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

Sources/apk/Utility/MemoryInputStream.swift

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: Apache-2.0
+
+import Foundation
+
+public struct MemoryInputStream: InputStream {
+  private var _buf: [UInt8]! = nil
+  private let _sli: ArraySlice<UInt8>
+  private let _len: Int
+  private var _idx = 0
+
+  public init(buffer: Data) {
+    self._len = buffer.count
+    self._buf = [UInt8](repeating: 0, count: self._len)
+    self._buf.withUnsafeMutableBytes { _ = buffer.copyBytes(to: $0) }
+    self._sli = self._buf[...]
+  }
+
+  public init(view: ArraySlice<UInt8>) {
+    self._sli = view
+    self._len = view.count
+  }
+
+  public mutating func seek(_ whence: StreamWhence) throws(StreamError) {
+    let (position, overflow) = switch whence {
+    case .set(let position):   (position, false)
+    case .current(let offset): self._idx.addingReportingOverflow(offset)
+    case .end(let offset):     self._len.addingReportingOverflow(offset)
+    }
+    if overflow {
+      throw .overflow
+    } else if position < 0 {
+      throw .seekRange
+    } else {
+      self._idx = position
+    }
+  }
+
+  public var tell: Int {
+    get throws(StreamError) {
+      self._idx
+    }
+  }
+
+  public mutating func read(_ count: Int) throws(StreamError) -> Data {
+    let beg = min(self._idx, self._len)
+    let end = min(self._idx + count, self._len)
+    let bytes = Data(self._sli[beg..<end])
+    self._idx += beg.distance(to: end)
+    return bytes
+  }
+
+  public mutating func next() -> UInt8? {
+    if self._idx < self._len {
+      let byte = self._sli[self._idx]
+      self._idx += 1
+      return byte
+    } else {
+      return nil
+    }
+  }
+}