[image-save-load]: support for stdin/stdout (apple#734)

- Closes apple#559
- Facilitates easy transfer between container applications that can use OCI tarfiles.

Author: saehejkang

Sources/ContainerCommands/Image/ImageLoad.swift

@@ -34,15 +34,39 @@ extension Application {
             transform: { str in
                 URL(fileURLWithPath: str, relativeTo: .currentDirectory()).absoluteURL.path(percentEncoded: false)
             })
-        var input: String
+        var input: String?
 
         @OptionGroup
         var global: Flags.Global
 
         public func run() async throws {
-            guard FileManager.default.fileExists(atPath: input) else {
-                print("File does not exist \(input)")
-                Application.exit(withError: ArgumentParser.ExitCode(1))
+            let tempFile = FileManager.default.temporaryDirectory.appendingPathComponent("\(UUID().uuidString).tar")
+            defer {
+                try? FileManager.default.removeItem(at: tempFile)
+            }
+
+            // Read from stdin; otherwise read from the input file
+            if input == nil {
+                guard FileManager.default.createFile(atPath: tempFile.path(), contents: nil) else {
+                    throw ContainerizationError(.internalError, message: "unable to create temporary file")
+                }
+
+                guard let fileHandle = try? FileHandle(forWritingTo: tempFile) else {
+                    throw ContainerizationError(.internalError, message: "unable to open temporary file for writing")
+                }
+
+                let bufferSize = 4096
+                while true {
+                    let chunk = FileHandle.standardInput.readData(ofLength: bufferSize)
+                    if chunk.isEmpty { break }
+                    fileHandle.write(chunk)
+                }
+                try fileHandle.close()
+            } else {
+                guard FileManager.default.fileExists(atPath: input!) else {
+                    print("File does not exist \(input!)")
+                    Application.exit(withError: ArgumentParser.ExitCode(1))
+                }
             }
 
             let progressConfig = try ProgressConfig(
@@ -57,7 +81,7 @@ extension Application {
             progress.start()
 
             progress.set(description: "Loading tar archive")
-            let loaded = try await ClientImage.load(from: input)
+            let loaded = try await ClientImage.load(from: input ?? tempFile.path())
 
             let taskManager = ProgressTaskCoordinator()
             let unpackTask = await taskManager.startTask()

Sources/ContainerCommands/Image/ImageSave.swift

@@ -46,7 +46,7 @@ extension Application {
             transform: { str in
                 URL(fileURLWithPath: str, relativeTo: .currentDirectory()).absoluteURL.path(percentEncoded: false)
             })
-        var output: String
+        var output: String?
 
         @Option(
             help: "Platform for the saved image (format: os/arch[/variant], takes precedence over --os and --arch)"
@@ -88,9 +88,35 @@ extension Application {
 
             guard images.count == references.count else {
                 throw ContainerizationError(.invalidArgument, message: "failed to save image(s)")
+            }
+
+            // Write to stdout; otherwise write to the output file
+            if output == nil {
+                let tempFile = FileManager.default.temporaryDirectory.appendingPathComponent("\(UUID().uuidString).tar")
+                defer {
+                    try? FileManager.default.removeItem(at: tempFile)
+                }
+
+                guard FileManager.default.createFile(atPath: tempFile.path(), contents: nil) else {
+                    throw ContainerizationError(.internalError, message: "unable to create temporary file")
+                }
 
+                try await ClientImage.save(references: references, out: tempFile.path(), platform: p)
+
+                guard let fileHandle = try? FileHandle(forReadingFrom: tempFile) else {
+                    throw ContainerizationError(.internalError, message: "unable to open temporary file for reading")
+                }
+
+                let bufferSize = 4096
+                while true {
+                    let chunk = fileHandle.readData(ofLength: bufferSize)
+                    if chunk.isEmpty { break }
+                    FileHandle.standardOutput.write(chunk)
+                }
+                try fileHandle.close()
+            } else {
+                try await ClientImage.save(references: references, out: output!, platform: p)
             }
-            try await ClientImage.save(references: references, out: output, platform: p)
 
             progress.finish()
             for reference in references {

Tests/CLITests/Subcommands/Images/TestCLIImages.swift

@@ -359,4 +359,65 @@ extension TestCLIImagesCommand {
             return
         }
     }
+
+    @Test func testImageSaveAndLoadStdinStdout() throws {
+        do {
+            // 1. pull image
+            try doPull(imageName: alpine)
+            try doPull(imageName: busybox)
+
+            // 2. Tag image so we can safely remove later
+            let alpineRef: Reference = try Reference.parse(alpine)
+            let alpineTagged = "\(alpineRef.name):testImageSaveAndLoadStdinStdout"
+            try doImageTag(image: alpine, newName: alpineTagged)
+            let alpineTaggedImagePresent = try isImagePresent(targetImage: alpineTagged)
+            #expect(alpineTaggedImagePresent, "expected to see image \(alpineTagged) tagged")
+
+            let busyboxRef: Reference = try Reference.parse(busybox)
+            let busyboxTagged = "\(busyboxRef.name):testImageSaveAndLoadStdinStdout"
+            try doImageTag(image: busybox, newName: busyboxTagged)
+            let busyboxTaggedImagePresent = try isImagePresent(targetImage: busyboxTagged)
+            #expect(busyboxTaggedImagePresent, "expected to see image \(busyboxTagged) tagged")
+
+            // 3. save the image and output to stdout
+            let saveArgs = [
+                "image",
+                "save",
+                alpineTagged,
+                busyboxTagged,
+            ]
+            let (stdoutData, _, error, status) = try run(arguments: saveArgs)
+            if status != 0 {
+                throw CLIError.executionFailed("command failed: \(error)")
+            }
+
+            // 4. remove the image through container
+            try doRemoveImages(images: [alpineTagged, busyboxTagged])
+
+            // 5. verify image is no longer present
+            let alpineImageRemoved = try !isImagePresent(targetImage: alpineTagged)
+            #expect(alpineImageRemoved, "expected image \(alpineTagged) to be removed")
+            let busyboxImageRemoved = try !isImagePresent(targetImage: busyboxTagged)
+            #expect(busyboxImageRemoved, "expected image \(busyboxTagged) to be removed")
+
+            // 6. load the tarball from the stdout data as stdin
+            let loadArgs = [
+                "image",
+                "load",
+            ]
+            let (_, _, loadErr, loadStatus) = try run(arguments: loadArgs, stdin: stdoutData)
+            if loadStatus != 0 {
+                throw CLIError.executionFailed("command failed: \(loadErr)")
+            }
+
+            // 7. verify image is in the list again
+            let alpineImagePresent = try isImagePresent(targetImage: alpineTagged)
+            #expect(alpineImagePresent, "expected \(alpineTagged) to be present")
+            let busyboxImagePresent = try isImagePresent(targetImage: busyboxTagged)
+            #expect(busyboxImagePresent, "expected \(busyboxTagged) to be present")
+        } catch {
+            Issue.record("failed to save and load image \(error)")
+            return
+        }
+    }
 }