Violet library crawler

A small utility to automatically download lecture slides on Violet.vn

This tool crawls a list of lecture slides on a subject-class basis, following the pattern that each subject-class contains a list of lessons for the whole academic year.

Usage instruction

This tool only supports those links that satisfy the following conditions:

1. The link must be unique to a subject-class level (Math 6, English 7, etc.)
2. Each subject-class contains a list of lessons available as first-level direct links (referred as lesson links).
3. Inside each lesson link, there should be only a list of lecture links, and no other deeper-level links exist in the main content.

The following screenshot is an example (conditions are highlighted in the image). You can click the image to navigate to the link:

Also in the above link, the lesson link are shown below:

To use this tool, you must have an existing Violet account to download lectures, as the system requires users to have member points to do so.

1. Login to baigiang.violet.vn and obtain the JSON cookie file of your session. You can use some Chrome extensions such as Cookie-Editor to get this JSON.
2. Paste the JSON cookie into the cookie.json file.
3. Paste the described link and type your favored author name.

The tool will download a whole list of lectures automatically. If your favorite author's lecture is not available, the tool will pick the one with the most download count on the first page of the lesson link for you.

Dependencies

• HtmlAgilityPack (for parsing HTML elements)
• Newtonsoft.Json (for parsing cookie text)

Limitations

Since I only spent 2 hours to write this rarely-use tool, and approximately 1 hour to write this readme, there is always room for improvement. I will write down some for example:

• This tool only handles those links satifying the above descriptions.
• This tool does not use a headless browser, but use a static HTML parser instead. Some startup JavaScript code in HTML pages will not run, and therefore some content is missing. Initially, I intended to download lectures with the most number of slides but I was lazy to do it.
• This tool does not support pagination. Each lesson link may have multiple numbered pages, but again I was lazy to handle them.
• This tool does not automatically login using input username and password, instead use the cookie file.

However, it will still be useful if you have a relative working as a teacher. Feel free to play around with it and make some modification, as well as making use of HTML crawler.