How to restrict access to a publication's resources (e.g. a sample)

[RahimMahmoudzadeh]

Greetings
I want to show my user only 10 pages of the book, for example, I wanted you to help me in this case, how can I show a preview of the book to the user?

[mrifni]

You better off creating a sample epub and a separate full epub file.

[RahimMahmoudzadeh]

Can you explain more about that?
Can not be with Readium?

[mickael-menu]

Like @mrifni mentioned, the most reliable and safest way would be to create your own sample EPUBs. No technique in Readium can fully prevent a user from accessing the full content.

However, you have several options to do this in Readium:

• (easy) If you just want to prevent accessing some resources in the EPUB, set a custom openPublication callback when using Streamer.open() and remove the links you want to restrict the access to from manifest.readingOrder.
• (easy) Observe the navigator.currentLocator value and when you receive a Locator that exceeds the allowed portion (e.g. checking locations.position or locations.totalProgression, then hide the navigator and show a message explaining that the user reached the end of the sample.
• (hard but safer) If you need to restrict a portion of a resource, implement a custom Fetcher and modify the HTML page on the fly when it is requested.

[RahimMahmoudzadeh]

Greetings
Thank you for your answer
I now want to use method 3

But I wanted to know how to implement a custom Fetcher and get the text in html and break them
Because now I can tell Readium to show, for example, only 3 of the chapters
But some chapters have a lot of text, I want to break that.

And did I understand correctly that the html operation is performed in the HtmlInjector class?

And is there a better way to delete some of the texts in the chapter at all?

Thanks again for your guidance

[mickael-menu]

No the HtmlInjector is a private implementation details, so you should not modify it.

You can wrap the default fetcher with your own TransformingFetcher, passing it a function that will modify the Resource on the fly:

val publication = streamer.open(
    asset,
    onCreatePublication = {
        fetcher = TransformingFetcher(fetcher, ::stripHtml)
    }
).getOrThrow()

fun stripHtml(resource: Resource): Resource =
    object : TransformingResource(resource) {
        override suspend fun transform(data: ResourceTry<ByteArray>): ResourceTry<ByteArray> =
            if (!resource.link().mediaType.isHtml)
                data
            else
                data.mapCatching {
                    val html = it.toString()
                    // Modify the HTML here...
                    html.toByteArray()
                }
    }