \brief whether named result sets are supported (0=disable, 1=enable) */
int named_result_sets;
} 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;
</pre><p>
In general, the server frontend expects that the
<code class="literal">bend_*result</code> pointer that you return is valid at
least until the next call to a <code class="literal">bend_* function</code>.
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.
</p><p>
The <code class="literal">errcode</code> should be zero if the initialization of
the backend went well. Any other value will be interpreted as an error.
The <code class="literal">errstring</code> isn't used in the current version, but
one option would be to stick it in the initResponse as a VisibleString.
The <code class="literal">handle</code> 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.
</p><p>
The <code class="literal">auth</code> member holds the authentication information
part of the Z39.50 Initialize Request. Interpret this if your serves
requires authentication.
</p><p>
The members <code class="literal">peer_name</code>,
<code class="literal">implementation_id</code>,
<code class="literal">implementation_name</code> and
<code class="literal">implementation_version</code> holds
DNS of client, ID of implementor, name
of client (Z39.50) implementation - and version.
</p><p>
The <code class="literal">bend_</code> - members are set to NULL when
<code class="function">bend_init</code> is called. Modify the pointers by
setting them to point to backend functions.
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="server.search.retrieve"></a>5.2. Search and Retrieve</h3></div></div></div><p>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.
</p><pre class="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 */
Z_OtherInformation *search_info; /* additional search info */
char *srw_sortKeys; /* holds SRU/SRW sortKeys info */
char *srw_setname; /* holds SRU/SRW generated resultsetID */
int *srw_setnameIdleTime; /* holds SRU/SRW life-time */
int estimated_hit_count; /* if hit count is estimated */
int partial_resultset; /* if result set is partial */
} bend_search_rr;
</pre><p>
The <code class="function">bend_search</code> handler is a fairly close
approximation of a protocol Z39.50 Search Request - and Response PDUs
The <code class="literal">setname</code> 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 <code class="literal">replace_set</code> is a boolean value
corresponding to the resultSetIndicator field in the protocol.
<code class="literal">num_bases/basenames</code> is a length of/array of character
pointers to the database names provided by the client.
The <code class="literal">query</code> 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
<code class="filename">include/yaz/z-core.h</code>. 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 <a class="link" href="tools.oid.html" title="2. Object Identifiers">
OID tools</a>.
</p><p>
The structure contains a number of hits, and an
<code class="literal">errcode/errstring</code> 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 <code class="literal">errstring</code>, 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.
</p><p>
The <code class="function">bend_search</code> handler is also called when
the frontend server receives a SRU SearchRetrieveRequest.
For SRU, a CQL query is usually provided by the client.
The CQL query is available as part of <code class="literal">Z_Query</code>
structure (note that CQL is now part of Z39.50 via an external).
To support CQL in existing implementations that only do Type-1,
we refer to the CQL-to-PQF tool described
<a class="link" href="tools.html#cql.to.pqf" title="1.3.3. CQL to PQF conversion">here</a>.
</p><p>
To maintain backwards compatibility, the frontend server
of yaz always assume that error codes are BIB-1 diagnostics.
For SRU operation, a Bib-1 diagnostic code is mapped to
SRU diagnostic.
</p><pre class="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 */
Odr_oid *request_format; /* format, transfer syntax (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? */
Odr_oid *output_format; /* response format/syntax (OID) */
int errcode; /* 0==success */
char *errstring; /* system error string or NULL */
int surrogate_flag; /* surrogate diagnostic */
char *schema; /* string record schema input/output */
} bend_fetch_rr;
</pre><p>
The frontend server calls the <code class="function">bend_fetch</code> handler
when it needs database records to fulfill a Z39.50 Search Request, a
Z39.50 Present Request or a SRU SearchRetrieveRequest.
The <code class="literal">setname</code> is simply the name of the result set
that holds the reference to the desired record.
The <code class="literal">number</code> is the offset into the set (with 1
being the first record in the set). The <code class="literal">format</code> field
is the record format requested by the client (See
<a class="xref" href="tools.oid.html" title="2. Object Identifiers">Section 2, “Object Identifiers”</a>).
A value of NULL for <code class="literal">format</code> indicates that the
client did not request a specific format.
The <code class="literal">stream</code> argument is an <acronym class="acronym">ODR</acronym> 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.
</p><p>
If a SRU SearchRetrieveRequest is received by the frontend server,
the <code class="literal">referenceId</code> is NULL and the
<code class="literal">format</code> (transfer syntax) is the OID for XML.
The schema for SRU is stored in both the
<code class="literal">Z_RecordComposition</code>
structure and <code class="literal">schema</code> (simple string).
</p><p>
In the structure, the <code class="literal">basename</code> is the name of the
database that holds the
record. <code class="literal">len</code> is the length of the record returned, in
bytes, and <code class="literal">record</code> is a pointer to the record.
<code class="literal">last_in_set</code> should be nonzero only if the record
returned is the last one in the given result set.
<code class="literal">errcode</code> and <code class="literal">errstring</code>, 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
<code class="literal">surrogate_flag</code> to 1 also.
</p><p>
If the <code class="literal">len</code> field has the value -1, then
<code class="literal">record</code> is assumed to point to a constructed data
type. The <code class="literal">format</code> field will be used to determine
which encoder should be used to serialize the data.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
If your backend generates structured records, it should use
<code class="function">odr_malloc()</code> on the provided stream for allocating
data: This allows the frontend server to keep track of the record sizes.
</p></div><p>
The <code class="literal">format</code> field is mapped to an object identifier
in the direct reference of the resulting EXTERNAL representation
of the record.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
The current version of YAZ only supports the direct reference mode.
</p></div><pre class="synopsis">
int (*bend_present) (void *handle, bend_present_rr *rr);
typedef struct {
char *setname; /* set name */
int start;
int number; /* record number */
Odr_oid *format; /* format, transfer syntax (OID) */
Z_ReferenceId *referenceId;/* reference ID */
Z_RecordComposition *comp; /* Formatting instructions */
ODR stream; /* encoding stream - memory source if required */
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;
</pre><p>
The <code class="function">bend_present</code> handler is called when
the server receives a Z39.50 Present Request.
The <code class="literal">setname</code>,
<code class="literal">start</code> and <code class="literal">number</code> is the
name of the result set - start position - and number of records to
be retrieved respectively. <code class="literal">format</code> and
<code class="literal">comp</code> is the preferred transfer syntax and element
specifications of the present request.
</p><p>
Note that this is handler serves as a supplement for
<code class="function">bend_fetch</code> and need not to be defined in order to
support search - and retrieve.
</p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="server.delete"></a>5.3. Delete</h3></div></div></div><p>
For back-ends that supports delete of a result set only one handler
must be defined.
</p><pre class="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;
</pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
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?
</p></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a name="server.scan"></a>5.4. Scan</h3></div></div></div><p>
For servers that wish to offer the scan service one handler
must be defined.
</p><pre class="synopsis">
int (*bend_scan)(void *handle, bend_scan_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 */
Odr_oid *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 */
/* scan term entries. The called handler does not have
to allocate this. Size of entries is num_entries (see above) */
struct scan_entry *entries;
bend_scan_status status;
int errcode;
char *errstring;
char *scanClause; /* CQL scan clause */
char *setname; /* Scan in result set (NULL if omitted) */
} bend_scan_rr;
</pre><p>
This backend server handles both Z39.50 scan
and SRU scan. In order for a handler to distinguish between SRU (CQL) scan
Z39.50 Scan , it must check for a non-NULL value of
<code class="literal">scanClause</code>.
</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
if designed today, it would be a choice using a union or similar,
but that would break binary compatibility with existing servers.
</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="server.main.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="server.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="server.invocation.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">4. Your main() Routine </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 6. Application Invocation</td></tr></table></div></body></html>
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