Now that the http_adapter has been in production use for a while, I have finally updated some of the documentation. The README.md was updated and a new document http_adapter_reference.md has been added. These documents are in markdown format, you can view them formatted on GitHub but you may need a markdown compatible tool to print them out correctly.
The Reference Manual is mostly compiled from information presented in this blog, but formatted into a single document.
You can download the latest released build of the http_adapter here. At the time of writing the latest build is v0.4.0-beta, which was released in February this year. It is in internal use for migrating a couple of old Content Gateway based services, so there is a good chance that if/when bugs are discovered a fix will be released (cannot promise anything, though).
JPLa is a member of the Content Gateway (CGW) to Opaali migration team, specialising in programming related issues and API usage.