Support path normalization

Closes #223

core/api/kotlinx-io-core.api

@@ -231,6 +231,7 @@ public final class kotlinx/io/files/Path {
 	public final fun getParent ()Lkotlinx/io/files/Path;
 	public fun hashCode ()I
 	public final fun isAbsolute ()Z
+	public final fun normalized ()Lkotlinx/io/files/Path;
 	public fun toString ()Ljava/lang/String;
 }
 

core/common/src/files/Paths.kt

@@ -40,6 +40,12 @@ public expect class Path {
      */
     public val isAbsolute: Boolean
 
+    /**
+     * Returns normalized version of this path where all `..` and `.` segments are resolved
+     * and all sequential path separators are collapsed.
+     */
+    public fun normalized(): Path
+
     /**
      * Returns a string representation of this path.
      *
@@ -174,3 +180,51 @@ private fun removeTrailingSeparatorsWindows(suffixLength: Int, path: String): St
     }
     return path.substring(0, idx)
 }
+
+internal fun Path.normalizedInternal(preserveDrive: Boolean, vararg separators: Char): String {
+    var isAbs = isAbsolute
+    var stringRepresentation = toString()
+    var drive = ""
+    if (preserveDrive && stringRepresentation.length >= 2 && stringRepresentation[1] == ':') {
+        drive = stringRepresentation.substring(0, 2)
+        stringRepresentation = stringRepresentation.substring(2)
+        isAbs = stringRepresentation.isNotEmpty() && separators.contains(stringRepresentation.first())
+    }
+    val parts = stringRepresentation.split(*separators)
+    val constructedPath = mutableListOf<String>()
+    for (idx in parts.indices) {
+        when (val part = parts[idx]) {
+            "." -> continue
+            ".." -> if (isAbs) {
+                constructedPath.removeLastOrNull()
+            } else {
+                if (constructedPath.isEmpty() || constructedPath.last() == "..") {
+                    constructedPath.add("..")
+                } else {
+                    constructedPath.removeLast()
+                }
+            }
+
+            else -> {
+                if (part.isNotEmpty()) {
+                    constructedPath.add(part)
+                }
+            }
+        }
+    }
+    return buildString {
+        append(drive)
+        var skipFirstSeparator = true
+        if (isAbs) {
+            append(SystemPathSeparator)
+        }
+        for (segment in constructedPath) {
+            if (skipFirstSeparator) {
+                skipFirstSeparator = false
+            } else {
+                append(SystemPathSeparator)
+            }
+            append(segment)
+        }
+    }
+}

core/common/test/files/SmokeFileTest.kt

@@ -443,6 +443,15 @@ class SmokeFileTest {
         source.close()  // there should be no error
     }
 
+    @Test
+    fun pathNormalize() {
+        assertEquals(Path(""), Path("").normalized())
+        assertEquals(Path("/a"), Path("/////////////a/").normalized())
+        assertEquals(Path("/e"), Path("/a/b/../c/../d/../../../e").normalized())
+        assertEquals(Path("../../e"), Path("a/b/../c/../d/../../../../e").normalized())
+        assertEquals(Path("a"), Path("a/././././").normalized())
+    }
+
     private fun constructAbsolutePath(vararg parts: String): String {
         return SystemPathSeparator.toString() + parts.joinToString(SystemPathSeparator.toString())
     }

core/common/test/files/SmokeFileTestWindows.kt

@@ -42,4 +42,12 @@ class SmokeFileTestWindows {
         // this path could be transformed to use canonical separator on JVM
         assertEquals(Path("//").toString(), Path("//").toString())
     }
+
+    @Test
+    fun pathNormalize() {
+        if (!isWindows) return
+        assertEquals(Path("C:a", "b", "c", "d", "e"), Path("C:a/b\\\\\\//////c/d\\e").normalized())
+        assertEquals(Path("C:$SystemPathSeparator"), Path("C:\\..\\..\\..\\").normalized())
+        assertEquals(Path("C:..", "..", ".."), Path("C:..\\..\\..\\").normalized())
+    }
 }

core/common/test/files/UtilsTest.kt

@@ -52,4 +52,12 @@ class UtilsTest {
         assertEquals("C:\\", removeTrailingSeparatorsW("C:\\"))
         assertEquals("C:\\", removeTrailingSeparatorsW("C:\\/\\"))
     }
+
+    @Test
+    fun normalizePathWithDrive() {
+        assertEquals("C:$SystemPathSeparator",
+            Path("C:\\..\\..\\..\\").normalizedInternal(true, WindowsPathSeparator, UnixPathSeparator))
+        assertEquals("C:..$SystemPathSeparator..$SystemPathSeparator..",
+            Path("C:..\\..\\..\\").normalizedInternal(true, WindowsPathSeparator, UnixPathSeparator))
+    }
 }

core/jvm/src/files/PathsJvm.kt

@@ -19,6 +19,14 @@ public actual class Path internal constructor(internal val file: File) {
 
     public actual override fun toString(): String = file.toString()
 
+    // Don't use File.normalize here as it may work incorrectly for absolute paths:
+    // https://youtrack.jetbrains.com/issue/KT-48354
+    public actual fun normalized(): Path = Path(path = if (isWindows) {
+        normalizedInternal(true, WindowsPathSeparator, UnixPathSeparator)
+    } else {
+        normalizedInternal(false, UnixPathSeparator)
+    })
+
     actual override fun equals(other: Any?): Boolean {
         if (this === other) return true
         if (other !is Path) return false

core/native/src/files/PathsNative.kt

@@ -52,6 +52,12 @@ public actual class Path internal constructor(
             if (path.isEmpty() || path == SystemPathSeparator.toString()) return ""
             return basenameImpl(path)
         }
+
+    public actual fun normalized(): Path = Path(path = if (isWindows) {
+        normalizedInternal(true, WindowsPathSeparator, UnixPathSeparator)
+    } else {
+        normalizedInternal(false, UnixPathSeparator)
+    })
 }
 
 public actual val SystemPathSeparator: Char = UnixPathSeparator

core/nodeFilesystemShared/src/files/PathsNodeJs.kt

@@ -63,6 +63,12 @@ public actual class Path internal constructor(
     actual override fun hashCode(): Int {
         return path.hashCode()
     }
+
+    public actual fun normalized(): Path = Path(path = if (isWindows) {
+        normalizedInternal(true, WindowsPathSeparator, UnixPathSeparator)
+    } else {
+        normalizedInternal(false, UnixPathSeparator)
+    })
 }
 
 public actual val SystemPathSeparator: Char by lazy {

core/wasmWasi/src/files/FileSystemWasm.kt

@@ -272,22 +272,6 @@ internal object WasiFileSystem : SystemFileSystemImpl() {
     }
 }
 
-private fun Path.normalized(): Path {
-    require(isAbsolute)
-
-    val parts = path.split(UnixPathSeparator)
-    val constructedPath = mutableListOf<String>()
-    // parts[0] is always empty
-    for (idx in 1 until parts.size) {
-        when (val part = parts[idx]) {
-            "." -> continue
-            ".." -> constructedPath.removeLastOrNull()
-            else -> constructedPath.add(part)
-        }
-    }
-    return Path(UnixPathSeparator.toString(), *constructedPath.toTypedArray())
-}
-
 public actual open class FileNotFoundException actual constructor(
     message: String?,
 ) : IOException(message)

core/wasmWasi/src/files/PathsWasm.kt

@@ -48,6 +48,8 @@ public actual class Path internal constructor(rawPath: String, @Suppress("UNUSED
         }
 
     public actual val isAbsolute: Boolean = path.startsWith(SystemPathSeparator)
+
+    public actual fun normalized(): Path = Path(path = normalizedInternal(false, SystemPathSeparator))
 }
 
 // The path separator is always '/'.