tart pull: re-try disk layer downloads by specifying "Range" header (#980)

Sources/tart/OCI/Layerizer/DiskV2.swift

@@ -44,7 +44,7 @@ class DiskV2: Disk {
           let compressedData = try (data as NSData).compressed(using: .lz4) as Data
           let compressedDataDigest = Digest.hash(compressedData)
 
-          try await retry(maxAttempts: 5, backoff: .exponentialWithFullJitter(baseDelay: .seconds(5), maxDelay: .seconds(60))) {
+          try await retry(maxAttempts: 5) {
             if try await !registry.blobExists(compressedDataDigest) {
               _ = try await registry.pushBlob(fromData: compressedData, chunkSizeMb: chunkSizeMb, digest: compressedDataDigest)
             }
@@ -208,11 +208,26 @@ class DiskV2: Disk {
             diskWritingOffset = try zeroSkippingWrite(disk, rdisk, fsBlockSize, diskWritingOffset, data)
           }
 
-          try await registry.pullBlob(diskLayer.digest) { data in
-            try filter.write(data)
+          var rangeStart: Int64 = 0
 
-            // Update the progress
-            progress.completedUnitCount += Int64(data.count)
+          try await retry(maxAttempts: 5) {
+            try await registry.pullBlob(diskLayer.digest, rangeStart: rangeStart) { data in
+              try filter.write(data)
+
+              // Update the progress
+              progress.completedUnitCount += Int64(data.count)
+
+              // Update the current range start
+              rangeStart += Int64(data.count)
+            }
+          } recoverFromFailure: { error in
+            if error is URLError {
+              print("Error pulling disk layer \(index + 1): \"\(error.localizedDescription)\", attempting to re-try...")
+
+              return .retry
+            }
+
+            return .throw
           }
 
           try filter.finalize()

Sources/tart/OCI/Registry.swift

@@ -20,6 +20,7 @@ enum HTTPCode: Int {
   case Ok = 200
   case Created = 201
   case Accepted = 202
+  case PartialContent = 206
   case Unauthorized = 401
   case NotFound = 404
 }
@@ -263,9 +264,21 @@ class Registry {
     }
   }
 
-  public func pullBlob(_ digest: String, handler: (Data) async throws -> Void) async throws {
-    let (channel, response) = try await channelRequest(.GET, endpointURL("\(namespace)/blobs/\(digest)"), viaFile: true)
-    if response.statusCode != HTTPCode.Ok.rawValue {
+  public func pullBlob(_ digest: String, rangeStart: Int64 = 0, handler: (Data) async throws -> Void) async throws {
+    var expectedStatusCode = HTTPCode.Ok
+    var headers: [String: String] = [:]
+
+    // Send Range header and expect HTTP 206 in return
+    //
+    // However, do not send Range header at all when rangeStart is 0,
+    // because it makes no sense and we might get HTTP 200 in return
+    if rangeStart != 0 {
+      expectedStatusCode = HTTPCode.PartialContent
+      headers["Range"] = "bytes=\(rangeStart)-"
+    }
+
+    let (channel, response) = try await channelRequest(.GET, endpointURL("\(namespace)/blobs/\(digest)"), headers: headers, viaFile: true)
+    if response.statusCode != expectedStatusCode.rawValue {
       let body = try await channel.asData().asText()
       throw RegistryError.UnexpectedHTTPStatusCode(when: "pulling blob", code: response.statusCode,
                                                    details: body)

Sources/tart/VMStorageOCI.swift

@@ -196,7 +196,7 @@ class VMStorageOCI: PrunableStorage {
       }
 
       try await withTaskCancellationHandler(operation: {
-        try await retry(maxAttempts: 5, backoff: .exponentialWithFullJitter(baseDelay: .seconds(5), maxDelay: .seconds(60))) {
+        try await retry(maxAttempts: 5) {
           // Choose the best base image which has the most deduplication ratio
           let localLayerCache = try await chooseLocalLayerCache(name, manifest, registry)
 
@@ -213,8 +213,7 @@ class VMStorageOCI: PrunableStorage {
           try await tmpVMDir.pullFromRegistry(registry: registry, manifest: manifest, concurrency: concurrency, localLayerCache: localLayerCache, deduplicate: deduplicate)
         } recoverFromFailure: { error in
           if error is URLError {
-            print("Error: \(error.localizedDescription)")
-            print("Attempting to re-try...")
+            print("Error pulling image: \"\(error.localizedDescription)\", attempting to re-try...")
 
             return .retry
           }