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time.gif

2017-08-11 * Haskell * Programming

This is an endless GIF that always shows the current time in UTC:

time.gif (reload if it fails)

Source Code

(From reports it doesn't seem to work on Safari, other browsers
should be fine.)

time.gif is written in Haskell and works by dynamically generating
each frame of the GIF and slowly feeding them over the HTTP
connection.

There is no guarantee that this GIF shows a reasonable time and this
is just for fun anyway, so better don't build your next project based
on the time from this GIF. If my server is overloaded, you can try
compiling it yourself and run it locally.

Update: Optimized, runs at less than 1% CPU with 500 simultaneous
connections open, LZW encoding reduces bandwidth from 4 KB/s to 300 B
/s.

-- Wait for incoming connections and start delivering a GIF to them
loop :: Int -> FrameSignal -> Socket -> IO ()
loop delay frameSignal sock = do
  (conn, _) <- accept sock

  forkIO $ body conn
  loop delay frameSignal sock

  where
    body c = do
      f <- receiveMSignal frameSignal
      sendAll c $ msg $ initialFrame (delay `div` 10000) f
      nextFrame c

    nextFrame c = do
      f <- receiveMSignal frameSignal
      sendAll c $ frame (delay `div` 10000) f
      nextFrame c

    msg content = B.intercalate "\r\n"
      [ "HTTP/1.0 200 OK"
      , "Server: gifstream/0.1"
      , "Content-Type: image/gif"
      , "Content-Transfer-Encoding: binary"
      , "Cache-Control: no-cache"
      , "Cache-Control: no-store"
      , "Cache-Control: no-transform"
      , ""
      , content
      ]

This is cannibalized from gifstream, which lets you play snake and
have people watch a GIF livestream. It was actually created as a
Christmas exercise for students of the Programming Paradigms course
at KIT.

snake

Discuss on Hacker News (2022-10-27) (previous thread from 2017-08-12)

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