Java-based server which works with Java-based web servers like Tomcat

There are presently four or more different Java server implementations. It would be useful to have a framework which handles the "HAPI parts" of the server, such as input validation and data handling, so that those setting up servers can focus on the data sources feeding into the server.

This will be a Java servlet which implements the HAPI protocol (version 3.1), using plugins written and maintained by the data steward. How these plugins connect will be documented below, and may evolve as the server matures, but the intent is that plugins for the Python server might also be used with this server implementation.

Much of this is inspired by the lessons learned implementing Das2Servers, where a perl script would hand off control to a reader, which would generate a stream of data on stdout which would go through the server and then out to the client. The Das2Server would perform additional operations, such as data reduction, before sending out the stream to the client. The state-of-the-art Das2Server is implemented in Python and provides caches of reduced data. The HAPI server has similarities, except that subsetting and formatting must be done to service the request.

This will provide a number of features which the other implementations may be missing. The mature HAPI server will handle input validation, protecting the server from hostile attacks. It may provide caching of data when the readers are slow, and also validate that reader responses are correct. Readers should be allowed to be sloppy, so that boilerplate code for subsetting needn't appear in each reader.

Last, we intend to support use with Docker containers, so that it can be set up easily at such sites. A war file will be the initial target and Docker container will be provided later.

There are a few groups who may use this server immediately. The HAPI server for the CDAWeb group's SSCWeb service is currently implemented as a secondary pass-through server (that calls the non-HAPI server and reformats the response as HAPI), so a full Java implementation could move this beyond the kind of web-scraping approach. ESAC intends to set up a HAPI server and is interested in this framework, and we hope to set up an initial version of the server in late May 2022. PDS-PPI has an existing server which might be more easily maintained using this framework. The CDAWeb server has known problems which need to be resolved.

• Initial implementation will be in March 2022.
• Deployment of support for SSCWeb at CDAWeb in April 2022.
• Containerize and deploy for testing at ESAC May 2022.
• Code matures over the next year

When changes are pushed to the github server, the war file is rebuilt and will be available within a minute or two at https://cottagesystems.com/autoplot/git/server-java/HapiServer/dist/HapiServer.war

For installation instuctions, see the wiki: https://github.com/hapi-server/server-java/wiki.