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Handle and display errors in browser (w/ hot reload)

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Resolves #7
This commit is contained in:
Sridhar Ratnakumar 2021-04-24 23:25:04 -04:00
parent 39d327b1d9
commit a661aa5848
3 changed files with 15 additions and 7 deletions
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2
README.md
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@ -45,7 +45,7 @@ pre-announce,
- CLI UX
- [x] opts
- [ ] logging
- [ ] [deal with errors](https://github.com/srid/memoir/issues/1)
- [x] [deal with errors](https://github.com/srid/memoir/issues/1)
- [ ] How to serve non-generated files (css, img, etc.)
- [ ] Publish Data.LVar to Hackage
- [ ] documentation ([guide](https://documentation.divio.com/))

2
docs/concepts/hot-reload.md
View File

@ -13,5 +13,5 @@ TODO
- data reload (filesystem.md)
- HTML templates implications
- link to tailwind (for shim trick)
- exceptions
- exception handling in browser view
- can run in production?

18
src/Ema/Server.hs
View File

@ -5,11 +5,12 @@
module Ema.Server where
import Control.Concurrent.Async (race)
import Control.Exception (try)
import Control.Exception (catch, try)
import Data.LVar (LVar)
import qualified Data.LVar as LVar
import qualified Data.Text as T
import Ema.Class (Ema (decodeRoute))
import GHC.IO.Unsafe (unsafePerformIO)
import NeatInterpolation (text)
import qualified Network.HTTP.Types as H
import qualified Network.Wai as Wai
@ -83,14 +84,21 @@ runServerWithWebSocketHotReload port model render = do
pure (H.status404, "No route")
Just r -> do
val <- LVar.get model
pure (H.status200, renderWithEmaShims val r)
let html = renderCatchingErrors val r
pure (H.status200, html <> emaStatusHtml <> wsClientShim)
f $ Wai.responseLBS status [(H.hContentType, "text/html")] v
renderWithEmaShims m r =
render m r <> emaStatusHtml <> wsClientShim
renderWithEmaHtmlShims m r =
render m r <> emaStatusHtml
renderCatchingErrors m r <> emaStatusHtml
renderCatchingErrors m r =
unsafeCatch (render m r) $ \(err :: SomeException) ->
encodeUtf8 $
"<html><head><meta charset=\"UTF-8\"></head><body><h1>Ema App threw an exception</h1><pre style=\"border: 1px solid; padding: 1em 1em 1em 1em;\">"
<> show @Text err
<> "</pre><p>Once you fix your code this page will automatically update.</body>"
routeFromPathInfo =
decodeRoute @model . fmap (fromString . toString)
unsafeCatch :: Exception e => a -> (e -> a) -> a
unsafeCatch x f = unsafePerformIO $ catch (seq x $ pure x) (pure . f)
-- | Return the equivalent of WAI's @pathInfo@, from the raw path string
-- (`document.location.pathname`) the browser sends us.