Initial implementation of APKINDEX, fetching, reading, parsing, & merging

Sources/apk/Utility/TarMemoryReader.swift

@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: Apache-2.0
+
+import Foundation
+
+public struct TarReader {
+  private static let tarBlockSize  = 512
+  private static let tarTypeOffset = 156
+  private static let tarNameOffset =   0
+  private static let tarNameSize   = 100
+  private static let tarSizeOffset = 124
+  private static let tarSizeSize   =  12
+
+  public enum Entry {
+    case file(name: String, data: Data)
+    case directory(name: String)
+  }
+
+  public static func read<S: InputStream>(_ stream: inout S) throws -> [Entry] {
+    var entries = [Entry]()
+
+    while true {
+      let tarBlock = try stream.read(Self.tarBlockSize)
+      if tarBlock.isEmpty { break }
+      if tarBlock.count < Self.tarBlockSize { throw TarError.unexpectedEndOfStream }
+
+      let type = UnicodeScalar(tarBlock[Self.tarTypeOffset])
+      switch type {
+      case "0":  // Regular file
+        // Read metadata
+        let name = try Self.readName(tarBlock)
+        let size = try Self.readSize(tarBlock)
+
+        // Read file data
+        var data = Data()
+        var bytesRemaining = size, readAmount = 0
+        while bytesRemaining > 0 {
+          //FIXME: just read the whole thing at once tbh
+          readAmount = min(bytesRemaining, Self.tarBlockSize)
+          let block = try stream.read(readAmount)
+          if block.count < readAmount { throw TarError.unexpectedEndOfStream }
+          data += block
+          bytesRemaining -= readAmount
+        }
+        entries.append(.file(name: name, data: data))
+
+        // Seek to next block
+        let seekAmount = Self.tarBlockSize - readAmount
+        if seekAmount > 0 {
+          try stream.seek(.current(seekAmount))
+        }
+      case "5":
+        // Directory
+        let name = try Self.readName(tarBlock)
+        entries.append(.directory(name: name))
+      case "\0":
+        // Null block, might also be a legacy regular file
+        break
+      case "x":
+        // Extended header block
+        try stream.seek(.current(Self.tarBlockSize))
+      // Symlink, Reserved, Character, Block, FIFO, Reserved, Global, ignore all these
+      case "1", "2", "3", "4", "6", "7", "g":
+        let size = try self.readSize(tarBlock)
+        let blockCount = (size - 1) / Self.tarBlockSize + 1  // Compute blocks to skip
+        try stream.seek(.current(Self.tarBlockSize * blockCount))
+      default: throw TarError.invalidType(type: type)  // Not a TAR type
+      }
+    }
+    return entries
+  }
+
+  private static func readName(_ tar: Data, offset: Int = Self.tarNameOffset) throws (TarError) -> String {
+    var nameSize = Self.tarNameSize
+    for i in 0...Self.tarNameSize {
+      if tar[offset + i] == 0 {
+        nameSize = i
+        break
+      }
+    }
+    let data = tar.subdata(in: offset..<offset + nameSize)
+    guard let name = String(data: data, encoding: .utf8) else { throw TarError.badNameField }
+    return name
+  }
+
+  private static func readSize(_ tar: Data, offset: Int = Self.tarSizeOffset) throws (TarError) -> Int {
+    let sizeData = tar.subdata(in: offset..<offset + Self.tarSizeSize)
+    let sizeEnd = sizeData.firstIndex(of: 0) ?? sizeData.endIndex  // Find the null terminator
+    guard
+      let sizeString = String(data: sizeData[..<sizeEnd], encoding: .ascii),
+      let result = Int(sizeString, radix: 0o10) else { throw TarError.badSizeField }
+    return result
+  }
+}
+
+public enum TarError: Error, LocalizedError {
+  case unexpectedEndOfStream
+  case invalidType(type: UnicodeScalar)
+  case badNameField, badSizeField
+
+  public var errorDescription: String? {
+    switch self {
+    case .unexpectedEndOfStream: "Stream unexpectedly ended early"
+    case .invalidType(let type): "Invalid block type \(type) found"
+    case .badNameField: "Bad name field"
+    case .badSizeField: "Bad size field"
+    }
+  }
+}
+
+public extension Array<TarReader.Entry> {
+  func firstFile(name firstNameMatch: String) -> Data? {
+    for entry in self {
+      if case .file(let name, let data) = entry {
+        if name == firstNameMatch {
+          return data
+        }
+      }
+    }
+    return nil
+  }
+}