PDF Streaming using Swift for iOS

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//
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//  Copyright © 2020-2025 PSPDFKit GmbH. All rights reserved.
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//
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//  The Nutrient sample applications are licensed with a modified BSD license.
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//  Please see License for details. This notice may not be removed from this file.
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//
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import PSPDFKit
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import PSPDFKitUI
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/// The streaming document example can download documents on a page-by-page basis,
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/// so opening is pretty much instant.
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///
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/// This can be useful if you have a large document that you'd like to stream to the user in individual pages.
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/// It requires that the document is split up into individual pages and accessible on your web server.
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///
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/// To test: Open a local webserver in the folder where the document can be found.
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/// A simple way is via python, which is installed by default on macOS:
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///
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/// - python -m SimpleHTTPServer 8000    # Python 2
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/// - python -m http.server              # Python 3
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///
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/// This example is a special case for fast display and comes with a few caveats:
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/// - The document needs to be separated on a server
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/// - Document outlines are not supported
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/// - Document page labels are not supported
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/// - Document Editor is not supported
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/// - Digital Signatures are not supported
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/// - The replaced document must have the same page count as the template part
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/// - Only documents with a uniform page size are supported correctly. The document size is defined by the first page.
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final class StreamingDocumentExample: Example {
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    override init() {
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        super.init()
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        title = "Streaming a document on-demand from a web-server"
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        self.contentDescription = "Demonstrates a way to load parts of a document on demand."
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        category = .documentDataProvider
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        priority = 10
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController {
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        let streamingHelper = StreamingDocumentGenerator()
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        let document = streamingHelper.streamingDocument
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        let controller = StreamingPDFViewController(document: document) {
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            $0.pageMode = .single
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            // page labels will be confusing for split documents
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            $0.isPageLabelEnabled = false
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            $0.thumbnailBarMode = .scrollable
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            // Use custom page view that shows download progress
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            $0.overrideClass(PDFPageView.self, with: StreamingPageView.self)
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            // These are optional, only if you need streaming thumbnails.
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            $0.overrideClass(ThumbnailBar.self, with: StreamingThumbnailBar.self)
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            $0.overrideClass(ThumbnailViewController.self, with: StreamingThumbnailViewController.self)
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        }
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        let clearCacheItem = UIBarButtonItem(title: "Clear Cache", image: nil, primaryAction: UIAction(title: "", image: nil, identifier: nil, discoverabilityTitle: nil, attributes: [], state: .off, handler: { [weak controller] _ in
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            controller?.stopDownloadingFiles()
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            SDK.shared.cache.clear()
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            try? FileManager.default.removeItem(at: document.streamingDefinition.downloadFolder)
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            let newDocument = StreamingDocument(streamingDefinition: document.streamingDefinition)
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            controller?.document = newDocument
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            controller?.downloadFile(pageIndex: 0)
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        }), menu: nil)
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        controller.navigationItem.setLeftBarButtonItems([clearCacheItem], for: .document, animated: false)
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        controller.navigationItem.leftItemsSupplementBackButton = true
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        // Show explain alert if there is no webserver running.
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        streamingHelper.showExampleAlertIfNeeded(on: controller)
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        return controller
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    }
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}