Add support for streaming LCP publications

[mickael-menu]

Added

LCP

• Support for streaming an LCP-protected publication from its License Document (LCPL).

---

Streaming an LCP protected package

If the server hosting the LCP protected package supports the HTTP HEAD method and HTTP Range requests, it is possible to stream directly an LCP protected publication from a License Document (.lcpl) file, without downloading the whole publication first.

Simply open the License Document directly using the PublicationOpener. Make sure you provide an HTTPClient (or an HTTPResourceFactory for additional customization) to the AssetRetriever.

// Instantiate the required components.
let httpClient = DefaultHTTPClient()
let assetRetriever = AssetRetriever(httpClient: httpClient)
let publicationOpener = PublicationOpener(
    parser: DefaultPublicationParser(
        httpClient: httpClient,
        assetRetriever: assetRetriever
    ),
    contentProtections: [
        lcpService.contentProtection(with: LCPDialogAuthentication()),
    ]
)

// Retrieve an `Asset` to access the LCPL content.
let url = FileURL(path: "/path/to/license.lcpl", isDirectory: false)
let asset = try await assetRetriever.retrieve(url: url).get()

// Open a `Publication` from the LCPL `Asset`.
let publication = try await publicationOpener.open(
    asset: asset,
    allowUserInteraction: true,
    sender: hostViewController
).get()

print("Opened \(publication.metadata.title)")

---

Possible improvements: servers not supporting HEAD requests and progressive streaming using the same HTTP request. This requires some breaking changes in the HTTPClient protocol, so postponing for 4.0.