Python CDP

Python CDP Generator (shortened to PyCDP) is a library that provides Python wrappers for the types, commands, and events specified in the Chrome DevTools Protocol. Currently supports CDP r970581 (Chrome 97).

The Chrome DevTools Protocol provides for remote control of a web browser by sending JSON messages over a WebSocket. That JSON format is described by a machine-readable specification. This specification is used to automatically generate the classes and methods found in this library.

Installation

You can install this library as a dependency on your project with:

pip install git+https://github.com/HMaker/python-cdp.git@latest

Change the git tag @latest if you need another version. To install for development, clone this repository, install Poetry package manager and run poetry install to install dependencies.

Usage

If all you want is automate Chrome right now, PyCDP includes a low-level client for asyncio and twisted:

import asyncio
from pycdp import cdp
from pycdp.browser import ChromeLauncher
from pycdp.asyncio import connect_cdp

async def main():
    chrome = ChromeLauncher(
        binary='/usr/bin/google-chrome', # linux path
        args=['--remote-debugging-port=9222', '--incognito']
    )
    # ChromeLauncher.launch() is blocking, run it on a background thread
    await asyncio.get_running_loop().run_in_executor(None, chrome.launch)
    conn = await connect_cdp('http://localhost:9222')
    target_id = await conn.execute(cdp.target.create_target('about:blank'))
    target_session = await conn.connect_session(target_id)
    await target_session.execute(cdp.page.enable())
    # you may use "async for target_session.listen()" to listen multiple events, here we listen just a single event.
    with target_session.safe_wait_for(cdp.page.DomContentEventFired) as navigation:
        await target_session.execute(cdp.page.navigate('https://chromedevtools.github.io/devtools-protocol/'))
        await navigation
    dom = await target_session.execute(cdp.dom.get_document())
    node = await target_session.execute(cdp.dom.query_selector(dom.node_id, 'p'))
    js_node = await target_session.execute(cdp.dom.resolve_node(node))
    print((await target_session.execute(cdp.runtime.call_function_on('function() {return this.innerText;}', js_node.object_id, return_by_value=True)))[0].value)
    await target_session.execute(cdp.page.close())
    await conn.close()
    await asyncio.get_running_loop().run_in_executor(None, chrome.kill)

asyncio.run(main())

the twisted client requires twisted and autobahn packages:

from twisted.python.log import err
from twisted.internet import reactor, defer, threads
from pycdp import cdp
from pycdp.browser import ChromeLauncher
from pycdp.twisted import connect_cdp

async def main():
    chrome = ChromeLauncher(
        binary='C:\Program Files\Google\Chrome\Application\chrome.exe', # windows path
        args=['--remote-debugging-port=9222', '--incognito']
    )
    await threads.deferToThread(chrome.launch)
    conn = await connect_cdp('http://localhost:9222', reactor)
    target_id = await conn.execute(cdp.target.create_target('about:blank'))
    target_session = await conn.connect_session(target_id)
    await target_session.execute(cdp.page.enable())
    await target_session.execute(cdp.page.navigate('https://chromedevtools.github.io/devtools-protocol/'))
    async with target_session.wait_for(cdp.page.DomContentEventFired):
        dom = await target_session.execute(cdp.dom.get_document())
        node = await target_session.execute(cdp.dom.query_selector(dom.node_id, 'p'))
        js_node = await target_session.execute(cdp.dom.resolve_node(node))
        print((await target_session.execute(cdp.runtime.call_function_on('function() {return this.innerText;}', js_node.object_id, return_by_value=True)))[0].value)
    await target_session.execute(cdp.page.close())
    await conn.close()
    await threads.deferToThread(chrome.kill)

def main_error(failure):
    err(failure)
    reactor.stop()

d = defer.ensureDeferred(main())
d.addErrback(main_error)
d.addCallback(lambda *args: reactor.stop())
reactor.run()

You also can use just the builtin CDP type wrappers with import pycdp.cdp on your own client implementation. If you want to try a different CDP version you can build new type wrappers with cdpgen command:

usage: cdpgen <arguments>

Generate Python types for the Chrome Devtools Protocol (CDP) specification.

optional arguments:
  -h, --help            show this help message and exit
  --browser-protocol BROWSER_PROTOCOL
                        JSON file for the browser protocol
  --js-protocol JS_PROTOCOL
                        JSON file for the javascript protocol
  --output OUTPUT       output path for the generated Python modules

JSON files for the CDP spec can be found at https://github.com/ChromeDevTools/devtools-protocol/tree/master/json

Example:

cdpgen --browser-protocol browser_protocol.json --js-protocol js_protocol.json --output /tmp/cdp

You can then include the /tmp/cdp package in your project and import it like the builtin CDP types.

Implementation of a CDP client

The pycdp.cdp package follows same structure of CDP domains, each domain is a Python module and each command a function in that module.

Each function is a generator with a single yield which is a Python dict, on the CDP wire format, containing the message that should be sent to the browser, on resumption the generator receives the message from browser:

import cdp

# Get all CDP targets
command = cdp.target.get_targets() # this is a generator
raw_cdp_request = next(command) # receive the yield
raw_cdp_response = send_cdp_request(raw_cdp_request) # you implement send_cdp_request, raw_cdp_request is the JSON object that should be sent to browser
try:
    command.send(raw_cdp_response) # send the response to the generator where raw_cdp_response is the JSON object received from browser, it will raise StopIteration
    raise RuntimeError("the generator didnt exit!") # this shouldnt happen
except StopIteration as result:
    response = result.value # the parsed response to Target.get_targets() command
print(response)

For implementation details check out the docs.

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PyCDP is licensed under the MIT License.

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