cdp-hs

A Haskell library for the Chrome Devtools Protocol (CDP), generated from the protocol's definition files.

Example usage

Ensure Chrome is running with the remote debugging port enabled:

$ chromium --headless --remote-debugging-port=9222 https://wikipedia.com

The following program can be used to print a page to PDF, with Base64 encoded data being read in chunks:

{-# LANGUAGE OverloadedStrings   #-}

module Main where

import Data.Maybe
import Data.Default
import qualified Data.ByteString.Base64.Lazy as Base64
import qualified Data.ByteString.Lazy as BL
import qualified Data.Text as T
import qualified Data.Text.Lazy as TL
import qualified Data.Text.Lazy.Encoding as TL

import qualified CDP as CDP

main :: IO ()
main = CDP.runClient def printPDF

printPDF :: CDP.Handle -> IO ()
printPDF handle = do
    -- send the Page.printToPDF command
    r <- CDP.sendCommandWait handle $ CDP.pPagePrintToPDF
        { CDP.pPagePrintToPDFTransferMode = Just CDP.PPagePrintToPDFTransferModeReturnAsStream
        }

    -- obtain stream handle from which to read pdf data
    let streamHandle = fromJust . CDP.pagePrintToPDFStream $ r

    -- read pdf data 24000 bytes at a time
    let params = CDP.PIORead streamHandle Nothing $ Just 24000
    reads <- whileTrue (not . CDP.iOReadEof) $ CDP.sendCommandWait handle params
    let dat = map decode reads
    BL.writeFile "mypdf.pdf" $ BL.concat dat

decode :: CDP.IORead -> BL.ByteString
decode ior = if (CDP.iOReadBase64Encoded ior == Just True)
    then Base64.decodeLenient lbs
    else lbs
  where
    lbs = TL.encodeUtf8 . TL.fromStrict . CDP.iOReadData $ ior

whileTrue :: Monad m => (a -> Bool) -> m a -> m [a]
whileTrue f act = do
    a <- act
    if f a
        then pure . (a :) =<< whileTrue f act
        else pure [a]

More examples can be found in examples.

Generating the CDP library

cabal run cdp-gen

Current state

Project board

Commands and events for all non-deprecated domains are supported.

Sessions can also be created with a target (such as a tab), which can be used to restrict the scope of commands and events for the target. See examples/sessions.hs for example usage.

Contributing

PRs are welcome! If you would like to discuss changes or have any feedback, feel free to open an issue.

Acknowledgements

This began as a Summer of Haskell / GSoC project. Albert Krewinkel (@tarleb), Jasper Van der Jeugt (@jaspervdj) and Romain Lesur (@RLesur) provided valuable feedback and support which along with raising the library's quality, has made this all the more enjoyable to work on.

References

• https://jaspervdj.be/posts/2013-09-01-controlling-chromium-in-haskell.html
• https://www.jsonrpc.org/specification