Gracefully Handling 'No Data' Requests

[cjolson64]

I've been building a basic web frontend for some datasets I have in ERDDAP and am running into a bit of messiness with some of my GET requests. When I run a query where there are no results, say because there is no data between the date ranges provided or some other type of filtering, I am getting a 404 error. I think 404 makes sense if the dataset cannot be found, but I feel like this should still give a 200 just with zero results, definitely open to having my mind changed though.

The real issue though is that whenever I get a 404 in this situation it comes back without CORS headers. Has anyone else run into this situation?

[thogar-computer]

hiya @cjolson64

we have been building out a frontend over our ERDDAP instance too. Current version is
https://linkedsystems.uk/dataportal/ severing content from https://linkedsystems.uk/erddap/index.html

we have also started making smaller custom dashboards for smaller collections of data sealevel

I'll mention this to one of our developers leading on the dashboard. @SarahSidders

but for what its worth, my option is that the returning of a 404 for when data cannot be found is correct, both in terms of the restful standard and in how I would expect an API to work.

the CORS issue is interesting, do you have control over the erddap instance or can you request changes from your web admin?

[ChrisJohnNOAA]

I do think 404 is the most appropriate response in the no data found case. You should be able to parse the included message to determine whether it's a bad query:

Error {
code=404;
message="Not Found: Your query produced no matching results. Query error: For variable=longitude axis#2=longitude Constraint="[(-6.23721928665664):1:(-6.23721928665664)]": Start="-6.23721928665664" is greater than the axis maximum=-56.23721928665664 (and even -56.212771548689716).";
}

or bad dataset:

Error {
code=404;
message="Not Found: Currently unknown datasetID=asdfasdf";
}

As for the headers issue, assuming you're talking about Access-Control-* headers, Those are handled outside of ERDDAP itself (so in Tomcat or other hosting server), or at least on a server by server basis by the admins. For the Tomcat instructions you can read more in their documentation.

[srstsavage]

I do wish a different HTTP status code had originally been chosen for this situation (requested dataset found, but no data matching query parameters), maybe 400 BAD REQUEST. Changing it or making it configurable now would be very painful though.

For the CORS issue, if you're using the axiom/docker-erddap Docker image the Tomcat org.apache.catalina.filters.CorsFilter is enabled by default.

https://tomcat.apache.org/tomcat-9.0-doc/config/filter.html

The CorsFilter configuration exists in web.conf, which is imported from the Unidata/tomcat-docker image.

https://github.com/Unidata/tomcat-docker/blob/latest/web.xml#L629-L641

I'm not seeing an option to enable CORS headers on error responses for org.apache.catalina.filters.CorsFilter, so if you're using it, you may want to set env var DISABLE_CORS=1 on your ERDDAP Docker container and stand up a CORS proxy in front of ERDDAP that your frontend can hit. nginx can do it quite well, as can a number of proxies built for this exact use case.