Proxy Reference
Operating Environment The YAZ proxy is a console program. After startup it spawns a child process (except on Windows or if option -X is given). The child process is the core of the proxy and it handles all communication with clients and servers. The parent process will restart the child process if it dies unexpectedly and report the reason. For options for YAZ proxy, see . As an option, the proxy may change user identity to a less privileged user.
Choosing the Backend Server When the proxy receives a Z39.50 Initialize Request from a Z39.50 client, it determines the backend server by the following rules: If the InitializeRequest PDU from the client includes an otherInfo element with OID 1.2.840.10003.10.1000.81.1, then the contents of that element specify the server to be used, in the usual YAZ address format (typically tcp:hostname:port) as described in the Addresses section of the YAZ manual. Otherwise, the Proxy uses the default server, if one was specified in the proxy configuration file. See . Otherwise, the Proxy uses the default server, if one was specified on the command-line with the -t option. Otherwise, the proxy closes the connection with the client. If the proxy receives an SRU request, the following rules are used. If default target has Explain information with a database that matches the path of the HTTP request of SRU that backend server is used for SRU operation. Otherwise the service will return HTTP 404 (Not found).
Keep-alive Facility The keep-alive is a facility where the proxy keeps the connection to the backend server - even if the client closes the connection to the proxy. If a new or another client connects to the proxy again and requests the same backend it will be reassigned to this backend. In this case, the proxy sends an initialize response directly to the client and an initialize handshake with the backend is omitted. When a client reconnects, query and record caching works better, if the proxy assigns it to the same backend as before. And the result set (if any) is re-used. To achieve this, Index Data defined a session cookie which identifies the backend session. The cookie is defined by the client and is sent as part of the Initialize Request and passed in an otherInfo element with OID 1.2.840.10003.10.1000.81.2. Clients that do not send a cookie as part of the initialize request may still better performance, since the init handshake is saved. Refer to on how to setup configuration parameters for keepalive.
Query Caching Simple stateless clients often send identical Z39.50 searches in a relatively short period of time (e.g. in order to produce a results-list page, the next page, a single full-record, etc). And for many targets, it's much more expensive to produce a new result set than to reuse an existing one. The proxy tries to solve that by remembering the last query for each backend target, so that if an identical query is received next, it is turned into Present Requests rather than new Search Requests. In a future we release will will probably allows for an arbitrary-sized cache for targets supporting named result sets. You can enable/disable query caching using option -o.
Record Caching As an option, the proxy may also cache result set records for the last search. The proxy takes into account the Record Syntax and CompSpec. The CompSpec includes simple element set names as well. By default the cache is 200000 bytes per session.
Query Validation The Proxy may also be configured to trap particular attributes in Type-1 queries and send Bib-1 diagnostics back to the client without even consulting the backend target. This facility may be useful if a target does not properly issue diagnostics when unsupported attributes are send to it.
Record Syntax Validation The proxy may be configured to accept, reject or convert records. When accepted, the target passes search/present requests to the backend target under the assumption that the target can honor the request (In fact it may not do that). When a record is rejected because the record syntax is "unsupported" the proxy returns a diagnostic to the client. Finally, the proxy may convert records. The proxy can convert from MARC to MARCXML and thereby offer an XML version of any MARC record as long as it is ISO2709 encoded. If the proxy is compiled with libXSLT support it can also perform XSLT on XML.
Other Optimizations We've had some plans to support global caching of result set records, but this has not yet been implemented.
Proxy Configuration File The Proxy may read a configuration file using option -c followed by the filename of a config file. The config file is XML based. The YAZ proxy must be compiled with libxml2 and libXSLT support in order for the config file facility to be enabled. See for an XML schema for the configuration. To check for a config file to be well-formed, the yazproxy may be invoked without specifying a listening port, i.e. yazproxy -c myconfig.xml If this does not produce errors, the file is well-formed.
Proxy Configuration Header 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>
target 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. ]]>
url 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).
target-timeout 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 .
client-timeout 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 .
max-sockets 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.
keepalive 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>
limit 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> Typically the values in the keepalive section are mugh higher than their equivalent limit counterparts (bandwidth, pdu).
attribute 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"/>
syntax 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. MARCXML conversion To accept USMARC and offer MARCXML XML plus Dublin Core (via XSLT conversion) but the following configuration could be used: <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>
explain 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, myhost.org 8000 mydatabase ]]> In the above case, the SRU service is available as http://myhost.org:8000/mydatabase.
cql2rpn 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.
preinit 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.
target-authentication 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.. none No authentication. There is no CDATA associated with this. anonymous Anonymous authentication. There is no CDATA associated with this. open Open authentication. The CDATA consists of the open authentication string. idPass IdPass authentication. The CDATA consists of three terms: user, group and password.
target-charset 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).
max-clients 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. Using the bash shell, you can set the limit with ulimit -nno. Use ulimit -a to display limits.
log 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: Logging options Option Description client-apdu Log APDUs as reported by YAZ for the communication between the client and the proxy. This facility is equivalent to the APDU logging that happens when using option -a, however this tells the proxy to log in the same file as given by -l. server-apdu Log APDUs as reported by YAZ for the communication between the proxy and the server (backend). clients-requests Log a brief description about requests transferred between the client and the proxy. The name of the request and the size of the APDU is logged. server-requests Log a brief description about requests transferred between the proxy and the server (backend). The name of the request and the size of the APDU is logged. client-ip Log the client IP for each log entry. By default, the client IP is only logged when a new session starts.
To log communication in details between the proxy and the backend, th following configuration could be used: server-apdu server-requests ]]>
max-connect 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).
limit-connect 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.
period-connect 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.
docpath 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. Care has been taken to ensure that hostile URLs are rejected - including strings such as .. and / (absolute file system access).
Proxy Manual Pages &yaz-proxy-ref;
OtherInformation Encoding The proxy uses the OtherInformation definition to carry information about the target address and cookie. OtherInformation ::= [201] IMPLICIT SEQUENCE OF SEQUENCE{ category [1] IMPLICIT InfoCategory OPTIONAL, information CHOICE{ characterInfo [2] IMPLICIT InternationalString, binaryInfo [3] IMPLICIT OCTET STRING, externallyDefinedInfo [4] IMPLICIT EXTERNAL, oid [5] IMPLICIT OBJECT IDENTIFIER}} -- InfoCategory ::= SEQUENCE{ categoryTypeId [1] IMPLICIT OBJECT IDENTIFIER OPTIONAL, categoryValue [2] IMPLICIT INTEGER} The categoryTypeId is either OID 1.2.840.10003.10.1000.81.1, 1.2.840.10003.10.1000.81.2 for proxy target and proxy cookie respectively. The categoryValue is set to 1. The value proxy and cookie is stored in element characterInfo of the information choice.
YAZ Proxy Configuration Schema Here an XML Schema for the YAZ proxy configuration file. The schema, yazproxy.xsd is located in sub directory etc of the distribution. ]]>