LIO.Web.Simple.TCB

This module exports a function run for creating a runner that is used to run a Web.Simple SimpleApplication in the LIO monad.

The runner is only available to trusted code since we do not impose any policy on how requests and responses should be handled. Middleware should be used on both ends to ensure safety. This module provides several such Middleware.

LIO applications

type SimpleLIOApplication p l = Priv p -> SimpleApplication (LIO l)

An LIO simple aplpication is an LIO computation mapping a set of privileges and request to a response. While privileges can be provided in terms of a e.g., Reader monad, in certain cases not having the privilege as part of the sate is cleaner.

type SimpleLIOMiddleware p l = SimpleLIOApplication p l -> SimpleLIOApplication p l

Simple LIO middleware.

Runners

run :: Label l => Port -> Middleware -> SimpleApplication (LIO l) -> LIO l ()

Run an LIO web app wrapped by some middleware. Since web servers can be quite messy it is important that you provide middleware to sanitize responses to prevent data leakage.

Since security properties vary across applications, we do not impose any conditions on the requests and reponses. The latter can be sanitized by supplying a middleware, while the former can simply be baked-into the app (as SimpleMiddleware.

runP :: (PrivDesc l p, Label l) => Port -> Middleware -> Priv p -> SimpleLIOApplication p l -> LIO l ()

Same as run, but run SimpleLIOApplications, i.e., applications that take privileges.

Middleware

browserLabelGuard :: MonadLIO l m => l -> SimpleMiddleware m

Middleware that ensures the Response from the application is readable by the client's browser (as determined by the result label of the app computation and the label of the browser). If the response is not readable by the browser, the middleware sends a 403 (unauthorized) response instead.

removeRequestHeaders :: Monad m => [HeaderName] -> SimpleMiddleware m

Remove certain headers from the request.

removeResponseHeaders :: Monad m => [HeaderName] -> SimpleMiddleware m

Remove certain headers from the response, e.g., Set-Cookie.

Templates

lioGetTemplateTCB :: Label l => FilePath -> LIO l Template

Function to use to get a template. When the underlying monad is LIO, it looks in the viewDirectory for the given file name and compiles the file into a template.

This function should be used only when the everything reachable from the viewDirectory is public.

To ensure that the function cannot be abused the function first cleans up the file path: if it starts out with a .., we consider this invalid as it can be used explore parts of the filesystem that should otherwise be unaccessible. Similarly, we remove any . from the path.

Since this funciton does not use the 'lio-fs' filesystem readFile, but rather the IO readFile, it should not be exposed to untrusted code.