Modern Concurrency: Getting Started
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Make sure the course server is running and continue with your project from the previous episode or open the starter project for this episode.
if let offset = offset {
// Add code for Cloud 9 plan
}
else {
result = try await URLSession.shared.bytes(from: url)
guard (result.response as? HTTPURLResponse)?.statusCode == 200 else {
throw "The server responded with an error."
}
}
if let offset = offset {
🟩
let urlRequest = URLRequest(url: url, offset: offset, length: size)
🟥
}
extension URLRequest {
init(url: URL, offset: Int, length: Int) {
self.init(url: url)
addValue("bytes=\(offset)-\(offset + length - 1)", forHTTPHeaderField: "Range")
}
}
0-19999 [offset 0, length 20000]
20000-39999 [offset 20000, length 20000]
40000-59999 [offset 40000, length 20000]
60000-77344 [offset 0, length 17345]
if let offset = offset {
let urlRequest = URLRequest(url: url, offset: offset, length: size)
🟩result = try await URLSession.shared.bytes(for: urlRequest)🟥
}
if let offset = offset {
let urlRequest = URLRequest(url: url, offset: offset, length: size)
result = try await URLSession.shared.bytes(for: urlRequest)
🟩
guard (result.response as? HTTPURLResponse)?.statusCode == 206 else {
throw "The server responded with an error."
}
🟥
}
func multiDownloadWithProgress(file: DownloadFile) async throws -> Data {
func partInfo(index: Int, of count: Int) -> (offset: Int, size: Int, name: String) {
let standardPartSize = Int((Double(file.size) / Double(count)).rounded(.up))
let partOffset = index * standardPartSize
let partSize = min(standardPartSize, file.size - partOffset)
let partName = "\(file.name) (part \(index + 1))"
return (offset: partOffset, size: partSize, name: partName)
}
let total = 4
let parts = (0..<total).map { partInfo(index: $0, of: total) }
// Add code here, replacing placeholder return statement
return Data()
}
downloadWithProgress(fileName: String, name: String, size: Int, offset: Int? = nil)
Call multiDownloadWithProgress(file:)
Start with part0: Define a promise with async let:
async let part0 =
downloadWithProgress(fileName: file.name, name: parts[0].name, size: parts[0].size, offset: parts[0].offset)
async let part0 =
downloadWithProgress(fileName: file.name, name: parts[0].name, size: parts[0].size, offset: parts[0].offset)
🟩
async let part1 =
downloadWithProgress(fileName: file.name, name: parts[1].name, size: parts[1].size, offset: parts[1].offset)
async let part2 =
downloadWithProgress(fileName: file.name, name: parts[2].name, size: parts[2].size, offset: parts[2].offset)
async let part3 =
downloadWithProgress(fileName: file.name, name: parts[3].name, size: parts[3].size, offset: parts[3].offset)
🟥
try await [part0, part1, part2, part3]
try await [part0, part1, part2, part3]
🟩.reduce(Data(), +)🟥
🟩return 🟥try await [part0, part1, part2, part3]
.reduce(Data(), +)
❌return Data()
isDownloadActive = true
Task { // delete downloadTask =
do {
fileData = try await model.🟩multiDownloadWithProgress🟥(file: file)
} catch { }
isDownloadActive = false
// delete timerTask...
}