[Build] fixes for tar output mode (#353)

Fixes https://github.com/apple/container/issues/347

Sources/ContainerBuild/BuildExporter.swift

@@ -1,129 +0,0 @@
-//===----------------------------------------------------------------------===//
-// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//   https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-//===----------------------------------------------------------------------===//
-
-import ContainerizationArchive
-import Foundation
-import GRPC
-import NIO
-
-actor BuildExporter: BuildPipelineHandler {
-    let output: OutputStream
-    let channel: AsyncThrowingStream<(AsyncStream<ClientStream>.Continuation, ServerStream), Swift.Error>.Continuation
-
-    public init(output: URL) throws {
-        guard let output = OutputStream(toFileAtPath: output.absolutePath(), append: true) else {
-            throw Error.couldNotInitializeOutput(output.absolutePath())
-        }
-        self.output = output
-        self.output.open()
-        var c: AsyncThrowingStream<(AsyncStream<ClientStream>.Continuation, ServerStream), Swift.Error>.Continuation?
-        let writeStream: AsyncThrowingStream<(AsyncStream<ClientStream>.Continuation, ServerStream), Swift.Error> = AsyncThrowingStream { continuation in
-            c = continuation
-        }
-        guard let c else {
-            throw Builder.Error.invalidContinuation
-        }
-        self.channel = c
-        Task.detached {
-            for try await packet in writeStream {
-                try await self.write(packet.0, packet.1)
-            }
-        }
-    }
-
-    nonisolated func accept(_ packet: ServerStream) throws -> Bool {
-        guard let buildTransfer = packet.getBuildTransfer() else {
-            return false
-        }
-        guard buildTransfer.stage() == "exporter" else {
-            return false
-        }
-        return true
-    }
-
-    func handle(_ sender: AsyncStream<ClientStream>.Continuation, _ packet: ServerStream) async throws {
-        self.channel.yield((sender, packet))  // guarantees ordering while being non-blocking
-    }
-
-    func write(_ sender: AsyncStream<ClientStream>.Continuation, _ packet: ServerStream) async throws {
-        guard let buildTransfer = packet.getBuildTransfer() else {
-            throw Error.buildTransferMissing
-        }
-        guard buildTransfer.stage() == "exporter" else {
-            throw Error.invalidStage(buildTransfer.stage() ?? "")
-        }
-        let buildID = packet.buildID
-        if buildTransfer.complete {
-            var transfer = BuildTransfer()
-            transfer.id = buildTransfer.id
-            transfer.direction = .outof
-            transfer.metadata = [
-                "os": "linux",
-                "stage": "exporter",
-            ]
-            var response = ClientStream()
-            response.buildID = buildID
-            response.buildTransfer = transfer
-            response.packetType = .buildTransfer(transfer)
-            sender.yield(response)
-
-            self.output.close()
-            return
-        }
-        try buildTransfer.data.withUnsafeBytes { rawBuf in
-            let bufPointer = rawBuf.bindMemory(to: UInt8.self)
-            if let baseAddr = bufPointer.baseAddress, bufPointer.count > 0 {
-                let n = self.output.write(baseAddr, maxLength: bufPointer.count)
-                if n < 0 || n < bufPointer.count {
-                    throw Error.writeError
-                }
-            }
-        }
-        var transfer = BuildTransfer()
-        transfer.id = buildTransfer.id
-        transfer.direction = .outof
-        transfer.metadata = [
-            "os": "linux",
-            "stage": "exporter",
-        ]
-        var response = ClientStream()
-        response.buildID = buildID
-        response.buildTransfer = transfer
-        response.packetType = .buildTransfer(transfer)
-        sender.yield(response)
-    }
-}
-
-extension BuildExporter {
-    enum Error: Swift.Error, CustomStringConvertible {
-        case buildTransferMissing
-        case invalidStage(String)
-        case couldNotInitializeOutput(String)
-        case writeError
-        var description: String {
-            switch self {
-            case .buildTransferMissing:
-                return "buildTransfer field missing in packet"
-            case .invalidStage(let stage):
-                return "stage \(stage) is invalid, expected 'exporter'"
-            case .couldNotInitializeOutput(let output):
-                return "could not open \(output) for writing"
-            case .writeError:
-                return "write failed"
-            }
-        }
-    }
-}

Sources/ContainerBuild/BuildPipelineHandler.swift

@@ -26,14 +26,8 @@ protocol BuildPipelineHandler: Sendable {
 public actor BuildPipeline {
     let handlers: [BuildPipelineHandler]
     public init(_ config: Builder.BuildConfig) async throws {
-        let exporters: [BuildPipelineHandler] = try config.exports.map { export in
-            guard let destination = export.destination else {
-                throw Builder.Error.invalidExport(export.rawValue, "dest is required")
-            }
-            return try BuildExporter(output: destination)
-        }
         self.handlers =
-            exporters + [
+            [
                 try BuildFSSync(URL(filePath: config.contextDir)),
                 try BuildRemoteContentProxy(config.contentStore),
                 try BuildImageResolver(config.contentStore),