bend_initresult (*bend_init)(bend_initrequest *r);
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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
bend_init handler is passed in the call to
statserv_start.
Unlike previous versions of YAZ, the bend_init also
serves as a handler that defines the Z39.50 services that the backend
wish to support. Pointers to all service handlers,
including search - and fetch must be specified here in this handler.
The request - and result structures are defined as
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_id;
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;
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In general, the server frontend expects that the
bend_*result pointer that you return is valid at
least until the next call to a bend_* function.
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.
The errcode should be zero if the initialization of
the backend went well. Any other value will be interpreted as an error.
The errstring isn't used in the current version, but
one option would be to stick it in the initResponse as a VisibleString.
The handle 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.
The auth member holds the authentication information
part of the Z39.50 Initialize Request. Interpret this if your serves
requires authentication.
The members peer_name,
implementation_id,
implementation_name and
implementation_version holds
DNS of client, ID of implementor, name
of client (Z39.50) implementation - and version.
The bend_ - members are set to NULL when
bend_init is called. Modify the pointers by
setting them to point to backend functions.
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.
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;
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The bend_search handler is a fairly close
approximation of a protocol Search Request - and Response PDUs
The setname 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 replace_set is a boolean value
corresponding to the resultSetIndicator field in the protocol.
num_bases/basenames is a length of/array of character
pointers to the database names provided by the client.
The query 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
include/yaz/z-core.h. 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
oid_getentbyoid function provided by YAZ.
The structure contains a number of hits, and an
errcode/errstring 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 errstring, 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.
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;
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The frontend server calls the bend_fetch handler
when it needs database records to fulfill a Search Request or a Present
Request.
The setname is simply the name of the result set
that holds the reference to the desired record.
The number is the offset into the set (with 1
being the first record in the set). The format field
is the record format requested by the client (See section
Object Identifiers). The value
VAL_NONE indicates that the client did not
request a specific format. The stream 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.
In the structure, the basename is the name of the
database that holds the
record. len is the length of the record returned, in
bytes, and record is a pointer to the record.
Last_in_set should be nonzero only if the record
returned is the last one in the given result set.
errcode and errstring, 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
surrogate_flag to 1 also.
If the len field has the value -1, then
record is assumed to point to a constructed data
type. The format field will be used to determine
which encoder should be used to serialize the data.
Note:
If your backend generates structured records, it should use
odr_malloc() on the provided stream for allocating
data: This allows the frontend server to keep track of the record sizes.
The format field is mapped to an object identifier
in the direct reference of the resulting EXTERNAL representation
of the record.
Note:
The current version of YAZ only supports the direct reference mode.
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;
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The bend_present handler is called when
the server receives a Present Request. The setname,
start and number is the
name of the result set - start position - and number of records to
be retrieved respectively. format and
comp is the preferred transfer syntax and element
specifications of the present request.
Note that this is handler serves as a supplement for
bend_fetch and need not to be defined in order to
support search - and retrieve.