OCI: pull blobs via file (#306)

* OCI: pull blobs via file

* Explain why we delete the downloaded file after opening a handle to it

* Further abstract away ways to fetch a URLRequest

* No need to cast HTTPURLResponse to HTTPURLResponse

* Fetcher: no need to be a delegate anymore

* Fetcher.fetch() can be made static

Sources/tart/Fetcher.swift

@@ -1,46 +1,49 @@
 import Foundation
 import AsyncAlgorithms
 
-class Fetcher: NSObject, URLSessionTaskDelegate, URLSessionDelegate, URLSessionDataDelegate {
-    let responseCh = AsyncThrowingChannel<URLResponse, Error>()
+class Fetcher {
+  static func fetch(_ request: URLRequest, viaFile: Bool = false) async throws -> (AsyncThrowingChannel<Data, Error>, HTTPURLResponse) {
+    if viaFile {
+      return try await fetchViaFile(request)
+    }
+
+    return try await fetchViaMemory(request)
+  }
+
+  private static func fetchViaMemory(_ request: URLRequest) async throws -> (AsyncThrowingChannel<Data, Error>, HTTPURLResponse) {
     let dataCh = AsyncThrowingChannel<Data, Error>()
 
-    func fetch(_ request: URLRequest) async throws -> (AsyncThrowingChannel<Data, Error>, URLResponse) {
-        let task = URLSession.shared.dataTask(with: request)
-        task.delegate = self
-        task.resume()
+    let (data, response) = try await URLSession.shared.data(for: request)
 
-        // Wait for the response and only then return
-        var iter = responseCh.makeAsyncIterator()
-        let response = try await iter.next()!
+    Task {
+      await dataCh.send(data)
 
-        return (dataCh, response)
+      dataCh.finish()
     }
 
-    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse) async -> URLSession.ResponseDisposition {
-        await responseCh.send(response)
+    return (dataCh, response as! HTTPURLResponse)
+  }
 
-        return .allow
+  private static func fetchViaFile(_ request: URLRequest) async throws -> (AsyncThrowingChannel<Data, Error>, HTTPURLResponse) {
+    let dataCh = AsyncThrowingChannel<Data, Error>()
+
+    let (fileURL, response) = try await URLSession.shared.download(for: request)
+
+    // Acquire a handle to the downloaded file and then remove it.
+    //
+    // This keeps a working reference to that file, yet we don't
+    // have to deal with the cleanup any more.
+    let fh = try FileHandle(forReadingFrom: fileURL)
+    try FileManager.default.removeItem(at: fileURL)
+
+    Task {
+      while let data = try fh.read(upToCount: 64 * 1024 * 1024) {
+        await dataCh.send(data)
+      }
+
+      dataCh.finish()
     }
 
-    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
-        let sema = DispatchSemaphore(value: 0)
-
-        Task {
-            await dataCh.send(data)
-            sema.signal()
-        }
-
-        sema.wait()
-    }
-
-    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
-        if let error = error {
-            // Premature termination
-            responseCh.fail(error)
-            dataCh.fail(error)
-        } else {
-            dataCh.finish()
-        }
-    }
+    return (dataCh, response as! HTTPURLResponse)
+  }
 }

Sources/tart/OCI/Registry.swift

@@ -226,7 +226,7 @@ class Registry {
   }
 
   public func pullBlob(_ digest: String, handler: (Data) throws -> Void) async throws {
-    let (channel, response) = try await channelRequest(.GET, endpointURL("\(namespace)/blobs/\(digest)"))
+    let (channel, response) = try await channelRequest(.GET, endpointURL("\(namespace)/blobs/\(digest)"), viaFile: true)
     if response.statusCode != HTTPCode.Ok.rawValue {
       let body = try await channel.asData().asText()
       throw RegistryError.UnexpectedHTTPStatusCode(when: "pulling blob", code: response.statusCode,
@@ -266,7 +266,8 @@ class Registry {
     headers: Dictionary<String, String> = Dictionary(),
     parameters: Dictionary<String, String> = Dictionary(),
     body: Data? = nil,
-    doAuth: Bool = true
+    doAuth: Bool = true,
+    viaFile: Bool = false
   ) async throws -> (AsyncThrowingChannel<Data, Error>, HTTPURLResponse) {
     var urlComponents = urlComponents
 
@@ -292,12 +293,12 @@ class Registry {
       currentAuthToken = nil
     }
 
-    var (channel, response) = try await authAwareRequest(request: request)
+    var (channel, response) = try await authAwareRequest(request: request, viaFile: viaFile)
 
     if doAuth && response.statusCode == HTTPCode.Unauthorized.rawValue {
       _ = try await channel.asData()
       try await auth(response: response)
-      (channel, response) = try await authAwareRequest(request: request)
+      (channel, response) = try await authAwareRequest(request: request, viaFile: viaFile)
     }
 
     return (channel, response)
@@ -372,7 +373,7 @@ class Registry {
     return nil
   }
 
-  private func authAwareRequest(request: URLRequest) async throws -> (AsyncThrowingChannel<Data, Error>, HTTPURLResponse) {
+  private func authAwareRequest(request: URLRequest, viaFile: Bool = false) async throws -> (AsyncThrowingChannel<Data, Error>, HTTPURLResponse) {
     var request = request
 
     if let token = currentAuthToken {
@@ -380,8 +381,6 @@ class Registry {
       request.addValue(value, forHTTPHeaderField: name)
     }
 
-    let (channel, response) = try await Fetcher().fetch(request)
-
-    return (channel, response as! HTTPURLResponse)
+    return try await Fetcher.fetch(request, viaFile: viaFile)
   }
 }

Sources/tart/VM.swift

@@ -63,9 +63,9 @@ class VM: NSObject, VZVirtualMachineDelegate, ObservableObject {
 
   static func retrieveIPSW(remoteURL: URL) async throws -> URL {
     // Check if we already have this IPSW in cache
-    let (channel, response) = try await Fetcher().fetch(URLRequest(url: remoteURL))
+    let (channel, response) = try await Fetcher.fetch(URLRequest(url: remoteURL))
 
-    if let hash = (response as! HTTPURLResponse).value(forHTTPHeaderField: "x-amz-meta-digest-sha256") {
+    if let hash = response.value(forHTTPHeaderField: "x-amz-meta-digest-sha256") {
       let ipswLocation = try IPSWCache().locationFor(fileName: "sha256:\(hash).ipsw")
 
       if FileManager.default.fileExists(atPath: ipswLocation.path) {