[container-build]: Support inline Dockerfile from stdin

Sources/ContainerCommands/BuildCommand.swift

@@ -207,7 +207,33 @@ extension Application {
                     buildFilePath = resolvedPath
                 }
 
-                let buildFileData = try Data(contentsOf: URL(filePath: buildFilePath))
+                let buildFileData: Data
+                // Dockerfile should be read from stdin
+                if file == "-" {
+                    let tempFile = FileManager.default.temporaryDirectory.appendingPathComponent("Dockerfile-\(UUID().uuidString)")
+                    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")
+                    }
+
+                    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()
+                    buildFileData = try Data(contentsOf: URL(filePath: tempFile.path()))
+                } else {
+                    buildFileData = try Data(contentsOf: URL(filePath: buildFilePath))
+                }
 
                 let systemHealth = try await ClientHealthCheck.ping(timeout: .seconds(10))
                 let exportPath = systemHealth.appRoot

Tests/CLITests/Subcommands/Build/CLIBuildBase.swift

@@ -144,6 +144,42 @@ class TestCLIBuildBase: CLITest {
         return response.output
     }
 
+    @discardableResult
+    func buildWithStdin(
+        tags: [String],
+        tempContext: URL,
+        dockerfileContents: String,
+        buildArgs: [String] = [],
+        otherArgs: [String] = []
+    ) throws -> String {
+        let contextDir: URL = tempContext.appendingPathComponent("context")
+        let contextDirPath = contextDir.absoluteURL.path
+        var args = [
+            "build",
+            "-f",
+            "-",
+        ]
+        for tag in tags {
+            args.append("-t")
+            args.append(tag)
+        }
+        for arg in buildArgs {
+            args.append("--build-arg")
+            args.append(arg)
+        }
+        args.append(contextDirPath)
+
+        args.append(contentsOf: otherArgs)
+
+        let stdinData = Data(dockerfileContents.utf8)
+        let response = try run(arguments: args, stdin: stdinData)
+        if response.status != 0 {
+            throw CLIError.executionFailed("build failed: stdout=\(response.output) stderr=\(response.error)")
+        }
+
+        return response.output
+    }
+
     enum FileSystemEntry {
         case file(
             _ path: String,

Tests/CLITests/Subcommands/Build/CLIBuilderTest.swift

@@ -456,5 +456,20 @@ extension TestCLIBuildBase {
             #expect(try self.inspectImage(tag2) == tag2, "expected to have successfully built \(tag2)")
             #expect(try self.inspectImage(tag3) == tag3, "expected to have successfully built \(tag3)")
         }
+
+        @Test func testBuildWithDockerfileFromStdin() throws {
+            let tempDir: URL = try createTempDir()
+            let dockerfile =
+                """
+                FROM scratch
+
+                ADD emptyFile /
+                """
+            let context: [FileSystemEntry] = [.file("emptyFile", content: .zeroFilled(size: 1))]
+            try createContext(tempDir: tempDir, dockerfile: "", context: context)
+            let imageName = "registry.local/stdin-file:\(UUID().uuidString)"
+            try buildWithStdin(tags: [imageName], tempContext: tempDir, dockerfileContents: dockerfile)
+            #expect(try self.inspectImage(imageName) == imageName, "expected to have successfully built \(imageName)")
+        }
     }
 }