where possible, use uninitialized [UInt8] buffers

Author: lhoward

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version: 5.8
+// swift-tools-version: 5.9
 
 import Foundation
 import PackageDescription

Sources/IORing/IORing.swift

@@ -545,7 +545,7 @@ private extension IORing {
     count: Int,
     link: Bool = false
   ) throws -> AsyncThrowingChannel<[UInt8], Error> {
-    var buffer = [UInt8](repeating: 0, count: count)
+    var buffer = [UInt8]._unsafelyInitialized(count: count)
     return try prepareAndSubmitMultishot(
       .recv,
       fd: fd,
@@ -695,7 +695,7 @@ public extension IORing {
   }
 
   func read(count: Int, from fd: FileDescriptorRepresentable) async throws -> [UInt8] {
-    var buffer = [UInt8](repeating: 0, count: count)
+    var buffer = [UInt8]._unsafelyInitialized(count: count)
     let nread = try await read(into: &buffer, count: count, from: fd)
     return Array(buffer.prefix(nread))
   }
@@ -722,7 +722,7 @@ public extension IORing {
   }
 
   func receive(count: Int, from fd: FileDescriptorRepresentable) async throws -> [UInt8] {
-    var buffer = [UInt8](repeating: 0, count: count)
+    var buffer = [UInt8]._unsafelyInitialized(count: count)
     try await io_uring_op_recv(fd: fd, buffer: &buffer)
     return buffer
   }
@@ -958,3 +958,11 @@ extension IORing: Hashable {
     ObjectIdentifier(self).hash(into: &hasher)
   }
 }
+
+package extension [UInt8] {
+  static func _unsafelyInitialized(count: Int) -> Self {
+    Self(unsafeUninitializedCapacity: count) { _, initializedCount in
+      initializedCount = count
+    }
+  }
+}

Sources/IORingUtils/Extensions.swift

@@ -30,10 +30,12 @@ extension Message: CustomStringConvertible {
     buffer: [UInt8],
     flags: UInt32 = 0
   ) throws {
-    var addressBuffer = [UInt8](repeating: 0, count: Int(address.size))
-    addressBuffer.withUnsafeMutableBytes { bytes in
+    let addressSize = Int(address.size)
+    let addressBuffer = [UInt8](unsafeUninitializedCapacity: Int(address.size)) { buffer,
+      initializedCount in
       var storage = address.asStorage()
-      _ = memcpy(bytes.baseAddress!, &storage, bytes.count)
+      _ = memcpy(buffer.baseAddress!, &storage, addressSize)
+      initializedCount = addressSize
     }
     try self.init(name: addressBuffer, buffer: buffer, flags: flags)
   }