container/Sources/ContainerizationArchive/Reader.swift

//===----------------------------------------------------------------------===//
// Copyright © 2025 Apple Inc. and the containerization 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 CArchive
import Foundation

public final class ArchiveReader {
    var underlying: OpaquePointer?
    let fileHandle: FileHandle?

    public convenience init(format: Format, filter: Filter, file: URL) throws {
        let fileHandle = try FileHandle(forReadingFrom: file)
        try self.init(format: format, filter: filter, fileHandle: fileHandle)
    }

    public init(format: Format, filter: Filter, fileHandle: FileHandle) throws {
        self.underlying = archive_read_new()
        self.fileHandle = fileHandle

        try archive_read_set_format(underlying, format.code)
            .checkOk(elseThrow: .unableToSetFormat(format.code, format))
        try archive_read_append_filter(underlying, filter.code)
            .checkOk(elseThrow: .unableToAddFilter(filter.code, filter))

        let fd = fileHandle.fileDescriptor
        try archive_read_open_fd(underlying, fd, 4096)
            .checkOk(elseThrow: { .unableToOpenArchive($0) })
    }

    // Initialize the archive reader by trying to auto detect the archive and compression format
    public init(file: URL) throws {
        self.underlying = archive_read_new()
        let fileHandle = try FileHandle(forReadingFrom: file)
        self.fileHandle = fileHandle
        try archive_read_support_filter_all(underlying)
            .checkOk(elseThrow: .failedToDetectFilter)
        try archive_read_support_format_all(underlying)
            .checkOk(elseThrow: .failedToDetectFormat)
        let fd = fileHandle.fileDescriptor
        try archive_read_open_fd(underlying, fd, 4096)
            .checkOk(elseThrow: { .unableToOpenArchive($0) })
    }

    deinit {
        archive_read_free(underlying)
        try? fileHandle?.close()
    }
}

extension CInt {
    fileprivate func checkOk(elseThrow error: @autoclosure () -> ArchiveError) throws {
        guard self == ARCHIVE_OK else { throw error() }
    }
    fileprivate func checkOk(elseThrow error: (CInt) -> ArchiveError) throws {
        guard self == ARCHIVE_OK else { throw error(self) }
    }

}

extension ArchiveReader: Sequence {
    public func makeIterator() -> Iterator {
        Iterator(reader: self)
    }

    public struct Iterator: IteratorProtocol {
        var reader: ArchiveReader

        public mutating func next() -> (WriteEntry, Data)? {
            let entry = WriteEntry()
            let result = archive_read_next_header2(reader.underlying, entry.underlying)
            if result == ARCHIVE_EOF {
                return nil
            }

            var data = Data()
            while true {
                let capacity = Int(data.isEmpty ? (entry.size ?? 4096) : 4096)

                var part = Data(count: capacity)
                let c = part.withUnsafeMutableBytes { (buffer: UnsafeMutableRawBufferPointer) in
                    archive_read_data(reader.underlying, buffer.baseAddress!, buffer.count)
                }
                guard c > 0 else { break }
                part.count = c
                data.append(part)
            }
            return (entry, data)
        }
    }
}

extension ArchiveReader {
    public convenience init(name: String, bundle: Data, tempDirectoryBaseName: String? = nil) throws {
        let baseName = tempDirectoryBaseName ?? "Unarchiver"
        let url = createTemporaryDirectory(baseName: baseName)!.appendingPathComponent(name)

        try bundle.write(to: url, options: .atomic)

        try self.init(format: .zip, filter: .none, file: url)
    }

    /// Extracts the contents of an archive to the provided directory.
    /// Currently only handles regular files and directories present in the archive.
    public func extractContents(to directory: URL) throws {
        let fm = FileManager.default
        var foundEntry = false
        for (entry, data) in self {
            guard let p = entry.path else { continue }
            foundEntry = true
            let type = entry.fileType
            let target = directory.appending(path: p)
            switch type {
            case .regular:
                try data.write(to: target, options: .atomic)
            case .directory:
                try fm.createDirectory(at: target, withIntermediateDirectories: true)
            default:
                continue
            }
            chmod(target.path(), entry.permissions)
            if let owner = entry.owner, let group = entry.group {
                chown(target.path(), owner, group)
            }
        }
        guard foundEntry else {
            throw ArchiveError.failedToExtractArchive("No entries found in archive")
        }
    }
}