Main Processing

The darc.process module contains the main processing logic of the darc module.

darc.process._process(worker)

Wrapper function to start the worker process.

Return type:

None

Parameters:

worker (process_crawler | process_loader) –

darc.process.process(worker)

Main process.

The function will register _signal_handler() for SIGTERM, and start the main process of the darc darkweb crawlers.

Parameters:

worker (Literal['crawler', 'loader']) – Worker process type.

Raises:

ValueError – If worker is not a valid value.

Return type:

None

Before starting the workers, the function will start proxies through

• darc.proxy.tor.tor_proxy()

• darc.proxy.i2p.i2p_proxy()

• darc.proxy.zeronet.zeronet_proxy()

• darc.proxy.freenet.freenet_proxy()

The general process can be described as following for workers of crawler type:

1. process_crawler(): obtain URLs from the requests link database (c.f. load_requests()), and feed such URLs to crawler().

   Note

   If FLAG_MP is True, the function will be called with multiprocessing support; if FLAG_TH if True, the function will be called with multithreading support; if none, the function will be called in single-threading.

2. crawler(): parse the URL using parse_link(), and check if need to crawl the URL (c.f. PROXY_WHITE_LIST, PROXY_BLACK_LIST , LINK_WHITE_LIST and LINK_BLACK_LIST); if true, then crawl the URL with requests.

   If the URL is from a brand new host, darc will first try to fetch and save robots.txt and sitemaps of the host (c.f. save_robots() and save_sitemap()), and extract then save the links from sitemaps (c.f. read_sitemap()) into link database for future crawling (c.f. save_requests()). Also, if the submission API is provided, submit_new_host() will be called and submit the documents just fetched.

   If robots.txt presented, and FORCE is False, darc will check if allowed to crawl the URL.

   Note

   The root path (e.g. / in https://www.example.com/) will always be crawled ignoring robots.txt.

   At this point, darc will call the customised hook function from darc.sites to crawl and get the final response object. darc will save the session cookies and header information, using save_headers().

   Note

   If requests.exceptions.InvalidSchema is raised, the link will be saved by save_invalid(). Further processing is dropped.

   If the content type of response document is not ignored (c.f. MIME_WHITE_LIST and MIME_BLACK_LIST), submit_requests() will be called and submit the document just fetched.

   If the response document is HTML (text/html and application/xhtml+xml), extract_links() will be called then to extract all possible links from the HTML document and save such links into the database (c.f. save_requests()).

   And if the response status code is between 400 and 600, the URL will be saved back to the link database (c.f. save_requests()). If NOT, the URL will be saved into selenium link database to proceed next steps (c.f. save_selenium()).

The general process can be described as following for workers of loader type:

1. process_loader(): in the meanwhile, darc will obtain URLs from the selenium link database (c.f. load_selenium()), and feed such URLs to loader().

   Note

   If FLAG_MP is True, the function will be called with multiprocessing support; if FLAG_TH if True, the function will be called with multithreading support; if none, the function will be called in single-threading.

2. loader(): parse the URL using parse_link() and start loading the URL using selenium with Google Chrome.

   At this point, darc will call the customised hook function from darc.sites to load and return the original Chrome object.

   If successful, the rendered source HTML document will be saved, and a full-page screenshot will be taken and saved.

   If the submission API is provided, submit_selenium() will be called and submit the document just loaded.

   Later, extract_links() will be called then to extract all possible links from the HTML document and save such links into the requests database (c.f. save_requests()).

After each round, darc will call registered hook functions in sequential order, with the type of worker ('crawler' or 'loader') and the current link pool as its parameters, see register() for more information.

If in reboot mode, i.e. REBOOT is True, the function will exit after first round. If not, it will renew the Tor connections (if bootstrapped), c.f. renew_tor_session(), and start another round.

darc.process.process_crawler()

A worker to run the crawler() process.

Warns:

HookExecutionFailed – When hook function raises an error.

Return type:

None

darc.process.process_loader()

A worker to run the loader() process.

Warns:

HookExecutionFailed – When hook function raises an error.

Return type:

None

darc.process.register(hook, *, _index=None)

Register hook function.

Parameters:

• hook (Callable[[Literal['crawler', 'loader'], List[Link]], None]) – Hook function to be registered.

• _index (int | None) –

Keyword Arguments:

_index – Position index for the hook function.

Return type:

None

The hook function takes two parameters:

1. a str object indicating the type of worker, i.e. 'crawler' or 'loader';

2. a list object containing Link objects, as the current processed link pool.

The hook function may raises WorkerBreak so that the worker shall break from its indefinite loop upon finishing of current round. Any value returned from the hook function will be ignored by the workers.

See also

The hook functions will be saved into _HOOK_REGISTRY.

darc.process._HOOK_REGISTRY: List[Callable[[Literal['crawler', 'loader'], List[Link]], None]] = []

List of hook functions to be called between each round.

Type:

List[Callable[[Literal[‘crawler’, ‘loader’], List[Link]]]

darc.process._WORKER_POOL: List[Process | Thread] = []

List of active child processes and/or threads.

Type:

List[Union[Process, Thread]]