Swift 5 migration: Handle changes in Data's pointer interface

Signed-off-by: Roopesh Chander <roop@roopc.net>

WireGuard/Shared/Model/Data+KeyEncoding.swift

@@ -13,8 +13,8 @@ extension Data {
             return nil
         }
         var out = Data(repeating: 0, count: Int(WG_KEY_LEN_HEX))
-        out.withUnsafeMutableBytes { outBytes in
-            self.withUnsafeBytes { inBytes in
+        out.withUnsafeMutableInt8Bytes { outBytes in
+            self.withUnsafeUInt8Bytes { inBytes in
                 key_to_hex(outBytes, inBytes)
             }
         }
@@ -25,7 +25,7 @@ extension Data {
     init?(hexKey hexString: String) {
         self.init(repeating: 0, count: Int(WG_KEY_LEN))
 
-        if !self.withUnsafeMutableBytes { key_from_hex($0, hexString) } {
+        if !self.withUnsafeMutableUInt8Bytes { key_from_hex($0, hexString) } {
             return nil
         }
     }
@@ -35,8 +35,8 @@ extension Data {
             return nil
         }
         var out = Data(repeating: 0, count: Int(WG_KEY_LEN_BASE64))
-        out.withUnsafeMutableBytes { outBytes in
-            self.withUnsafeBytes { inBytes in
+        out.withUnsafeMutableInt8Bytes { outBytes in
+            self.withUnsafeUInt8Bytes { inBytes in
                 key_to_base64(outBytes, inBytes)
             }
         }
@@ -47,8 +47,34 @@ extension Data {
     init?(base64Key base64String: String) {
         self.init(repeating: 0, count: Int(WG_KEY_LEN))
 
-        if !self.withUnsafeMutableBytes { key_from_base64($0, base64String) } {
+        if !self.withUnsafeMutableUInt8Bytes { key_from_base64($0, base64String) } {
             return nil
         }
     }
 }
+
+extension Data {
+    func withUnsafeUInt8Bytes<R>(_ body: (UnsafePointer<UInt8>) -> R) -> R {
+        assert(!isEmpty)
+        return self.withUnsafeBytes { (ptr: UnsafeRawBufferPointer) -> R in
+            let bytes = ptr.bindMemory(to: UInt8.self)
+            return body(bytes.baseAddress!) // might crash if self.count == 0
+        }
+    }
+
+    mutating func withUnsafeMutableUInt8Bytes<R>(_ body: (UnsafeMutablePointer<UInt8>) -> R) -> R {
+        assert(!isEmpty)
+        return self.withUnsafeMutableBytes { (ptr: UnsafeMutableRawBufferPointer) -> R in
+            let bytes = ptr.bindMemory(to: UInt8.self)
+            return body(bytes.baseAddress!) // might crash if self.count == 0
+        }
+    }
+
+    mutating func withUnsafeMutableInt8Bytes<R>(_ body: (UnsafeMutablePointer<Int8>) -> R) -> R {
+        assert(!isEmpty)
+        return self.withUnsafeMutableBytes { (ptr: UnsafeMutableRawBufferPointer) -> R in
+            let bytes = ptr.bindMemory(to: Int8.self)
+            return body(bytes.baseAddress!) // might crash if self.count == 0
+        }
+    }
+}