Rack::ESI is an implementation of a small (but still very useful!) subset of ESI (Edge Side Includes). ESI tackles the problem of caching dynamic web content by recognizing that some content parts are static (at least for a while) and thereby cachable. Rack::ESI's primary raison d'être is to act as a substitue for real ESI processors during application development to keep your software setup simple. However, it can also be used standalone in production together with Ryan Tomayko's Rack::Cache to enable caching without leaving the rosy world of Ruby.
srcis an absolute path to be handled by the Rack application.