pdf-proxy

prototype proxy server for hypothesis

How it works

This is a prototype of a pdf cors proxy server implemented in nginx and lua. Lua is an interpreted language similar to Python. It is used to perform some simple logic and templating at the nginx layer.

When a request to the proxy is issued at for example: localhost:9081/http://example.com/pdf.pdf it is routed to the '/' endpoint which issues a request to localhost:9081/id_/http://example.com/pdf.pdf. This is a non-blocking request. Once it completes, it looks at the Content-Type response header to see if it contains a pdf type and if it does it issues a redirect to localhost:9081/pdf/http://example.com/pdf.pdf. If the content type does not match a pdf it is routed to localhost:9080/http://example.com/pdf.pdf (aka via).

The /pdf/ endpoint responds with the pdf and the hypothesis client embeded in an html page. This pdf page also contains a url to the proxied pdf: localhost:9081/id_/http://example.com/pdf.pdf Note this is the same endpoint that was hit in the original request to check the Content-Type header. Due to nginx caching, that means this second request will return the cached response as opposed to issueing a second request to the host pdf server.

Note it is also using redirects which means the next time this page needs to proxy a pdf or an html page it won't run the Content-Type check again which will save time.

Future Considerations

Note there is a TODO in the code to clear cookies coming back from the server that hosts the pdf.

Using /id_/ for the pdf proxy may be problematic and catch via proxy requests as well so if we put this on top of via we may need to rename that endpoint.

While redirecting means we don't run the Content-Type header check again, there may be some issues with doing this-we may not want to rewrite the url to the redirected url. Also note caching would still be at play here so it may not be a big performance hit to run the check again since the response to get the Content-Type header would already be cached.

Getting Started

Note this is dependent on H, the Client, and Via so those services also need to be running.

To run:

docker-compose up -d

To stop:

docker-compose down

Running in Development Mode

Alternatively, to see logging from nginx you can run:

docker-compose run --service-ports pdf-proxy

To stop ctrl-C and run:

docker-compose rm -f pdf-proxy