Save PDFs to a Custom Data Provider on iOS

class YourDataProvider: NSObject, NSSecureCoding, DataProviding {

    // MARK: Properties

    var size: UInt64 {
        // Returns the size of the data.
        guard let data = self.data else { return 0 }
        return UInt64(data.count)
    }

    var uid: String {
        // This can be anything that uniquely identifies your data:
        // the resource name from the original data, the UUID — you name it.
        return uniqueIdentifierForYourData
    }

    // [...]

    // MARK: DataProviding

    func readData(withSize size: UInt64, atOffset offset: UInt64) -> Data {
        guard let data = self.data else { return Data() }
        // We have to clamp the given size and offset to make sure we don't try
        // to read data that doesn't exist.
        let length = self.size
        let clampedOffset = min(offset, length)
        let clampedSize = min(size, length - clampedOffset)
        // Actually return the data.
        let range: Range = Int(clampedOffset)..<Int(clampedOffset+clampedSize)
        return data.subdata(in: range)
    }
}

@interface YourDataProvider : NSObject <PSPDFDataProviding> @end

@implementation YourDataProvider

#pragma mark - Properties

- (uint64_t)size {
    // Returns the size of the data.
    return self.data.length;
}

- (NSString *)UID {
    // This can be anything that uniquely identifies your data:
    // the resource name from the original data, the UUID — you name it.
    return uniqueIdentifierForYourData;
}

// [...]

#pragma mark - PSPDFDataProviding

- (NSData *)readDataWithSize:(uint64_t)size atOffset:(uint64_t)offset {
    // We have to clamp the given size and offset to make sure we don't try
    // to read data that doesn't exist.
    const NSUInteger length = self.size;
    NSUInteger clampedOffset = MIN((NSUInteger)offset, length);
    NSUInteger clampedSize =  MIN((NSUInteger)size, length - clampedOffset);
    // Actually return the data.
    return [self.data subdataWithRange:NSMakeRange(clampedOffset, clampedSize)];
}

@end

class YourDataSink: NSObject, DataSink {

    // MARK: Properties

    private(set) var isFinished = false
    let options: DataSinkOptions
    var writtenData = Data()

    // MARK: Lifecycle

    init(options: DataSinkOptions) {
        self.options = options
        super.init()
    }

    // MARK: DataSink

    func write(_ data: Data) -> Bool {
        // We append the passed-in data to our `writtenData`.
        writtenData.append(data)
        return true
    }

    func finish() -> Bool {
        // If you're implementing compression or encryption writing, you might need
        // to tell the compression or encryption library that you're finished
        // writing. You can do this here. For our purposes with the `Data`, we
        // don't need to do anything.
        isFinished = true
        return true
    }
}

@interface YourDataSink : NSObject <PSPDFDataSink>

@property (nonatomic, readonly) PSPDFDataSinkOptions options;
@property (nonatomic, readonly) NSMutableData *writtenData;

@end

@interface YourDataSink ()

@property (nonatomic) BOOL isFinished;

@end

@implementation YourDataSink

- (instancetype)initWithOptions:(PSPDFDataSinkOptions)options {
    if ((self = [super init])) {
        // We initialize `writtenData` with an empty mutable `NSMutableData`.
        _writtenData = [NSMutableData data];
        _options = options;
    }
    return self;
}

- (BOOL)writeData:(NSData *)data {
    // We append the passed-in data to our `writtenData`.
    [self.writtenData appendData:data];
    return YES;
}

- (BOOL)finish {
    // If you're implementing compression or encryption writing, you might need
    // to tell the compression or encryption library that you are finished
    // writing. You can do this here. For our purposes with the `NSData`, we
    // don't need to do anything.
    self.isFinished = YES;
    return YES;
}

@end

class YourDataProvider: NSObject, NSSecureCoding, PSPDFDataProviding {

    // ... your previous implementation ...

    var additionalOperationsSupported: PSPDFDataProvidingAdditionalOperations {
        // Signal to PSPDFKit that this data provider can support writing by
        // returning the following option:
        return .write
    }

    func createDataSink(options: PSPDFDataSinkOptions) -> PSPDFDataSink {
        // When PSPDFKit wants to write to the data provider, it will call this
        // method and it passes in if it wants to overwrite or append to the file.
        return YourDataSink(options: options)
    }

    func replace(with replacementDataSink: PSPDFDataSink) -> Bool {
        // After PSPDFKit finishes writing, it passes in the data sink
        // that was previously created in `-createDataSinkWithOptions:`.
        let dataSink = replacementDataSink as! YourDataSink

        // We have to check if we have to overwrite or append.
        if dataSink.options.contains(.append) {
            // We have to append the data.
            guard let data = data else { return false }
            var replacementData = data
            replacementData.append(dataSink.writtenData)
        } else {
            // We can simply replace our data.
            data = dataSink.writtenData
        }

        return true
    }
}

@implementation YourDataProvider

// ... your previous implementation ...

- (PSPDFDataProvidingAdditionalOperations)additionalOperationsSupported {
    // Signal to PSPDFKit that this data provider can support writing by
    // returning the following option:
    return PSPDFDataProvidingAdditionalOperationWrite;
}

- (id<PSPDFDataSink>)createDataSinkWithOptions:(PSPDFDataSinkOptions)options {
    // When PSPDFKit wants to write to the data provider, it will call this
    // method and passes in if it wants to overwrite or append to the file.
    return [[YourNSDataSink alloc] initWithOptions:options];
}

- (BOOL)replaceWithDataSink:(id<PSPDFDataSink>)replacementDataSink {
    // After PSPDFKit finishes writing, it passes in the data sink
    // that was previously created in `-createDataSinkWithOptions:`.
    YourNSDataSink *dataSink = (YourNSDataSink*)replacementDataSink;
    // We have to check if we have to overwrite or append.
    if (dataSink.options & PSPDFDataSinkOptionAppend) {
        // We have to append the data.
        NSMutableData *replacementData = [self.data mutableCopy];
        [replacementData appendData:dataSink.writtenData];
        self.data = replacementData;
    } else {
        // We can simply replace our data.
        self.data = dataSink.writtenData;
    }
    return YES;
}

@end