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December 10, 2015 19:18
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EventSource streaming using Haskell and redis brpop.
Use redis-cli to push some data in the "val" list and see it appear in your browser.
It is not that hard... finally. There are some events not appearing at the beginning of the sequence, I don't know why, after that it works well.
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| <!doctype html> | |
| <html> | |
| <head><title>Index</title> | |
| </head> | |
| <body> | |
| <script type="text/javascript"> | |
| var source = new EventSource('eventsource'); | |
| source.onmessage = function (e) { | |
| var newListItem = document.createElement("LI"); | |
| newListItem.appendChild(document.createTextNode(e.data)); | |
| document.getElementById("list").appendChild(newListItem); | |
| }; | |
| </script> | |
| <ul id="list"> | |
| </ul> | |
| </body> | |
| </html> |
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| {-# LANGUAGE OverloadedStrings #-} | |
| module Main where | |
| import Control.Applicative | |
| import Snap.Core | |
| import Snap.Util.FileServe | |
| import Snap.Http.Server | |
| import Data.Monoid (mconcat) | |
| import Blaze.ByteString.Builder.Char8 | |
| import Blaze.ByteString.Builder | |
| import Data.Enumerator.List (generateM) | |
| import Database.Redis | |
| getVal :: IO Builder | |
| getVal = do | |
| conn <- connect defaultConnectInfo | |
| runRedis conn $ do | |
| Right (Just (_, val)) <- brpop ["val"] 1000 | |
| return $ fromByteString val | |
| dataField :: Builder -> Builder | |
| dataField b = mconcat [fromString "data: ", b, fromString "\n\n", flush] | |
| eventHandler :: Snap () | |
| eventHandler = do | |
| modifyResponse $ | |
| setContentType "text/event-stream" . | |
| setResponseCode 200 . | |
| setResponseBody (generateM $ fmap (Just . dataField) getVal) | |
| main :: IO () | |
| main = quickHttpServe $ | |
| ifTop (serveFile "static/index.html") <|> | |
| route [ ("eventsource", eventHandler) ] |
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