Tried a few things to try making memory streams faster, the answer may be in just biting the bullet and making streams classes though

Sources/apk/Utility/MemoryInputStream.swift

@@ -4,25 +4,52 @@
  */
 
 import Foundation
+import System
 
 public struct MemoryInputStream: InputStream {
-  private var _buf: [UInt8]! = nil
+  private var _buf: ContiguousArray<UInt8>! = nil
   private let _sli: ArraySlice<UInt8>
+  private let _ptr: UnsafeBufferPointer<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._buf = .buffer(.allocate(capacity: self._len))
+    if case .buffer(let buf) = _buf {
+      _ = buffer.copyBytes(to: buf)
+      self._ptr = .init(start: buf.baseAddress, count: self._len)
+    } else { fatalError() }
+    */
+    self._buf = .init(repeating: 0, count: self._len)
+    self._buf.withUnsafeMutableBufferPointer { buf in
+      _ = buffer.copyBytes(to: buf)
+    }
     self._sli = self._buf[...]
+    self._ptr = self._sli.withUnsafeBufferPointer(\.self)
   }
 
   public init(view: ArraySlice<UInt8>) {
-    self._sli = view
     self._len = view.count
+    /*
+    self._buf = .slice(view)
+    if case .slice(let sli) = _buf {
+      self._ptr = sli.withUnsafeBufferPointer(\.self)
+    } else { fatalError() }
+    */
+    self._sli = view
+    self._ptr = self._sli.withUnsafeBufferPointer(\.self)
   }
 
+  /*
+  deinit {
+    if case .buffer(let buf) = _buf {
+      buf.deallocate()
+    }
+  }
+  */
+
   public mutating func seek(_ whence: StreamWhence) throws(StreamError) {
     let (position, overflow) = switch whence {
     case .set(let position):   (position, false)
@@ -47,7 +74,7 @@ public struct MemoryInputStream: InputStream {
   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])
+    let bytes = Data(self._ptr[beg..<end])
     self._idx += beg.distance(to: end)
     return bytes
   }
@@ -58,16 +85,25 @@ public struct MemoryInputStream: InputStream {
     let len = beg.distance(to: end)
     let buf = UnsafeMutableRawBufferPointer(start: buffer, count: len)
     self._idx += len
-    return self._sli.copyBytes(to: buf, from: beg..<end)
+    return self._ptr.copyBytes(to: buf, from: beg..<end)
   }
 
   public mutating func next() -> UInt8? {
-    if self._idx < self._len {
+    if _fastPath(self._idx < self._len) {
-      let byte = self._sli[self._idx]
+      defer { self._idx += 1 }
-      self._idx += 1
+      return self._ptr[self._idx]
-      return byte
     } else {
       return nil
     }
   }
 }
+
+/*
+fileprivate extension MemoryInputStream {
+  enum Storage {
+    //case buffer(_: UnsafeMutableBufferPointer<UInt8>)
+    case buffer(_: ContiguousArray<UInt8>)
+    case slice(_: ArraySlice<UInt8>)
+  }
+}
+*/