Eduardo Trujillo

Working with Hakyll has been great so far, but it seems the fun ends right after your site is generated and copied over to the remote server. From there, you have to deal with Nginx or Apache configuration files for the final touches, such as redirections, cache policies, or additional headers.

I’ve seen applications, such as XMonad, which employ Haskell scripts in-lieu of configuration files, and it’s generally an enjoyable experience due to the added flexibility and customization it provides.

With that in mind, wouldn’t it be nice if the web server was in Haskell as well? After all, Hakyll has a preview function that works well enough. So, it shouldn’t be too hard to replicate that and add some custom logic on top of it.

Well, that’s exactly what I was wondering during the past few days, and (perhaps not too) surprisingly, it only took half a day’s worth of work to get a working prototype.

To get the job done, I added a new target to my Hakyll project’s cabal file, and included warp, wai-static-app, and a bunch of WAI middleware (wai-extra) as dependencies. The rest was merely a process of putting all the pieces together and ensuring the site behaved as expected.

## The result

• A fast static site server.
• Support for HTTP 2.0 and HTTPS.
• Customized configurations for production, staging, and development.
• A more complete solution than hakyll server, since the site behaves exactly like it would on production.
• A clear path for adding more logic in the future (API, Proxy, etc).

The server code is a few orders of magnitude larger than a simple configuration file, but it’s also under 200 lines of code.

{-# LANGUAGE OverloadedStrings #-}

import           Control.Concurrent                   (forkIO)
import qualified Data.ByteString                      as BS (ByteString, pack)
import           Data.Maybe                           (fromMaybe, mapMaybe)
import           Data.Monoid                          ((<>))
import           Data.String                          (fromString)
import qualified Data.Text                            as T (Text, concat, pack)
import qualified Data.Text.Encoding                   as TE (encodeUtf8)
import           Network.Wai                          (Application, Middleware,
pathInfo)
import           Network.Wai.Application.Static       (defaultWebAppSettings,
ss404Handler,
ssIndices, ssMaxAge,
ssRedirectToIndex,
staticApp)
import           Network.Wai.Handler.Warp             (defaultSettings, run,
setPort)
import           Network.Wai.Handler.WarpTLS          (runTLS,
tlsSettingsChain)
import           Network.Wai.Middleware.ForceDomain   (forceDomain)
import           Network.Wai.Middleware.ForceSSL      (forceSSL)
import           Network.Wai.Middleware.Gzip          (def, gzip)
import           Network.Wai.Middleware.RequestLogger (logStdout)
import           Network.Wai.Middleware.Vhost         (redirectTo)
import           Safe                                 (lastMay)
import           System.Environment                   (lookupEnv)
import           WaiAppStatic.Types                   (MaxAge (MaxAgeSeconds),
toPiece)

-- | The core application.
-- It serves files from _site which is where Hakyll will place the generated
-- site.
staticSite :: Maybe String -> Application
staticSite path = staticApp
(defaultWebAppSettings $fromString$ fromMaybe "_site" path)
{ ssIndices  = mapMaybe (toPiece . T.pack) ["index.html"]
, ssRedirectToIndex = False
, ss404Handler = Just redirectApp
, ssMaxAge = MaxAgeSeconds 3600
}

-- | 404 handler.
-- We will redirect users to a 404 page if we can't locate the resource they
-- are looking for.
redirectApp :: Application
redirectApp req sendResponse = sendResponse $redirectTo "/" -- | Gzip compression middleware. gzipMiddleware :: Middleware gzipMiddleware = gzip def -- | Domain redirection middleware. -- When the site is live, we want to redirect users to the right domain name -- regarles of whether they arrive from a www. domain, the server's IP address -- or a spoof domain which is pointing to this server. domainMiddleware :: Middleware domainMiddleware = forceDomain (\domain -> case domain of "localhost" -> Nothing "chromabits.com" -> Nothing _ -> Just "chromabits.com") -- | Common headers middleware. headersMiddleware :: Middleware headersMiddleware = addHeaders [ ("X-Frame-Options", "SAMEORIGIN") , ("X-XSS-Protection", "1; mode=block") , ("X-Content-Type-Options", "nosniff") ] -- | Strict Transport Security middleware. stsHeadersMiddleware :: Middleware stsHeadersMiddleware = addHeaders [("Strict-Transport-Security", "max-age=31536000; includeSubdomains")] -- | Content Security Policy middleware. -- Here we add the CSP header which includes the policies for this blog. cspHeadersMiddleware :: Middleware cspHeadersMiddleware = addHeaders [("Content-Security-Policy", TE.encodeUtf8$ glue policies)]
where
glue :: [T.Text] -> T.Text
glue [] = "default-src 'none'"
glue [x] = x
glue xs = T.concat $map (\x -> T.concat [x, "; "]) (init xs) ++ [last xs] policies :: [T.Text] policies = [ "default-src 'self'" , "script-src 'self' 'unsafe-inline' https://use.typekit.net" <> " https://cdn.mathjax.org https://connect.facebook.net" <> " https://*.twitter.com https://cdn.syndication.twimg.com" <> " https://gist.github.com" <> " https://*.google-analytics.com/ga.js" , "img-src 'self' https: data: platform.twitter.com" , "font-src 'self' data: https://use.typekit.net" <> " https://cdn.mathjax.org" , "style-src 'self' 'unsafe-inline' https://use.typekit.net" <> " platform.twitter.com https://assets-cdn.github.com" , "frame-src https://www.youtube.com https://www.slideshare.net" <> " staticxx.facebook.com www.facebook.com" ] -- | De-indefify middleware. -- Redirects any path ending in /index.html to just /. deindexifyMiddleware :: Middleware deindexifyMiddleware app req sendResponse = if lastMay (pathInfo req) == Just "index.html" then sendResponse$ redirectTo newPath
else app req sendResponse
where
newPath :: BS.ByteString
newPath = TE.encodeUtf8 $processPath oldPath processPath :: [T.Text] -> T.Text processPath xs = case xs of [] -> "/" _ -> T.concat$ map prefixSlash xs

oldPath :: [T.Text]
oldPath = init $pathInfo req prefixSlash :: T.Text -> T.Text prefixSlash x = T.concat ["/", x] -- | Serves a WAI Application on the specified port. -- The target port is printed to stdout before hand, which can be useful for -- debugging purposes. listen :: Int -> Application -> IO () listen port app = do -- Inform which port we will be listening on. putStrLn$ "Listening on port " ++ show port ++ "..."
-- Serve the WAI app using Warp
run port app

-- | Serves a WAI Application on the specified port.
-- The target port is printed to stdout before hand, which can be useful for
-- debugging purposes.
listenTLS :: Int -> Application -> IO ()
listenTLS port app = do
certPath <- lookupEnv "BLOG_TLS_CERT"
chainPath <- lookupEnv "BLOG_TLS_CHAIN"
keyPath <- lookupEnv "BLOG_TLS_KEY"

let tlsSettings = tlsSettingsChain
(fromMaybe "cert.pem" certPath)
[fromMaybe "fullchain.pem" chainPath]
(fromMaybe "privkey.pem" keyPath)
let settings = setPort port defaultSettings

-- Inform which port we will be listening on.
putStrLn $"Listening on port " ++ show port ++ " (TLS)..." -- Serve the WAI app using Warp runTLS tlsSettings settings app -- | The entry point of the server application. main :: IO () main = do stage <- lookupEnv "BLOG_STAGE" path <- lookupEnv "BLOG_PATH" let liveMiddleware = logStdout$ cspHeadersMiddleware
$headersMiddleware$ domainMiddleware
$forceSSL$ deindexifyMiddleware
$gzipMiddleware$ staticSite path

-- Depending on the stage we will choose a different set of middleware to
-- apply to the application.
case fromMaybe "dev" stage of
-- "Production"
"live" -> do
forkIO $listenTLS 443$ stsHeadersMiddleware liveMiddleware
listen 80 liveMiddleware
"staging" -> do
forkIO $listenTLS 8443 liveMiddleware listen 8080 liveMiddleware -- "Development" _ -> listen 9090 (logStdout$ headersMiddleware
$deindexifyMiddleware$ gzipMiddleware

### forceDomain and forceSSL

To redirect users from an insecure (HTTP) site to a secure (HTTPS) site, the you can use the forceSSL.

To redirect users to the right domain name, you can use forceDomain, however, you need to pass in a custom function which specifies when and to which domains users should be redirected to.

I prefer to use the naked domain for my blog, so I redirect anything that is not chromabits.com:

domainMiddleware :: Middleware
domainMiddleware = forceDomain
(\domain -> case domain of
"localhost" -> Nothing
"chromabits.com" -> Nothing
_ -> Just "chromabits.com")

### No more index.html

One thing I don’t like about static sites is having .html extensions on the URL. In Hakyll, I managed to partially work around this problem by simply making sure that most paths result in index.html (e.g. /archive/ is actually /archive/index.html). However, you could still technically get to the index.html path if you visit it directly.

With this server, I wanted to add an additional redirect rule that would redirect users away from paths with index.html. It is implemented on the code above as deindexifyMiddleware.

In the future, I might consider writing a smarter middleware capable of handling more paths (e.g. /archive would simply be /archive.html).

### Middleware stacks

Something that was not immediately obvious to me from reading the wai documentation was how to chain middleware together. By looking at the types, I eventually realized that a Middleware takes in an Application and returns a new Application which is wrapped with the middleware. This means that you can simply feed each middleware to the next one and end up with an application that is wrapped in the entire stack.

type Middleware = Application -> Application

However, you will need to pay special attention to the order in which they are applied. For me, it was important that the logger middleware was at the top of the stack so that every request was logged.

-- Everything is logged.
site = logStdout $forceSSL$ app

-- Some redirects will not be logged.
site = forceSSL $logStdout$ app