Helper extension over Foundation Data to compress/decompress it using given Compression algorithm. Originally designed for brotli compression/decompression of network request/response.

Data+Compression.swift

import Compression

extension Data {
    
    /// Compresses the data using the specified compression algorithm.
    func compressed(using algo: Algorithm, pageSize: Int = 65536) throws -> Data {
        var outputData = Data()
        let filter = try OutputFilter(.compress, using: algo, bufferCapacity: pageSize, writingTo: { $0.flatMap({ outputData.append($0) }) })
        
        var index = 0
        let bufferSize = count
        
        while true {
            let rangeLength = Swift.min(pageSize, bufferSize - index)
            
            let subdata = self.subdata(in: index ..< index + rangeLength)
            index += rangeLength
            
            try filter.write(subdata)
            
            if (rangeLength == 0) { break }
        }
        
        return outputData
    }
    
    /// Decompresses the data using the specified compression algorithm.
    func decompressed(from algo: Algorithm, pageSize: Int = 65536) throws -> Data {
        var outputData = Data()
        let bufferSize = count
        var decompressionIndex = 0
        
        let filter = try InputFilter(.decompress, using: algo) { (length: Int) -> Data? in
            let rangeLength = Swift.min(length, bufferSize - decompressionIndex)
            let subdata = self.subdata(in: decompressionIndex ..< decompressionIndex + rangeLength)
            decompressionIndex += rangeLength
            
            return subdata
        }
        
        while let page = try filter.readData(ofLength: pageSize) {
            outputData.append(page)
        }
        
        return outputData
    }
}