containertool: Squash unnecessary layers of RegistryClient extensions

Author: euanh

Sources/containertool/Extensions/RegistryClient+Layers.swift

@@ -36,15 +36,24 @@ extension RegistryClient {
         }
     }
 
+    typealias DiffID = String
+    struct ImageLayer {
+        var descriptor: ContentDescriptor
+        var diffID: DiffID
+    }
+
     // A layer is a tarball, optionally compressed using gzip or zstd
     // See https://github.com/opencontainers/image-spec/blob/main/media-types.md
-    func uploadImageLayer(
+    func uploadLayer(
         repository: String,
-        layer: [UInt8],
+        contents: [UInt8],
         mediaType: String = "application/vnd.oci.image.layer.v1.tar+gzip"
-    ) async throws -> ContentDescriptor {
-        // The layer blob is the gzipped tarball
-        let blob = Data(gzip(layer))
-        return try await putBlob(repository: repository, mediaType: mediaType, data: blob)
+    ) async throws -> ImageLayer {
+        // The diffID is the hash of the unzipped layer tarball
+        let diffID = digest(of: contents)
+        // The layer blob is the gzipped tarball;  the descriptor is the hash of this gzipped blob
+        let blob = Data(gzip(contents))
+        let descriptor = try await putBlob(repository: repository, mediaType: mediaType, data: blob)
+        return ImageLayer(descriptor: descriptor, diffID: diffID)
     }
 }

Sources/containertool/containertool.swift

@@ -152,20 +152,19 @@ enum AllowHTTP: String, ExpressibleByArgument, CaseIterable { case source, desti
 
         // MARK: Upload resource layers
 
-        typealias DiffID = String
-        var resourceLayers: [(descriptor: ContentDescriptor, diffID: String)] = []
+        var resourceLayers: [RegistryClient.ImageLayer] = []
         for resourceDir in resources {
             let resourceTardiff = try Archive().appendingRecursively(atPath: resourceDir).bytes
-            let resourceLayer = try await destination.uploadImageLayer(
+            let resourceLayer = try await destination.uploadLayer(
                 repository: destination_image.repository,
-                layer: resourceTardiff
+                contents: resourceTardiff
             )
 
             if verbose {
-                log("resource layer: \(resourceLayer.digest) (\(resourceLayer.size) bytes)")
+                log("resource layer: \(resourceLayer.descriptor.digest) (\(resourceLayer.descriptor.size) bytes)")
             }
 
-            resourceLayers.append((resourceLayer, digest(of: resourceTardiff)))
+            resourceLayers.append(resourceLayer)
         }
 
         // MARK: Upload the application layer
@@ -256,16 +255,3 @@ enum AllowHTTP: String, ExpressibleByArgument, CaseIterable { case source, desti
         print(destination_image)
     }
 }
-
-extension RegistryClient {
-    typealias DiffID = String
-    struct ImageLayer {
-        var descriptor: ContentDescriptor
-        var diffID: DiffID
-    }
-    func uploadLayer(repository: String, contents: [UInt8]) async throws -> ImageLayer {
-        let diffID = digest(of: contents)
-        let descriptor = try await self.uploadImageLayer(repository: repository, layer: contents)
-        return ImageLayer(descriptor: descriptor, diffID: diffID)
-    }
-}