Archive websites using headless Google Chrome and its DevTools protocol.
The following dependencies must be present to run crocoite:
It is recommended to prepare a virtualenv and let pip handle the dependency resolution for Python packages instead:
cd crocoite virtualenv -p python3 sandbox source sandbox/bin/activate pip install .
One-shot commandline interface and pywb playback:
crocoite-grab --output example.com.warc.gz http://example.com/ rm -rf collections && wb-manager init test && wb-manager add test example.com.warc.gz wayback & $BROWSER http://localhost:8080
The naive approach of fetching a HTML page, parsing it and extracting links to referenced resources therefore is not sufficient to create a faithful snapshot of these web applications. A full browser, capable of running scripts and providing modern Web API’s is absolutely required for this task. Thankfully Google Chrome runs without a display (headless mode) and can be controlled by external programs, allowing them to navigate and extract or inject data. This section describes the solutions crocoite offers and explains design decisions taken.
crocoite captures resources by listening to Chrome’s network events and requesting the response body using Network.getResponseBody. This approach has caveats: The original HTTP requests and responses, as sent over the wire, are not available. They are reconstructed from parsed data. The character encoding for text documents is changed to UTF-8. And the content body of HTTP redirects cannot be retrieved due to a race condition.
But at the same time it allows crocoite to rely on Chrome’s well-tested network stack and HTTP parser. Thus it supports HTTP version 1 and 2 as well as transport protocols like SSL and QUIC. Depending on Chrome also eliminates the need for a man-in-the-middle proxy, like warcprox, which has to decrypt SSL traffic and present a fake certificate to the browser in order to store the transmitted content.
WARC records generated by crocoite therefore are an abstract view on the resource they represent and not necessarily the data sent over the wire. A URL fetched with HTTP/2 for example will still result in a HTTP/1.1 request/response pair in the WARC file. This may be undesireable from an archivist’s point of view (“save the data exactly like we received it”). But this level of abstraction is inevitable when dealing with more than one protocol.
crocoite also interacts with and therefore alters the grabbed websites. It does
so by injecting behavior scripts into the site. Typically these are written
scripts then perform different tasks: Extracting targets from visible
hyperlinks, clicking buttons or scrolling the website to to load more content,
as well as taking a static screenshot of
<canvas> elements for the DOM
snapshot (see below).
Replaying archived WARC’s can be quite challenging and might not be possible with current technology (or even at all):
- Some sites request assets based on screen resolution, pixel ratio and supported image formats (webp). Replaying those with different parameters won’t work, since assets for those are missing. Example: missguided.com.
- Some fetch different scripts based on user agent. Example: youtube.com.
- Range requests (Range: bytes=1-100) are captured as-is, making playback difficult
crocoite offers two methods to work around these issues. Firstly it can save a
DOM snapshot to the WARC file. It contains the entire DOM in HTML format minus
<script> tags after the site has been fully loaded and thus can be
does not work any more. Secondly it also saves a screenshot of the full page,
so even if future browsers cannot render and display the stored HTML a fully
rendered version of the website can be replayed instead.
crocoite is built with the Unix philosophy (“do one thing and do it well”) in
crocoite-grab can only save a single page. If you want recursion
crocoite-recursive, which follows hyperlinks according to
It can either recurse a maximum number of levels or grab all pages with the
same prefix as the start URL:
crocoite-recursive --policy prefix http://www.example.com/dir/ output
will save all pages in
/dir/ and below to individual files in the output
output. You can customize the command used to grab individual
pages by appending it after
output. This way distributed grabs (ssh to a
different machine and execute the job there, queue the command with Slurm, …)
A simple IRC bot (“chromebot”) is provided with the command
It reads its configuration from a config file like the example provided in
contrib/chromebot.ini and supports the following commands:
- a <url> -j <concurrency> -r <policy>
- Archive <url> with <concurrency> processes according to recursion <policy>
- s <uuid>
- Get job status for <uuid>
- r <uuid>
- Revoke or abort running job with <uuid>
- Uses Google Chrome as well, but intercepts traffic using a proxy. Supports distributed crawling and immediate playback.