Announcing: yesod-gitrepo

I'm happy to announce the first release of a new package, yesod-gitrepo. This package encapsulates a pattern I've used a number of times, namely: loading and refreshing content from a Git repository. Below is the current contents of the README.md file.

This code is currently being used in production, and should be pretty stable. That said, it has not received a huge amount of battle testing yet. So please due test corner cases before shipping it in production for your site.

yesod-gitrepo provides a means of embedding content from a Git repository inside a Yesod application. The typical workflow is:

• Use gitRepo to specify a repository and branch you want to work with.
• Provide a function that will perform some processing on the cloned repository.
• Use grContent in your Handler functions to access this parsed data.
• Embed the GitRepo as a subsite that can be used to force a refresh of the data.
• Set up a commit handler that pings that URL. On Github, this would be a webhook.

This is likely easiest to understand with a concrete example, so let's go meta: here's an application that will serve this very README.md file. We'll start off with language extensions and imports:

{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes       #-}
{-# LANGUAGE TemplateHaskell   #-}
{-# LANGUAGE TypeFamilies      #-}
import           ClassyPrelude.Yesod
import           Text.Markdown
import           Yesod.GitRepo

Now we're going to create our foundation datatype. We need to give it one field: the GitRepo value containing our parsed content. Our content will simply be the text inside README.md, wrapped up in a Markdown newtype for easy rendering. This gives us:

data App = App
    { getGitRepo :: GitRepo Markdown
    }

instance Yesod App

And now let's set up our routes. We need just two: a homepage, and the subsite. Our subsite type is GitRepo Markdown (as given above). We replace the space with a hyphen as an escaping mechanism inside Yesod's route syntax:

mkYesod "App" [parseRoutes|
/ HomeR GET
/refresh RefreshR GitRepo-Markdown getGitRepo
|]

Next up is our home handler. We start off by getting the current content parsed from the repository:

getHomeR :: Handler Html
getHomeR = do
    master <- getYesod
    content <- liftIO $ grContent $ getGitRepo master

Then it's just some normal Hamlet code:

    defaultLayout $ do
        setTitle "yesod-gitrepo sample"
        [whamlet|
            <p>
                <a href=@{RefreshR GitRepoRoute}>
                    Force a refresh at
                    @{RefreshR GitRepoRoute}
            <article>#{content}
        |]

And finally, our main function. We pass in the repo URL and branch name, plus a function that, given the filepath containing the cloned repo, processes it and generates a Markdown value. Finally, we provide the generated repo value to our App constructor and run it:

main :: IO ()
main = do
    repo <- gitRepo
        "https://github.com/snoyberg/yesod-gitrepo"
        "master"
        $ \fp -> fmap Markdown $ readFile $ fp </> "README.md"
    warp 3000 $ App repo

Give it a shot. You should have a webapp hosting this very README file!