LatisVlad/SmartReader

SmartReader is a .NET Standard 2.0 library to extract the main content of a web page, based on a port of the Readability library by Mozilla, which in turn is based on the famous original Readability library.

You can do it the standard way, by using the NuGet package.

PM> Install-Package SmartReader

There are already other similar good projects, but they don't support .NET Core and they are based on old version of Readability. The original library is already quite stable, but there are always improvement to be made. So by relying on a original library maintained by such a competent organization we can piggyback on their hard work and user base.

There are also some improvements: it returns an author and publication date, the language of the article, the featured image, a list of images and an indication of the time needed to read it.

Feel free to suggest new features.

There are mainly two ways to use the library. The first is by creating a new Reader object, with the URI as the argument, and then calling the GetArticle method to obtain the extracted Article. The second one is by using one of the static methods ParseArticle of Reader directly, to return an Article. Both ways are available also through an async method, called respectively GetArticleAsync and ParseArticleAsync. The advantage of using an object, instead of the static method, is that it gives you the chance to set some options.

There is also the option to parse directly a String or Stream that you have obtained by some other way. This is available either with ParseArticle methods or by using the proper Reader constructor. In either case, you also need to give the original URI. It will not re-download the text, but it need the URI to make some checks and modifications on the links present on the page. If you cannot provide the original uri, you can use a fake one, like https:\\localhost.

If the extraction fails, the returned Article object will have the field IsReadable set to false.

The content of the article is unstyled, but it is wrapped in a div with the id readability-content that you can style yourself.

The library tries to detect the correct encoding of the text, if the correct tags are present in the text.

On the Article object you can call GetImagesAsync to obtain a Task for a list of Image objects, representing the images found in the extracted article. The method is async because it makes HEAD Requests, to obtain the size of the images and only returns the ones that are bigger then the specified size. The size by default is 75KB. This is to exclude things such as images used in the UI.

You can customize the regular expressions that are used to determine whether a part of the document will be inside the article. There are two methods to do this:

• void AddOptionToRegularExpression(RegularExpressions expression, string option)
  Add an option (i.e., usually a CSS class name) to the regular expression.
  
• void ReplaceRegularExpression(RegularExpressions expression, string newExpression)
  Replace the selected regular expression.
  

The type RegularExpression is an enum that can have one of the following values, corresponding to a regular expression:

• UnlikelyCandidates
• PossibleCandidates
  • Positive (increases chances to keep the element)
  • Negative (decreases chances to keep the element)
  • Extraneous (note: this regular expression is not used anywhere at the moment)
  • Byline
  • Videos
  • ShareElements

Except for the Videos regular expression, they all represent values of attributes, classes, etc. of tags. You should look at the code to understand how each of the regular expression is used.

The Videos regular expression represents a domain of origin of an embedded video. Since this is a string representing a regular expression, you have to remember to escape any dot present. This option is used to determine if an embed should be maintained in the article, because people generally want to see videos. If an embed matches one of the domains of this option is maintained, otherwise it is not.

// how to add the domain example.com
AddOptionToRegularExpression(RegularExpressions.Videos, "example\.com");

The library allows the user to add custom operations. I.e., to perform arbitrary modifications to the article before is processed or it is returned to the user. A custom operation receives as argument the article (an IElement). For custom operations at the beginning, the element is the entire document; for custom operations executed after the processing is complete, the element is the article extracted.

// example of custom operation
void AddInfo(AngleSharp.Dom.IElement element)
{       
    // we add a paragraph to the first div we find
	element.QuerySelector("div").LastElementChild.InnerHtml += "<p>Article parsed by SmartReader</p>";
}

static void RemoveElement(AngleSharp.Dom.IElement element)
{
    // we remove the first element with class removeable
    element.QuerySelector(".removeable")?.Remove();
}

[..]
Reader reader = // ..

// add a custom operation at the start
reader.AddCustomOperationStart(RemoveElement);

// add a custom operation at the end
reader.AddCustomOperationEnd(AddInfo);

As you can see the custom operation operate on an IElement and it would normally rely on the AngleSharp API. AngleSharp is the library that SmartReader uses to parse and manipulate HTML. The API of the library follows the standard structure that you can use in JavaScript, so it is intuitive to use. If you need any help to use it, consult their documentation.

Normally the library strips all classes of the elements except for page. This is done because classes are used to govern the display of the article, but they are irrelevant to the content itself. However, there is an option to preserve other classes. This is mostly useful if you want to perform custom operations on certain elements and you need CSS classes to identify them.

You can preserve classes using the property ClassesToPreserve which is an array of class names that will be preserved. Note that this has no effect if an element that contains the class is eliminated from the extracted article. This means that the option does not maintain the element in any case, it just maintains the class if the element is kept in the extracted article.

Reader reader = // ..

// preserve the class info
reader.ClassesToPreserve = new string[] { "info" };

The class page is always kept, no matter the value you assign to this option.

By default all web requests made by the library use the User Agent SmartReader Library. This can be changed by using the function SetCustomUserAgent.

Reader.SetCustomUserAgent("SuperAwesome App - for any issue contact [email protected]");

This function will change the user agent for all subsequent web requests with any object of the class.

Using the GetArticle method.

SmartReader.Reader sr = new SmartReader.Reader("https://arstechnica.co.uk/information-technology/2017/02/humans-must-become-cyborgs-to-survive-says-elon-musk/");

sr.Debug = true;
sr.Logger = new StringWriter();

SmartReader.Article article = sr.GetArticle();
var images = article.GetImagesAsync();

if(article.IsReadable)
{
	// do something with it	
}

Using the ParseArticle static method.

SmartReader.Article article = SmartReader.Reader.ParseArticle("https://arstechnica.co.uk/information-technology/2017/02/humans-must-become-cyborgs-to-survive-says-elon-musk/");

if(article.IsReadable)
{
	// do something with it
}

• int MaxElemsToParse
  Max number of nodes supported by this parser.
  Default: 0 (no limit)
• int NTopCandidates
  The number of top candidates to consider when analyzing how tight the competition is among candidates.
  Default: 5
• bool Debug
  Set the Debug option. If set to true the library writes the data on Logger.
  Default: false
• TextWriter Logger
  Where the debug data is going to be written.
  Default: null
• bool ContinueIfNotReadable
  The library tries to determine if it will find an article before actually trying to do it. This option decides whether to continue if the library heuristics fails. This value is ignored if Debug is set to true
  Default: true
• int CharThreshold
  The minimum number of characters an article must have in order to return a result.
  Default: 500
• String[] ClassesToPreserve
  The CSS classes that must be preserved in the article.
  Default: ["page"]

• Uri Uri
  Original Uri
• String Title
  Title
• String Byline
  Byline of the article, usually containing author and publication date
• String Dir
  Direction of the text
• String FeaturedImage
  The main image of the article
• String Content
  Html content of the article
• String TextContent
  The pure text of the article
• String Excerpt
  A summary of the article, based on metadata or first paragraph
• String Language
  Language string (es. 'en-US')
• String Author
  Author of the article
• String SiteName
  Name of the site that hosts the article
• int Length
  Length of the text of the article
• TimeSpan TimeToRead
  Average time needed to read the article
• DateTime? PublicationDate
  Date of publication of the article
• bool IsReadable
  Indicate whether we successfully find an article

It's important to be aware that the fields Byline, Author and PublicationDate are found independently of each other. So there might be some inconsistencies and unexpected data. For instance, Byline may be a string in the form "@Date by @Author" or "@Author, @Date" or any other combination used by the publication.

The TimeToRead calculation is based on the research found in Standardized Assessment of Reading Performance: The New International Reading Speed Texts IReST. It should be accurate if the article is written in one of the languages in the research, but it is just an educated guess for the others languages.

The FeaturedImage property holds the image indicated by the Open Graph or Twitter meta tags. If neither of these is present, and you called the GetImagesAsync method, it will be set with the first image found.

The demo project is a simple ASP.NET Core webpage that allows you to input an address and see the results of the library.

The console project is a Console program that allows you to see the results of the library on a random test page.

In case you want to build the Nuget package yourself you can use the following command.

 nuget pack .\SmartReader.csproj -OutputDirectory "..\nupkgs\" -Prop Configuration=Release

The command must be issued inside the src/SmartReader folder.

Any request made with certain HTTP APIs of .NET (like HttpClient, WebClient, etc.) follows the permitted values of security protocols that are set in the property ServicePointManager.SecurityProtocol. So, it determines which versions of the TLS protocol can use. In recent versions of .NET Framework (and other .NETs platforms) the default value of this property has been changed to SecurityProtocolType.SystemDefault which basically means whatever combinations of values is deemed the best by the current framework. This is the ideal value because if any TLS version stops being secure the code does not need to be updated.

This might cause some issues, because a web server might not be able to fulfill the request. Usually this is because it uses an old version of the SSL/TLS protocol like SSL 3.0. SmartReader neither specifies a SecurityProtocol value for the requests made with its internal HttpClient, nor it provides a method to change it. That's because if we did that this would affect all requests made with certain HTTP APIs, even the ones made by other parts of your code. So, if you need to access some article on an old, insecure web server you might set the proper value of SecurityProtocol yourself.

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

Alternatively, you can retrieve the content yourself in some other way and just use SmartReader to extract the article from the text.

SmartReader does not perform any security check on the input. If you are using Smart Reader with untrusted input and you are displaying the content to the user, it is your responsibility to make sure that nothing bad happens.

The Readability team suggests using a sanitizer library. On .NET you could the HTML Sanitizer library. They also recommend using CSP to add further defense-in-depth restrictions to what you allow the resulting content to do.

The project uses the Apache License.

• Unosviluppatore
• Dan Rigby
• Yasindn
• Jamie Lord
• Gábor Gergely
• AndySchmitt
• Andrew Lombard

Thanks to all the people involved.