feat: exclusive mutable access to files

src/main/kotlin/app/revanced/patcher/data/impl/ResourceData.kt

@@ -19,31 +19,66 @@ class ResourceData(private val resourceCacheDirectory: File) : Data, Iterable<Fi
     override fun iterator() = resourceCacheDirectory.walkTopDown().iterator()
 
     inner class XmlFileHolder {
-        operator fun get(inputStream: InputStream, outputStream: OutputStream) =
-            DomFileEditor(inputStream, lazyOf(outputStream))
+        operator fun get(inputStream: InputStream) =
+            DomFileEditor(inputStream)
+
+        operator fun get(path: String): DomFileEditor {
+            return DomFileEditor(this@ResourceData[path])
+        }
 
-        operator fun get(path: String) = DomFileEditor(this@ResourceData[path])
     }
 }
 
+/**
+ * DomFileEditor is a wrapper for a file that can be edited as a dom document.
+ *
+ * @param inputStream the input stream to read the xml file from.
+ * @param outputStream the output stream to write the xml file to. If null, the file will not be written.
+ */
 class DomFileEditor internal constructor(
     private val inputStream: InputStream,
-    private val outputStream: Lazy<OutputStream>,
+    private val outputStream: Lazy<OutputStream>? = null,
 ) : Closeable {
+    // path to the xml file to unlock the resource when closing the editor
+    private var filePath: String? = null
+
+    /**
+     * The document of the xml file
+     */
     val file: Document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(inputStream)
         .also(Document::normalize)
 
     // lazily open an output stream
     // this is required because when constructing a DomFileEditor the output stream is created along with the input stream, which is not allowed
     // the workaround is to lazily create the output stream. This way it would be used after the input stream is closed, which happens in the constructor
-    constructor(file: File) : this(file.inputStream(), lazy { file.outputStream() })
+    constructor(file: File) : this(file.inputStream(), lazy { file.outputStream() }) {
+        filePath = file.path
 
-    override fun close() {
-        val result = StreamResult(outputStream.value)
-        TransformerFactory.newInstance().newTransformer().transform(DOMSource(file), result)
-
-        inputStream.close()
-        outputStream.value.close()
+        // prevent sharing mutability of the same file between multiple instances of DomFileEditor
+        if (locks.contains(filePath))
+            throw IllegalStateException("Can not create a DomFileEditor for that file because it is already locked by another instance of DomFileEditor.")
+        locks.add(filePath!!)
     }
 
+    override fun close() {
+        inputStream.close()
+
+        // if the output stream is not null, do not close it
+        outputStream?.let {
+            val result = StreamResult(it.value)
+            TransformerFactory.newInstance().newTransformer().transform(DOMSource(file), result)
+
+            it.value.close()
+        }
+
+        // remove the lock, if it exists
+        filePath?.let {
+            locks.remove(it)
+        }
+    }
+
+    private companion object {
+        // list of locked file paths
+        val locks = mutableListOf<String>()
+    }
 }