HAPI: An API for Streaming ASCII Data over HTTP

The Heliophysics Application Programming Interface (HAPI) is a recently developed standard for serving time series data over HTTP. The output format is CSV ASCII and a server may support an optional binary format. The primary design considerations were (1) The metadata provided should be at a minimum that which is required for a program reading the data to produce a plot with sensible labels, (2) that data be delivered as a single stream (no individual files) and (3) A basic HAPI server should be straightforward to implement. One of the use cases the standard was developed for is a data provider who has a collection of files in directories who wants to give users the ability to access the data through an API. Here we describe (1) The HAPI API, (2) Autoplot, IDL, Javascript, MATLAB, and Python client scripts developed to interface with a HAPI server, and (3) A reference server that allows a data provider to serve HAPI data provided that they have a command line program that can emit a simple ASCII-formatted stream given a time range. We conclude by noting that the types of data structures that the server can support are common to a large set of geophysical communities.