Using YAZ proxy As mentioned in the introduction the YAZ proxy has many uses. This chapter includes a few examples. The YAZ Proxy is useful for debugging SRU/Z39.50 software, logging APDUs, redirecting Z39.50 packages through firewalls, etc. Furthermore, it offers facilities that often boost performance for connection-less Z39.50 clients such as web gateways. Unlike most other server software, the proxy runs single-threaded, single-process. Every I/O operation is non-blocking so it is very lightweight and extremely fast. It does not store any state information on the hard drive, except any log files you ask for. Using the Proxy to Log APDUs Suppose you use a commercial Z39.50 client for which you do not have source code, and it's not behaving how you think it should when running against some specific server that you have no control over. One way to diagnose the problem is to find out what packets (APDUs) are being sent and received, but not all client applications have facilities to do APDU logging. No problem. Run the proxy on a friendly machine, get it to log APDUs, and point the errant client at the proxy instead of directly at the server that's causing it problems. Suppose the server is running on, port 18398. Run the proxy on the machine of your choice, say like this: yazproxy -a - -t tcp:@:9000 (The -a - option requests APDU logging on standard output, -t specifies where the backend target is, and tcp:@:9000 tells the proxy to listen on port 9000 and accept connections from any machine.) Now change your client application's configuration so that instead of connecting to port 18398, it connects to port 9000, and start it up. It will work exactly as usual, but all the packets will be sent via the proxy, which will generate a log like this: Using a configuration file In the default backend server was specified by a command line option. The same proxy behavior can be achieved by creating a configuration with the following contents: client-apdu ]]> The proxy is started with The last target section is used for all servers except foo. Had the the last section been omitted, then only foo could be reached via the proxy. Offering SRU/Z39.50 service In order to offer SRU service we must be specify sufficient information to allow the proxy to convert from SRU to Z39.50. This involves translating CQL queries to Type-1 (also called RPN/PQF), since most Z39.50 servers do not support CQL. The conversion is specified by the cql2rpn element. We must also ensure that the server can return at least one kind of XML record (Dublin-Core recommended). An explain record for the SRU service must also be created. The following is a relatively simple configuration file for such a service. This service lives on, port 9000. The database is gils. The backend server is also (port 210) as given by url. The server may return USMARC/MARC21 (Z39.50/SRU) and MARCXML (SRU only) as specified by the syntax elements. 240 180 marcxml 0 9000 gils ]]> The conversion from CQL to RPN is specified by a file whose name, relative to the working directory, is given in the cql2rpn element. A complete Bath/DC conversion file, is provided as part of the yazproxy distribution in the etc subdirectory. Explain information is embedded in the configuration file. Note that in this example,only a few mandatory explain elements are specified. A well-behaving server should describe index sets, indexes, record schemas as well.