Experiment with path mapping

okio/src/commonMain/kotlin/okio/FileSystemExtension.kt

@@ -18,5 +18,35 @@ package okio
 /**
  * Marks an object that can be attached to a [FileSystem], and that supplements the file system's
  * capabilities.
+ *
+ * Implementations must support transforms to input and output paths with [PathMapper]. To simplify
+ * implementation, use [PathMapper.NONE] by default and use [chain] to combine mappers.
+ *
+ * ```kotlin
+ * class DiskUsageExtension private constructor(
+ * private val pathMapper: PathMapper,
+ * ) : FileSystemExtension {
+ * constructor() : this(PathMapper.NONE)
+ *
+ * override fun map(pathMapper: PathMapper): FileSystemExtension {
+ * return DiskUsageExtension(chain(pathMapper, this.pathMapper))
+ * }
+ *
+ * fun sizeOnDisk(path: Path): Long {
+ * val mappedPath = pathMapper.onPathParameter(path, "sizeOnDisk", "path")
+ * return lookUpSizeOnDisk(mappedPath)
+ * }
+ *
+ * fun largestFiles(): Sequence<Path> {
+ * val largestFiles: Sequence<Path> = lookUpLargestFiles()
+ * return largestFiles.map {
+ * pathMapper.onPathResult(it, "largestFiles")
+ * }
+ * }
+ * }
+ * ```
  */
-interface FileSystemExtension
+interface FileSystemExtension {
+ /** Returns a file system of the same type, that applies [pathMapper] to all paths. */
+ fun map(pathMapper: PathMapper) : FileSystemExtension
+}

okio/src/commonMain/kotlin/okio/Okio.kt

@@ -85,3 +85,30 @@ inline fun <reified E : FileSystemExtension> FileSystem.extend(extension: E): Fi
 
 /** Returns the extension for [E] if it exists, and null otherwise. */
 inline fun <reified E : FileSystemExtension> FileSystem.extension(): E? = extension(E::class)
+
+
+fun chain(outer: PathMapper, inner: PathMapper): PathMapper {
+ return object : PathMapper {
+ override fun onPathParameter(path: Path, functionName: String, parameterName: String): Path {
+ return inner.onPathParameter(
+ outer.onPathParameter(
+ path,
+ functionName,
+ parameterName,
+ ),
+ functionName,
+ parameterName,
+ )
+ }
+
+ override fun onPathResult(path: Path, functionName: String): Path {
+ return outer.onPathResult(
+ inner.onPathResult(
+ path,
+ functionName,
+ ),
+ functionName,
+ )
+ }
+ }
+}

okio/src/commonMain/kotlin/okio/PathMapper.kt

@@ -0,0 +1,13 @@
+package okio
+
+interface PathMapper {
+ fun onPathParameter(path: Path, functionName: String, parameterName: String): Path
+ fun onPathResult(path: Path, functionName: String): Path
+
+ companion object {
+ val NONE = object : PathMapper {
+ override fun onPathParameter(path: Path, functionName: String, parameterName: String) = path
+ override fun onPathResult(path: Path, functionName: String) = path
+ }
+ }
+}