The proxy config file must have a root element called proxy and scoped within namespace xmlns="http://indexdata.dk/yazproxy/schema/0.9/". All information except an optional XML header must be stored within the proxy element.

     <?xml version="1.0"?>
     <proxy xmlns="http://indexdata.dk/yazproxy/schema/0.9/">
      <!-- content here .. -->
     </proxy>
    

The element target which may be repeated zero or more times with parent element proxy contains information about each backend target. The target element have two attributes: name which holds the logical name of the backend target (required) and default (optional) which (when given) specifies that the backend target is the default target - equivalent to command line option -t.

     <?xml version="1.0"?>
     <proxy xmlns="http://indexdata.dk/yazproxy/schema/0.9/">
      <target name="server1" default="1">
       <!-- description of server1 .. -->
      </target>
      <target name="server2">
       <!-- description of server2 .. -->
      </target>
     </proxy>
      
     

The url which may be repeated one or more times should be the child of the target element. The CDATA of url is the Z-URL of the backend.

Multiple url element may be used. In that case, then a client initiates a session, the proxy chooses the URL with the lowest number of active sessions, thereby distributing the load. It is assumed that each URL represents the same database (data).

The element target-timeout is the child of element target and specifies the amount in seconds before a target session is shut down.

This can also be specified on the command line by using option -T. Refer to OPTIONS in Section 10, “Proxy Manual Pages”.

The element client-timeout is the child of element target and specifies the amount in seconds before a client session is shut down.

This can also be specified on the command line by using option -i. Refer to OPTIONS in Section 10, “Proxy Manual Pages”.

The element max-sockets is the child of element target and specifies the maximum number of sockets to use for the target for all sessions using it. In other words: maximum number of Z39.50 session to the target.

The keepalive element holds information about the keepalive Z39.50 sessions. Keepalive sessions are proxy-to-backend sessions that is no longer associated with a client session.

The keepalive element which is the child of the targetholds two elements: bandwidth and pdu. The bandwidth is the maximum total bytes transferred to/from the target. If a target session exceeds this limit, it is shut down (and no longer kept alive). The pdu is the maximum number of requests sent to the target. If a target session exceeds this limit, it is shut down. The idea of these two limits is that avoid very long sessions that use resources in a backend (that leaks!).

The following sets maximum number of bytes transferred in a target session to 1 MB and maximum of requests to 400.

      <keepalive>
       <bandwidth>1048576</bandwidth>
       <pdu>400</pdu>
      </keepalive>
     

The limit section specifies bandwidth/pdu requests limits for an active session. The proxy records bandwidth/pdu requests during the last 60 seconds (1 minute). The limit may include the elements bandwidth, pdu, retrieve and search. The bandwidth measures the number of bytes transferred within the last minute. The pdu is the number of requests in the last minute. The retrieve holds the maximum records to which may be retrieved in one Present Request. The search is the maximum number of searches within the last minute.

If a bandwidth/pdu/search limit is reached the proxy will postpone the requests to the target and wait one or more seconds. The idea of the limit is to ensure that clients that downloads hundreds or thousands of records do not hurt other users.

The following sets maximum number of bytes transferred per minute to 500Kbytes, maximum number of records retrievals to 40 and maximum number of searches to 20.

      <limit>
       <bandwidth>524288</bandwidth>
       <retrieve>40</retrieve>
       <search>20</search>
      </limit>
     

The attribute element specifies accept or reject or a particular attribute type, value pair. Well-behaving targets will reject unsupported attributes on their own. This feature is useful for targets that do not gracefully handle unsupported attributes.

Attribute elements may be repeated. The proxy inspects the attribute specifications in the order as specified in the configuration file. When a given attribute specification matches a given attribute list in a query, the proxy takes appropriate action (reject, accept).

If no attribute specifications matches the attribute list in a query, it is accepted.

The attribute element has two required attributes: type which is the Attribute Type-1 type, and value which is the Attribute Type-1 value. The special value/type * matches any attribute type/value. A value may also be specified as a list with each value separated by comma, a value may also be specified as a list: low value - dash - high value.

If attribute error is given, that holds a Bib-1 diagnostic which is sent to the client if the particular type, value is part of a query.

If attribute error is not given, the attribute type, value is accepted and passed to the backend target.

A target that supports use attributes 1,4, 1000 through 1003 and no other use attributes, could use the following rules:

      <attribute type="1" value="1,4,1000-1003"/>
      <attribute type="1" value="*" error="114"/>
     

The syntax element specifies accept or reject or a particular record syntax request from the client. It also allows record conversion of XML records via XSLT.

The syntax has one required attribute: type which is the Preferred Record Syntax.

If attribute error is given, that holds a Bib-1 diagnostic which is sent to the client if the particular record syntax is part of a present - or search request.

If attribute error is not given, the record syntax is accepted and passed to the backend target.

If attribute marcxml is given, the proxy will perform MARC21 to MARCXML conversion. In this case the type should be XML. The proxy will use preferred record syntax USMARC/MARC21 or backendtype (if given) against the backend target. For the special case where backendtype is opac the proxy will convert the OPAC record to OPACXML.

When marcxml is used, yazproxy assumes that records retrieved from the backend are encoded in the MARC-8 character set. This is correct for most MARC21 based systems, but not for other MARC variants or UTF-8 based MARC21 systems. The backendcharset attribute specifies the character set of the MARC records to be converted.

If attribute backendtype is given, that holds the record syntax to be transmitted to backend.

If attribute backendelementset is given, that holds elementset to be transmitted to backend. An empty value of backendelementset has the effect of omitting any Comp-Spec (and elementset) sent to backend.

If backendelementset is omitted, the element set from client is used, except if marcxml is used. In that case (using marcxml), no Comp-Spec and no elementset is sent to backend.

If attribute stylesheet is given, the proxy will convert XML record from server via XSLT. It is important that the content from server is XML. If used in conjunction with attribute marcxml, the MARC to MARCXML/OPACXML conversion takes place before the XSLT conversion takes place.

If attribute identifier is given that is the SRU record schema identifier for the resulting output record (after MARCXML and/or XSLT conversion).

If sub element title is given (as child element of syntax, then that is the official SRU name of the resulting record schema.

If sub element name is given that is an alias for the record schema identifier. Multiple names may be specified.

       <proxy>
       <target name="mytarget">
       ..
       <syntax type="usmarc"/>
       <syntax type="xml" marcxml="1"
         identifier="info:srw/schema/1/marcxml-v1.1"
         <title>MARCXML<title>
         <name>marcxml<name>
       </syntax>
       <syntax type="xml" marcxml="1" stylesheet="MARC21slim2SRWDC.xsl"
         identifier="info:srw/schema/1/dc-v1.1">
         <title>Dublin Core<title>
         <name>dc<name>
       </syntax>
       <syntax type="*" error="238"/>
       ..
       </target>
       </proxy>
      

The explain element includes Explain information for SRU about the server in the target section. This information must have a serverInfo element with a database that this target must be available as (URL path). For example,

      <explain xmlns="http://explain.z3950.org/dtd/2.0/">     
        <serverInfo>
          <host>myhost.org</host>
          <port>8000</port>
          <database>mydatabase</database>
        </serverInfo>
        <!-- remaining Explain stuff -->
      </explain>
      
     

In the above case, the SRU service is available as http://myhost.org:8000/mydatabase.

The content of the cql2rpn element specifies the path from the working directory to a CQL-to-RPN conversion file for the server in the target section. This element is required for SRU searches to operate against Z39.50 servers that don't support CQL. Most Z39.50 servers only support Type-1/RPN so this is usually required.

See YAZ documentation for more information about the CQL to PQF conversion. See also the pqf.properties in the etc (or prefix/share/yazproxy) directory of the YAZ proxy distribution.

The element preinit is the child of element target and specifies the number of spare connection to a target. By default no spare connection are created by the proxy. If the proxy uses a target exclusive or a lot, the preinit session will ensure that target sessions have been made before the client makes a connection and will therefore reduce the connect-init handshake dramatically. Never set this to more than 5.

The element target-authentication specifies fixed authentication information to be sent to the backend target.

This element takes a an attribute type which is the authenticatin type to be used..

The element target-charset specifies the native character set that the target uses for queries.

If this is specified the proxy will act as a Z39.50 server supporting character set negotiation. And in SRU mode it will convert from UTF-8 (UNICODE) to this native character set (if possible).

The element max-clients is the child of element proxy and specifies the total number of allowed connections to targets (all targets). If this limit is reached the proxy will close the least recently used connection.

Note, that many Unix systems impose a system on the number of open files allowed in a single process, typically in the range 256 (Solaris) to 1024 (Linux). The proxy uses 2 sockets per session + a few files for logging. As a rule of thumb, ensure that 2*max-clients + 5 can be opened by the proxy process.

The element log is the child of element proxy and specifies what to be logged by the proxy.

Specify the log file with command-line option -l.

The text of the log element is a sequence of options separated by white space. See the table below:

To log communication in details between the proxy and the backend, th following configuration could be used:

      <target name="mytarget">
       <log>server-apdu server-requests</log>
      </target>
      
     

The element max-connect is a child of element proxy and specifies the maximum number of connections to be initiated within the last minute (or value of period-connect.

If the maximum number is reached the proxy will terminate the just initiated session (connection terminated).

The element max-connect is a child of element proxy and specifies the limit of number of connections to be initiated within the last minute (or value of period-connect.

If the maximum number is reached the proxy delays the first operation in the session by one second.

The element period-connect is a child of element proxy and specifies period - in the number of seconds that limit-connect and max-connect should measure connections.

If period-connect is omitted, 60 seconds is used.

The element docpath is a child of element proxy and specifies an allowed HTTP path for local file access. Using docpath the proxy may return static file content.

The value of docpath both serves as a HTTP path prefix and as a local file prefix. If a value of etc is used only URLs with the prefix /etc/ results in a local file access to the directory etc within the working directory of yazproxy.