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NAME
zebrasrv - Zebra Server
SYNOPSIS
zebrasrv [-install] [-installa] [-remove] [-a file] [-v level] [-l file] [-u uid] [-c config]
[-f vconfig] [-C fname] [-t minutes] [-k kilobytes] [-d daemon] [-w dir] [-p pidfile] [-ziDST1]
[listener-spec...]
DESCRIPTION
Zebra is a high-performance, general-purpose structured text indexing and retrieval engine. It reads
structured records in a variety of input formats (e.g. email, XML, MARC) and allows access to them
through exact boolean search expressions and relevance-ranked free-text queries.
zebrasrv is the Z39.50 and SRU frontend server for the Zebra search engine and indexer.
On Unix you can run the zebrasrv server from the command line - and put it in the background. It may also
operate under the inet daemon. On WIN32 you can run the server as a console application or as a WIN32
Service.
OPTIONS
The options for zebrasrv are the same as those for YAZ' yaz-ztest. Option -c specifies a Zebra
configuration file - if omitted zebra.cfg is read.
-a file
Specify a file for dumping PDUs (for diagnostic purposes). The special name - (dash) sends output to
stderr.
-S
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. The server can only
accept a single connection in this mode.
-1
Like -S but after one session the server exits. This mode is for debugging only.
-T
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.
-s
Use the SR protocol (obsolete).
-z
Use the Z39.50 protocol (default). This option and -s 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.
-l file
Specify an output file for the diagnostic messages. The default is to write this information to
stderr
-c config-file
Read configuration information from config-file. The default configuration is ./zebra.cfg
-f vconfig
This specifies an XML file that describes one or more YAZ frontend virtual servers. See section
VIRTUAL HOSTS for details.
-C fname
Sets SSL certificate file name for server (PEM).
-v level
The log level. Use a comma-separated list of members of the set
{fatal,debug,warn,log,malloc,all,none}.
-u uid
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.
-w working-directory
The server changes to this working directory during before listening on incoming connections. This
option is useful when the server is operating from the inetd daemon (see -i).
-p pidfile
Specifies that the server should write its Process ID to file given by pidfile. A typical location
would be /var/run/zebrasrv.pid.
-i
Use this to make the the server run from the inetd server (UNIX only). Make sure you use the logfile
option -l in conjunction with this mode and specify the -l option before any other options.
-D
Use this to make the server put itself in the background and run as a daemon. If neither -i nor -D is
given, the server starts in the foreground.
-install
Use this to install the server as an NT service (Windows NT/2000/XP only). Control the server by
going to the Services in the Control Panel.
-installa
Use this to install and activate the server as an NT service (Windows NT/2000/XP only). Control the
server by going to the Services in the Control Panel.
-remove
Use this to remove the server from the NT services (Windows NT/2000/XP only).
-t minutes
Idle session timeout, in minutes. Default is 60 minutes.
-k size
Maximum record size/message size, in kilobytes. Default is 1024 KB (1 MB).
-d daemon
Set name of daemon to be used in hosts access file. See hosts_access(5) and tcpd(8).
A listener-address consists of an optional transport mode followed by a colon (:) followed by a listener
address. The transport mode is either a file system socket unix, a SSL TCP/IP socket ssl, or a plain
TCP/IP socket tcp (default).
For TCP, an address has the form
hostname | IP-number [: portnumber]
The port number defaults to 210 (standard Z39.50 port) for privileged users (root), and 9999 for normal
users. The special hostname "@" is mapped to the address INADDR_ANY, which causes the server to listen on
any local interface.
The default behavior for zebrasrv - if started as non-privileged user - is to establish a single TCP/IP
listener, for the Z39.50 protocol, on port 9999.
zebrasrv @
zebrasrv tcp:some.server.name.org:1234
zebrasrv ssl:@:3000
To start the server listening on the registered port for Z39.50, or on a filesystem socket, and to drop
root privileges once the ports are bound, execute the server like this from a root shell:
zebrasrv -u daemon @
zebrasrv -u daemon tcp:@:210
zebrasrv -u daemon unix:/some/file/system/socket
Here daemon is an existing user account, and the unix socket /some/file/system/socket is readable and
writable for the daemon account.
Z39.50 PROTOCOL SUPPORT AND BEHAVIOR
Z39.50 Initialization
During initialization, the server will negotiate to version 3 of the Z39.50 protocol, and the option bits
for Search, Present, Scan, NamedResultSets, and concurrentOperations will be set, if requested by the
client. The maximum PDU size is negotiated down to a maximum of 1 MB by default.
Z39.50 Search
The supported query type are 1 and 101. All operators are currently supported with the restriction that
only proximity units of type "word" are supported for the proximity operator. Queries can be arbitrarily
complex. Named result sets are supported, and result sets can be used as operands without limitations.
Searches may span multiple databases.
The server has full support for piggy-backed retrieval (see also the following section).
Z39.50 Present
The present facility is supported in a standard fashion. The requested record syntax is matched against
the ones supported by the profile of each record retrieved. If no record syntax is given, SUTRS is the
default. The requested element set name, again, is matched against any provided by the relevant record
profiles.
Z39.50 Scan
The attribute combinations provided with the termListAndStartPoint are processed in the same way as
operands in a query (see above). Currently, only the term and the globalOccurrences are returned with the
termInfo structure.
Z39.50 Sort
Z39.50 specifies three different types of sort criteria. Of these Zebra supports the attribute
specification type in which case the use attribute specifies the "Sort register". Sort registers are
created for those fields that are of type "sort" in the default.idx file. The corresponding character
mapping file in default.idx specifies the ordinal of each character used in the actual sort.
Z39.50 allows the client to specify sorting on one or more input result sets and one output result set.
Zebra supports sorting on one result set only which may or may not be the same as the output result set.
Z39.50 Close
If a Close PDU is received, the server will respond with a Close PDU with reason=FINISHED, no matter
which protocol version was negotiated during initialization. If the protocol version is 3 or more, the
server will generate a Close PDU under certain circumstances, including a session timeout (60 minutes by
default), and certain kinds of protocol errors. Once a Close PDU has been sent, the protocol association
is considered broken, and the transport connection will be closed immediately upon receipt of further
data, or following a short timeout.
Z39.50 Explain
Zebra maintains a "classic" Z39.50 Explain[1] database on the side. This database is called IR-Explain-1
and can be searched using the attribute set exp-1.
The records in the explain database are of type grs.sgml. The root element for the Explain grs.sgml
records is explain, thus explain.abs is used for indexing.
Note
Zebra must be able to locate explain.abs in order to index the Explain records properly. Zebra will
work without it but the information will not be searchable.
THE SRU SERVER
In addition to Z39.50, Zebra supports the more recent and web-friendly IR protocol SRU[2]. SRU can be
carried over SOAP or a REST-like protocol that uses HTTP GET or POST to request search responses. The
request itself is made of parameters such as query, startRecord, maximumRecords and recordSchema; the
response is an XML document containing hit-count, result-set records, diagnostics, etc. SRU can be
thought of as a re-casting of Z39.50 semantics in web-friendly terms; or as a standardisation of the
ad-hoc query parameters used by search engines such as Google and AltaVista; or as a superset of A9's
OpenSearch (which it predates).
Zebra supports Z39.50, SRU GET, SRU POST, SRU SOAP (SRW) - on the same port, recognising what protocol is
used by each incoming requests and handling them accordingly. This is a achieved through the use of Deep
Magic; civilians are warned not to stand too close.
Running zebrasrv as an SRU Server
Because Zebra supports all protocols on one port, it would seem to follow that the SRU server is run in
the same way as the Z39.50 server, as described above. This is true, but only in an uninterestingly
vacuous way: a Zebra server run in this manner will indeed recognise and accept SRU requests; but since
it doesn't know how to handle the CQL queries that these protocols use, all it can do is send failure
responses.
Note
It is possible to cheat, by having SRU search Zebra with a PQF query instead of CQL, using the
x-pquery parameter instead of query. This is a non-standard extension of CQL, and a very naughty
thing to do, but it does give you a way to see Zebra serving SRU ``right out of the box''. If you
start your favourite Zebra server in the usual way, on port 9999, then you can send your web browser
to:
http://localhost:9999/Default?version=1.1
&operation=searchRetrieve
&x-pquery=mineral
&startRecord=1
&maximumRecords=1
This will display the XML-formatted SRU response that includes the first record in the result-set
found by the query mineral. (For clarity, the SRU URL is shown here broken across lines, but the
lines should be joined together to make single-line URL for the browser to submit.)
In order to turn on Zebra's support for CQL queries, it's necessary to have the YAZ generic front-end
(which Zebra uses) translate them into the Z39.50 Type-1 query format that is used internally. And to do
this, the generic front-end's own configuration file must be used. See the section called “YAZ SERVER
VIRTUAL HOSTS”; the salient point for SRU support is that zebrasrv must be started with the
-f frontendConfigFile option rather than the -c zebraConfigFile option, and that the front-end
configuration file must include both a reference to the Zebra configuration file and the CQL-to-PQF
translator configuration file.
A minimal front-end configuration file that does this would read as follows:
<yazgfs>
<server>
<config>zebra.cfg</config>
<cql2rpn>../../tab/pqf.properties</cql2rpn>
</server>
</yazgfs>
The <config> element contains the name of the Zebra configuration file that was previously specified by
the -c command-line argument, and the <cql2rpn> element contains the name of the CQL properties file
specifying how various CQL indexes, relations, etc. are translated into Type-1 queries.
A zebra server running with such a configuration can then be queried using proper, conformant SRU URLs
with CQL queries:
http://localhost:9999/Default?version=1.1
&operation=searchRetrieve
&query=title=utah and description=epicent*
&startRecord=1
&maximumRecords=1
SRU PROTOCOL SUPPORT AND BEHAVIOR
Zebra running as an SRU server supports SRU version 1.1, including CQL version 1.1. In particular, it
provides support for the following elements of the protocol.
SRU Search and Retrieval
Zebra supports the searchRetrieve operation.
One of the great strengths of SRU is that it mandates a standard query language, CQL, and that all
conforming implementations can therefore be trusted to correctly interpret the same queries. It is with
some shame, then, that we admit that Zebra also supports an additional query language, our own Prefix
Query Format (PQF[3]). A PQF query is submitted by using the extension parameter x-pquery, in which case
the query parameter must be omitted, which makes the request not valid SRU. Please feel free to use this
facility within your own applications; but be aware that it is not only non-standard SRU but not even
syntactically valid, since it omits the mandatory query parameter.
SRU Scan
Zebra supports scan operation. Scanning using CQL syntax is the default, where the standard scanClause
parameter is used.
In addition, a mutant form of SRU scan is supported, using the non-standard x-pScanClause parameter in
place of the standard scanClause to scan on a PQF query clause.
SRU Explain
Zebra supports explain.
The ZeeRex record explaining a database may be requested either with a fully fledged SRU request (with
operation=explain and version-number specified) or with a simple HTTP GET at the server's basename. The
ZeeRex record returned in response is the one embedded in the YAZ Frontend Server configuration file that
is described in the the section called “YAZ SERVER VIRTUAL HOSTS”.
Unfortunately, the data found in the CQL-to-PQF text file must be added by hand-craft into the explain
section of the YAZ Frontend Server configuration file to be able to provide a suitable explain record.
Too bad, but this is all extreme new alpha stuff, and a lot of work has yet to be done ..
There is no linkage whatsoever between the Z39.50 explain model and the SRU explain response (well, at
least not implemented in Zebra, that is ..). Zebra does not provide a means using Z39.50 to obtain the
ZeeRex record.
Other SRU operations
In the Z39.50 protocol, Initialization, Present, Sort and Close are separate operations. In SRU, however,
these operations do not exist.
• SRU has no explicit initialization handshake phase, but commences immediately with searching,
scanning and explain operations.
• Neither does SRU have a close operation, since the protocol is stateless and each request is
self-contained. (It is true that multiple SRU request/response pairs may be implemented as multiple
HTTP request/response pairs over a single persistent TCP/IP connection; but the closure of that
connection is not a protocol-level operation.)
• Retrieval in SRU is part of the searchRetrieve operation, in which a search is submitted and the
response includes a subset of the records in the result set. There is no direct analogue of Z39.50's
Present operation which requests records from an established result set. In SRU, this is achieved by
sending a subsequent searchRetrieve request with the query cql.resultSetId=id where id is the
identifier of the previously generated result-set.
• Sorting in CQL is done within the searchRetrieve operation - in v1.1, by an explicit sort parameter,
but the forthcoming v1.2 or v2.0 will most likely use an extension of the query language, CQL
sorting[4].
It can be seen, then, that while Zebra operating as an SRU server does not provide the same set of
operations as when operating as a Z39.50 server, it does provide equivalent functionality.
SRU EXAMPLES
Surf into http://localhost:9999 to get an explain response, or use
http://localhost:9999/?version=1.1&operation=explain
See number of hits for a query
http://localhost:9999/?version=1.1&operation=searchRetrieve
&query=text=(plant%20and%20soil)
Fetch record 5-7 in Dublin Core format
http://localhost:9999/?version=1.1&operation=searchRetrieve
&query=text=(plant%20and%20soil)
&startRecord=5&maximumRecords=2&recordSchema=dc
Even search using PQF queries using the extended naughty parameter x-pquery
http://localhost:9999/?version=1.1&operation=searchRetrieve
&x-pquery=@attr%201=text%20@and%20plant%20soil
Or scan indexes using the extended extremely naughty parameter x-pScanClause
http://localhost:9999/?version=1.1&operation=scan
&x-pScanClause=@attr%201=text%20something
Don't do this in production code! But it's a great fast debugging aid.
YAZ SERVER VIRTUAL HOSTS
The Virtual hosts mechanism allows a YAZ frontend server to support multiple backends. A backend is
selected on the basis of the TCP/IP binding (port+listening address) and/or the virtual host.
A backend can be configured to execute in a particular working directory. Or the YAZ frontend may perform
CQL[5] to RPN conversion, thus allowing traditional Z39.50 backends to be offered as a SRU[2] service.
SRU Explain information for a particular backend may also be specified.
For the HTTP protocol, the virtual host is specified in the Host header. For the Z39.50 protocol, the
virtual host is specified as in the Initialize Request in the OtherInfo, OID 1.2.840.10003.10.1000.81.1.
Note
Not all Z39.50 clients allows the VHOST information to be set. For those the selection of the backend
must rely on the TCP/IP information alone (port and address).
The YAZ frontend server uses XML to describe the backend configurations. Command-line option -f specifies
filename of the XML configuration.
The configuration uses the root element yazgfs. This element includes a list of listen elements, followed
by one or more server elements.
The listen describes listener (transport end point), such as TCP/IP, Unix file socket or SSL server.
Content for a listener:
CDATA (required)
The CDATA for the listen element holds the listener string, such as tcp:@:210, tcp:server1:2100, etc.
attribute id (optional)
identifier for this listener. This may be referred to from server sections.
Note
We expect more information to be added for the listen section in a future version, such as CERT file
for SSL servers.
The server describes a server and the parameters for this server type. Content for a server:
attribute id (optional)
Identifier for this server. Currently not used for anything, but it might be for logging purposes.
attribute listenref (optional)
Specifies listener for this server. If this attribute is not given, the server is accessible from all
listener. In order for the server to be used for real, however, the virtual host must match (if
specified in the configuration).
element config (optional)
Specifies the server configuration. This is equivalent to the config specified using command line
option -c.
element directory (optional)
Specifies a working directory for this backend server. If specified, the YAZ frontend changes current
working directory to this directory whenever a backend of this type is started (backend handler
bend_start), stopped (backend handler hand_stop) and initialized (bend_init).
element host (optional)
Specifies the virtual host for this server. If this is specified a client must specify this host
string in order to use this backend.
element cql2rpn (optional)
Specifies a filename that includes CQL[5] to RPN conversion for this backend server. See CQL[5]
section in YAZ manual. If given, the backend server will only "see" a Type-1/RPN query.
element explain (optional)
Specifies SRU[2] ZeeRex content for this server - copied verbatim to the client. As things are now,
some of the Explain content seems redundant because host information, etc. is also stored elsewhere.
The format of the Explain record is described in detail, with examples, on the file at the ZeeRex[6]
web-site.
The XML below configures a server that accepts connections from two ports, TCP/IP port 9900 and a local
UNIX file socket. We name the TCP/IP server public and the other server internal.
<yazgfs>
<listen id="public">tcp:@:9900</listen>
<listen id="internal">unix:/var/tmp/socket</listen>
<server id="server1">
<host>server1.mydomain</host>
<directory>/var/www/s1</directory>
<config>config.cfg</config>
</server>
<server id="server2">
<host>server2.mydomain</host>
<directory>/var/www/s2</directory>
<config>config.cfg</config>
<cql2rpn>../etc/pqf.properties</cql2rpn>
<explain xmlns="http://explain.z3950.org/dtd/2.0/">
<serverInfo>
<host>server2.mydomain</host>
<port>9900</port>
<database>a</database>
</serverInfo>
</explain>
</server>
<server id="server3" listenref="internal">
<directory>/var/www/s3</directory>
<config>config.cfg</config>
</server>
</yazgfs>
There are three configured backend servers. The first two servers, "server1" and "server2", can be
reached by both listener addresses - since no listenref attribute is specified. In order to distinguish
between the two a virtual host has been specified for each of server in the host elements.
For "server2" elements for CQL[5] to RPN conversion is supported and explain information has been added
(a short one here to keep the example small).
The third server, "server3" can only be reached via listener "internal".
SEE ALSO
zebraidx(1)
AUTHORS
Index Data
NOTES
1. Z39.50 Explain
https://www.loc.gov/z3950/agency/markup/07.html
2. SRU
https://www.loc.gov/standards/sru/
3. PQF
http://www.indexdata.com/yaz/doc/tools.html#PQF
4. CQL sorting
http://zing.z3950.org/cql/sorting.html
5. CQL
http://www.loc.gov/standards/sru/cql/
6. ZeeRex
http://zeerex.z3950.org/